WO2019086918A1

WO2019086918A1 - Flow measurement of fluid containing solid by bottom-fed flume

Info

Publication number: WO2019086918A1
Application number: PCT/IB2017/001228
Authority: WO
Inventors: Jacques Orban; Miloud MOUZOURI; Vishwanathan Parmeshwar
Original assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp
Current assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp
Priority date: 2017-08-15
Filing date: 2017-08-15
Publication date: 2019-05-09
Anticipated expiration: 2020-02-15

Abstract

A system for measuring flow-out on a drilling rig. The system having a bottom flume box, where two fluids are alternately fed into the bottom flume box. The fluids are directed in a vertical direction creating a horizontal fluid level to reach the exit throat. A level sensor is placed above the horizontal fluid level to measure the height of the fluid in a location where the velocity gradient in the vertical direction is minimized. The fluid flows out of the bottom flume box through a throat section located at a height near the top of the bottom flume box. The height measurement of the horizontal fluid level is used for the determination of the total flow out from the drilling rig.

Description

FLOW MEASUREMENT OF FLUID CONTAINING SOLID BY

BOTTOM-FED FLUME

BACKGROUND

[0001] During drilling, mud is circulated into the well via the drill-string and back to surface via the annulus. In normal condition, the flow is acting like in a close loop system: the flow-out should match the flow-in.

[0002] In some specific conditions, fluid influx may occur form the formation into the well- bore. Such influx may require special recovery procedure, called "well control". If proper detection of the influx or improper recovery procedure, the well issue may degenerate into blowout. Well control and blowout prevention has become an important concern in the oil and gas drilling industry for a number of reasons. Well blowouts cause higher drilling costs, possible loss of life, and waste of natural resources. An influx can be defined as a well control problem in which the pressure found within the drilled formation is greater than the mud or fluid pressure acting on the borehole or face of the formation. This formation pressure causes fluids to flow from the formation into the well bore. In almost all drilling operations, the operator attempts to maintain a hydrostatic pressure greater than the formation pressure and thus prevent kicks. On occasion however, and for various reasons, the formation pressure exceeds the mud pressure and an influx will occur. Influxes have become even more common due to the present trend of increasing drilling rates by lower the over-balance of pressure and using lighter drilling mud.

[0003] Influx may be limited as the volume of formation fluid which enters in the well may be limited in time. When the limited amount of formation fluid (i.e., gas) reaches the surface, fluid may be expelled at higher rate for a short time: such event is commonly called "well-kick". If the down-hole influx induces a large amount of formation fluid in the well-bore, the flow-out may greatly increases. Normally such event may be detected by the driller and a well killing procedure may be performed, requiring the closing of the blow out preventer (BOP) and circulation of mud through the well-bore. If not detected on time, the influx may become a blowout. [0004] Another event that may be encountered when drilling a well is drilling fluid loss into the formation. This problem, also referred to as "lost circulation," occurs where the drilling fluid is flowing into a subterranean formation through which the borehole passes. Such event may occur when the well pressure is larger than the formation pressure, while the formation has large permeability or fractured. The fractures may be initially present or may have been induced by the drilling process. Loss may be partial or total. In case of total loss, the pumped flow rate is entering in the loss formation, and the level in the annulus may be dropped from the surface so that the well-pressure in front of the loss formation is adequately forcing the flow into the loss formation. Such condition should be detected quickly by a driller to prevent damage to such a formation and excessive loss of the drilling fluid.

[0005] In loss situation, the pressure along the well, or in the upper sections of the well, is lower with the risk of engaging an influx situation from another formation bearing gas or oil: this situation combining loss at certain depth and influx at another depth is quite complex to control. The risk of accident may be quite large and the procedure for recovery quite long.

[0006] A number of kick or lost circulation indicators can be observed at the surface before these events have time to result in a dangerous blowout or excessive time has elapsed since the beginning of lost circulation. These indicators may include, for example: flow rate change, flowing well with pumps off, and pit volume change.

[0007] Flow-out is a key measurement for drilling rig. When associated with adequate flow- in measurement, it allows for the detection of a kick or loss processes. Such processes are highly critical for high risk associated with the loss of control within the well-bore during drilling process. Loss processes may directly affect the drilling safety, as a kick may turn into a blow-out with high risk for the people and equipment. Even if such events are not occurring, well-bore and formation damage may occur during uncontrolled processes.

[0008] Thus, one way of detecting kicks and losses can be by comparing the flow rate of mud into the well with the flow rate of mud out of the well, where a surfeit or deficit of flow indicate the two events, respectively. The most common method to measure flow-out on drilling rig is by using a paddle flow sensor. Such a flow detection system is commonly not better than 20% accuracy. It requires a reset to the flow-in values as a reference frequently and requires that the reset procedure is performed when there is no kick or loss in the well-bore, which may be difficult to determine, especially when drilling at balance or slightly under-balance. Furthermore, the paddle has limited reproducibility due to bearing friction and a potential layer of cuttings at the bottom of the flow-line. Also, the paddle flow output is influenced by other parameters such as fluid density and rheology, as well as other factors of the mud by gas and cuttings.

[0009] Kick and loss are also commonly detected by monitoring the amount of fluid in the mud tank, or pit volume. This is obtained by installing level sensor in each mud tank. The knowledge of the mud level in a tank allows for the determination of the volume, when the tank geometry is known. At best, such technique may allow one to determine a gain or loss with an accuracy of about five to ten barrels based on the sensitivity of level sensors installed above a tank. However, such accuracy is theoretical because mud may be lost during cleaning of the cuttings (in the shaker or centrifuge, for example), or there may be agitation in the tank, creating surface level perturbations that impact the local level determination by the level sensor. Further, the measured pit volume may be affected by mud operators or other personnel who may extract or add some volumes of mud to perform modifications or to adapt the mud properties and volume.

[0010] The flow rate of fluid from the formation may be compared to the flow rate of fluid entering and exiting the system by the following equations:

AVol_Pit= V_influx+ AV (1)

With

AVol_pit : increase of mud-pit volume

Vinfiux : total produced fluid at down-hole condition

AV : total influx expansion in well-bore

Qout = Qin + Qinflux + Δν/Δί (2)

With

well

Qinfiux : down-hole influx rate

Δν/Δί : influx expansion rate in well-bore

(1) <=> integral versus time of (2) [0011] Different type of flowmeters exists. They typically require a full pipe with defines velocity profile. However, they may be not easily installed or adapted to the return-line and the fluid flowing out of the well during drilling:

[0012] - Coriolis flowmeters are quite accurate, but they create pressure drop. Installation in the return line require complex U-tune piping and require the usage of the large size device.

[0013] - Electro-magnetic flow meters are also extremely accurate, but they require that the fluid is electrically conductive, which is not the case with oil-base-mud. Electromagnetic flowmeter requires full-pipe flow with axisymmetrical velocity profile: such conditions are difficult to achieve in the return line.

[0014] - Turbine requires full pipe, axisymmetrical velocity profile and high Reynolds number; such conditions are difficult to achieve in the return line.

[0015] - Acoustic flow meter may also be used to measure the flow of fluid. However, this type of system may suffer from acoustic attenuation, as the received signal may be of low amplitude, or even lost. The attenuation increases drastically with mud density and presence of gas.

[0016] Flume systems are commonly used to measure flow-rate in river and sewage. A flume system is shaped in such a way that the flow condition passes form sub-critical (calm) flow to super-critical (torrential) flow. The measurement is the difference of levels between the two flow conditions. A model allows to determine the flow-rate form the knowledge of these levels. Such measurement techniques is relatively accurate but there is an influence of the fluid properties, such as rheology, on the levels. To use accurately such flume system, an additional measurement is required to determine the effect of rheology and density on the flow condition. Also, the flume system requires that the initial flow is sub-critical. A long entry section may be required to ensure such condition. This is particularly true if the supply line is fairly inclined. Along this relatively long entry section, the fluid velocity would be low and cuttings would sediment with the risk of plugging the entry section of the flume system. SUMMARY OF THE CLAIMED EMBODIMENTS

[0017] One or more embodiments disclosed herein relate to a process for measuring flow- out on a drilling rig by flowing a fluid into a flume box which is configured to have an upward supply flow of the fluid through the flume box. The fluid then flows out of the flume box. The height of the fluid in the flume box is measured, and the flow measurement is determined a flow measurement based on the measured height.

[0018] One or more embodiments disclosed herein also relate to a system for measuring flow-out on a drilling rig. The system includes a bottom supplied flume box, wherein a fluid is fed into the bottom of the bottom supplied flume box creating a horizontal fluid level. The bottom fed flume box also includes a throat section located at a height near the top of the bottom supplied flume box, and a level sensor located above the horizontal fluid level near the throat section.

[0019] One or more embodiments disclosed herein also relate to a system for measuring flow-out on a drilling rig. The system includes a bottom flume box, wherein a fluid is fed into the flume box. The bottom flume box also includes a first section which allows the supplied fluid to flow downwards in the flume box in front of a central baffle, and a second section which allows the fluid to flow upwards after passing below the central baffle. The bottom flume box also includes a throat section located above the section of upwards flow, and a level sensing system located near the throat section.

[0020] Other aspects and advantages will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is an illustration of a bottom fed flume box according to embodiments disclosed herein.

[0022] Figure 2 shows various shapes of the intersection of the expanded vertical flow zone and inclined flow line of Figure 1.

[0023] Figure 3 shows schematic flow responses for the shapes shown Figure 2.

[0024] Figure 4 is a top view of a bottom fed flume box according to embodiments disclosed herein. [0025] Figure 5 is an illustration of an installation location of a bottom fed flume box according to embodiments disclosed herein.

[0026] Figure 6 is an illustration of another installation location of a bottom fed flume box according to embodiments disclosed herein.

[0027] Figure 7 is a cross-sectional side view of a two supply bottom flume box according to embodiments disclosed herein.

[0028] Figure 8 is a front view of the two supply bottom flume box shown in Figure 7.

[0029] Figure 9 is a three-dimensional illustration of a two supply bottom flume box according to embodiments disclosed herein.

[0030] Figure 10 is a three-dimensional illustration of components of two supply bottom flume box according to embodiments disclosed herein.

[0031] Figure 11 is an illustration of distribution boxes according to embodiments disclosed herein.

[0032] Figure 12 is an illustration fluid flow through a two supply bottom flume box according to embodiments disclosed herein.

[0033] Figure 13 is an illustration of fluid flow through a two supply bottom flume box according to embodiments disclosed herein.

[0034] Figure 14 is an illustration of fluid flow through a two-supply bottom flume box according to one or more embodiments.

[0035] Figure 15 is an illustration of two supply bottom flume box according to embodiments disclosed herein.

[0036] Figure 15B is an illustration of a bottom flume box according to embodiments disclosed herein.

[0037] Figures 16-18 illustrate distribution boxes used with a two supply flume box according to the present disclosure.

[0038] Figure 19 is an illustration of two supply bottom flume box according to embodiments disclosed herein.

[0039] Figure 20 is an illustration of two supply bottom flume box according to embodiments disclosed herein. [0040] Figure 21 is an illustration of two supply bottom flume box according to embodiments disclosed herein.

[0041] Figures 22 A and 22B is an illustration of a calibration system according to embodiments disclosed herein.

[0042] Figure 23 is an illustration of cleaning system according to embodiments disclosed herein.

[0043] Figure 24 is an illustration of a bottom flume box according to embodiments disclosed herein.

[0044] Figure 25 is an illustration of cleaning system according to embodiments disclosed herein.

DETAILED DESCRIPTION

[0045] In one aspect, embodiments herein relate to measurement of flow-out on a drilling rig using a modified flume box. Specifically, embodiments relate to a modified flume box where the flow reaches the throat area of flow transition as a nearly vertical upwards flow. Such modified flume box may be incorporated, for example, on a drilling rig. Other embodiments relate to the processes for measuring flow-out of mud on a rig.

[0046] Flume systems may be open-channel flow systems. Traditional flume boxes are used in applications for flow measurement in river and sewage, for example. In such devices, there is a flow transition from sub-critical flow to super-critical flow which corresponds to an energy conversion (from potential to kinetic). For a set total energy, two flow conditions may be present. A conventional horizontal flume, or H-flume, box has the flow moving axially into the box as sub-critical flow to reach the exit throat. At the exit throat, the flow reaches super critical condition, and the fluid is moving at higher velocity.

[0047] The principle underlying a flume system is the use of a shaped, static structure that is used to restrict the flow of free surface fluid, such as water, and cause the conversion of potential energy into kinetic energy, in such a way so as to develop a relationship between the water level and the flow rate. Flumes use a change in elevation, a contraction of the sidewalls, or a combination of the two to accelerate slow, sub-critical (Froude number or Fr<l) flow to a supercritical state (Fr>l), where Fr = V / (gD)^I/2, (3) where V is the water velocity, g is gravity, and D is hydraulic depth (or cross- sectional area of flow / top width).

This acceleration of flow creates upstream conditions where the flow rate can be determined by measuring the water level at a single point. The relationship between the water level at the point of measurement and the flow rate can be obtained by test data (short-throated flumes) or derived formula.

[0048] Conventional flume may be either venturi flume or H-flume. When considering the flow of a given fluid through a H-flume, there is unique relation between the fluid level before the throat and the flow rate. The relation between level and flow rate is based on geometry. When considering a certain level sensor accuracy, it is then possible to determine the flow accuracy.

[0049] The flow along the flume -box and in the flume throat is affected by hydraulic friction loss. In the sub-critical zone, the flow may often be laminar. In the throat, the flow may become turbulent. Due to the hydraulic friction loss in the sub-critical zone and in the exit throat, more potential energy must be dissipated. This translates to an additional loss of elevation along the fluid movement in the sub-critical section. The higher the hydraulic loss, the higher the level in that section. The fluid rheology is the primary element affecting the hydraulic loss. The relation between fluid level and flow rate is affected at the secondary level by this hydraulic loss. A model may also be used to estimate the effect of viscosity on the measurement and potentially correction for the hydraulic drag may be determined for high accuracy of flow determination.

[0050] A typical H-fiume box must be long in relation to the width (3 to 5 times the width) so that the sub-critical flow is well established over the whole section before reaching the exit throat. In practical term, the flume box may need a width of 2.7 ft, for example, and a length of 10 ft to operate with flow up to 1500 GPM. With such design, the fluid moves relatively slowly in the box, as it is a sub-critical flow. In such condition, when the fluid is loaded with cuttings, some sedimentation of these cuttings may occurs along the bottom and walls of the box. The sedimentation may be estimated by the Stake's law. Using such an estimate allows for a model for the sedimentation process to be built. The estimation of sedimentation in the box may be necessary as cuttings create a serious issue in conventional H-fiume boxes.

[0051] In one or more embodiments disclosed herein is a bottom fed flume box. Such a box uses the same principle as a conventional flume box (a shaped, static structure that is used to restrict the flow of free surface fluids in such a way so as to develop a relationship between the fluid level and the flow rate), but in accordance with the present disclosure, fluid is introduced at the bottom of the flume box and allowed to flow in a vertical plane. In one or more embodiment, the bottom-fed flume may be a type as illustrated in Fig. 1. As illustrated, a fluid 1 , such as mud, is initially flowing vertically in the system and into bottom-fed flume box 100. The feeding into bottom-fed flume box 100 is made from the vertical fluid supply pipe 2. Introducing the fluid in such a vertical fashion may allow for proper transport of solids (such as cuttings) and/or gases that may also be entrained in or carried by the fluid. While there may be velocity slippage due to the difference of density of the multiple phases or components, in a time average consideration, the presence of multiple phases or components may have limited, or no, effect on the average flow rate of the phases (liquid, solid, gas) as long as the concentration of solid and gas versus liquid stays below a certain threshold, such as less than 10%.

[0052] Axially above the vertical supply pipe 2 is a diffuser zone 4, and axially above diffuser zone 4 is expanded vertical flow zone 6. In the expanded vertical flow zone 6, the velocity of the fluid is reduced from its velocity through the vertical supply pipe 2 due to the increase in cross section 8 of expanded vertical flow zone 6, relative to vertical supply pipe 2. A level sensor 12 may be placed so as to measure the fluid level or upper surface of fluid 18 in the expanded vertical flow zone 6, which may be related to flow rate, as discussed herein. The diffuser zone 4, as the transition between the vertical supply pipe 2 and expanded vertical flow zone 6, allows proper flow distribution towards the expanded vertical flow zone 6. An inclined flow line 16 extends at a negative slope away from the expanded vertical flow zone 6. The shape of the intersection of two cylinders (such as expanded vertical flow zone 6 and inclined flow line 16) would generally be an ellipse. The ellipse may allow a progressive convergence of the flow towards the transition zone 10 to the flow-line 16. The ellipse shape may also allow the level measurement to perform at an adequate distance from the transition zone 10. The inclined flow line should ensure open-channel flow along the flow line 16. Near the connection to the transition zone 10, the flow line 16 must be inclined sufficiently to ensure super-critical flow in the flow line. Generally, a slope above 5 degrees should be sufficient. The flow line 16 may be circular. The fluid free-surface within the vertical flow zone 6, the transition zone 19 and flow line 16 is indicated as 18.

[0053] Depending on the location of installation of bottom- fed flume box 100, a tubular bore guide 14 may be located at the upper end of flume box through which a tubular such as a drill string, etc. may be run into the bore of the supply section 2 well. In one embodiment this bottom-fed flume may be installed at the top of the well as bell-nipple. It can be even installed above the BOP of the well. The tubular (i.e., drill-string) may be lowered in the bore of the well via the guide 14. Such tubular may provide a flow in of fluid to the well.

[0054] It is envisioned that the shape of the inclined flow line 16 may be varied so as to create different transition zone 10 shapes (shown, for example, in Fig. 2), including other shapes conventionally used in the throat of flumes (such as venturi and H-flumes). The section of this flow-line 16 may progressively be modified from that initial specific section towards a circular section after a few feet of flow-line.

[0055] The transition zone 10 may also include a throat section which may aid in the transition from sub-critical to super-critical flow. The height of the throat section may be located proximate to the top of the bottom- fed flume box 100 such that the velocity of the fluid in the vertical direction is minimized, thus enabling a steady level measurement 20.

[0056] When used on a drilling rig, fluid may flow from the well through the vertical supply pipe 2, into the expanded vertical flow zone 6 (via the diffuser zone 4) and then through or along the inclined flow line 16. Thus, this structure is used to restrict the flow of fluid in such a way that the fluid flow transitions from sub-critical to super-critical so as to develop a relationship between the fluid level and the flow rate. In the vertical flow zone 6, the fluid may exhibit sub-critical flow (Froude number or Fr<l , also often referred to as tranquil flow) and vertical velocity. Specifically, in the expanded vertical flow zone 6, the horizontal component of the fluid velocity is low enough in the region of the vertical axis so that the flow is sub-critical. The horizontal component is sub-critical so that the transition from sub-critical to super critical allows for the use of the principle of flumes so as to develop a relationship between the fluid level and the flow rate. However, upon transitioning into the inclined flow line 16, the fluid transitions from sub-critical flow to super-critical flow (Fr>l, also referred to as torrential flow). In fact, the intersection or transition zone 10 between the expanded vertical flow zone 6 and the inclined flow line 16 (and the discontinuity in the section) is the location of flow transition, where the flow is critical with a Froude number being equal to one. In the bottom fed flume box, the fluid flow transitions to a horizontal direction to enter in the inclined flow line 16 which may be inclined downward to induce flow out from the expanded vertical flow zone 6. The inclination of the flow line 16 may be sufficient to induce the flow to transition from sub- critical to super-critical within the transition zone 10.

[0057] As mentioned above, a level sensor 12 is placed so as to measure the level 20 of fluid in the expanded vertical flow zone 6. Such location may be, for example, opposite the intersection with the inclined flow line 16. In one or more embodiments, the expanded vertical zone 6 may be shaped to have an oval or elliptical horizontal cross-sectional shape (shown, for example, in Fig. 4) to provide a proper distance between the level sensor 12 measurement and the transition zone 10, where critical flow occurs, as fluid flow transitions into the inclined flow line 16 for flow-out. This oval or elliptical shape may also allow for the installation of the level sensor 12 in such a position as to not interfere with the tubular bore guide 14 (or drill string (not shown)) which may pass through the bore of the system. The level sensor 12 may be one any suitable type such as a radar based sensor.

[0058] In such a bottom fed flume box, it may also be advantageous to locate the level sensor 12 in such a location that horizontal fluid flow toward the transition zone 10 is minimized. This may allow for a more stable fluid level or horizontal surface 18 resulting a more accurate level measurement. The measured distance 20 will allow to determine the level L of fluid above the lowest point of the transition zone 10 and thus be related to the total flow-out of the system. [0059] To increase the resolution of flow measurement, the variation of level in the expanded vertical flow zone 6 should have a larger dependence on the flow rate. For such objective, the intersection between the expanded vertical flow zone 6 and the inclined flow line 16 of Fig. 1 may be shaped as illustrated in Fig. 2, which shows various shapes 24, 26, 28. For example, the exit may be shaped to have a triangular flume shape 24, an elliptical shape 26, or an optimized shape 28, where optimized shape 28 is based on the anticipated effect on volumetric flow rate Q as it depends on the measured fluid level L, shown in Fig. 3, where the short dashed curve corresponds to the triangular shape 24, the long dashed curve corresponds to the elliptical shape 26, and the solid line corresponds to the optimized shape 28. It is understood that the optimized shape may be determined by varying the shape and determining the impact on the flow rate Q/fluid level L to create a more proportional flow response versus level relationship. Due to the selection of the shape of the transition zone, the relationship between level and flow-rate may be adapted to the application requirement. For example, the shape 28 can be tuned to make the relationship more linear, and this could be beneficial with simple processing systems. The triangular shape may require higher level at the input for small flow rate to increase the accuracy of small flow detection. The common circular shape (or elliptical 26) may be the least linear, but may be the easier one to build.

[0060] It is envisioned that the geometry of such transition may be extended for a given length of the inclined flow line 16 shown in Fig. 1 , but that after some distance, the flow- line 16 could revert to a conventional cylindrical pipe.

[0061] Further, in one or more embodiments, the optimized shape 28 (or any shape) may be achieved through the use of an insert 30 (shown in Figure 4, which is a top view of the bottom fed flume box of Fig. 1) at the inlet end of inclined flow line 16 having an inner geometry of the desired or optimized shape 28.

[0062] Further, is as shown in Fig. 4, the intersection 22 between the two zones 6, 16 may also include a radiused or rounded transition to allow for lower local flow perturbations to occur when the fluid enter in the flowline 16. With proper shaping of the upstream section of flowline 16 and the rounded transition 22, the flow response versus the level maybe more proportional, and the level sensitivity to total flow may be particularly improved at low flow, or no flow. Further, one or more baffles 32, 34 may be included within the vertical expansion zone to reduce perturbation of the measured flow level. Specifically a plurality of tangent plate baffles 32 may be included to limit Taylor vortexes from being present by cutting them along their vertical axis. In one or more embodiments, the tangent plate baffies 32 may be placed to have a plurality of columns of baffles, each adjacent column of baffies being offset relative to the neighboring column(s) of baffles, to form a "checkerboard" arrangement of baffies 32. Further, a plurality of rotation suppression baffles 34 may be placed adjacent the transition zone 10 to reduce the effect of Couette rotation flow, which may be generated by the drill-string rotation, at the entrance to the inclined flow line 16. Thus, baffies 32, 34 reduce the effect of flow conditions caused by the rotation of the drill string 36 that could otherwise generate some perturbation at the entrance of the inclined flow line 16 and some perturbation of the measured level 20.

Given that it is envisioned that the bottom-fed flume may be used to determine flow of a mud out of a well, it is envisioned that the mud may include solid particles such as drill cuttings as well as gases. Thus, the cuttings will flow with the fluid through the system from the vertical fluid supply 2 to the inclined flow line 16. In the vertical fluid supply 2, cuttings are transported by vertical drag following Stoke 's law. There may be some slippage between fluid and solid due to the density differences; however, on average, the solid rate will be proportional to the fluid rate. The presence of cuttings in the mud may affect the apparent average fluid density, however, this effect may have little or no influence on the flow in the system as the change of density affects the initial potential energy as well as the kinetic energy through the critical zone. Advantageously, by using a bottom fed flume design, the effect of density on the flow estimation may be minimized. However, the cuttings may need to be accelerated in the horizontal direction due to viscous drag. This would lead to an estimated flow-rate that may be higher than the real value. In one or more embodiments disclosed below, a correction for this reduction of total energy (horizontal flow) due to viscous dissipation is discussed. Additionally, the shape of the throat section may be such that the formation of a deposit due to sedimentation when operating at a low flow, or no flow, is minimized. [0064] Additionally, the presence of gas in the mud may be managed properly with the bottom fed flume box. The gas increases the volume of fluid reaching the expanded vertical flow zone 6 and the level is pushed upwards. This gas may escape at the upper surface 18, and some gas may flow with the liquid through the inclined flow line 16. The gas flowing through the inclined flow line 16 does not influence the energy in this section, as the kinetic energy is not affected, as the gas mass is negligible. As such, the bottom fed flume box may also be capable of determining the total flow of a liquid/gas mixed fluid, as well as a three phase system: solid, liquid, and gas, which is not achievable using conventional systems.

[0065] Referring back to Figure 1 , the level sensor 12 may be positioned so that it measures the fluid level at a point where horizontal velocity is low. As shown in Fig. 1 , the level sensor 12 is positioned near the wall opposite to the inclined flow line 16. At such a region, the horizontal velocity gradient is near zero. While rheology of a fluid will impact the hydraulic drag of a fluid and thus level measurement (and falsely indicating that there is greater flow) in a conventional H-flume, the bottom fed flume box of the present disclosure may advantageously reduce the effect of viscosity loss along the horizontal movement towards the critical flow section as there no "bottom" to the flume box to cause the drag complication. Thus, unlike a conventional H-flume design, the horizontal velocity profile according to the present embodiments may have minimum perturbations due to this low velocity gradient. While the horizontal velocity distribution may be affected by the presence of the side wall in the expanded vertical flow zone 6, the wetted perimeter is typically small, so there may be minimum loss due to this effect.

[0066] Referring now to Figure 5, Figure 5 illustrates an embodiment of a drilling rig system that may incorporate the bottom fed flume box of the present disclosure. As illustrated, the drilling rig 300 includes a number of components related to the return of wellbore fluids from the well 302. Generally, as fluid returns from a well, it flows upward through a blow out preventer (BOP) stack and rotating control device (RCD) to a bell nipple that is fitted with a side outlet to allow the fluid to flow back to mud treating equipment through a flow line. In one or more embodiments, the flume box of the present disclosure may be integrated with the bell nipple. Thus, as illustrated, fluid flows from the well 302 through blowout preventer stack 1 12 and rotating control device 106. A bell nipple extension 104 is secured to the top of the RCD 106 (unless an RCD is omitted, in which case to the top of the BOP stack) and may function as the vertical supply pipe 2 from Fig. 1. The bell nipple 102 (also referred to as a catch-can) may be structured as the bottom flume box 100 from Fig. 1 (including a diffusion zone and vertical expansion zone, for example). An inclined flow line 1 16 extends downwardly and outwardly from the bell nipple 102, carrying fluid away from well into downstream mud treatment components. Fluid flowing through bell nipple 102 exhibits sub-critical flow, which transitions at flume box 100 to super-critical flow into and through inclined flow line 116 to shakers 302. In the event that RCD 106 is closed, fluid may be diverted through RCD discharge line. Such diversion may occur, for example, when it is desired to proceed with managed pressure drilling with fluid flowing through managed pressure drilling choke manifold 1 14 to mud gas separator 110.

However, it is intended that the bottom-fed flume box may be installed elsewhere in the mud return flow path. For example, referring now to Figure 6, another embodiment of an installation of a bottom fled flume box is shown. In these embodiments, the flume box is downstream of the bell nipple. As illustrated, fluid flows from the well 302 through blowout preventer stack 1 12 and rotating control device 106. A bell nipple extension 104 and bell nipple 102 is secured to the top of the RCD 106 (unless an RCD is omitted, in which case to the top of the BOP stack). A flow line 1 16 extends downwardly and outwardly from the bell nipple 102, carrying fluid away from well through a bottom fed flume box 100 into downstream mud treatment components, including, for example shakers and other separators. In the event that RCD 106 is closed, fluid may be diverted through RCD discharge line. Such diversion may occur, for example, when it is desired to proceed with managed pressure drilling with fluid flowing through managed pressure drilling choke manifold (MPD) 114 to mud gas separator 110. As illustrated, fluid also flows from mud gas separator 1 10 into the bottom fed flume box 100. Thus, while the embodiment shown in Figure 5 measures the flow rate of the fluid flowing through the bell nipple 102 into an inclined flow line 1 16 (also referred to as a return line), the embodiment shown in Figure 6 may measure fluid flowing through the bell nipple 102 or through an MPD manifold 114. [0068] In one or more embodiments, Figs. 7-13 illustrate an example of the flume box that may be used in the system of Figure 6 and installed at a header tank, for example, prior to a shale shaker. As illustrated in Fig. 7 (a cross-sectional side view), Fig. 8 (a front view), Fig. 9 (a three-dimensional perspective view), and Fig. 10 (a three-dimensional detailed partial view) the fluid flow may be provided to the flume box 100 via two flow lines, a return supply line 200 directly from the bell nipple and a mud gas separator line 202. Supply lines 200 and 202 may flow into distribution boxes 220, 222, which spread the fluid (and flow) across the width of flume box. As fluid enters distribution boxes 220, 222 from one of these supply lines 200, 202, the fluid may turn inside the distributor box 220, 222 towards the backside of the flume box 100. After exiting the distribution boxes 220, 222, the horizontal backwards flow is forced downwards by the shape of the box cover 206 and by rounded baffle 204 located between box cover 206 and exit from distribution boxes 220, 222. Fluid will continue to flow towards the bottom 208 of the flume box 100 through a diffuser zone 209.

[0069] At the bottom 208 of the flume box 100, the fluid will turn upwards as guided by the inner circular guide 210. Then the fluid moves upwards in the upwards flow zone 212 to the flume supply zone 218, where it has sub-critical flow, after which it reaches the throat section 216 (and achieves super critical flow). As the fluid fills the flume supply zone 218, the level sensor 12 may measure the height 20 of the fluid in the flume supply zone 218 before the fluid exits the flume box 100 via throat section 216. The height of the fluid corresponds to the total flow through the system. Further, it is also envisioned that, similar to as discussed above with respect to Fig. 4, the flume box may include an optional insert 217 designed to vary the internal geometry of the flume box 100 in the sub-critical and/or super-critical flow zones so as to have an optimal fluid level/flow response relationship in the flume supply zone 218.

[0070] In some embodiments, the fluid in the return supply line 200 may flow as through an open-channel. As the return supply line 200 is long, it may commonly be less than half full. However, the velocity may be high, such as between 20 and 30 ft/s. Thus, distribution box 220 may have a horizontal flat bottom. Due to the sudden change of slope between the return line 200 and the distribution box 220, the fluid in the open-channel may go from critical flow conditions and return to a sub-critical flow as the fluid passes into the flume box.

[0071] As illustrated in Fig. 10 and 11 , the distribution boxes 220 of the supply line 200 may be equipped with internal wings 224 which forces the fluid to make the 90 degrees turn towards the backside of the flume box. Distribution box 222 may be equipped with similar wings 224. These wings 224 extend over the whole vertical height of the box. Each wing 224 affects a vertical slice of the flow and ensures an adequate flow distribution towards the diffuser zone 209 of the flume box 100. The internal wings 224 operate in such a way as to change the direction of fluid flow into the two supply bottom flume box 100 and ensure the fluid flow is distributed along the length of the two supply bottom flume box. Further, the distribution box 222 for the MGS supply line 202 has a window opening towards the diffuser zone 209 of the flume box. This opening may be more limited in height as the lower line of the window defines the static level in the MGS. By limiting the window height, the variation in level in the MGS in function with the flow is limited. As shown in Figs. 13 and 14, the internal wings which collect a vertical slice of the total flow in distribution box 222, inclined plates 225 may be included to help collect the fluid across the entire height of the box 222 and force the fluid through the limited height window. By using two stacked distribution boxes 220, 222 as illustrated, there is limited fluid exchange between the two potential fluid supplies 200, 202.

[0072] Fig. 12 illustrates the fluid flow path when the fluid supplied from the return supply line 200. The fluid is fed into the distributor box 220 and is directed by the internal wings (not shown) towards the back of the two supply bottom flume box 100. The fluid will then flow up through the flume supply zone 218 (in which the fluid displays sub-critical flow) in the front of the two supply bottom flume box 100 toward the throat section 216 (where the fluid exhibits super-critical flow). As the fluid level height increases, the level sensor 12 will measure the height 20 of the horizontal fluid level within the flume supply zone 218. This measure allows for the determination of the flow out from the system.

[0073] Similar to Fig. 12, Figs. 13 and 14 illustrate the fluid flow path when the fluid supplied from the mud gas separator supply line 202. The fluid is fed into the distributor box 222 and is directed by the inclined plates 225 and internal wings 224 towards the back of the two supply bottom flume box 100. The fluid will then flow up through the flume supply zone 218 (in which the fluid displays sub-critical flow) in the front of the two supply bottom flume box 100 toward the throat section 216 (where the fluid exhibits supercritical flow). As the fluid level height increases, the level sensor 12 will measure the height 20 of the horizontal fluid level. This measure allows for the determination of the flow out from the system. As illustrated, due to the design of the distribution boxes, there is minimal back flow from the return supply 200 or mud gas separator supply 202. This may result in a more accurate level measurement and, thus, a more accurate determination of the flow out from the system.

Fig. 15 illustrates another embodiment of a two supply bottom flume box where the MGS supply 202 and return supply 200 are in-line with the flume box. Such box may be installed near the shakers as shown in figure 6. Like numbers represent like elements with respect to Fig. 4. The return supply line 200 may have open channel flow therethrough. The flow is distributed over the full width of the flume box 100 due to the use of a distribution boxes 230, 232, which expands the fluid width-wise through the of internal structures such as baffles or internal wings. The distribution box 230 for return supply line 200 is shown in Fig. 16. As illustrated, distribution box 230 may be equipped with baffles 231 which spread the fluid across the distribution box 230 horizontally. The distribution box 232 for MGS supply line 202 is shown in Fig. 17 (side view) and Fig. 18 (top view). As illustrated in Fig. 18, distribution box 232 may be equipped with baffles 233 which spread the fluid across the distribution box 232 horizontally. Referring again to Fig. 15, within the flume box 100, the flow turns downwards upon encountering the central baffle 210 and the guidance baffle 204 provided proximate the window at distribution boxes 230, 232 and central baffie 210, which directs the fluid flow through a diffusion zone 209 to the bottom 208 of the flume box 100. Upon reaching the bottom, the fluid flow turns upwards through a vertical upwards flow zone and has sub-critical flow. The contactless level sensor 12 still measures the distance 20 which allows to determine the height of the fluid as the fluid within the upwards flow zone 212, prior to the fluid nearing the throat section 216 where it experiences super-critical flow. The two supply bottom flume box may also be fitted with overflow baffles 207. In some operating conditions, supplied fluids from either supply lines (200 or 202) may not find sufficient passage below the central baffler 210. Therefore, the supplied fluid passes above the baffle 210. The overflow baffles 207 may be configured to ensure that the fluid flowing above the central baffle 210 is not jetted towards the exit throat 216 but forced downwards to the flume supply zone 218. Overflow baffles 207 may also allow for the overflow fluid to be added to the fluid flowing from the bottom 208 of the two supply bottom flume box 100 such that the total flow may be measured by level sensor 12.

[0075] Referring to Fig. 15B, it is also envisioned that the flume box may be equipped with a single supply line form typically the bell-nipple (line 200), rather than the two supply lines as illustrated in Fig. 15. For example, in one or more embodiments, the flume box may include supply line 200, without supply line 202 or vice versa. If supply line 202 is omitted, then baffle 204 may also be omitted as illustrated, for example. Fig. l5B also illustrated one or more embodiments related to the flow in the zone 209. In such an embodiment, the central baffle 210 may have a curvature 211 which may be designed to guide the fluid 200a along toward the bottom of the flume box and pass the lower baffle 210a. The fluid 200a may pass below lower baffle 210a, in some embodiments. Further, cuttings 200b may be directed over lower baffle 210a, remixing with fluid 200a in flume supply zone 218. The flow paths 200a and 200b may correspond to fluid (200a) and heavier solids (200b).

[0076] Fig. 19 illustrates the fluid flow when fluid is entering from the MGS supply 202.

The fluid is fed from the MGS supply line 202 through the distribution box 232 into the back of the two supply bottom flume box 100. The fluid will then be turned downwards by baffle 204 and central baffle 210. Upon reaching the bottom 208 of the two supply bottom flume box 100, the fluid then flows up in the front of the two supply bottom flume box 100 through the upwards flow zone 212 toward the throat section 216 where it will reach supercritical flow. As the fluid level height increases, the level sensor 12 will measure the height 20 of the horizontal fluid level in flume supply zone 218. This measure allows for the determination of the flow out from the system.

[0077] Fig. 20 illustrates the fluid flow when fluid is entering from the return supply line

200. The fluid is fed from the return supply line 200 through the distribution box 230 into the back of the two supply bottom flume box 100. The fluid will then be turned downwards by baffle 204 and central baffie 210. Upon reaching the bottom 208 of the two supply bottom flume box 100, the fluid then flows up in the front of the two supply bottom flume box 100 through the upwards flow zone 212 toward the throat section 216 where it will reach super-critical flow. As the fluid level height increases, the level sensor 12 will measure the height 20 of the horizontal fluid level in the flume supply zone 218. This measure allows for the determination of the flow out from the system. The position of the return supply line 200 is such that there is minimal back flow through MGS supply line 202. This may enable a more accurate height measurement, which in turn may enable a more accurate determination of the flow out of the system.

[0078] Referring back to Fig. 6, the two supply bottom flume boxes 100 described above may be located next to the header tank on the shaker skid 302 of a drilling rig 300. The MGS supply line 202 and the return supply line 200 are illustrated. In normal operation, the two supply bottom flume box 100 allows for the flow out of fluid the well bore 302 to the header tank. When placed in such a position, it may also be possible to measure the flow out from both of the mud gas separator 110 and return supply line 200, enabling measurement of the total flow out from the system.

[0079] Referring now to Fig. 21 , another embodiment of a flume box 100 is shown. In this embodiment, the flume box 100 includes multiple fluid level sensors 12, 13, 14, which may be placed, for example to measure the fluid in the upwards flow zone 212, the diffusion zone 209, and/or the throat section 216, respectively. In one or more embodiments, it may be necessary to estimate one or more properties of the fluid such as viscosity, density, rheology, or hydraulic friction. Thus, it may be desirable to conduct multiple fluid level measurements 20, 21, 22 in order to account for fluid viscosity on the determined flow rate. For example, a controller 400 may obtain two level measurements. From the primary measurement at level sensor 12, the controller determines the corresponding flow rate, illustrated by horizontal arrows, (considering a reference fluid of defined viscosity, such as water). Then, using model data, the controller determines the corresponding modeled "secondary flume level", which is compared to the measured secondary flume level by level sensor 14. While illustrated as being downstream of primary level sensor 12, second level sensor 14 may be located upstream, or downstream of the primary level sensor 12. When a mismatch exists between the modeled and measured fluid levels at the second level sensor, iterations may be made on the apparent viscosity of the fluid to have the best match between the modeled secondary level and measured secondary level. It is also envisioned that other processes to correct for rheology and/or density may be used. For example, a rheometer (not illustrated) may be used to obtain rheological models of fluid during mud flow at the flume box 100. The controller 400 may communicate with a database of predetermined rheological data and identify from the database, the corresponding flow through the flume box 100 and apply a correction for flow output based on the change in fluid properties.

[0080] In another embodiment, the level sensor 14 may be positioned at a distance D from the edge of the exit throat. The distance D may be selected to minimize the effect of rheology on the flow estimate based on the level measurement of the sensor 14. Such optimization may be conducted by CFD or by experiment for a range of fluid properties. In practical application drilling mud may be considered as Bingham-Plastic fluid characterized by Yield-value and plastic velocity. Distance D could be in the range of 2/3 of the length of throat length. Distance D may also be 10 to 80% of the length of the throat. With such positioning, the effect of rheology of the relation between flow rate and level may be minimized.

[0081] Further, the third level sensor 13 may be included, for example, in order to monitor the fluid flow in the diffuser zone 209 to minimize or avoid overflow. This may detect the accumulation of solid in the bottom of the flume box. Such deposit may generate some flow restriction below the central baffie 210 with a risk of overflow above the baffie 201.

[0082] In or more embodiments, relation between flow-rate and fluid level in the flume box may have to be determined. In some embodiment, the relation between flow-rate and level may initially be provided by either flow modeling or lab calibration. Additionally, a set of correction coefficients may have to be determined for each level of fluid in the flume system with the current fluid flow. These situations may be handled by performing a field calibration of the response of the flume system versus known flow-rate. Fig. 22A illustrates one possible method of calibration of the flow-out measurement of the flume system 400 versus an accumulated volume of fluid to be transferred. When associated with a shaker skid 402 the flow calibration may be performed by comparing the time to fill the tank. For such application, level sensor may be provided to monitor the level of fluid in the tank 410, and determine the amount of fluid accumulated in that tank by knowing the geometry of that tank. The valves 404 may be also equipped with actuator for remote control, the transfer pump 408 may be equipped with a variable speed motor. First, the calibration tank 410 is emptied (to a defined low level) by pumping. Then the pump 408 is stopped and valves 404 is closed as the mud flow continues, the tank is filling. During this operation the centrifugal degasser 412 may be kept active. The filling of the tank may be detected by the level sensor which provides the level data 416. By knowing the geometry of the tank 410 and the rate of change of the level 416, the rig computer may determine the increase of fluid in the tank 410 and calculate the flow rate filling the tank. The same flow rate must pass through the flume box 400. During the same time period, the level through the flume box is measured and the flume -box flow-rate is also determined using the predetermined relation (flow-rate versus level) for that flume -box. The rig computer can then calculate the ratio between the two flow-rates which becomes the new calibration coefficient for the flume -box for a particular flow rate.

In some application, the flow rate calibration may be performed for various flow- rates, allowing the determination of multiple calibration points. After the calibration period, the rig computer may use the flow calibrations to correct the flow estimate obtained by the flume -box. The process may include:

a. Measuring of the flume -box level

b. Estimating the flow-rate through the flume -box based on an initial defined relationship.

c. Selecting the calibration coefficient from the multiple calibration points for this current uncorrected flume flow-rate, and interpolating between the available points, creating the current flow correction. d. Applying the current flow correction and obtaining the flume -box flow rate according to the relationship: flume box flow-rate = currently flow correction X uncorrected flume flow-rate.

[0084] Figure 22B illustrates another embodiment of the tanks system associated to the shale shaker and vacuum degasser. Due to the operation of the vacuum degasser, partitions may be added in the tank system. Additional valves may be required to ensure fluid transfer between compartments. However, with proper control of the valve 404, 406, 414, and pump 408, the same filling procedure may be achieved as described above. The same calibration process may also be applied.

[0085] In one or more embodiments a drain line may need to be supplied with the bottom flume box. Figure 23 illustrates an embodiment where the flume box 100 is supplied with a drain port 500 located at the bottom 208 of the flume box 100. Drain port 500 may have a nozzle, such as a venture nozzle, which controls the flow to that drain. In one or more embodiments, the flume box may be installed in the vicinity of the header tank which can be connected to multiple shale shakers. Figure 24 illustrates the flow path of the retune line 200 through the flume -box 100, to a header tank 510 and finally to one or more shale- shakers through exit 512. As illustrated, the flow path via the drain-pipe 504 may allow the sediment and fallen cutting at the bottom of the flume -box 100 to be evacuated into the header tank 510. The drain-pipe 504 may be inclined to allow the movement of the sediment and cutting towards the header box 510. The drain-pipe 504 flow may be limited by an orifice 506 while allowing proper cutting flow. The drain-pipe 504 may be equipped with a valve (as illustrated in Figure 23), or with a flow restriction as illustrated in Figure 24. In the case of an orifice 506 or nozzle (Figure 24), a fluid flow may be present through that drain-line during the sustained flow period. The flow-rate though the drain-pipe 504 may be driven by the difference in height 508 between the fluid in the flume box 100 and the height of fluid in header tank 510, and the size of the restriction.

[0086] With a 3 inch nozzle and the considered difference of level between the flume box

100 and the header box downstream of flume box 100, the flow through the drain may be less than 50 GPM. In an embodiment where the total flow is in the order of 1000 GPM of mud containing 4% cutting, the volume ratio would be in the range of 2%. This drain port 500 may adequately allow for the removal of cuttings which settle at the bottom 208 of the flume box 100. The exit line of the drain port 500 may be fed to any suitable location for fluid handling, such as a header box on a shale shaker, for example, which may also receive the flow from the throat section 216 of the flume box 100. The flow-rate through the drainpipe may be estimated and added to the flow through the flume exit throat. This drain-pipe flow may be estimated by using the formula related to an orifice or venturi:

Qdrain = K π D² V2 ΔΙ

With

Qdrain = flow-rate through the drain pipe

AL = Difference of fluid level between the flume-box and header tank D = diameter of the orifice in the drain-pipe

[0088] The flow in the drain-pipe may be estimated form the difference of level measured at the exit of the flume box and the level in the header tank of the shale shaker. The flow rate through the drain-pipe may be added to the flow determined at the exit of the flume box, so that the total flow rate reaching the flume box can be determined.

[0089] If it is expected that the flow in the header tank varies with flow rate, it may be necessary to add a level sensor in the header tank.

[0090] Illustrated in Fig. 25 is another embodiment involving a flushing port 502 to remove the potential settling of cuttings 505 in the bottom 208 of the flume box 100. When a low flow, or no flow, occurs in the flume -box, the flushing port 502 may activate and flushing fluid may be pumped in the flume box 100. This pumping of fluid may allow for cuttings 505 to be pumped up and to exit the throat section 216, thus cleaning the flume box 100. After cuttings have been removed, normal flow may resume and the height measurement 20 of the fluid level by level sensor 12 may resume. [0091] In reference to the level measurements (as illustrated in figure 21), the level LI may be obtained in a relatively still area, as the fluid movement is not generating large surface fluctuation. However CFD study demonstrated that level L2 may allow for the prediction of the flow-rate with less dependence form the fluid rheology. However, as the fluid is moving at high velocity as it passes through the critical section, the fluid surface is more unstable and the level L2 may be affected by vertical oscillation. For L2, a contactless sensor may be used, such as radar level system. It may be mounted perpendicular to the fluid surface. The reference fluid surface may be the mid- flow average condition.

[0092] Furthermore, the filtering effect of the level L2 may be performed in the flow-rate dimension. In other word, the level may be converted in flow-rate by applying the none- linear relationship. The low-pass filter may be applied on the estimated non-filter flow rate.

[0093] Level measurement (such as L3) may be performed in stilling well, allowing the use of either pressure gauge to determine the hydrostatic pressure in the well or float level sensor.

[0094] The various level measurements may be obtained by using radar sensors working as pulse-echo detection through the air above the fluid. Ultra-sonic, pulse-echo sensors may also be used either through the air above the fluid or directly through the fluid. In one or more embodiments, the level in the flume box may be determined by using a pressure gauge to obtain the hydrostatic pressure generated by the layer of fluid in the flume box or the exit throat.

[0095] Pulse-echo sensing methods may require the sensor to be installed at a certain distance above the fluid so that the transmitted pulse wave travel through air is for a certain distance. Such distance may be 1 foot or may be a few feet. In one or more embodiments, such installation may not be convenient due to space constraint above the fluid (such as for example, where the bottom fed flume box is below the rig floor). In such a situation, the sensor may be installed horizontally, and a reflector may be used to re-direct the wave travel by 90 degrees, thereby measuring the fluid level. While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.

Claims

CLAIMS What is claimed:

1. A process for measuring flow-out on a drilling rig, the process comprising:

flowing a fluid into a flume box configured to have an upward supply flow of the fluid through the flume box;

flowing the fluid out of the flume box;

measuring a height of the fluid in the flume box; and

calculating a flow measurement based on the measured height.

2. The process of claim 1 , wherein the measuring is performed in the presence of a liquid phase and a gas phase in the fluid, such that the total flow is determined from a level measurement in a sub-critical flow region.

3. The process of claim 1 , wherein the measuring is performed in the presence of a liquid phase, a solid phase, and a gas phase in the fluid, such that the total flow is determined from a level measure in a sub-critical flow region.

4. The process of claim 1 , wherein the measuring is performed in an exit throat of the flume box such that the total flow is determined from the measured level.

5. The process of claim 4, wherein a sensor is installed in the exit throat at a selected axial position to minimize effect of fluid rheology on the relationship between flow rate and fluid level.

6. The process of claim 1, wherein the fluid flowing into the flume box flows into a bottom of the flume box and is moving in the vertical plane so that a cutting sedimentation is suppressed or limited.

7. The process of claim 1, further comprising alternatively flowing from two independent fluid supply systems into the flume box.

8. The process of claim 1 , further comprising calibrating the flow measurement against a change of volume versus time in a tank associated with the flowing fluid.

9. The process of claim 8, further comprising calibrating flow rate for a plurality of flow rates.

10. The process of claim 1, further comprising determining a relationship between flow rate and fluid level by flow modeling.

1 1. The process of claim 10, wherein the flow modeling includes determination of fluid rheology.

12. The process of claim 1 , further comprising selecting a relationship between the flow rate and the horizontal fluid level.

13. The process of claim 1, further comprising limiting, by a choke or nozzle, a second flow path at the bottom of a flume box to clear sediments at the bottom of the flume box to a header box of a shale shaker of a drilling rig.

14. The process of claim 13, further comprising determining flow rate through the choke or nozzle and adding it to the flow rate estimate through the flume exit throat.

15. The process of claim 13, further comprising determining the flow rate through the second flow path from one or more level measurements in the flume box and the header tank.

16. A system for measuring flow-out on a drilling rig, the system comprising:

a bottom supplied flume box, wherein a fluid is fed into a bottom of the bottom supplied flume box creating a horizontal fluid level;

a throat section located at a height proximate the top of the bottom supplied flume box; and

a level sensor located to determine the horizontal fluid level proximate the throat section.

17. The system of claim 16, wherein the bottom supplied flume box is shaped such that a flow distribution across a horizontal cross section creates a velocity reduction in the fluid before reaching the throat section.

18. The system of claim 16, wherein a shape of the throat section is such that a selected relation between the flow rate and the horizontal fluid level is created.

19. The system of claim 18, wherein the shape of the throat section is such that the formation of a deposit when operating at a low flow, or no flow, is minimized.

20. The system of claim 16, wherein the level sensor is located above a flow section where there is no, or limited, velocity gradient in a vertical plane.

21. The system of claim 16, wherein the level sensor is located in the throat section.

22. The system of claim 21 , wherein the level sensor is located at a distance of 10 to 80% of the throat length from an entrance of the exit throat.

23. The system of claim 16, further comprising a second flow sensor located within the throat section which allows for correction of flow rate based on fluid rheology.

24. The system of claim 16, wherein the bottom supplied flume box is configured to be installed at a header box of a shale shaker on the drilling rig.

25. The system of claim 16, wherein the bottom supplied flume box is configured to be installed at a well bell-nipple of the drilling rig.

26. A system for measuring flow-out on a drilling rig, the system comprising:

a bottom flume box, wherein a fluid is fed into the flume box;

a first section configured for allowing the supplied fluid to flow downwards in the flume box in front of a central baffie;

a second section configured for allowing the fluid to flow upwards after passing below the central baffie;

a throat section located above the section of upwards flow; and

a level sensing system located proximate the throat section.

27. The system of claim 26, wherein the flume box is a two supply flume box, wherein fluids forming two different fluid lines are alternately fed into the two supply flume box.

28. The system of claim 27, wherein the two supply bottom flume box is configured to alternately accept fluid from a return supply line and a mud gas separator supply line of the drilling rig.

29. The system of claim 26, wherein the bottom flume box is configured to be installed at a header box of a shale shaker of the drilling rig.

30. The system of claim 29, wherein a bottom of the bottom flume box is shaped such that a potential sediment cutting is collected in a space which can be cleaned by a jetting or pumping effect.

31. The system of claim 30, wherein the bottom of the bottom flume box is shaped such that a potential sediment cutting is drained directly to the header tank.

32. The system of claim 31 , further comprising a choke or nozzle to limit the flow rate through the drain.

33. The system of claim 25, further comprising:

a second level sensor positioned in a location of the bottom flume box to allow for the determination of the potential sediment cutting; and

a third level sensor positioned in a location of the bottom flume box to allow for the determination of one or more rheological properties of the fluid.

34. The system of claim 26, further comprising a flume box insert configured to increase a fluid velocity or a height of the horizontal fluid level.