GB2512760A

GB2512760A - A method and apparatus for monitoring undesirable drill solids in a circulating drilling fluid

Info

Publication number: GB2512760A
Application number: GB201409108A
Authority: GB
Inventors: David Wood
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-05-22
Filing date: 2014-05-22
Publication date: 2014-10-08
Also published as: GB201409108D0

Abstract

An apparatus 1 for determining undesirable solids in drilling fluid from screen underflow of a shale shaker screen comprises a wet sifting device 2 dressed with one, two or three single-layered square mesh screen panels, a positive displacement pump 3 with a stroke counter for drawing a fluid sample into the apparatus and a containment vessel 4 to collect the undesirable solids. The screen panels may comprise pre-tensioned mesh. The wet sifting devices preferably generate a circular, horizontal and spiral pattern of travel to discharge any oversized fraction retained by the mesh screen. A method for monitoring undesirable solids in a circulating drilling fluid comprises pumping a drilling fluid from below a shale shaker screen to the apparatus of the invention, weighing the solids discarded by the wet sifting device and measuring the volume of drilling fluid pumped to the apparatus.

Description

A METHOD AND APPARTUS FOR MONITORING UNDESIRABLE DRILL

SOLIDS IN A CIRCULATING DRILLING FLUID.

A shale shaker is a general oilfield term for a vibrating device used to screen solids from circulating drilling fluid or flowable slurry. The majority of shale shakers flow the drilling fluid or flowable slurry over a rectangular screening surface. Solids under the screen aperture size are moved in such a manner that encourages them to pass through the screen, these solids are termed "undersized". Solids that are larger than the screen aperture and as such cannot pass through the screen are retained by the screen and transported off the screen. These solids are generally termed "oversized". Any fluid discharged with the oversized solids is generally termed "screen overflow" fluids carrying solids are encouraged to pass through the screen is generally termed "screen underilow". During normal drilling operations conventional shale shakers will remove 30% to 70% of circulating solids from a drilling fluid or slurry with variations in cut point from 45 microns to 25 mm. All drill solids above 74 microns are undesirable in any drilling fluid. Shale shakers are the most important and easiest to use solids removal equipment.They are the first line of defence once drilling fluid is returned from the well bore. In most cases they are highly cost-effective. If shale shakers are used with torn screens, fluids bypassing screens, incorrectly sized screen panels, or worn parts, undesirable drill solids will pass into the active system and further degrade causing low gravity solids to increase which is detrimental to the drilling operations.

The introduction of double and triple deck shale shakers has reduced the requirements for secondary fluids processing equipment while increasing the importance of efficient operation of shale shakers packages on drilling rigs. The shape of the vibrational motion of modern shale shakers is generally linear or balanced elliptical.

The uphill solids conveyance achievable with use of linear or balanced elliptical allows the processing of greater flow rates. The use of linear and elliptical motion has become feasible with the development of improved screen design. The life of shaker screens has been extended with the introduction of repairable multi mesh layered bonded and pretensioned screen panels. Other design improvements are available in wire cloth, rectangular weaves, non-metallic screens, and three dimensional screen surfaces. Examples of such shale shaker screen panels' are detailed in patents GB2382037A United Wire Ltd and US5944197A Southwest Wire Cloth Inc. Most screens used and classified as fine mesh' are layered screens and they contain more than one layer of woven wire cloth.

Layered screens may use wire cloths that are dissimilar.

The finest mesh is the top layer however this layer is often coarser than indicated by the screen mesh designation issued by the manufacturer.

The use of the term "mesh" when considering the capabilities of shaker screens was made obsolete by the introduction of oblong mesh and multi layer screens which resulted in the formation of variations of apertures within a shaker screen matrix. Fig 2 shows photomicrographs (60x) of four different screens from four different manufactures supplied prior to the

introduction of API RP 13C.

This demonstrates the confusion caused by non standard screen nomenclature.

The American Petroleum Institute represents all aspects of the U.S. petroleum and natural gas industry. In December 2004, the API passed RP13C titled "Recommended Practice on Drilling Fluids Processing Systems Evaluation". The recommended practice combined and updated two previous separate documents RP13C and RPI3E. While RP13C covers a number of subjects relating to fluids treatment systems.

The revised shale shaker screen testing procedures and numbering convention ensures all screens which are tested according to RP13C have the same API screen number. And remove solids of a similar size based on their D100 cut point. This cut paint is the absolute cut point and any particle larger than this value will not pass through the screen under laboratory test conditions. RPI3C does not predict the performance of a multi layered screen in the field but if all other variables are equal screens from different manufactures with the same API Screen designation or API number will have equivalent 0100 cut points.

The Dl 00 absolute cut point of a multi layered screen increases over its useful operational life. The initial causes of this increase are interaction screen wear between the top fine meshes which changes the size of the various apertures formed within the screen matrix.

Later in the screens operational life the failure of the mesh used to support the finer meshes occurs this is more serious as this allows much larger particles into the active system. Other issues that allow oversized particles past shale shakers includes the inexperience of shaker hands who maintain the equipment, leaking or open bypass valves, incorrectly fitted screen panels, worn screen seals, worn wear components in screen baskets and using a combination of screen panels from different manufactures at the same time on the same shale shaker. An industrial 2ft wet screening process is usually a continuous one. Undersize particles are invariably left in the oversize fraction, mainly because the material does not remain on the screen for a sufficiently long period. Oversize particles may be found in the undersize fraction if the screen mesh is non-uniform, punctured or inadequately sealed around its edges.

It would be beneficial to a drilling operation to be able to determine in real time the rate of wear for operational multilayer shale shaker screens and the corresponding increase in volume of particles in excess of the D100 size of the expected undersized fraction passing operational multilayer shale shaker screens and shale shakers on single or multiple numbers of operational units.

The object of the present invention is to provide an apparatus and method of determining undesirable drilling solids in a circulating drilling fluid.

Therefore according to the present invention there is provided an apparatus and method of determining undesirable drill solids in the undersized fraction passing an API RC 1 3C compliant operational multilayer shaker screen and single or multiple numbers of operational shale shakers while determining the rate of wear and increase in the volume of particles above the D100 particle size of the expected undersized fraction.

Advantageous features of the apparatus according to the invention are set forth in dependent patent claims 2 and 3.

Furthermore, the method is characterised in that it comprises of pumping a drilling fluid sample from below an API RC 1 3C compliant screen to the apparatus, weighing the undesirable drill solids, discarded by the wet sifting device, determining the volume of drilling fluid pumped to the wet sifting device using a positive displacement pump fitted with a stroke counter. Advantageous features of the apparatus according to the invention are set forth in dependent patent claim 4 and 5.

The invention will now be described in more detail by means of examples, and reference made to the appended drawings.

Figure 1 is a cross-section of the apparatus according to the invention.

Figure 2 shows photomicrographs (60x) of meshes of different shale shaker screens from four different manufactures supplied prior to the

introduction of APR RP 13C.

Fig 1 shows a cross-section of wet sifting device (2) a positive displacement pump (3) with a stroke counter and method of adjusting pump speed, a suitable solids containment vessel (4) to collect and allow weighing of the undesirable drill solids, and the apparatus (1).

Fig 2 shows photomicrographs (BOx) of four different screens from four different manufactures. This demonstrates the confusion caused by non-standard screen nomenclature supplied prior to the introduction of APR RP 13C.

Preferably a wet sifting device (2) is placed downstream of the single or multiple numbers of shale shakers adjacent to the drilling fluid flow containing the undersized fraction.

Typically the wet sifting device (2) generates a circular horizontal and spiral pattern of travel to discharge any oversized fraction retained by the pretensioned square mesh sieve test screen fitted into the wet sifting device.

Preferably a positive displacement pump (3) with a stroke counter is placed downstream of the single or multiple shale shakers adjacent to the drilling fluid flow containing the undersized fraction.

Typically the positive displacement pump (3) is connected to recover and transfer a representative sample of the drilling fluid containing the undersized fraction at an adjustable and measureable pump rate.

Typically the wet sifting device (2) may have one, two or three screen decks and each screen deck assembly will include a single oversized fraction discharge spout.

Preferably the drilling fluid recovered contains a representative sample of the undersized fraction passing the multilayered screens or other particles and fluids passing the single or multiple operational shale shakers.

Typically the wet sifting device (2) may have one, two or three screen decks and each screen deck would be dressed with a pretension square mesh comparable to an ASTM test sieve or ISO test sieve mesh or equivalent standard grade specification of known separation ability.

Typically the pretensioned screen assembly when dressed with a pretensioned square mesh comparable to a ASTM test sieve or ISO test sieve mesh or equivalent standard grade would have a anti blinding system incorporated below the square mesh.

Typically the wet sifting device(2) may have one, containment vessel (4) to contain any oversized fraction discharged from each spout, and allow any whole fluid to gravity drain out of the containment vessel.

Typically the wet sifting device (2) and apparatus (1) has particular interest in particles in excess of 74 microns contained within the undersized fraction, other sized particles may be of interest.

Typically a simple multiplication can be carried out to determine the volume in pounds/ barrel (wet weight) of the undesirable drill solids, by the following steps.

a/Weight of containment vessel empty minus the weight of containment vessel full = wet weight of collected sample.

b/ Strokes of positive displacement pump multiplied by volume of fluid displaced per stroke of pump = volume of fluid processed by wet sifting device.

Example 1

Wet weigh of collected solids sample = 2 pounds.

Volume of fluid processed by wet sifting device = 0.5 barrels.

Therefore four pounds / barrel of undesirable drill solids are recorded.

Example 2

Wet weigh of collected solids sample = 0.5 pounds Volume of fluid processed by wet sifting device = 1 barrel Therefore 0.5 pounds / barrel of undesirable drill solids are recorded.

Dry weigh of the solids sample can be calculated by collecting a representive solids sample, using a 50m1 retort to heat the sample which will evaporate and separate fluid and solid fractions of the sample.

Typically a sampling period would be determined by the volume of undesirable drill solids been discarded into the containment vessel (4) Typically the upper most pretensioned screen panel would be renewed after one to five days of operation.

Typically all the pretensioned screen panels located in the wet sifting device (2) would be changed at the start of a new hole section.

Typically if economically viable used and unserviceable pretensioned screen panels would be returned to the manufacturer for recycling.