CN106814018A - A kind of tight rock gas phase relative permeability measurement apparatus and method - Google Patents

Abstract

The invention discloses a tight rock gas phase relative permeability measuring device, which comprises: a core holder, a confining pressure pump, a variable-volume upstream pressure chamber, a variable-volume downstream pressure chamber, a high-pressure gas source, a console and nuclear magnetic resonance instrument; the gas outlet of the high-pressure gas source is connected to the inlet of the variable-volume upstream pressure chamber through valve a, the first pressure controller and valve b in turn, and the outlet of the variable-volume upstream pressure chamber is clamped with the rock core through valve c The core holder is connected with the inlet of the variable-volume downstream pressure chamber through the valve d, and the outlet of the variable-volume downstream pressure chamber is connected with the pressure relief port through the valve f; the core holder is set in the nuclear magnetic resonance instrument inside the measuring chamber. The present invention also provides a set of measuring methods based on the measuring device. The invention has the beneficial effect of being able to quickly and effectively measure the gas relative permeability of tight rocks.

Description

Device and method for measuring gas phase relative permeability of tight rock

technical field

The invention relates to a device and a method for measuring gas phase relative permeability of tight rock, belonging to the field of gas relative permeability measurement.

Background technique

Natural gas resources in low-permeability tight reservoirs account for a large proportion of geological resources in my country. Accurately measuring the physical properties of such reservoir rocks (such as gas phase relative permeability) is very important for reservoir gas well production calculation, dynamic analysis, numerical simulation, etc. However, it is currently difficult to accurately measure the gas/water relative permeability of tight rocks.

The existing laboratory tests of gas/water relative permeability refer to GB/T 28912-2012 (Method for Determination of Relative Permeability of Two-phase Fluids in Rocks), that is, the steady-state method and the unsteady-state method are used to measure the gas permeability. / water relative permeability. The steady-state method is to inject gas/water into the rock sample at a constant rate at a certain flow rate until the pressure at both ends of the inlet and outlet of the rock sample and the gas/water flow through the rock sample are stable, and the water saturation of the rock sample does not change anymore. The effective permeability and relative permeability are directly calculated by Darcy's formula; this method is suitable for rocks with good permeability (it is easy to achieve stability), but it is invalid for tight rocks because the stability time is too long.

However, the determination of gas/water relative permeability of low-permeability tight rocks generally adopts the unsteady-state method in the standard GB/T28912-2012, that is, the test sample is saturated with water first, and gas is injected at a certain pressure or flow rate to displace the saturated water rock. In the same way, the relationship between displacement pressure, water production and gas production over time was recorded, and special attention was paid to the observation and recording of the water breakthrough time node, and then the gas/water relative permeability was calculated by the J.B.N method; although this method shortened the test time, The test efficiency is improved, but the influence of capillary pressure is ignored (capillary phenomenon is very prominent in tight reservoirs (see: capillary pressure and permeability relationships in tight gas sands [Wells et al., 1985]), and the relative permeability of gas/water In addition, there is often a lag in the determination of the water breakthrough time node, which makes the effective measurement of the gas/water relative permeability unable to be guaranteed.

Contents of the invention

In view of the above-mentioned problems and deficiencies, the technical problem to be solved by the present invention is: how to provide a method that can quickly measure the gas relative permeability under the condition of considering the effect of capillary pressure, and can reduce the number of steps due to the traditional measuring device and its measuring method. A gas-phase relative permeability measurement device that is cumbersome and easily leads to human error.

The present invention also provides a set of measuring methods based on the measuring device.

In order to solve the above problems, the present invention adopts the following technical solutions.

A tight rock gas phase relative permeability measurement device, which includes: a core holder, a confining pressure pump, a variable-volume upstream pressure chamber, a variable-volume downstream pressure chamber, a high-pressure gas source, a console, and a nuclear magnetic resonance instrument; A core is loaded in the core holder, and a thermometer is arranged on the core holder;

The gas outlet of the high-pressure gas source is connected to the inlet of the variable-volume upstream pressure chamber through the valve a, the first pressure controller and the valve b in sequence, and the outlet of the variable-volume upstream pressure chamber is clamped with the rock core through the valve c connected to the front end of the device; the rear end of the core holder is connected to the inlet of the variable volume downstream pressure chamber through the valve d, and the outlet of the variable volume downstream pressure chamber is connected to the pressure relief port through the valve f; the core holder The rear end of the holder is connected to the drain port through the valve e; the gas outlet of the confining pressure pump is connected to the front end of the core holder through the valve g and the second pressure controller in turn;

A valve h is provided between the front end of the core holder and the inlet of the variable volume downstream pressure chamber;

The upstream pressure sensor P1 for monitoring the pressure value of the variable volume upstream pressure chamber is electrically connected to the console; the downstream pressure sensor P2 for monitoring the pressure value of the variable volume downstream pressure chamber is electrically connected to the console; the variable volume upstream pressure chamber A differential pressure sensor is arranged between the outlet of the variable volume downstream pressure chamber and the inlet of the variable volume downstream pressure chamber, and the differential pressure sensor is electrically connected to the console; the thermometer is electrically connected to the console.

Further, the core holder is arranged inside the measurement cavity of the nuclear magnetic resonance instrument.

A method for measuring gas phase relative permeability of tight rocks, comprising the following steps:

S1. Put the dried rock core into the core holder, open the valve g, and after applying the set confining pressure to the rock core with the confining pressure pump, adjust the volume of the variable volume upstream pressure chamber and the variable volume downstream pressure chamber to The value matching the pore volume of the rock sample, open valve h, valve d, valve c, valve a and valve b, close valve e and valve f, apply the pressure in the system to the design value P _m , after the system is stable, close Valve b, valve a, valve c, and valve h keep valve d open;

S2. Open valve a and valve b, and apply a pulse to the variable volume upstream pressure chamber. When the pressure in the variable volume upstream pressure chamber rises and reaches the set pressure, close valve a and valve b, and wait until the variable volume upstream pressure chamber When the pressure of the pressure chamber is stable, open the valve c until the pressure of the variable volume upstream pressure chamber and the pressure of the variable volume downstream pressure chamber tend to be stable, then stop the experiment;

S3. The computer on the console acquires the pressure value P ₁ of the variable-volume upstream pressure chamber, the pressure value P ₂ of the variable-volume downstream pressure chamber, the pressure difference △P between the upstream and downstream and the temperature t through the data acquisition card, and obtains the upstream and downstream pressure The relation curve of difference △P and time, and calculate the slope α ₁ ;

According to formula 1, the absolute permeability k _ab under internal pressure P _m is calculated before saturated water:

Among them, the dimension of α ₁ is s ^-1 ; μ is the viscosity of the gas, the dimension is mPa·s; L is the length of the rock sample, the dimension is cm; f _z is the coefficient related to the properties of nitrogen, which is dimensionless; The cross-sectional area of the sample, dimension cm ² ; P _m is the pore pressure, dimension MPa; V ₁ is the total volume of the upstream water tank, pipelines and valves upstream of the rock sample, dimension cm ³ ; V ₂ is the water tank downstream of the rock sample and the total volume of pipelines and valves, dimension cm ³ ; k _ab is the absolute permeability;

S4. Take out the core from the core holder and saturate it with water, then put the core back into the core holder, turn on the nuclear magnetic resonance instrument to check whether the water content in the core reaches the saturation requirement, observe the water saturation of the core in real time, and close the valve d, valve f and valve h, refer to the gas-water capillary pressure curve of the rock core to select the corresponding displacement pressure difference, open the valve valve e, valve c, valve b and valve a, and use nitrogen to displace the water in the rock core, when the NMR When it is observed in the resonance instrument that the water saturation reaches the preset value β%, close the valve e, open the valve d, valve f and valve h, repeat steps S1-S3, and obtain the relationship curve between the upstream and downstream pressure difference △P and time, And calculate the slope α ₂ ;

Calculated according to formula 2: when the water saturation in the core is β%, the permeability k _ap under the internal pressure P _m is:

Among them, the dimension of α ₂ is s ^-1 ; k _ap is the apparent permeability;

The gas relative permeability k _r is obtained according to formula 3:

S5. Continue to use nitrogen to displace the water in the core, repeat S4, and according to formula 1, formula 2 and formula 3, the gas phase permeability at different water saturations can be obtained.

The present invention has the following beneficial effects: (1) no need to spend a lot of time measuring the stable flow rate of low-permeability rock cores; (2) gas phase permeability at multiple saturations can be obtained in a short time; (3) real-time monitoring and judging system stability, and help to adjust the test plan and test process, try to avoid the existence of system and human error. (4) The effect of capillary pressure is considered in the measurement process, so that the effective measurement of gas/water relative permeability is guaranteed.

In summary, the present invention has the beneficial effect of being able to quickly and effectively measure the gas relative permeability of tight rocks.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

In the figure, 1-valve a, 2-valve b, 3-valve c, 4-valve d, 5-valve e, 6-valve f, 7-valve g, 8-valve h, 9-confining pressure pump, 10 -pressure controller 1, 11-pressure controller 2, 12-differential pressure sensor, 13-upstream pressure sensor, 14-downstream pressure sensor, 15-thermometer, 16-drainage port, 17-pressure relief port, 18-core clamp Holder, 19-nuclear magnetic resonance instrument, 20-variable volume upstream pressure chamber, 21-variable volume downstream pressure chamber, 22-console, 23-high pressure gas source.

detailed description

As shown in Fig. 1: the present invention is a kind of device of non-steady-state method measuring gas relative permeability, and device structure characteristic is as follows: it mainly consists of rock core holder 18, confining pressure pump 9, variable volume upstream pressure chamber 20, Composed of variable volume downstream pressure chamber 21, high pressure gas source 23, console 22 and nuclear magnetic resonance instrument 19;

The invention can be used to measure the gas phase relative permeability in the oil/gas two-phase seepage and the gas phase relative permeability in the gas/water two-phase seepage, and the gas phase relative permeability in the gas/water two-phase seepage will be described below.

The rock core for testing is loaded in the rock core holder 18, and a thermometer is arranged on the rock core holder. Both the variable-volume upstream pressure chamber 20 and the variable-volume downstream pressure chamber 21 can be adjusted in volume, and the volume of the variable-volume upstream pressure chamber 20 is larger than the variable-volume downstream pressure chamber 21. Due to the different combinations of upstream and downstream volumes, the pressure The total time of pulse propagation is different from the total pressure drop that can be generated. Therefore, an adjustable pressure chamber is used. According to the different volume ratios of the upstream and downstream pressure chambers, combined with the actual situation, the gas permeability at this saturation can be measured more accurately. .

The gas outlet of the high-pressure gas source 23 is connected to the inlet of the first pressure controller 10 through the valve a1, and the outlet of the first pressure controller 10 is connected to the inlet of the variable volume upstream pressure chamber 20 through the valve b2, and the variable volume upstream The outlet of the pressure chamber 20 is connected to the front end of the rock core holder 18 through the valve c3, and the rear end of the rock core holder 18 is connected to the inlet of the variable volume downstream pressure chamber 21 through the valve d4, and the variable volume downstream pressure chamber 21 The outlet of the valve f6 is connected with the pressure relief port 17; the rear end of the core holder 18 is connected with the drain port 16 through the valve e5; the gas outlet of the confining pressure pump 9 is connected with the valve g7 and the second pressure controller 11 in turn. The front end of the core holder 18 is connected; a valve h8 is arranged between the front end of the core holder 18 and the inlet of the variable volume downstream pressure chamber 21; the upstream pressure sensor P113 for monitoring the pressure value of the variable volume upstream pressure chamber It is electrically connected with the console 22; the downstream pressure sensor P214 for monitoring the pressure value of the variable volume downstream pressure chamber is electrically connected with the console 22; the outlet of the variable volume upstream pressure chamber 20 is connected with the outlet of the variable volume downstream pressure chamber 21 A differential pressure sensor 12 is arranged between the inlets, and the differential pressure sensor 12 is electrically connected to the console 22 ; the thermometer 15 is electrically connected to the console 22 .

The present invention uses the pressure pulse method to realize the measurement, and its measurement principle is as follows: to measure the gas relative permeability by the pressure pulse method, first apply a certain amount of pulse to the upstream of the rock, so that the gas can seep in one dimension inside the rock, the upstream pressure decreases, and the downstream pressure Adding, you can get the relationship curve and data of the pressure difference and time between the upstream and downstream of the rock. Based on Darcy's law and the continuity equation of gas, the numerical solution of the gas diffusion equation can be obtained; the numerical solution of the diffusion equation is used to explain the experimental data obtained by the transient pulse method, and the permeability of the rock is obtained, that is, the absolute permeability of the rock . After the rock is saturated with water, put it into the core holder, and use the nuclear magnetic resonance device to monitor the nitrogen to displace the water. At this time, a water saturation of β% is formed. Assuming that the water will not move in the experiment, a certain amount of pulse is applied to the upstream , the relationship curve and data of the pressure difference between the upper and lower reaches of the rock at this water saturation and time can be obtained, and then the permeability at this gas saturation can be obtained, that is, the gas phase permeability of the rock. The formula for calculating the relative gas permeability is as follows :

Wherein: α is the slope of the relationship between the pressure difference and time of two fittings respectively, dimension s ^-1 . μ is the viscosity of the gas in mPa·s. L is the rock sample length, dimension cm. f _z is a coefficient related to the properties of nitrogen, dimensionless. A is the cross-sectional area of the rock sample, in cm ² . p _m is the pore pressure in mPa. V ₁ is the total volume of the upstream water tank, pipelines and valves upstream of the rock sample, in cm ³ . V ₂ is the total volume of water tanks, pipelines and valves downstream of the rock sample, in cm ³ . k _ab is the absolute permeability. k _ap is the gas phase permeability. k _r is the gas relative permeability.

Establishment of water saturation: measure the gas-water capillary pressure curve of the rock sample, select different capillary pressures accordingly, each capillary pressure corresponds to a water saturation β%, and measure the selected saturated capillary pressure in the experiment Permeability of the gas phase at . Each saturation corresponds to a capillary pressure, so the size of the pulse in the experiment, that is, the selection of △P has an upper limit, and the pressure difference △p in the experiment is designed by the size of the porosity and the pressure selected on the capillary pressure curve. , the volume of the variable volume downstream pressure chamber.

The core holder is placed in the NMR instrument, and the entire core holder is in a hydrogen-free state.

The upstream total volume V ₁ and the downstream total volume V ₂ are determined prior to testing.

The specific method of measuring gas relative permeability by pressure pulse is divided into the following steps:

S1. Put the dried core into the core holder, open the valve g7, apply the set confining pressure to the core with the confining pressure pump 9, adjust the variable volume upstream pressure chamber 20 and the variable volume downstream pressure chamber 21 For the most suitable volume size (that is, the value that matches the pore volume of the rock sample), open valve h8, valve d4, valve c3, valve a1, valve b2, close valve e5, and valve f6, and apply the pressure in the system to Design value P _m , after the system stabilizes (about two hours), close valve b2, valve a1, valve c3 and valve h8, and keep valve d4 open;

S2. Open the valve a1 and the valve b2, apply a pulse to the variable volume upstream pressure chamber 20, when the pressure of the variable volume upstream pressure chamber rises and reaches the set pressure, close the valve a1 and the valve b2, wait until the variable volume When the pressure of the upstream pressure chamber is stable, open the valve c3 until the pressure of the variable volume upstream pressure chamber and the pressure of the variable volume downstream pressure chamber tend to be stable, then stop the experiment;

S3. The computer on the console acquires the pressure value P ₁ of the variable-volume upstream pressure chamber, the pressure value P ₂ of the variable-volume downstream pressure chamber, the pressure difference △P between the upstream and downstream and the temperature t through the data acquisition card, and obtains the upstream and downstream pressure The relation curve of difference △P and time, and calculate the slope α ₁ ;

According to formula 1, the absolute permeability k _ab under internal pressure P _m is calculated before saturated water:

Among them, the dimension of α ₁ is s ^-1 ; μ is the viscosity of the gas, the dimension is mPa·s; L is the length of the rock sample, the dimension is cm; f _z is the coefficient related to the properties of nitrogen, which is dimensionless; The cross-sectional area of the sample, dimension cm ² ; P _m is the pore pressure, dimension MPa; V ₁ is the total volume of the upstream water tank, pipelines and valves upstream of the rock sample, dimension cm ³ ; V ₂ is the water tank downstream of the rock sample and the total volume of pipelines and valves, dimension cm ³ ; k _ab is the absolute permeability;

S4. Take out the core from the core holder and saturate it with water (refer to GB/T 28912-2012) and then put it back into the core holder 18, turn on the nuclear magnetic resonance instrument 19 to check whether the water volume in the core reaches the saturation requirement and real-time Observe the water saturation of the core, close valve d4, valve f6 and valve h8, select the corresponding displacement pressure difference according to the gas-water capillary pressure curve of the core, open valve e5, valve c3, valve b2 and valve a1, and use nitrogen to displace When the water in the core is observed from the nuclear magnetic resonance instrument and the water saturation reaches the preset value β%, close the valve e5, open the valve d4, the valve f6 and the valve h8, repeat steps S1-S3, and obtain the pressure difference between the upstream and downstream The relationship curve between △P and time, and calculate the slope α ₂ ;

Calculated according to formula 2: when the water saturation in the core is β%, the permeability k _ap under the internal pressure P _m is:

Among them, the dimension of α ₂ is s ^-1 ; k _ap is the apparent permeability;

The gas relative permeability k _r is obtained according to formula 3:

S5. Continue to use nitrogen to displace the water in the core, repeat S4, and according to formula 1, formula 2 and formula 3, the gas phase permeability at different water saturations can be obtained.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims (3)

1. a kind of tight rock gas phase relative permeability measurement apparatus, it is characterised in that including：Core holding unit (18), confined pressure Pump (9), variable-volume upstream pressure room (20), variable-volume downstream pressure room (21), high-pressure air source (23) and console (22)； Rock core is mounted with the core holding unit (18), core holding unit (18) is provided with thermometer (15)；

The gas outlet of the high-pressure air source (23) pass sequentially through valve a (1), first pressure controller (10) and valve b (2) with can The import of variable volume upstream pressure room (20) is connected, and the outlet of the variable-volume upstream pressure room (20) passes through valve c (3) Front end with core holding unit (18) is connected；Pressed with variable-volume downstream by valve d (4) rear end of core holding unit (18) The import of power room (21) is connected, and the outlet of the variable-volume downstream pressure room (21) is by valve f (6) and pressure relief opening (17) It is connected；The rear end of core holding unit (18) is connected by valve e (5) with discharge outlet (16)；The outlet of confined pressure pump (9) is successively It is connected with the front end of core holding unit (18) by valve g (7) and second pressure controller (11)；

Valve h is provided between the front end of the core holding unit (18) and the import of the variable-volume downstream pressure room (21) (8)；

Upstream pressure sensor P1 (13) for monitoring variable-volume upstream pressure chamber pressure force value is electrically connected with console (22)； Downstream pressure sensor P2 (14) for monitoring variable-volume downstream pressure chamber pressure force value is electrically connected with console (22)；It is described Pressure difference is provided between the outlet of variable-volume upstream pressure room (20) and the import of the variable-volume downstream pressure room (21) Sensor (12), the differential pressure pickup (12) electrically connects with console (22)；The thermometer (15) and console (22) electricity Connection.

2. gas phase relative permeability measurement apparatus in a kind of tight rock according to claim 1, it is characterised in that described Core holding unit (18) is arranged on inside the measurement chamber of NMR (19).

3. a kind of tight rock gas phase relative permeability measuring method, it is characterised in that it is comprised the following steps：

S1, the rock core of drying is put into core holding unit, opens valve g (7), applying setting to rock core with confined pressure pump (9) encloses After pressure, the volume of variable-volume upstream pressure room (20) and variable-volume downstream pressure room (21) is adjusted to and rock sample pore-body The value that matches of product, opens valve h (8), valve d (4), valve c (3), valve a (1) and valve b (2), closing valve e (5) and Valve f (6), design load P is applied to by pressure in system_m, after after system stabilization, close valve b (2), valve a (1), valve c (3) and valve h (8), valve d (4) is stayed open；

S2, opening valve a (1) and valve b (2), a pulse is applied to variable-volume upstream pressure room (20), works as variable-volume When upstream pressure chamber pressure rises and reaches the pressure for setting, valve a (1) and valve b (2) are closed, treat variable-volume upstream During balancing gate pit's pressure stability, valve c (3) is opened, until variable-volume upstream pressure chamber pressure and variable-volume downstream pressure room When pressure tends towards stability, stop experiment；

Computer on S3, console collects variable-volume upstream pressure chamber pressure force value P by data collecting card₁, can variant Product downstream pressure chamber pressure force value P₂, upstream and downstream pressure differential △ P and temperature t, show that the relation of upstream and downstream pressure differential △ P and time is bent Line, and calculate slope₁；

Calculated according to formula 1：Before saturation water, internal pressure P_mUnder absolute permeability k_ab：

Wherein, α₁Dimension be s^-1；μ is the viscosity of gas, dimension mPas；L is rock sample length, dimension cm；f_zIt is and nitrogen The coefficient of qualitative correlation, dimensionless；A is the sectional area of rock sample, dimension cm²；P_mIt is pore pressure, dimension MPa；V₁It is rock sample upstream Upstream water tank and pipeline, the cumulative volume of valve, dimension cm³；V₂It is water tank and pipeline, the cumulative volume of valve in rock sample downstream, amount Guiding principle cm³；k_abIt is absolute permeability；

S4, rock core is taken out and again puts back in core holding unit (18) rock core after saturation water from core holding unit, open nuclear-magnetism Resonance instrument (19) checks that rock core includes the water saturation whether water volume reaches saturation requirement and real-time monitored rock core, shutoff valve Door d (4), valve f (6) and valve h (8), corresponding displacement pressure difference is chosen with reference to the rock core air water capillary pressure curve, opens valve Gate valve door e (5), valve c (3), valve b (2) and valve a (1), with nitrogen flooding for the water in rock core, when from NMR It was observed that when water saturation reaches preset value β %, closing valve e (5), valve d (4), valve f (6) and valve h (8), weight are opened Multiple step S1-S3, draws the relation curve of upstream and downstream pressure differential △ P and time, and calculate slope₂；

Calculated according to formula 2：When water saturation is β % in rock core, internal pressure P_mUnder permeability k_ap：

Wherein, α₂Dimension be s^-1；k_apIt is apparent permeability；

Gas relative permeability k is drawn according to formula 3_r：

S5, continuation nitrogen flooding repeat S4 for the water in rock core, and it is full to can obtain different water according to formula 1, formula 2 and formula 3 With the gas phase permeability under degree.