Method and device for measuring minimum starting pressure of reservoir

Abstract

The invention relates to the field of petroleum geology engineering, in particular to a method and device for measuring the minimum starting pressure of a reservoir stratum.The method comprises the steps that a saturated rock sample is loaded into a core holder, and a displacement pump is started to discharge gas in the core holder; the confining pressure value of the core holder is gradually adjusted to a first preset threshold value by the ring pressure tracking pump, and in the detection process, the confining pressure value is kept to be larger than the core inlet pressure value; and starting the displacement pump, displacing the rock core at the flow speed of a second preset threshold value, observing the pressure value of the rock core inlet through the pressure gauge, and selecting a corresponding displacement simulation method according to the pressure gradient value of the rock core inlet to determine the minimum starting pressure. The method is simple in measuring process, high in operability, high in precision and wide in applicability, the corresponding displacement simulation method is selected in a grading mode by monitoring the pressure threshold value, the error of the minimum starting pressure is reduced, and the precision is higher.

Description

Technical Field

[0001] This invention relates to the field of petroleum geological engineering, specifically to a method and apparatus for determining the minimum starting pressure of a reservoir. Background Technology

[0002] In petroleum exploration, low-permeability tight gas reservoirs, characterized by narrow pore throats, poor pore connectivity, high capillary resistance, and generally high water saturation, tend to exhibit unique seepage characteristics distinct from medium- to high-permeability gas reservoirs. Experiments show that when the water saturation of the core exceeds a certain threshold, gas seepage exhibits low-velocity non-Darcy flow characteristics, indicating the presence of an initiating pressure gradient.

[0003] Chinese invention patent CN101968423B discloses a method for testing the start-up pressure of low-permeability reservoirs. The method involves placing a 0.8–1.5 m long core sample into a multi-pressure-measuring-point core holder to simulate reservoir conditions and apply confining pressure. The core sample is then evacuated, and saturated with formation water to the original reservoir pore pressure. The backpressure valve pressure is set to a specified test pore fluid pressure value. The formation water flow rate through the core chamber is set to 0.1–1 mL / min, gradually decreasing to zero, and the pressure difference between each measuring point and the inlet is recorded. The start-up pressure gradient is calculated using the pressure difference data between different measuring points and the inlet. The calculation formula is: GradP = (PAB / LAB + PAC / LAC + …) / n, where PAB, PAC… represent the pressure difference in segments AB, AC… of the core sample, and n represents the number of measuring points.

[0004] However, oil and gas exhibit nonlinear characteristics when seeping in tight and low-permeability oil and gas reservoirs. A typical feature is the existence of a minimum starting pressure. However, it does not take into account the different minimum starting pressures corresponding to the fluid flow discharged from the core holder under different pressures. Therefore, the obtained minimum starting pressure has a certain error.

[0005] The minimum rock initiation pressure refers to the minimum pressure difference required for stable fluid migration within a rock. The magnitude of this minimum initiation pressure determines the ease with which oil and gas can flow out of the rock's pores, directly impacting oil extraction efficiency. Therefore, the minimum rock initiation pressure is an important experimental method in petroleum geological engineering, and a method and apparatus for determining the minimum reservoir initiation pressure are urgently needed. Summary of the Invention

[0006] To avoid the aforementioned problems in the prior art, the present invention aims to provide a method and apparatus for determining the minimum start-up pressure of a reservoir.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for determining the minimum start-up pressure of a reservoir, comprising the following steps:

[0008] S1: Load the saturated rock sample into the core holder, turn on the displacement pump to expel the gas in the core holder, and turn off the displacement pump after the core holder discharges a continuous flow of liquid.

[0009] S2: The confining pressure value of the core holder is gradually adjusted to the first preset threshold by the ring pressure tracking pump. During the detection process, the confining pressure value is always kept greater than the core inlet pressure value.

[0010] S3: Start the displacement pump and displace the core at a flow rate of the second preset threshold. Observe the core inlet pressure value through the pressure gauge. If the core inlet pressure gradient value is greater than or equal to the third preset threshold, the constant pressure displacement method is used to conduct experimental displacement simulation to determine the minimum starting pressure. If the core inlet pressure gradient value is less than the third preset threshold, the constant rate displacement method is used to conduct experimental displacement simulation to determine the minimum starting pressure.

[0011] It should be noted that the setting of various preset thresholds and the setting of confining pressure values ​​should refer to the conventions for velocity sensitivity evaluation experiments in the standard SY / T 5358-2010 "Evaluation Method for Reservoir Sensitivity Flow Experiment".

[0012] The present invention is further configured such that, in step S2, the difference between the confining pressure and the core inlet pressure is 1.5 MPa to 2.0 MPa; and a pressure gauge is provided at the inlet of the core holder.

[0013] By setting the parameters of the annular pressure tracking pump, the confining pressure is kept greater than the core inlet pressure, which is obtained in real time through a pressure gauge.

[0014] The present invention is further configured such that the first preset threshold is 2 MPa, the second preset threshold is 0.1 ml / min, and the third preset threshold is 2 MPa / cm.

[0015] The present invention is further configured such that the constant pressure displacement method is as follows: the displacement pump gradually increases the pressure from a first preset threshold. When the pressure increases by 1 MPa, the weight change of the liquid flowing out of the core holder is recorded by a balance within a time period, and the flow rate of the liquid at each pressure point is calculated. The flow rate is measured 3 times at each pressure point. When the relative deviation between the flow rates at that pressure point is less than 3%, that pressure point is taken as the minimum starting pressure.

[0016] The flow rate is calculated as the ratio of the difference in volume change of the liquid flow to time.

[0017] The present invention is further configured such that the constant-speed displacement method specifically involves the displacement pump starting from a flow rate of a second preset threshold and gradually increasing the speed. When the flow rate increases by 0.1 ml / min, the weighing result of the balance within the time period is recorded and the flow rate is calculated. The experimental pressure is recorded by a pressure gauge and measured 3 times at each flow rate. When the relative pressure deviation is less than 3%, the pressure is taken as the minimum starting pressure.

[0018] The present invention also includes a device for determining the minimum start-up pressure of a reservoir, comprising a displacement pump, a ring pressure tracking pump, a pressure gauge, a six-way valve, a core holder, a balance, and a beaker; the six-way valve is connected to the inlet of the core holder via a pipeline, and the pressure gauge is installed on the six-way valve; the six-way valve is also connected to the displacement pump and the ring pressure tracking pump via pipelines respectively.

[0019] The annular pressure tracking pump is connected to the inlet of the outer wall of the core holder via a pipeline; the outlet of the core holder is connected to a beaker via a pipeline, and the beaker is placed on the balance.

[0020] The invention is further configured such that: the displacement pump is used to provide displacement fluid to the core holder; the annular pressure tracking pump is used to detect the annular pressure of the core holder; the pressure gauge is used to detect the inlet pressure of the core holder; the beaker is used to receive the fluid flow discharged from the core holder; and the balance is used to weigh the mass of the fluid flow.

[0021] The present invention is further configured such that the pipeline is a steel pressure pipeline.

[0022] In summary, the beneficial effects of the above-mentioned technical solution of the present invention are as follows:

[0023] 1. This invention discloses a method and apparatus for determining the minimum starting pressure of a reservoir. The determination process is simple, highly operable, highly accurate, and widely applicable. Based on the fact that the minimum starting pressure corresponds to different pressures in the fluid flow discharged from the core holder under different pressures, this invention reduces the error in minimum starting pressure and achieves higher accuracy by monitoring pressure thresholds and selecting the corresponding displacement simulation method in stages.

[0024] 2. The device described in this invention is applicable to both constant pressure displacement method and constant speed displacement method. The appropriate method can be selected according to the working conditions, and it has a wide range of applications. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1A flowchart illustrating a method for determining the minimum start-up pressure of a reservoir, provided in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of an apparatus for determining the minimum start-up pressure of a reservoir, provided in an embodiment of the present invention.

[0028] The meanings of the reference numerals in the attached figures are as follows:

[0029] 101. Displacement pump; 102. Six-way valve; 103. Ring pressure tracking pump; 104. Pressure gauge; 105. Core holder; 106. Balance; 107. Beaker. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of the present invention, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of the present invention.

[0031] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0032] Example 1:

[0033] like Figures 1-2 As shown in the preferred embodiment of the present invention, a method for determining the minimum start-up pressure of a reservoir includes the following steps:

[0034] S1: Fill the device for determining the minimum start-up pressure of the reservoir with experimental water and conduct a pressure test. The relative change rate of pressure drop is less than 1% after 30 minutes to be considered qualified. Load the saturated rock sample into the core holder 105, turn on the displacement pump 101 to purge the gas in the core holder 105, and turn off the displacement pump 101 after a continuous flow of liquid is discharged from the core holder 105.

[0035] In this embodiment, the following parameters were used before displacement: test pressure: (0~70) MPa, accuracy ±0.05 MPa; test temperature: (0~150) ℃, accuracy ±0.1 ℃; displacement rate: (0~10) ml / min, displacement accuracy 0.5%.

[0036] Specifically, the displacement fluid used in the displacement process is selected based on the core sample:

[0037] The displacement fluid comprises: undegassed crude oil or blended crude oil from the same formation, wherein the water content of the undegassed crude oil is not higher than 0.5%; those skilled in the art can adjust the oil-water viscosity ratio according to experimental requirements to obtain the oil for degassing experiments. The blended crude oil is prepared by blending different types of white oil or neutral kerosene. The blended crude oil is filtered using medium-speed filter paper before the experiment. Specifically, the neutral kerosene is depolarized kerosene.

[0038] Water used in the displacement process:

[0039] Experimental water is typically prepared in-house based on formation water analysis data from the block. Alternatively, standard saline or potassium chloride solution with the same salinity as the formation water can be used. If formation water data is unknown, a standard saline or potassium chloride solution with a salinity of 8% (mass fraction) is used. The standard saline solution formula is as follows:

[0040] NaCl: CaCl2: MgCl2.6H2O=7:0.6:0.4.

[0041] Rock sample preparation during displacement: Select representative rock samples and drill plunger rock samples with a diameter of 2.50±0.1cm and a length of 3.00cm~7.00cm. The processing method shall be performed in accordance with GB / T 29172. The cleaning and drying of the rock samples shall be performed in accordance with GB / T 29172. The porosity and gas permeability of the rock samples shall be determined in accordance with GB / T 29172. The dried, constant-weight cores shall be vacuumed and saturated with simulated formation water in accordance with GB / T 29172.

[0042] After evacuation, the core is pressurized to over 20 MPa and the constant pressure is maintained for no less than 24 hours to ensure that the core is fully saturated and to obtain a rock sample saturated with simulated formation water.

[0043] Weigh the rock sample after it has been saturated with simulated formation water, and calculate the effective pore volume using the following formula:

[0044]

[0045] In the formula:

[0046] V P m1 is the effective pore volume of the rock sample, in milliliters (mL); m2 is the mass of the rock sample saturated with simulated formation water, in grams (g); m3 is the mass of the dry rock sample, in grams (g); ρ0 is the density of the simulated formation water, in grams per cubic centimeter (g / cm³). 3 );

[0047] The determination of water density during the displacement process shall be carried out in accordance with the provisions of SY / T 5523, and therefore will not be elaborated further.

[0048] Determination of rock sample saturation: Compare the pore volume obtained after evacuating the rock sample from saturated formation water with the pore volume obtained by nitrogen gas method. The two data should satisfy the relationship given by the following formula.

[0049]

[0050] In the formula: V pHe This represents the pore volume obtained by the helium gas method, expressed in milliliters (mL).

[0051] S2: The confining pressure value of the core holder 105 is gradually adjusted to a first preset threshold value by the annular pressure tracking pump 103. In this embodiment, the first preset threshold value is 2 MPa. During the detection process, the confining pressure value is always kept greater than the core inlet pressure value; the difference between the confining pressure value and the core inlet pressure is 1.5 MPa to 2.0 MPa; a pressure gauge 104 is installed at the inlet of the core holder 105.

[0052] By setting the parameters of the annular pressure tracking pump 103, the confining pressure value is kept greater than the core inlet pressure, which is obtained in real time through the pressure gauge 104.

[0053] S3: Start the displacement pump and displace the core at a flow rate of 0.1 ml / min in this embodiment. Observe the core inlet pressure value through a pressure gauge and compare the core inlet pressure gradient value with the third preset threshold. In this embodiment, the third preset threshold is set to 2 MPa / cm. If the pressure gradient at both ends of the core exceeds 2 MPa / cm after stabilization, the constant pressure displacement method is selected for the experimental displacement simulation; if the pressure gradient at both ends of the core is less than 2 MPa / cm after stabilization, the constant rate displacement method is selected for the experimental displacement simulation.

[0054] The constant pressure displacement method specifically involves: the displacement pump gradually increasing the pressure from a first preset threshold. For every 1 MPa increase, the weight change of the fluid flowing from the core holder is recorded using a balance over a given time period, and the fluid flow rate at each pressure point is calculated. The flow rate is measured three times at each pressure point. When the relative deviation between the flow rates at each pressure point is less than 3%, that pressure point is designated as the minimum starting pressure. The fluid flow rate is calculated as the ratio of the difference in fluid volume change to time.

[0055] The constant-rate displacement method is as follows: the displacement pump starts from the second preset threshold flow rate and gradually increases the speed. For every 0.1 ml / min increase, the weighing result of the balance is recorded and the flow rate is calculated. The experimental pressure is recorded by the pressure gauge. The pressure is measured 3 times at each flow rate. When the relative pressure deviation is less than 3%, the pressure is taken as the minimum starting pressure.

[0056] Example 2:

[0057] like Figure 2As shown, an apparatus for determining the minimum reservoir start-up pressure, applicable to the method for determining the minimum reservoir start-up pressure described in Example 1, includes: a displacement pump 101, a ring pressure tracking pump 103, a pressure gauge 104, a core holder 105, a balance 106, and a beaker 107; the apparatus further includes a six-way valve 102, on which the pressure gauge 104 is installed; the six-way valve 102 is connected to the inlet of the core holder 105 via a pipeline; the pressure gauge 104 is used to detect the inlet pressure of the core holder 105;

[0058] The six-way valve 102 is connected to the displacement pump 101 via a pipeline; the displacement pump 101 is used to provide displacement fluid to the core holder 105.

[0059] The six-way valve 102 is connected to the annular pressure tracking pump 103 via a pipeline; the annular pressure tracking pump 103 is used to detect the annular pressure of the core holder 105.

[0060] The annular pressure tracking pump 103 is connected to the inlet of the outer wall of the core holder 105 via a pipeline; the outlet of the core holder 105 is connected to the beaker 107 via a pipeline.

[0061] Preferably, the pipeline is a steel pressure pipeline;

[0062] The beaker 107 is placed on the balance 106. The beaker 107 is used to receive the liquid flow discharged from the core holder 105, and the balance 106 is used to weigh the mass of the liquid flow.

[0063] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the minimum start-up pressure of a reservoir, characterized in that, Includes the following steps: S1: Load the saturated rock sample into the core holder, turn on the displacement pump to expel the gas in the core holder, and turn off the displacement pump after the core holder discharges a continuous flow of liquid. S2: The confining pressure value of the core holder is gradually adjusted to the first preset threshold by the ring pressure tracking pump. During the detection process, the confining pressure value is always kept greater than the core inlet pressure value. S3: Start the displacement pump and displace the core at a flow rate of the second preset threshold. Observe the core inlet pressure value through the pressure gauge. If the core inlet pressure gradient value is greater than or equal to the third preset threshold, the constant pressure displacement method is used to conduct experimental displacement simulation to determine the minimum starting pressure. If the core inlet pressure gradient value is less than the third preset threshold, the constant rate displacement method is used to conduct experimental displacement simulation to determine the minimum starting pressure.

2. The method for determining the minimum start-up pressure of a reservoir according to claim 1, characterized in that, In step S2, the difference between the confining pressure and the core inlet pressure is 1.5 MPa to 2.0 MPa; a pressure gauge is installed at the inlet of the core holder.

3. The method for determining the minimum start-up pressure of a reservoir according to claim 1, characterized in that, The first preset threshold is 2 MPa, the second preset threshold is 0.1 ml / min, and the third preset threshold is 2 MPa / cm.

4. The method for determining the minimum start-up pressure of a reservoir according to claim 1, characterized in that, The constant pressure displacement method is as follows: the displacement pump gradually increases the pressure from the first preset threshold. When the pressure increases by 1 MPa, the weight change of the liquid flowing out of the core holder is recorded by a balance within a time period, and the flow rate at each pressure point is calculated. The flow rate is measured 3 times at each pressure point. When the relative deviation between the flow rates at that pressure point is less than 3%, that pressure point is taken as the minimum starting pressure.

5. The method for determining the minimum start-up pressure of a reservoir according to claim 1, characterized in that, The constant-rate displacement method is as follows: the displacement pump starts from the second preset threshold flow rate and gradually increases the speed. When the speed increases by 0.1 ml / min, the weighing result of the balance is recorded and the flow rate is calculated. The experimental pressure is recorded by the pressure gauge. The pressure is measured 3 times at each flow rate. When the relative pressure deviation is less than 3%, the pressure is taken as the minimum starting pressure.

6. An apparatus for determining the minimum start-up pressure of a reservoir, applicable to the method for determining the minimum start-up pressure of a reservoir as described in any one of claims 1-5, characterized in that, The system includes a displacement pump, a ring pressure tracking pump, a pressure gauge, a six-way valve, a core holder, a balance, and a beaker. The six-way valve is connected to the inlet of the core holder via a pipeline, and the pressure gauge is installed on the six-way valve. The six-way valve is also connected to the displacement pump and the ring pressure tracking pump via pipelines. The annular pressure tracking pump is connected to the inlet of the outer wall of the core holder via a pipeline; the outlet of the core holder is connected to a beaker via a pipeline, and the beaker is placed on the balance.

7. The apparatus for determining the minimum start-up pressure of a reservoir according to claim 6, characterized in that, The displacement pump is used to supply displacement fluid to the core holder; the annular pressure tracking pump is used to detect the annular pressure of the core holder; the pressure gauge is used to detect the inlet pressure of the core holder; the beaker is used to receive the fluid flow discharged from the core holder; and the balance is used to weigh the mass of the fluid flow.

8. The apparatus for determining the minimum start-up pressure of a reservoir according to claim 6, characterized in that, The pipeline is a steel pressure pipeline.

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