A core contamination level testing device and method

Abstract

The application provides a core pollution degree testing device and method, which comprises the following modules: a true triaxial stratum simulation module for simulating pollution of a simulated rock sample; a drilling fluid circulation module for providing the simulated rock sample with drilling fluid required for the pollution simulation; and a permeability measurement module for obtaining permeability of the simulated rock sample. The true triaxial loading module is used to restore the reservoir state more realistically and simulate the invasion, deposition and aging of the weighted mud under the condition, so as to accurately evaluate the mud pollution degree and provide an important theoretical basis for scientifically and efficiently increasing and restoring production of the well polluted by the mud.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas development, and particularly relates to a core pollution degree testing device and method. BACKGROUND

[0002] In deep well drilling, abnormal high pressure strata are often drilled. In order to ensure the safety of the drilling process, barite powder is generally added as a weighting agent to maintain a positive pressure difference drilling. In addition, the long drilling period of deep wells leads to a long soaking time of the drilling fluid, which makes the drilling fluid invade the strata. The barite powder, carboxymethyl cellulose, polyacrylamide, xanthan gum and other plant-derived or synthetic polymer components in the drilling fluid are filtered into the surrounding well wall with the drilling fluid filtrate, and then migrate, transform and form a mud cake, thereby causing pollution of the reservoir.

[0003] At present, in the process of experimental research on mud pollution, many problems are caused due to the limitation of the device. The existence of these problems leads to the fact that the experiment often cannot well simulate the conditions of the actual operation, such as:

[0004] (1) The conventional experimental device can only apply a circumferential stress to the surface of the rock sample, and cannot perform triaxial stress loading, which leads to the fact that the pollution environment of the reservoir cannot be more truly simulated.

[0005] (2) The anisotropy of the real strata is ignored, and it is assumed that the pollution degree of the drilling fluid on both sides of the wellbore is always consistent, which leads to an error in the permeability. SUMMARY

[0006] The purpose of the present application is to provide a core pollution degree testing device, which solves the defect that the existing mud pollution experimental device cannot well simulate the conditions of the actual operation.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0008] The core pollution degree testing device provided by the present application comprises:

[0009] a true triaxial stratum simulation module for simulating the pollution of the simulated rock sample;

[0010] a drilling fluid circulation module for providing the simulated rock sample with the drilling fluid required for the pollution simulation;

[0011] a permeability measurement module for obtaining the permeability of the simulated rock sample.

[0012] Preferably, the true triaxial stratum simulation module comprises an annular pressure applying plate, a simulated wellbore, a core clamping box, a Y-axis pressure applying piece and an X-axis pressure applying piece. The Y-axis pressure applying piece and the X-axis pressure applying piece are respectively arranged at the side walls of the core clamping box in the Y-axis direction and the X-axis direction, and are used to provide the core clamping box with the Y-axis direction pressure and the X-axis direction pressure.

[0013] The annular pressure plate is arranged at the upper end of the core holder box to provide Z-axis direction pressure to the core holder box;

[0014] The top of the core holder box is further provided with a heat transfer assembly for transferring heat to the core holder box, and the heat transfer assembly is arranged at the lower end of the annular pressure plate;

[0015] The cavity of the core holder box is provided with a simulated rock sample, and the simulated wellbore is arranged in the inner cavity of the simulated rock sample.

[0016] Preferably, the Y-axis pressure device comprises a Y-axis No. 1 hydraulic bag, a Y-axis No. 2 hydraulic bag, a Y-axis pumping pump group and a Y-axis pump group liquid supply tank, wherein the Y-axis No. 1 hydraulic bag and the Y-axis No. 2 hydraulic bag are respectively arranged at two outer walls in the Y-axis direction of the core holder box; the inlet and outlet ports of the Y-axis No. 1 hydraulic bag and the Y-axis No. 2 hydraulic bag are communicated with the Y-axis pumping pump group and the Y-axis pump group liquid supply tank through the Y-axis pumping pump group.

[0017] Preferably, the X-axis pressure device comprises an X-axis No. 1 hydraulic bag, an X-axis No. 2 hydraulic bag, an X-axis pumping pump group and an X-axis pump group liquid supply tank, wherein the X-axis No. 1 hydraulic bag and the X-axis No. 2 hydraulic bag are respectively arranged at two outer walls in the X-axis direction of the core holder box; the inlet and outlet ports of the X-axis No. 1 hydraulic bag and the X-axis No. 2 hydraulic bag are communicated with the X-axis pumping pump group and the X-axis pump group liquid supply tank through the X-axis pumping pump group.

[0018] Preferably, the drilling fluid circulation module comprises a drilling fluid inlet pipeline, an injection pump, a drilling fluid storage tank, a drilling fluid circulation power pump and a drilling fluid outlet pipeline, wherein:

[0019] One end of the drilling fluid inlet pipeline is connected to the inlet port of the simulated wellbore in the true triaxial stratum simulation module, and the other end is connected to the drilling fluid storage tank through the injection pump;

[0020] One end of the drilling fluid outlet pipeline is connected to the outlet port of the simulated wellbore, and the other end is connected to the drilling fluid storage tank through the drilling fluid circulation power pump.

[0021] Preferably, the permeability measurement module comprises a nitrogen cylinder, a pressure reducing valve, an inlet end pressure gauge, an inlet end valve, an inlet pipeline, an outlet three-way joint, an outlet valve, an outlet pipeline, an outlet end pressure gauge and a gas flow meter, wherein:

[0022] The pressure reducing valve is installed at the gas outlet of the nitrogen cylinder, and the pressure reducing valve is connected to the gas inlet port formed on the core holder box in the true triaxial stratum simulation module through the inlet pipeline;

[0023] The inlet pipeline is provided with an inlet end pressure gauge and an inlet end valve;

[0024] The outlet pipeline is connected to the simulated wellbore in the true triaxial stratum simulation module.

[0025] The gas outlet pipeline is provided with a gas outlet end valve, a gas flow meter and a gas outlet end pressure gauge.

[0026] A core contamination degree testing method comprises the following steps:

[0027] The initial permeability of the simulated rock sample is calculated by using a permeability measurement module;

[0028] The simulated rock sample is simulated for drilling fluid circulation in the drilling process by using a true triaxial loading module and a drilling fluid circulation module;

[0029] The contaminated permeability of the simulated rock sample is calculated by using a permeability measurement module;

[0030] The core contamination degree is calculated according to the initial permeability and the contaminated permeability.

[0031] Preferably, the initial permeability of the simulated rock sample is calculated by using a permeability measurement module, and the specific method is as follows:

[0032] The gas inlet pipeline is communicated with the left gas inlet of the core clamping box; the right gas inlet and the liquid outlet of the core clamping box are blocked;

[0033] The gas inlet end valve and the gas outlet end valve are opened, and the core clamping box is ventilated until the readings of the gas inlet end pressure gauge, the gas outlet end pressure gauge and the gas flow meter are stable;

[0034] The gas inlet end pressure, the gas outlet end pressure and the outlet gas flow under a plurality of different average pressures of the inlet and outlet ends are recorded;

[0035] The absolute permeability of the left side of the initial rock sample is calculated according to the obtained gas inlet end pressure, gas outlet end pressure and outlet gas flow;

[0036] The gas inlet pipeline is communicated with the right gas inlet of the core clamping box; the left gas inlet and the liquid outlet of the core clamping box are blocked;

[0037] The gas inlet end valve and the gas outlet end valve are opened, and the core clamping box is ventilated until the readings of the gas inlet end pressure gauge, the gas outlet end pressure gauge and the gas flow meter are stable;

[0038] The gas inlet end pressure, the gas outlet end pressure and the outlet gas flow under a plurality of different average pressures of the inlet and outlet ends are recorded;

[0039] The absolute permeability of the right side of the initial rock sample is calculated according to the obtained gas inlet end pressure, gas outlet end pressure and outlet gas flow.

[0040] ​​Preferably, the simulation of drilling fluid circulation in the drilling process is simulated on the simulated rock sample by using the true triaxial loading module and the drilling fluid circulation module, and the specific method is as follows:

[0041] Close the inlet valve and the outlet valve;

[0042] Apply the preset Z-axis pressure to the core clamping box by using the annular pressure plate;

[0043] Apply the preset Y-axis pressure to the core clamping box by using the Y-axis pressure applying piece;

[0044] Apply the preset X-axis pressure to the core clamping box by using the X-axis pressure applying piece;

[0045] Load the preset temperature to the core clamping box by using the heat transfer assembly;

[0046] Open the drilling fluid inlet valve and the drilling fluid outlet valve;

[0047] Start the injection pump to inject the drilling fluid into the simulated wellbore, and then start the drilling fluid circulation power pump to pump the drilling fluid flowing out of the core clamping box back to the drilling fluid storage tank;

[0048] After the drilling fluid circulation is completed, keep the temperature and pressure loading and stand the simulated rock sample for a preset time.

[0049] Preferably, the contaminated permeability of the simulated rock sample is calculated by using the permeability measurement module, and the specific method is as follows:

[0050] Connect the inlet pipeline with the left inlet of the core clamping box, and block the right inlet and the outlet of the core clamping box;

[0051] Open the inlet valve and the outlet valve, and ventilate the core clamping box until the readings of the inlet pressure gauge, the outlet pressure gauge and the gas flow meter are stable;

[0052] Record the inlet pressure, the outlet pressure and the outlet gas flow under multiple groups of different average pressures of the inlet and the outlet Calculate the absolute permeability of the left side of the contaminated rock sample according to the obtained inlet pressure, outlet pressure and outlet gas flow;

[0053] Connect the inlet pipeline with the right inlet of the core clamping box, and block the left inlet and the outlet of the core clamping box;

[0054] Open the inlet valve and the outlet valve, and ventilate the core clamping box until the readings of the inlet pressure gauge, the outlet pressure gauge and the gas flow meter are stable;

[0055] Record the inlet pressure, the outlet pressure and the outlet gas flow under multiple groups of different average pressures of the inlet and the outlet

[0056] ​the inlet pressure, the outlet pressure and the outlet gas flow rate of the left side of the core sample;

[0057] The absolute permeability of the right side of the core sample after pollution is calculated according to the obtained inlet pressure, outlet pressure and outlet gas flow rate.

[0058] Preferably, the pollution degree of the core sample is calculated by the following formula:

[0059]

[0060] In the formula, B1 is the pollution degree of the drilling fluid; K ∞1L is the absolute permeability of the left side of the initial core sample; K ∞1R is the absolute permeability of the right side of the initial core sample; K ∞2L is the absolute permeability of the left side after pollution; K ∞2R is the absolute permeability of the right side after pollution.

[0061] Compared with the prior art, the present application has the following beneficial effects:

[0062] The core sample pollution degree testing device provided by the present application restores the reservoir state more realistically by using the true triaxial loading module and simulates the invasion, deposition and aging process of the weighted mud under the condition, and then accurately evaluates the pollution degree of the mud, thereby providing an important theoretical basis for scientifically and efficiently increasing and restoring production of the downhole.

[0063] For the evaluation of the pollution degree, the permeability is an important index, and the evaluation is usually performed by comparing the degree of decrease of the permeability of the core sample after pollution (the permeability of the core sample after pollution / the initial permeability of the core sample). In the conventional pollution degree evaluation experiment, it is assumed that the reservoirs on both sides of the wellbore are homogeneous, and therefore the overall permeability of the core sample is generally measured.

[0064] The core sample pollution degree evaluation method provided by the present application considers that the non-homogeneity in the actual reservoir will result in a large difference between the initial permeability of the formation on both sides of the wellbore and the permeability of the core sample after pollution. The evaluation method measures the absolute permeability of the left side of the initial core sample, the absolute permeability of the right side of the initial core sample, the absolute permeability of the left side after pollution and the absolute permeability of the right side after pollution, respectively, and calculates the degree of decrease of the permeability of the core sample on the left side and the right side (the permeability of the core sample after pollution on the left side or the right side / the initial permeability of the core sample). The average of the degrees of decrease of the permeability of the core sample on the left side and the right side is taken as the index for evaluating the pollution degree of the core sample. The evaluation of the pollution degree is more in accordance with the actual situation. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is a structural schematic diagram of the device involved in the present application;

[0066] Figure 2 is a side view of the device to which the present application relates. DETAILED DESCRIPTION

[0067] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, circuits, and

[0068] It will be understood that the terms "comprises" and / or "comprising," when used in this specification, include the presence of one or more features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0069] It will also be understood that the term "and / or," when used in this specification, includes the possibility of both there being a combination of the associated listed items as well as there being only one of the associated listed items.

[0070] As used in this specification and claims, the terms "if", "for example", and "like", can be construed to perform a similar function as the terms "when" or "once" or "in response to determining" or "in response to detecting". Similarly, the phrase "if it is determined" or "if [a described condition or event] is detected" can be construed to mean "once it is determined" or "in response to determining" or "once [the described condition or event] is detected" or "in response to detecting [a described condition or event]".

[0071] In addition, the terms "first", "second", "third", etc. as used in the description of the specification and the appended claims are not used to denote or imply relative importance but are used to distinguish one element from another.

[0072] Reference throughout this specification to "one embodiment" or "an embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, the appearances of the phrases "in one embodiment", "in some embodiments", "in other embodiments", "in additional embodiments", and so on, in various places throughout this specification are not necessarily all referring to the same embodiment, unless otherwise specified. The terms "comprise", "comprising", "has", "having", and variants thereof are meant to be open-ended transitional phrases, unless otherwise specifically noted.

[0073] Embodiment 1

[0074] As Figure 1 , Figure 2 shown, the core pollution degree testing device provided by the embodiment comprises a true triaxial stratum simulation module, a drilling fluid circulation module and a permeability measurement module, wherein the true triaxial stratum simulation module is connected with the drilling fluid circulation module and the permeability measurement module.

[0075] The true triaxial stratum simulation module is used for simulating pollution of a simulated rock sample.

[0076] The drilling fluid circulation module is used for providing drilling fluid to the true triaxial stratum simulation module.

[0077] The permeability measurement module is used for obtaining the permeability of the simulated rock sample 21 in the true triaxial stratum simulation module.

[0078] Working principle of the present application:

[0079] The present application is provided with a true triaxial loading module, a servo press 11 is connected to the outer ring of the pressure plate 1 of the true triaxial loading module, and Z-axis pressure is applied to the core clamping box 6. The X-axis and Y-axis stress (horizontal stress) loading relies on the independent hydraulic capsules (i.e. Y-axis No. 1 hydraulic capsule 7, Y-axis No. 2 hydraulic capsule 8, X-axis No. 1 hydraulic capsule 9, X-axis No. 2 hydraulic capsule 10) on the outside of the two sides of the X-axis and the two sides of the Y-axis of the core clamping box 6, and the liquid in the hydraulic capsules is pumped to continuously expand and pressurize, thereby exerting pressure on the core clamping box 6. Independent pump groups (Y-axis pump group 14, X-axis pump group 16) are used for the X-axis and Y-axis, and the liquid in the Y-axis pump group liquid tank 15 and the X-axis pump group liquid tank 17 is pumped into the hydraulic capsules (Y-axis No. 1 hydraulic capsule 7, Y-axis No. 2 hydraulic capsule 8) on the two sides of the Y-axis and the hydraulic capsules (X-axis No. 1 hydraulic capsule 9, X-axis No. 2 hydraulic capsule 10) on the two sides of the X-axis. Since independent pump groups are used, the pressure of the X-axis and Y-axis can be adjusted accordingly, so that the X-axis and Y-axis can be loaded in a combined state with unequal stress, thereby simulating the actual horizontal stress difference of the stratum. In addition, the present application is provided with an upper cover plate with built-in resistance plate to heat the rock sample and simulate the actual temperature of the stratum.

[0080] Under the condition of fully restoring the actual stress of the stratum and the actual temperature of the stratum, drilling fluid is pumped into the core and circulated for a certain period of time to simulate the invasion process of the drilling fluid. After the invasion, the core is left to stand for a certain period of time under the same temperature and pressure as before, to simulate the deposition and aging of the drilling fluid in the stratum.

[0081] The true tri-axial stratum simulation module comprises an annular pressure plate 1, an upper cover plate with built-in resistance plate 2, a through-hole end cover 3, a pressure bearing block 4, a simulated wellbore 5, a core clamping box 6, a Y-axis No. 1 hydraulic capsule 7, a Y-axis No. 2 hydraulic capsule 8, a X-axis No. 1 hydraulic capsule 9, a X-axis No. 2 hydraulic capsule 10, a servo booster 11, a Y-axis pressure sensor 12, a X-axis pressure sensor 13, a Y-axis pumping pump group 14, a Y-axis pump group liquid supply tank 15, a X-axis pumping pump group 16, a X-axis pump group liquid supply tank 17, a supporting column 18, a side partition plate 19, a stainless steel cushion block 20, a simulated rock sample 21 and a temperature control box 22, wherein:

[0082] Each of the four outer walls of the core clamping box 6 is provided with a side partition plate 19.

[0083] The outer side of the core clamping box 6 is provided with four supporting columns 18, and the supporting columns 18 are arranged outside the side partition plates 19.

[0084] The upper end of the four supporting columns 18 is provided with the upper cover plate with built-in resistance plate 2.

[0085] The lower end of the core clamping box 6 is provided with a stainless steel cushion block 20, and the stainless steel cushion block 20 is fixed to the middle and lower segments of the supporting columns 18 by welding.

[0086] The upper end of the core clamping box 6 is provided with a through-hole end cover 3 and two pressure bearing blocks 4, and the two pressure bearing blocks 4 are arranged on the two sides of the through-hole end cover 3.

[0087] The core clamping box 6 is connected to the pressure bearing blocks 4 and the threaded holes on the stainless steel cushion block 20 by screws, so as to achieve the purpose of sealing the two sides.

[0088] The simulated rock sample 21 is arranged in the inner cavity of the core clamping box 6, and the simulated wellbore 5 is arranged in the central inner cavity of the simulated rock sample 21.

[0089] The core clamping box 6 and the frame are provided with four independent hydraulic capsules, namely the Y-axis No. 1 hydraulic capsule 7, the Y-axis No. 2 hydraulic capsule 8, the X-axis No. 1 hydraulic capsule 9 and the X-axis No. 2 hydraulic capsule 10.

[0090] The Y-axis No. 1 hydraulic capsule 7 and the Y-axis No. 2 hydraulic capsule 8 are connected with the Y-axis pumping pump group 14 and the Y-axis pump group liquid supply tank 15. The X-axis No. 1 hydraulic capsule 9 and the X-axis No. 2 hydraulic capsule 10 are connected with the X-axis pumping pump group 16 and the X-axis pump group liquid supply tank 17.

[0091] The core clamping box 6 is connected with the Y-axis pressure sensor 12 and the X-axis pressure sensor 13 for real-time monitoring of the pressure in the Y-axis and X-axis directions.

[0092] The annular pressure plate 1 applies pressure to the upper cover plate 2 through the external servo booster 11 to simulate the overburden pressure, and the upper cover plate 2 is connected to the supporting column 18 and the pressure bearing block 4 through screws.

[0093] The resistance block is placed inside the upper cover plate 2 and connected to the temperature control box 22, which needs to be externally connected to a 220V AC power supply.

[0094] The core clamping box 6 is sleeved with a sealing rubber ring, which is specifically sleeved on the simulated rock sample 21.

[0095] The simulated rock sample 21 is a cubic structure.

[0096] The simulated wellbore 5 vertically passes through the entire simulated rock sample 21, and the upper port of the simulated wellbore 5 is threaded to be connected and locked with the through-hole end cover 3.

[0097] The drilling fluid circulation module includes a drilling fluid inlet pipeline 23, a drilling fluid inlet end valve 24, an injection pump 25, a drilling fluid storage tank 26, a drilling fluid circulation power pump 27, a drilling fluid outlet pipeline 28, and a drilling fluid outlet end valve 29.

[0098] The liquid suction end of the injection pump 25 is connected to the upper end of the drilling fluid storage tank 26 through the drilling fluid inlet pipeline 23, one end of the drilling fluid inlet pipeline 23 is connected to the through-hole end cover 3 in the true triaxial stratum simulation module, and the other end is connected to the liquid outlet end of the injection pump 25. After the pump is started, the drilling fluid can be pumped into the simulated wellbore 5 along the drilling fluid inlet pipeline 23, and then flow to the drilling fluid outlet pipeline 28 connected to the lower part of the core clamping box 6 along the wellbore, and the other end of the drilling fluid outlet pipeline 28 is connected to the drilling fluid circulation power pump 27 to pump the drilling fluid back to the drilling fluid storage tank 26.

[0099] The permeability measurement module includes a nitrogen cylinder 30, a pressure reducing valve 31, an inlet pressure gauge 32, an inlet valve 33, an inlet pipeline 34, a three-way joint 35, an outlet valve 36, an outlet pipeline 37, an outlet pressure gauge 38, and a gas flow meter 39.

[0100] The core clamping box 6 has an inlet on each of the two side walls in the Y-axis direction, which are the left inlet and the right inlet.

[0101] The pressure reducing valve 31 is installed at the outlet of the nitrogen cylinder 30 to control the gas flow rate, and the pressure reducing valve 31 is connected to the inlet on the core clamping box 6 through the inlet pipeline 34.

[0102] The air inlet pipeline 34 is provided with an air inlet pressure gauge 32 and an air inlet valve 33. The gas flows out from the air outlet pipeline 37 connected to the upper end through-hole end cover 3 through the simulated wellbore 5. The air outlet pipeline 37 is connected to the drilling fluid inlet pipeline 23 using a three-way joint 35 at the air outlet end, and is provided with an air outlet valve 36. The air outlet pipeline 37 is connected to a gas flow meter 39 and an air outlet pressure gauge 38.

[0103] The working process of this embodiment:

[0104] When conducting the experimental test, the initial permeability of the simulated rock sample 21 is first measured. Figure 1 As shown, a simulated rock sample 21 is prepared, and the large outcrop rock sample is cut into cubes along the bedding and perpendicular bedding directions, and a wellbore is drilled in the center of the cube simulated rock sample 21 for placing the simulated wellbore 5.

[0105] Place the simulated rock sample 21 into the core clamping box 6, connect the internal thread of the through-hole end cover 3 with the external thread of the simulated wellbore 5, place the two pressure blocks 4 on the upper end of the core clamping box 6, press them with the upper end cover 2, and drive screws into the threaded holes to fix the pressure blocks 4 and the upper end cover 2.

[0106] The pressure reducing valve 31 is connected to the nitrogen cylinder 30 via an inlet line 34. The inlet line 34 is equipped with an inlet pressure gauge 32 and is connected to the left inlet of the core clamping box 6. The inlet line 34 is provided with an inlet valve 35. The drilling fluid inlet line 23 connected to the upper through-hole end cap 3 is equipped with an outlet tee joint 35 for connecting to an outlet line 37. The outlet line 37 is connected to an outlet valve 36, an outlet pressure gauge 38, and a gas flow meter 39.

[0107] Finally, the threaded holes on the side of the core clamping box 6 not connected to the air inlet line 34 and at the bottom are sealed with screws.

[0108] Open the inlet valve 33, outlet valve 36 and nitrogen bottle 30, wait for the inlet pressure gauge 32, outlet pressure gauge 38 and gas flow meter 39 to read stable, and then record the average pressure of several different inlet and outlet ports. The inlet pressure P1, outlet pressure P2, and outlet gas flow Q0 data under different average pressures are The gas seepage flow pattern under the same conditions is basically the same. It is necessary to keep the pressure difference ΔP at both ends of the inlet and outlet constant while increasing and decreasing the inlet and outlet pressures at the same time.

[0109] The calculation formula of gas permeability is shown in (1):

[0110]

[0111] Where K gis the permeability, D; Q0 is the outlet gas flow rate; P0 is the atmospheric pressure, atm; μ is the fluid viscosity, mPa·s; L is the lateral length of the rock sample, cm; A is the lateral area of ​​the core, cm 2 ; P1 and P2 are the gauge pressures at the inlet and outlet, atm.

[0112] Calculate the corresponding gas permeability under different average pressures and make the gas permeability K g1L and the inverse of the mean pressure The straight line relationship diagram between them, and find the straight line in K g1L The intercept K on the axis ∞1L as the absolute permeability on the left side of the initial rock sample.

[0113] Connect the air inlet line 34 to the air inlet on the right side of the core clamping box 6, and seal the threaded holes on the left side and the lower end of the core clamping box 6 with screws.

[0114] Open the inlet valve 33, outlet valve 34 and nitrogen bottle 30, wait for the inlet pressure gauge 32, outlet pressure gauge 38 and gas flow meter 39 to read stable, and then record the average pressure of several different inlet and outlet ports. The inlet pressure P1, outlet pressure P2, and outlet gas flow Q0 data under different average pressures are The gas seepage flow pattern under the same conditions is basically the same. It is necessary to keep the pressure difference ΔP at both ends of the inlet and outlet constant while increasing and decreasing the inlet and outlet pressures at the same time.

[0115] According to formula 1, the corresponding gas permeability K under different average pressures is calculated. g1R . Make gas permeability K g1R and the inverse of the mean pressure The straight line relationship diagram between them, and find the straight line in K g1R The intercept K on the axis ∞1R as the absolute permeability on the right side of the initial rock sample.

[0116] Use the drilling fluid circulation module to simulate the drilling fluid circulation process during drilling.

[0117] Close the air inlet valve 33 and the air outlet valve 36, remove the air inlet pipeline 34, and install the Y-axis No. 1 hydraulic bag 7, the Y-axis No. 2 hydraulic bag 8, the X-axis No. 1 hydraulic bag 9, the X-axis No. 2 hydraulic bag 10 and the partitions 19 on both sides.

[0118] The simulated wellbore 5 is connected to the drilling fluid inlet pipeline 23 provided with a drilling fluid inlet valve 24 and the injection pump 25, the injection pump 25 is connected to the upper end of the drilling fluid storage tank 26, the lower threaded hole of the core holder 6 is connected to the drilling fluid outlet pipeline 28, the drilling fluid outlet valve 29 is installed on the drilling fluid outlet pipeline 28, and the drilling fluid circulating power pump 26 is connected to the drilling fluid outlet pipeline 28 and the drilling fluid storage tank 25 connected to the drilling fluid circulating power pump 27.

[0119] A pressure value is preset using the true triaxial loading module, the servo booster 11 is started to apply pressure to the annular pressure plate 1, thereby applying Z-axis pressure to the core holder 6, and the servo booster 11 is completed until the pressure is applied. Start the Y-axis pumping pump group 14, pump the liquid in the Y-axis pump group liquid tank 15 into the Y-axis No. 1 hydraulic bag 7 and the Y-axis No. 2 hydraulic bag 8 at the same time, and monitor the change of the Y-axis loading pressure by the Y-axis pressure sensor 12 for the Y-axis No. 1 hydraulic bag 7 and the Y-axis No. 2 hydraulic bag 8 until the Y-axis stress is loaded to the expected value. Then start the X-axis pumping pump group 16, pump the liquid in the X-axis pump group liquid tank 17 into the X-axis No. 1 hydraulic bag 9 and the X-axis No. 2 hydraulic bag 10 at the same time, and monitor the change of the X-axis loading pressure by the X-axis pressure sensor 13 for the Y-axis No. 1 hydraulic bag 9 and the Y-axis No. 2 hydraulic bag 10 until the X-axis stress is loaded to the expected value. Complete the loading of triaxial stress.

[0120] A predetermined temperature is given to the digital display control temperature box 22, which controls the start of heating of the resistance plate in the upper cover plate 2. After the temperature is loaded to the preset temperature, the drilling fluid inlet valve 24 and the drilling fluid outlet valve 29 are opened, the injection pump 25 is started to inject drilling fluid into the simulated wellbore 5, and then the drilling fluid circulating power pump 27 is started to pump the drilling fluid flowing out from the core holder 6 back to the drilling fluid storage tank 25, simulating the circulation process of the drilling fluid in the drilling process.

[0121] After the drilling fluid circulation is completed, the simulated rock sample is kept at a constant temperature and pressure, and the deposition and aging of the drilling fluid in the formation are simulated.

[0122] The permeability of the contaminated rock sample is measured.

[0123] The two side partitions 19 of the device are removed, and the gas inlet pipeline 34 is connected to the left gas inlet of the core holder 6.

[0124] The gas inlet valve 33, the gas outlet valve 34, the nitrogen cylinder 30, the gas inlet pressure gauge 32, the gas outlet pressure gauge 38 and the gas flow meter 39 are opened, and several groups of data of the gas inlet pressure P1, the gas outlet pressure P2 and the outlet gas flow Q0 under different average pressures are recorded. ​ The gas seepage flow pattern under the same conditions is basically the same. It is necessary to keep the pressure difference ΔP at both ends of the inlet and outlet constant while increasing and decreasing the inlet and outlet pressures at the same time.

[0125] According to formula 1, the corresponding gas permeability under different average pressures is calculated to make the gas permeability K g2L and the inverse of the mean pressure The straight line relationship diagram between them, and find the straight line in K g2L The intercept K on the axis ∞2L As the absolute permeability on the left side of the rock sample after contamination.

[0126] Connect the air inlet line 34 to the threaded hole on the right side of the core holding box 6, and seal the threaded holes on the left side and the lower end of the core holding box 6 with screws.

[0127] Open the inlet valve 33, outlet valve 34 and nitrogen bottle 30, wait for the inlet pressure gauge 32, outlet pressure gauge 38 and gas flow meter 39 to read stable, and then record the average pressure of several different inlet and outlet ports. The inlet pressure P1, outlet pressure P2, and outlet gas flow Q0 data under different average pressures are The gas seepage flow pattern under the same conditions is basically the same. It is necessary to keep the pressure difference ΔP at both ends of the inlet and outlet constant while increasing and decreasing the inlet and outlet pressures at the same time.

[0128] According to formula 1, the corresponding gas permeability K under different average pressures is calculated. g2R . Make gas permeability K g2R and the inverse of the mean pressure The straight line relationship diagram between them, and find the straight line in K g2R The intercept K on the axis ∞2R As the absolute permeability on the right side of the rock sample after contamination.

[0129] The calculation formula for the degree of drilling fluid contamination is as follows:

[0130]

[0131] Where, B1 is the degree of drilling fluid contamination, %; K ∞1L is the absolute permeability on the left side of the initial rock sample, D; K ∞1R is the absolute permeability on the right side of the initial rock sample, D; K ∞2L D is the absolute permeability of the left side of the drilling fluid contaminated rock sample after it is contaminated. K ∞2R is the absolute permeability on the right side of the rock sample after being contaminated by drilling fluid, D.

[0132] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for testing the degree of core contamination, characterized in that: Based on a core contamination degree testing device, the device includes: True triaxial formation simulation module for contamination simulation of simulated rock samples; A drilling fluid circulation module for providing drilling fluid required for pollution simulation to the simulated rock sample; Permeability measurement module for obtaining the permeability of simulated rock samples; The true triaxial formation simulation module comprises an annular pressure plate (1), a simulated wellbore (5), a core clamping box (6), a Y-axis pressure member and an X-axis pressure member, wherein the Y-axis pressure member and the X-axis pressure member are respectively arranged on the side walls of the core clamping box (6) in the Y-axis direction and the X-axis direction, so as to provide Y-axis direction pressure and X-axis direction pressure to the core clamping box (6); The annular pressure plate (1) is placed at the upper end of the core clamping box (6) to provide pressure in the Z-axis direction to the core clamping box (6); The top of the core clamping box (6) is also provided with a heat transfer component for transferring heat to the core clamping box (6), and the heat transfer component is placed at the lower end of the annular pressure plate (1); A simulated rock sample (21) is provided in the cavity of the core clamping box (6), and the simulated wellbore (5) is vertically placed in the inner cavity of the simulated rock sample (21); The method comprises the following steps: The initial permeability of the simulated rock sample (21) is calculated using a permeability measurement module; The true triaxial loading module and the drilling fluid circulation module are used to simulate the drilling fluid circulation during the drilling process of the simulated rock sample (21); The contaminated permeability of the simulated rock sample (21) is calculated using a permeability measurement module; The core contamination degree is calculated based on the initial permeability and contaminated permeability; The initial permeability of the simulated rock sample (21) is calculated using the permeability measurement module. The specific method is: Connect the air inlet line (34) to the air inlet on the left side of the core holding box (6); seal the air inlet on the right side of the core holding box (6) and the liquid outlet of the simulated wellbore (5); Open the air inlet valve (33) and the air outlet valve (36), and ventilate the core holding box (6) until the readings of the air inlet pressure gauge (32), the air outlet pressure gauge (38) and the gas flow meter (39) are stable; Record the average pressure of multiple groups of different inlet and outlet ends Inlet pressure, outlet pressure and outlet gas flow rate under The absolute permeability of the left side of the initial rock sample is calculated based on the obtained inlet pressure, outlet pressure and outlet gas flow rate; Connect the air inlet line (34) to the right air inlet of the core holding box (6); seal the left air inlet of the core holding box (6) and the liquid outlet of the simulated wellbore (5); Open the air inlet valve (33) and the air outlet valve (36), and ventilate the core holding box (6) until the readings of the air inlet pressure gauge (32), the air outlet pressure gauge (38) and the gas flow meter (39) are stable; Record the average pressure of multiple groups of different inlet and outlet ends Inlet pressure, outlet pressure and outlet gas flow rate under The absolute permeability on the right side of the initial rock sample is calculated based on the obtained inlet pressure, outlet pressure and outlet gas flow rate; The contaminated permeability of the simulated rock sample (21) is calculated using the permeability measurement module. The specific method is: Connect the air inlet line (34) to the air inlet on the left side of the core holding box (6); seal the air inlet on the right side of the core holding box (6) and the liquid outlet of the simulated wellbore (5); Open the air inlet valve (33) and the air outlet valve (36), and ventilate the core holding box (6) until the readings of the air inlet pressure gauge (32), the air outlet pressure gauge (38) and the gas flow meter (39) are stable; Record the average pressure of multiple groups of different inlet and outlet ends Inlet pressure, outlet pressure and outlet gas flow rate under The absolute permeability of the left side of the contaminated rock sample is calculated based on the obtained inlet pressure, outlet pressure and outlet gas flow rate; Connect the air inlet line (34) to the right air inlet of the core holding box (6); seal the left air inlet of the core holding box (6) and the liquid outlet of the simulated wellbore (5); Open the air inlet valve (33) and the air outlet valve (36), and ventilate the core holding box (6) until the readings of the air inlet pressure gauge (32), the air outlet pressure gauge (38) and the gas flow meter (39) are stable; Record the average pressure of multiple groups of different inlet and outlet ends Inlet pressure, outlet pressure and outlet gas flow rate under The absolute permeability of the right side of the contaminated rock sample is calculated based on the obtained inlet pressure, outlet pressure and outlet gas flow rate; The degree of core contamination is calculated using the following formula: Where, B1 is the degree of drilling fluid contamination; K ∞1L is the absolute permeability on the left side of the initial rock sample; K ∞1R is the absolute permeability on the right side of the initial rock sample; K ∞2L is the absolute permeability on the left side after pollution; K ∞2R is the absolute permeability on the right side after pollution.

2. A method for testing the degree of core contamination according to claim 1, characterized in that: The true triaxial loading module and the drilling fluid circulation module are used to simulate the drilling fluid circulation during the drilling process of the simulated rock sample (21). The specific method is: Close the air inlet valve (33) and the air outlet valve (36); Applying a Z-axis preset pressure to the core clamping box (6) using an annular pressure plate (1); Applying a Y-axis preset pressure to the core clamping box (6) using a Y-axis pressure member; Applying an X-axis preset pressure to the core clamping box (6) using an X-axis pressure member; Using a heat transfer component to apply a preset temperature to the core holding box (6); Open the drilling fluid inlet valve (24) and the drilling fluid outlet valve (29); Starting the injection pump (25) to inject the drilling fluid into the simulated wellbore (5), and then starting the drilling fluid circulation power pump (27) to pump the drilling fluid flowing out of the core clamping box (6) back to the drilling fluid storage tank (26); After the drilling fluid circulation is completed, the simulated rock sample (21) is left to stand for a preset time while maintaining the temperature and pressure loading.

3. A method for testing the degree of core contamination according to claim 1, characterized in that: The Y-axis pressure member comprises a Y-axis No. 1 hydraulic bladder (7), a Y-axis No. 2 hydraulic bladder (8), a Y-axis pumping pump group (14) and a Y-axis pump group liquid supply tank (15), wherein the Y-axis No. 1 hydraulic bladder (7) and the Y-axis No. 2 hydraulic bladder (8) are respectively placed on the two outer walls of the core clamping box (6) in the Y-axis direction; the liquid inlets and outlets of the Y-axis No. 1 hydraulic bladder (7) and the Y-axis No. 2 hydraulic bladder (8) are connected to the Y-axis pump group liquid supply tank (15) through the Y-axis pumping pump group (14).

4. A method for testing the degree of core contamination according to claim 1, characterized in that: The X-axis pressure member includes an X-axis No. 1 hydraulic bladder (9), an X-axis No. 2 hydraulic bladder (10), an X-axis pumping pump group (16) and an X-axis pump group liquid supply tank (17), wherein the X-axis No. 1 hydraulic bladder (9) and the X-axis No. 2 hydraulic bladder (10) are respectively placed on the two outer walls of the core clamping box (6) in the X-axis direction; the liquid inlets and outlets of the X-axis No. 1 hydraulic bladder (9) and the X-axis No. 2 hydraulic bladder (10) are connected to the X-axis pump group liquid supply tank (17) through the X-axis pumping pump group (16).

5. A method for testing the degree of core contamination according to claim 1, characterized in that: The drilling fluid circulation module comprises a drilling fluid inlet pipeline (23), an injection pump (25), a drilling fluid storage tank (26), a drilling fluid circulation power pump (27) and a drilling fluid outlet pipeline (28), wherein: One end of the drilling fluid inlet pipeline (23) is connected to the fluid inlet of the simulated wellbore (5) in the true triaxial formation simulation module, and the other end is connected to the drilling fluid storage tank (26) via the injection pump (25); One end of the drilling fluid outlet pipeline (28) is connected to the fluid outlet of the simulated wellbore (5), and the other end is connected to the drilling fluid storage tank (26) via a drilling fluid circulation power pump (27).

6. A method for testing the degree of core contamination according to claim 1, characterized in that: The permeability measurement module comprises a nitrogen bottle (30), a pressure reducing valve (31), an inlet pressure gauge (32), an inlet valve (33), an inlet pipeline (34), an outlet three-way connector (35), an outlet valve (36), an outlet pipeline (37), an outlet pressure gauge (38) and a gas flow meter (39), wherein: The pressure reducing valve (31) is installed at the gas outlet of the nitrogen bottle (30), and the pressure reducing valve (31) is connected to the gas inlet opened on the core clamping box (6) in the true triaxial formation simulation module through the gas inlet pipeline (34); The air intake pipeline (34) is provided with an air intake pressure gauge (32) and an air intake valve (33); The gas outlet pipeline (37) is connected to the simulated wellbore (5) in the true triaxial formation simulation module; The gas outlet pipeline (37) is provided with a gas outlet valve (36), a gas flow meter (39) and a gas outlet pressure gauge (38).

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