Method for acquiring formation pressure of reservoir

Abstract

The invention provides a method for acquiring formation pressure of a reservoir, which comprises the following steps of: replacing fluid in an oil and gas shaft based on negative pressure perforation, enabling the fluid in the reservoir to seep into the oil and gas shaft, and acquiring first liquid column pressure based on a pressure meter; after the first liquid column pressure is obtained, equivalent fluid is injected into the oil-gas wellbore, and second liquid column pressure is obtained based on a pressure meter; when the first condition is met, first formation pressure is obtained based on the first liquid column pressure and the second liquid column pressure; by means of the method for obtaining the formation pressure of the reservoir, the problem that the formation pressure of the reservoir of a low-permeability and ultra-low-permeability compact oil shale oil reservoir is difficult to obtain can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil extraction, and in particular to a method for obtaining formation pressure of a reservoir. Background Art

[0002] Low-permeability and extra-low-permeability tight oil shale is an important successor resource for petroleum at home and abroad. It has been difficult to obtain the formation pressure of the reservoir of low-permeability and extra-low-permeability tight oil shale reservoirs using existing technologies. The reason is that the reservoir permeability of this type of oil reservoir is low. During the seepage process, the fluid is affected by factors such as capillary pressure and surface tension, resulting in a starting pressure gradient, forming a cofferdam effect inside the reservoir, so that the measured formation pressure of the reservoir changes with the change of the liquid column pressure in the oil and gas wellbore. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a method for obtaining the formation pressure of a reservoir, which can eliminate the influence of the cofferdam effect formed by the starting pressure gradient and solve the problem of difficulty in obtaining the formation pressure of a reservoir in a low-permeability and ultra-low-permeability dense oil shale reservoir.

[0004] In a first aspect, an embodiment of the present invention provides a method for obtaining formation pressure of a reservoir, characterized by comprising:

[0005] A method for obtaining formation pressure of a reservoir, characterized by comprising:

[0006] Step 1: displacing the fluid in the oil and gas wellbore based on negative pressure perforation, so that the fluid in the reservoir seeps into the oil and gas wellbore, and obtaining a first liquid column pressure based on a pressure gauge;

[0007] Step 2: After obtaining the first liquid column pressure, inject an equivalent fluid into the oil and gas wellbore, and obtain the second liquid column pressure based on the pressure gauge;

[0008] Step 3: When the first condition is met, the first formation pressure is obtained based on the first liquid column pressure and the second liquid column pressure.

[0009] Preferably, the first condition in step 3 includes:

[0010] Second fluid volume Q in The first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula:

[0011] Q in =Q1+Q out

[0012] or the second fluid volume Q in Slightly larger than the first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula:

[0013] Q in >Q1+Q out

[0014] or the second fluid volume Q in The first volume Q1, the first fluid volume Q out As the pressure increases to P win When , the sum of the fluid volumes required in the oil and gas wellbore is expressed by the following formula:

[0015] Q in =Q1+Q out +Q 井筒 ×C t ×P win

[0016] Preferably, the first fluid volume Q out The first volume Q1 is obtained by the following steps, specifically including:

[0017] Step 301: Acquire the first volume Q1;

[0018] Step 302: Obtain the first fluid volume Q based on the first liquid level depth H1 and the second liquid level depth H2 out , expressed by the following formula:

[0019] Q out =(H1-H2)×S1

[0020] Preferably, obtaining the first liquid column pressure based on the pressure gauge in step 1 includes:

[0021] Based on the pressure gauge directly measuring the pressure of the first liquid column,

[0022] Or based on the pressure gauge measuring the fluid gradient profile in the oil and gas wellbore, the first liquid column pressure is calculated through the fluid gradient profile in the oil and gas wellbore.

[0023] Preferably, obtaining the second liquid column pressure based on the pressure gauge in step 1 includes:

[0024] Based on the direct measurement of the fluid gradient profile in the oil and gas wellbore by the pressure gauge, the second liquid column pressure is calculated through the fluid gradient profile in the oil and gas wellbore,

[0025] Alternatively, the wellhead pressure after the injection of the equivalent fluid is measured by the pressure gauge, and a conversion calculation is performed based on the wellhead pressure to obtain the second liquid column pressure.

[0026] Preferably, the test time of the pressure recovery test when obtaining the first liquid column pressure is ensured to be the same as the test time of the pressure drop test when obtaining the second liquid column pressure; if they are not the same, the pressure change rate in the pressure recovery test and the pressure drop test is less than the specified pressure, and the pressure recovery test and the pressure drop test are terminated.

[0027] The beneficial effects of the present invention are as follows: the present invention replaces the fluid in the oil and gas wellbore based on negative pressure perforation, allowing the fluid in the reservoir to seep into the oil and gas wellbore, obtaining a first liquid column pressure, and after obtaining the first liquid column pressure, injecting an equivalent fluid into the oil and gas wellbore to obtain a second liquid column pressure; when the first condition is met, the first formation pressure is obtained based on the first liquid column pressure and the second liquid column pressure. Based on the technical solution provided by the present invention, the influence of the cofferdam effect formed by the startup pressure gradient can be eliminated, and the formation pressure of the reservoir of low-permeability and ultra-low-permeability tight oil shale reservoirs can be conveniently obtained.

[0028] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic flow chart of a method for obtaining formation pressure of a reservoir provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] A method for obtaining the formation pressure of a reservoir provided by an embodiment of the present invention can eliminate the influence of the cofferdam effect formed by the starting pressure gradient, and solve the problem of difficulty in obtaining the formation pressure of a reservoir in a low-permeability or ultra-low-permeability dense oil shale reservoir.

[0034] To facilitate understanding of this embodiment, Figure 1 A method for obtaining the formation pressure of a reservoir disclosed in an embodiment of the present invention is introduced in detail.

[0035] Embodiment 1:

[0036] A method for obtaining the formation pressure of a reservoir disclosed in an embodiment of the present invention comprises the following specific steps:

[0037] Step 1: displacing the fluid in the oil and gas wellbore based on negative pressure perforation, so that the fluid in the reservoir seeps into the oil and gas wellbore, and obtaining the first liquid column pressure based on the pressure gauge;

[0038] Among them, the first liquid column pressure P wout It is the fluid pressure after the fluid seeps from the reservoir into the oil and gas wellbore and is balanced;

[0039] Negative pressure perforating displaces fluids in oil and gas wellbores, including the following methods:

[0040] Method 1: lower the perforating string into the oil and gas wellbore. When the oil and gas wellhead pressure drops to zero, use the perforating string to displace the fluid in the oil and gas wellbore and perform negative pressure perforation.

[0041] Method 2: Use coiled tubing as the perforating string. When the wellhead pressure drops to zero, replace the fluid in the wellbore and perform negative pressure perforation.

[0042] Specifically, based on sufficient negative pressure perforation, the perforating string can be used to displace the fluid in the wellbore, so that a pressure difference is generated between the pressure of the wellbore liquid column at the middle depth of the perforating string and the formation pressure, and the pressure difference is used to make the fluid in the reservoir seep into the wellbore;

[0043] After replacing the fluid in the oil and gas wellbore, perforate and close the oil and gas well, so that the pressure gauge is located at the middle depth of the perforated layer, or the pressure gauge is located at the position closest to the middle depth of the perforated layer according to the pipe string structure, and the pressure recovery test is performed on the oil and gas wellbore through the pressure gauge to obtain the first liquid column pressure P wout ;

[0044] Preferably, the first liquid column pressure P is obtained based on the pressure gauge wout include:

[0045] Direct measurement of the first liquid column pressure P based on the pressure gauge wout, or based on the pressure gauge measuring the fluid gradient profile in the oil and gas wellbore, the first liquid column pressure P is calculated by the fluid gradient profile in the oil and gas wellbore wout .

[0046] In this embodiment, under the premise of ensuring well control safety, after negative pressure perforation, the maximum volume of the fluid in the wellbore replaced is the volume of the fluid in the wellbore above the top boundary of the perforated reservoir.

[0047] Step 2: After obtaining the first liquid column pressure, inject an equivalent fluid into the oil and gas wellbore, and obtain the second liquid column pressure based on the pressure gauge;

[0048] Among them, the second liquid column pressure P win The fluid pressure in the oil and gas wellbore after the equivalent fluid is injected into the oil and gas wellbore, wherein the equivalent fluid volume is equal to the sum of the fluid volume after the equilibrium of the fluid seeping from the reservoir to the oil and gas wellbore and the fluid volume replaced in the oil and gas wellbore by negative pressure perforation;

[0049] Specifically, after obtaining the first liquid column pressure, an equivalent fluid is injected into the wellbore, the oil and gas well is closed, and the pressure gauge is located at the middle depth of the perforated layer, or the pressure gauge is located at the position closest to the middle depth of the perforated layer according to the pipe string structure, and the pressure drop test is performed on the oil and gas wellbore through the pressure gauge to obtain the second liquid column pressure P win ;

[0050] Preferably, the second liquid column pressure P is obtained based on the pressure gauge win include:

[0051] Based on the direct measurement of the fluid gradient profile in the oil and gas wellbore by the pressure gauge, the second liquid column pressure P is calculated through the fluid gradient profile in the oil and gas wellbore. win ;

[0052] Or measure the wellhead pressure after injecting equivalent fluid through a pressure gauge, and calculate based on the wellhead pressure to obtain the second liquid column pressure P win , expressed as follows:

[0053] P win =p0+h×ρ×g

[0054] Where p0 is the wellhead pressure after injection of equivalent fluid;

[0055] h is the vertical depth of the perforated reservoir;

[0056] ρ is the fluid density in the wellbore;

[0057] g is the acceleration due to gravity;

[0058] Preferably, the test time of the pressure recovery test when obtaining the first liquid column pressure is ensured to be the same as the test time of the pressure drop test when obtaining the second liquid column pressure; if they are not the same, the pressure change rate in the pressure drop test is less than the specified pressure, and the pressure recovery test and the pressure drop test are terminated.

[0059] In this embodiment, the prescribed pressure is 0.05 MPa / d.

[0060] Step 3: When the first condition is met, obtaining a first formation pressure based on the first liquid column pressure and the second liquid column pressure;

[0061] In this embodiment, it is assumed that there is a starting pressure gradient in the reservoir. Based on this, the first homogeneous reservoir seepage equation is expressed by the following formula:

[0062]

[0063] Where, λ is the reservoir starting pressure gradient;

[0064] r e is the fluid sweep radius;

[0065] r w is the outer radius of the wellbore;

[0066] K is the reservoir permeability;

[0067] q is the daily liquid volume of stable production or injection;

[0068] μ is the viscosity of the injected fluid;

[0069] P i The formation pressure of the reservoir of the low-permeability and ultra-low-permeability tight oil shale reservoir, i.e., the first formation pressure;

[0070] Specifically, the pump truck injects fluid into the oil and gas wellbore at the minimum displacement. After the fluid is injected into the reservoir from the oil and gas wellbore, the oil and gas well is closed. At this time, the liquid column pressure P in the oil and gas wellbore is w and the first formation pressure P i The equilibrium stop can be reached, and the second homogeneous reservoir seepage equation is expressed by the following formula:

[0071] P w -P i =λ(r e -r w )

[0072] Among them, P w is the liquid column pressure in the oil and gas wellbore, including but not limited to: the first liquid column pressure P wout Or the second liquid column pressure P win ; The first formation pressure is the formation pressure of the reservoir;

[0073] When the first condition is met, the cofferdam effect formed by the start-up pressure gradient can be eliminated by combining the first homogeneous reservoir seepage equation and the second homogeneous reservoir seepage equation. wout and the second liquid column pressure P win , obtain the first formation pressure P i , expressed by the following formula:

[0074] P i =0.5×(P wout +P win )

[0075] Preferably, the first condition includes:

[0076] Second fluid volume Q in The first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula:

[0077] Q in =Q1+Q out

[0078] Wherein, the first fluid volume is the volume of fluid flowing from the reservoir into the oil and gas wellbore;

[0079] Or the second fluid volume Q in Slightly larger than the first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula:

[0080] Q in >Q1+Q out

[0081] At this time, the second fluid volume Q in Slightly larger than the first volume Q1 and the first fluid volume Q out The reason for the sum of is that in actual operation, the second fluid volume also includes the volume of the Christmas tree and the test lubricant preventer that is not filled with fluid after the oil and gas wellhead pressure drops to zero, and the fluid volume required to increase the oil and gas wellbore pressure; based on this, the second fluid volume is slightly larger than the first volume Q1 and the first fluid volume Q out sum;

[0082] Or the second fluid volume Q in The first volume Q1, the first fluid volume Q out As the pressure increases to P win When , the sum of the fluid volumes required in the oil and gas wellbore is expressed by the following formula:

[0083] Q in =Q1+Q out +Q 井筒 ×C t ×Pwin

[0084] Among them, Q 井筒 is the volume of the actual oil and gas wellbore, C t is the fluid compressibility coefficient;

[0085] At this time, the second fluid volume Q in The first volume Q1, the first fluid volume Q out As the pressure increases to P win The reason why the sum of the fluid volumes required in the oil and gas wellbore is that in actual operation, the fluid has a certain compressibility coefficient. When the fluid is injected into Q1+Q out When the volume of fluid injected into the formation is smaller than the volume of fluid flowing out of the negative pressure perforation, the actual wellbore volume Q needs to be fully considered. 井筒 and the fluid compressibility coefficient C t ;

[0086] Preferably, the first fluid volume Q out The first volume Q1 is obtained by the following steps, specifically including:

[0087] Step 301: Obtain a first volume Q1;

[0088] Specifically, negative pressure perforation is performed based on method 1 to obtain a first volume, where the first volume is the volume of the fluid in the oil and gas wellbore that has been replaced;

[0089] Based on method 2, negative pressure perforation is performed to obtain a first volume, which is the sum of the volume of the fluid in the oil and gas wellbore replaced and the volume of the fluid discharged from the oil and gas wellhead during the process of the perforating string being lowered into the oil and gas wellbore; wherein the volume of the fluid in the oil and gas wellbore replaced is obtained through a metering tank;

[0090] Step 302: Obtaining a first fluid volume Q based on the first liquid level depth H1 and the second liquid level depth H2 out , expressed by the following formula:

[0091] Q out =(H1-H2)×S1

[0092] S1 is the cross-sectional area of ​​the fluid in the oil and gas wellbore;

[0093] Specifically, the first liquid level depth H1 is obtained by the following method, including:

[0094] Before negative pressure perforating based on method 1, the first liquid level depth H1 is obtained by a pressure gauge or a liquid level echo sounder;

[0095] When the first liquid level depth is obtained based on the pressure gauge, the liquid level depth in the oil and gas wellbore is estimated. When the liquid level depth is outside the test range of the liquid level echo sounder, the fluid gradient profile in the oil and gas wellbore is measured using the pressure gauge. Based on the change of the fluid gradient profile, the first liquid level depth before negative pressure perforation is obtained;

[0096] In this embodiment, the accuracy of the pressure gauge is greater than or equal to 0.1%;

[0097] When the first liquid level depth is obtained based on the liquid level echometer, the liquid level depth in the oil and gas wellbore is estimated. When the liquid level depth is within the test range of the liquid level echometer, the first liquid level depth before negative pressure perforation is directly measured using the liquid level echometer.

[0098] Calculating and obtaining the first liquid level depth H1 based on the first volume Q1 in method 1 or method 2 includes:

[0099] Based on the fluid cross-sectional area S1 and the first volume Q1 in the oil and gas wellbore, the first liquid level depth H1 is obtained, which is expressed by the following formula:

[0100]

[0101] Specifically, after negative pressure perforating is performed based on method 1 or method 2, obtaining the second liquid level depth H2 includes:

[0102] After replacing the fluid in the oil and gas wellbore, perforation is performed and the oil and gas well is closed, so that the pressure gauge is located at the middle depth of the perforated layer, or the pressure gauge is located at the position closest to the middle depth of the perforated layer according to the pipe string structure, and a pressure recovery test is performed on the oil and gas wellbore through the pressure gauge. When the pressure change rate is less than the specified pressure, the pressure recovery test is terminated, and the fluid gradient profile in the oil and gas wellbore is measured based on the pressure gauge, and the second liquid level depth H2 is calculated through the fluid gradient profile in the oil and gas wellbore;

[0103] Or when the second liquid level depth is obtained based on the liquid level echometer, the liquid level depth in the oil and gas wellbore is estimated. When the liquid level depth is within the test range of the liquid level echometer, the second liquid level depth H2 before negative pressure perforating is directly measured using the liquid level echometer.

[0104] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes 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 invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for obtaining the formation pressure of a reservoir, characterized in that: include: Step 1: displacing the fluid in the oil and gas wellbore based on negative pressure perforation, so that the fluid in the reservoir seeps into the oil and gas wellbore, and obtaining a first liquid column pressure based on a pressure gauge; Step 2: After obtaining the first liquid column pressure, inject an equivalent fluid into the oil and gas wellbore, and obtain the second liquid column pressure based on the pressure gauge; Step 3: When the first condition is met, the first formation pressure is obtained based on the first liquid column pressure and the second liquid column pressure.

2. A method for obtaining reservoir formation pressure according to claim 1, characterized in that: The first condition in step 3 includes: Second fluid volume Q in The first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula: Q in =Q1+Q out or the second fluid volume Q in Slightly larger than the first volume Q1 and the first fluid volume Q out The sum is expressed by the following formula: Q in >Q1+Q out or the second fluid volume Q in The first volume Q1, the first fluid volume Q out As the pressure increases to P win When , the sum of the fluid volumes required in the oil and gas wellbore is expressed by the following formula: Q in =Q1+Q out +Q 井筒 ×C t ×P win 。 3. A method for obtaining reservoir formation pressure according to claim 2, characterized in that: The first fluid volume Q out The first volume Q1 is obtained by the following steps, specifically including: Step 301: Acquire the first volume Q1; Step 302: Obtain the first fluid volume Q based on the first liquid level depth H1 and the second liquid level depth H2 out , expressed by the following formula: Q out =(H1-H2)×S1。 4. A method for obtaining reservoir formation pressure according to claim 1, characterized in that: Acquiring the first liquid column pressure based on the pressure gauge in step 1 includes: Based on the pressure gauge directly measuring the pressure of the first liquid column, Or based on the pressure gauge measuring the fluid gradient profile in the oil and gas wellbore, the first liquid column pressure is calculated through the fluid gradient profile in the oil and gas wellbore.

5. A method for obtaining reservoir formation pressure according to claim 1, characterized in that: Acquiring the second liquid column pressure based on the pressure gauge in step 1 includes: Based on the direct measurement of the fluid gradient profile in the oil and gas wellbore by the pressure gauge, the second liquid column pressure is calculated through the fluid gradient profile in the oil and gas wellbore, Or measure the wellhead pressure after injecting the equivalent fluid by the pressure gauge, and perform conversion calculation based on the wellhead pressure to obtain the second liquid column pressure P win , expressed by the following formula: P win =p0+h×ρ×g。 6. A method for obtaining reservoir formation pressure according to claim 1, characterized in that: Also includes: Ensure that the test time of the pressure recovery test when obtaining the first liquid column pressure is the same as the test time of the pressure drop test when obtaining the second liquid column pressure; If they are not the same, the pressure change rate in the pressure recovery test and the pressure drop test is less than the specified pressure, and the pressure recovery test and the pressure drop test are terminated.

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