A method for determining the development distance of shale oil reservoirs

Abstract

The present invention discloses a method for determining the development distance of shale oil reservoirs, and belongs to the field of oil and gas exploration and development. The method comprises the following steps in sequence: (1) determining the original physical property characteristic parameters of the reservoir, obtaining the core sample of the production layer, and determining its pore size distribution and wettability; (2) preparing a quartz capillary test model: etching a U-shaped and regularly arranged channel on an acrylic plate, placing a quartz capillary in the channel and sintering and fixing it, using an alcohol lamp to burn a visible window along the length direction in the center of the acrylic plate, and then calibrating the scale; (3) using a quartz capillary to simulate the reservoir pores, and by measuring the distance that the simulated oil advances in the quartz capillary under a certain pressure gradient, the maximum development distance of shale oil under the pore radius is determined. The present invention comprehensively considers the influence of the reservoir pore size distribution characteristics and wettability characteristics, has a reliable principle, is easy to operate, has accurate test results, and has broad market application prospects.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas exploration and development, and in particular relates to a method for determining a movable distance in a shale oil reservoir development process. Background Art

[0002] As conventional oil resources are becoming increasingly depleted, shale oil reservoirs have become a key area for the development of oil and gas reservoir resources in my country in the future (Zou Caineng, Zhu Rukai, Wu Songtao, et al. Conventional and unconventional oil and gas accumulation types, characteristics, mechanisms and prospects - taking tight oil and tight gas in China as an example [J]. Acta Petrolei Sinica, 2012, 33(2): 173-187). Shale reservoirs have extremely low porosity and low permeability, no natural production capacity, and shale oil reservoirs have developed micro-nanopores. Capillary forces have a significant impact on the development distance of shale oil reservoirs. Therefore, accurately determining the movable distance during the development process of shale oil reservoirs is of great significance for guiding the development of shale oil reservoirs.

[0003] At present, there is no method to determine the utilization distance during the development of shale oil reservoirs. The existing technical means are all aimed at determining the movable pore radius of shale oil. There are mainly the following methods: First, nuclear magnetic resonance technology is used in the laboratory to test the core pore size distribution and the T2 characteristic spectrum of the core before and after the throughput experiment. The measured T2 spectrum is converted into an oil spectrum using the deconvolution analysis method to quantitatively characterize the mobility of shale oil (Bao Wancheng. Nuclear magnetic resonance research on shale oil mobility [D]. China University of Petroleum (East China), 2021). In addition, nuclear magnetic resonance is combined with high-speed centrifugation experiments to calculate The degree of fluid mobilization in machine pores and inorganic pores is also used (Li Zijin. Experimental study on shale oil mobility based on nuclear magnetic resonance technology [D]. China University of Petroleum (East China), 2020); second, based on molecular dynamics simulation, the pore radius is calculated when shale oil molecules exist in the pores in an adsorbed state, and the weighted average is taken to calculate the mobilization limit of shale oil (Sun Zhixue, Yin Yifan, Song Wentong. A method for determining the mobilization limit of shale oil based on molecular dynamics simulation [P]. Shandong Province: CN116519731B, 2023-08-25).

[0004] The above methods have the following problems: (1) The current experimental methods and molecular dynamics simulations are limited to determining the lower limit of the movable pore radius of shale oil, and there is no method or means to evaluate the movable distance of shale oil reservoirs; (2) The experimental methods for determining the movable pore radius of shale oil all require the use of nuclear magnetic resonance equipment. By measuring the characteristic peaks of the core before and after gas injection, the range of shale oil mobilized by gas is indirectly determined. The experimental process is cumbersome and requires the use of complex mathematical inversion to convert the characteristic spectrum into an oil spectrum. It is not possible to expand and transform it to determine the utilization distance experiment; (3) In the molecular dynamics simulation calculation, it is assumed that the pore radius in the adsorbed state is the movable limit, and it is not considered that the pressure reduction in actual development causes some shale oil to be converted from the adsorbed state to the free state. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the development and production distance of a shale oil reservoir. The method simulates reservoir pores by etching a quartz capillary on a glass plate, and then measures the distance that the simulated oil advances in the quartz capillary under a certain pressure gradient, so as to determine the maximum production distance of shale oil under the pore radius. The present invention comprehensively considers the influence of reservoir pore size distribution characteristics and wetting characteristics, has a reliable principle, is easy to operate, has high precision, and has broad market application prospects.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0007] A method for determining the development and producing distance of a shale oil reservoir comprises the following steps in sequence:

[0008] (1) Determine the original physical property characteristic parameters of the reservoir

[0009] 1) According to the original formation fluid PVT data, determine the original reservoir formation pressure P0 (MPa) and original formation temperature T0 (℃), and refer to the national standard GB / T 26981-2020 "Analysis method of physical properties of oil and gas reservoir fluids" to test the viscosity of crude oil under formation conditions μ o (mPa.s);

[0010] 2) Determine the ion composition, concentration and mineralization of the reservoir formation water based on the on-site water quality analysis report;

[0011] 3) Obtain core samples from the production layer, use micro-CT scanning to determine the pore size distribution in the [r1, r2] interval (μm), and test the wettability of the core samples in accordance with the industry standard SY / T 5153-2017 “Method for determination of wettability of reservoir rocks”;

[0012] (2) Preparation of quartz capillary test model

[0013] 1) According to the pore size distribution of the core sample, a quartz capillary with a radius of r (μm) and a total length of k (m) is selected, and r1≤r≤r2. If the wettability of the core sample is oil-wet, a 20% n-heptane-crude oil mixture system is injected into the quartz capillary for a soaking time of t to modify the quartz capillary to oil-wet, and then the quartz capillary is cleaned;

[0014] 2) Select an acrylic plate with a length of l (m) and a width of d (m), set circular grooves at both ends of the acrylic plate as the injection port and the outflow port of the fluid, and then etch U-shaped and regularly arranged channels on the acrylic plate. The cross-section of the channel is semicircular, with a radius or depth of 1.2r, and is connected to the circular grooves at both ends;

[0015] 3) Place the quartz capillary in the channel and sinter it to fix it. The circular grooves at both ends connect the inlet and outlet of the quartz capillary. Use an alcohol lamp to burn a visible window in the center of the acrylic plate along the length direction. Then mark the scale on the acrylic plate. The scales at different positions correspond to the length of the quartz capillary from the inlet to the position. Wrap a resistance wire around the outside of the acrylic plate. The quartz capillary test model is completed.

[0016] (3) Determination of the travel distance of crude oil in a quartz capillary

[0017] 1) Prepare simulated oil under the conditions of original formation temperature T0 (℃) and original formation pressure P0 (MPa), prepare brine according to the on-site water quality analysis report, and put the prepared simulated oil and brine into intermediate containers respectively;

[0018] 2) The inlet end of the quartz capillary test model is connected to the displacement pump through the simulated oil intermediate container and the brine intermediate container, and the outlet end is connected to the back pressure valve, and pressure gauges are set at both ends;

[0019] 3) The resistance wire wrapped around the acrylic plate is electrified, the temperature is set to the original formation temperature T0, the displacement pump is set to the original formation pressure P0, the configured brine is injected into the quartz capillary at a constant pressure from the inlet end until the reading of the pressure gauge at the outlet end is consistent with the original formation pressure, the back pressure pump connected to the back pressure valve is turned on, and the back pressure pump is set to a constant pressure P0 to complete the pressure building;

[0020] 4) Close the valve of the salt water intermediate container, open the valve of the simulated oil intermediate container, and continue to increase the pressure of the displacement pump to inject simulated oil into the quartz capillary to ensure that each pressure point P i (MPa) The oil-water interface can appear in the visual window and remain stable for 48 hours without moving. The scale of the oil-water interface on the acrylic plate is read out, and the corresponding capillary length is L i (m), that is, the distance of crude oil movement under this pressure is L i , the corresponding displacement pressure difference is ΔP i (MPa) = P i -P0, plot displacement pressure difference ΔP i - Crude oil mobilization distance L i The relationship curve of is obtained, thus obtaining the movable distance of shale oil under different displacement pressure differences when the reservoir pore radius is r.

[0021] Furthermore, in the step (2), the immersion time t is determined by the following process: a quartz plate with a clean surface is selected and immersed in a 20% n-heptane-crude oil mixture system, and the wetting angles of the quartz plates at different immersion times are tested respectively with reference to the industry standard SY / T 5153-2017 "Method for Determination of Wettability of Reservoir Rocks", and a wetting angle-immersion time relationship curve is obtained. The immersion time when the quartz plate shows stable oil wetness is t.

[0022] Furthermore, in step (3), the viscosity of the simulated oil and the mineralization of the brine are tested under formation conditions to make them consistent with the formation crude oil and formation water. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the shale pore radius distribution diagram.

[0024] Figure 2 This is the wetting angle-immersion time relationship curve of the quartz plate after being treated with 20% n-heptane-crude oil system.

[0025] Figure 3 It is a U-shaped and regularly arranged channel etched on the acrylic plate.

[0026] Figure 4 A visible window and calibrated scale are burned in the center of the acrylic plate along the length direction.

[0027] Figure 5 Diagram of a testing rig for developing the producing distance for shale oil reservoirs.

[0028] In the figure: 1, 21—displacement pump, back pressure pump; 2, 3, 5, 6, 8, 9, 17, 19, 22—valves; 4—simulated oil intermediate container; 7—salt water intermediate container; 10, 16, 20—pressure gauges; 11—injection port; 12—visual window; 13—quartz capillary test model; 14—observation system; 15—outlet; 18—back pressure valve; 23—beaker.

[0029] Figure 6 This is the relationship curve between displacement pressure difference and crude oil moving distance. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to the accompanying drawings and examples, so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, they are all protected.

[0031] A method for determining the development and producing distance of a shale oil reservoir comprises the following steps in sequence:

[0032] (1) Determination of reservoir original physical property characteristic parameters

[0033] 1) According to the original formation fluid PVT data, the original formation pressure of the reservoir is determined to be 35MPa and the original formation temperature is 75℃. Referring to the national standard GB / T 26981-2020 "Analysis method of physical properties of oil and gas reservoir fluids", the viscosity μ of the oil sample under formation conditions is tested. o =0.34mPa.s;

[0034] 2) According to the on-site water quality analysis report, determine the ion composition, concentration and mineralization of the reservoir formation water. The ion concentration and composition are shown in Table 1:

[0035] Table 1 Mineral composition of formation water

[0036]

[0037] 3) Obtain core samples from the main production layer and use micro-CT scanning to determine that the pore size distribution is in the range of 2μm-80μm (see Figure 1 ), and refer to the industry standard SY / T 5153-2017 "Method for determination of wettability of reservoir rocks" to test the wettability of representative rocks in the reservoir, which is oil-wet;

[0038] (2) Preparation of quartz capillary test model

[0039] 1) Select a quartz plate with a clean surface and soak it in a 20% n-heptane-crude oil mixture system. Refer to the industry standard SY / T5153-2017 "Measurement method for wettability of reservoir rocks" to test the wetting angle of the quartz plate at different immersion times, and obtain the wetting angle-immersion time relationship curve (see Figure 2 ), the quartz plate showed stable oil-wetting characteristics after immersion for 48 h;

[0040] 2) According to the pore size distribution of the core sample, a quartz capillary with a radius of 25 μm and a length of 10 m was selected, and a 20% n-heptane-crude oil mixture system was injected into the quartz capillary for 48 h to modify the quartz capillary, and then the quartz capillary was cleaned;

[0041] 3) An acrylic plate with a length of 1 m and a width of 0.6 m was selected, and circular grooves were dug at both ends of the plate as the injection port and the outflow port of the fluid. Then, U-shaped and regularly arranged channels were etched on the acrylic plate. The cross-section of the channel was semicircular, with a radius or depth of 30 μm, and was connected to the circular grooves at both ends. The shape was as follows: Figure 3 As shown;

[0042] 4) Place the quartz capillary into the channel and sinter it to fix it. The circular grooves at both ends connect the inlet and outlet ends of the quartz capillary. Use an alcohol lamp to burn a visual window along the length direction in the center of the acrylic plate, and then mark the scale on the acrylic plate (see Figure 4 ), the scales at different positions correspond to the length of the quartz capillary from the inlet end to the position, and the resistance wire is wound on the outside of the acrylic plate, and the quartz capillary test model is completed;

[0043] (3) Determination of the travel distance of crude oil in a quartz capillary

[0044] 1) Prepare simulated oil under the conditions of original formation temperature of 75°C and original formation pressure of 35MPa, prepare brine according to the on-site water quality analysis report, test the viscosity of simulated oil under formation conditions to be μ=0.34mPa.s, and the mineralization of brine to be 51948mg / L, and put the prepared simulated oil and brine into intermediate containers respectively;

[0045] 2) Place the quartz capillary test model in the test device (see Figure 5 ), the device comprises a displacement pump 1, a back pressure pump 21, a simulated oil intermediate container 4, a brine intermediate container 7, a quartz capillary test model 13, an observation system 14, a back pressure valve 18 and a beaker 23, the quartz capillary test model has a fluid injection port 11 and an outflow port 15 at both ends, a visual window 12 (the visual window is connected to the observation system 14) is arranged in the middle, the fluid injection port 11 is connected to the displacement pump 1 through the simulated oil intermediate container 4 and the brine intermediate container 7 respectively, the outflow port 15 is connected to the back pressure valve 18, and pressure gauges 10 and 16 are arranged at both ends;

[0046] 3) The resistance wire wrapped around the acrylic plate is energized, the temperature is set to the original formation temperature of 75°C, the displacement pump 1 is set to the original formation pressure of 35 MPa, valves 2, 6, 8, and 9 are opened, and the brine is injected into the quartz capillary at a constant pressure from the inlet end until the reading of the pressure gauge 16 is consistent with the original formation pressure, valves 17, 19, and 22 connected to the back pressure valve 18 are opened, and the back pressure pump 21 is set to a constant pressure of 35 MPa to complete the pressure building;

[0047] 4) Close valves 6 and 8 of the brine intermediate container, open valves 3 and 5 of the simulated oil intermediate container, continue to increase the pressure of the displacement pump 1 to inject simulated oil into the quartz capillary, and move the observation system 14 within the range of the visual window 12 to find the oil-water interface, ensuring that each pressure point P i The oil-water interface can appear in the visual window and remain stable for 48 hours without moving. Read the scale of the oil-water interface on the acrylic plate at this time. The corresponding capillary length is L i (m), that is, the distance of crude oil movement under this pressure is L i , the corresponding displacement pressure difference is ΔP i (MPa) = P i -P0, plot displacement pressure difference ΔP i - Crude oil production and migration distance L i The relationship curve (see Figure 6 ), thus obtaining the movable distance of shale oil with a reservoir pore radius of r under different displacement pressure differences (results are shown in Table 2).

[0048] Table 2 Shale oil production distance under different pressure differences in quartz capillary

[0049] <![CDATA[P i ,MPa]]> <![CDATA[ΔP i ,MPa]]> <![CDATA[L i ,m]]> 36.96 1.96 1.5 38.83 3.83 3.0 42.50 7.50 4.5 44.39 9.39 5.0 49.69 14.69 6.0 53.37 18.37 6.5 57.98 22.98 7.0

Claims

1. A method for determining the development distance of a shale oil reservoir comprises the following steps in sequence: (1) Determine the original physical property characteristic parameters of the reservoir 1) Determine the original reservoir pressure based on the original formation fluid PVT data P 0 , original formation temperature T 0 , testing the viscosity of crude oil under formation conditions μ o ; 2) Determine the ion composition, concentration and mineralization of the reservoir formation water based on the on-site water quality analysis report; 3) Obtain core samples from the production layer, determine their pore size distribution in the interval [r1, r2], and test the wettability of the core samples; (2) Preparation of quartz capillary test model 1) According to the pore size distribution of the core sample, select a radius of r The total length is k If the core sample is oil-wet, a quartz capillary with a diameter of 200 mm and r1≤r≤r2 is used. If the wettability of the core sample is oil-wet, a 20% n-heptane-crude oil mixture is injected into the quartz capillary for a soaking time of t , modifying the quartz capillary to be oil-wet, and then cleaning the quartz capillary; 2) Select the length l , width is d The acrylic plate is provided with circular grooves at both ends as the injection port and the outflow port of the fluid, and then U-shaped and regularly arranged channels are etched on the acrylic plate. The cross section of the channel is semicircular, and the radius or depth is 1.2 r and connected with the circular grooves at both ends; 3) Place the quartz capillary in the channel and sinter it to fix it. The circular grooves at both ends connect the inlet and outlet of the quartz capillary. Use an alcohol lamp to burn a visible window in the center of the acrylic plate along the length direction. Then mark the scale on the acrylic plate. The scales at different positions correspond to the length of the quartz capillary from the inlet to the position. Wrap the resistance wire on the outside of the acrylic plate. The quartz capillary test model is completed. (3) Determine the travel distance of crude oil in a quartz capillary 1) At the original formation temperature T 0 , original formation pressure P 0 Prepare simulated oil under the conditions, prepare brine according to the on-site water quality analysis report, and put the prepared simulated oil and brine into intermediate containers respectively; 2) The inlet end of the quartz capillary test model is connected to the displacement pump through the simulated oil intermediate container and the brine intermediate container, and the outlet end is connected to the back pressure valve, and pressure gauges are set at both ends; 3) Energize the resistance wire wrapped around the acrylic plate and set the temperature to the original formation temperature T 0 , the displacement pump is set to the original formation pressure P 0 , inject the configured brine into the quartz capillary at constant pressure from the inlet end until the reading of the pressure gauge at the outlet end is consistent with the original formation pressure, turn on the back pressure pump connected to the back pressure valve, and set the back pressure pump to a constant pressure P 0 , complete the pressure building; 4) Close the valve of the salt water intermediate container, open the valve of the simulated oil intermediate container, and continue to increase the pressure of the displacement pump to inject simulated oil into the quartz capillary to ensure that each pressure point P i The oil-water interface can appear in the visual window and remain stable for 48 hours. The scale of the oil-water interface on the acrylic plate is read out, and the corresponding capillary length is L i , that is, the distance of crude oil movement under this pressure is L i , the corresponding displacement pressure difference is ΔP i = P i -P 0 , plot the displacement pressure difference ΔP i - Crude oil mobilization distance L i The relationship curve of the reservoir pore radius is obtained as r The movable distance of shale oil under different displacement pressure differences.

2. A method for determining the development and producing distance of a shale oil reservoir according to claim 1, characterized in that: In the step (2), the soaking time t The determination is made through the following process: a quartz plate with a clean surface is selected and immersed in a 20% n-heptane-crude oil mixture system. The wetting angle of the quartz plate at different immersion times is tested to obtain a wetting angle-immersion time relationship curve. The quartz plate is immersed for a time of stable oil wetting. t .

3. A method for determining the development and producing distance of a shale oil reservoir according to claim 1, characterized in that: In the step (3), the viscosity of the simulated oil and the salinity of the brine are tested under formation conditions so that they are consistent with the viscosity of the formation crude oil and the salinity of the formation water, respectively.

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