An optimization method for volume fracturing of low-pressure reservoirs in tight oil reservoirs

Abstract

This invention relates to the field of oil and gas engineering, and particularly to an optimization method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs during hydraulic fracturing. The optimization method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs involves: selecting a suitable energy-enhancing medium for the target reservoir; obtaining a rock reservoir coefficient for evaluating the geological quality of the low-pressure reservoir; obtaining a rock heterogeneity coefficient for evaluating the engineering quality of the low-pressure reservoir; establishing a comprehensive effect evaluation factor that is directly proportional to the proportion of produced fluid in the horizontal well fracturing section, directly proportional to the rock reservoir coefficient, and inversely proportional to the rock heterogeneity coefficient; and selecting the energy-enhancing fracturing method corresponding to a comprehensive effect evaluation factor > 0.001mD as the preferred energy-enhancing method, thereby achieving optimization of low-pressure reservoir volumetric fracturing. This invention significantly reduces testing costs, has a simple and feasible calculation method, and is also applicable to the optimization of volumetric fracturing of similar low-pressure reservoirs, showing good application prospects and providing technical guidance for the efficient development of unconventional low-pressure reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to an optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs during hydraulic fracturing. Background Technology

[0002] China possesses extremely rich tight oil reservoir resources with enormous development potential, holding significant exploration and development prospects in the unconventional oil and gas sector. Horizontal well volumetric fracturing is crucial for increasing production. Large-scale slippery volumetric fracturing creates hydraulic fractures and interconnected fractures, forming a complex fracture network that acts as a "highway" for oil and gas migration—this is the core of unconventional volumetric fracturing. Formation energy is a key factor influencing single-well productivity, continuously impacting stable production and EUR (Earnings per Hour). China's continental tight oil reservoirs, particularly those in the Ordos Basin, are characterized by low-pressure, low-permeability reservoirs with pressure coefficients of only 0.7–0.8. Extensive field practice has shown that fracturing fluid replenishment can rapidly increase formation pressure. However, compared to North American tight oil and gas reservoirs, extensive core sampling in the field confirms that Chinese tight oil exhibits strong heterogeneity, discontinuous sand bodies, well-developed sand-mud interbedded layers, extremely dense pore channels, poor connectivity, and limited replenishment methods. Furthermore, due to the presence of natural fractures in tight reservoirs, current testing methods struggle to accurately measure their occurrence, density, morphology, and development degree. This leads to significant variations in individual well performance on the same platform after replenishment of low-pressure reservoirs. Therefore, optimization methods for the optimal replenishment medium and method are urgently needed to guide the efficient development of low-pressure reservoirs. Domestic and international scholars and major oilfields have primarily employed the following methods for optimizing volumetric fracturing in low-pressure reservoirs: (1) A fracturing fluid and fracturing method for low-pressure, high-pour-point oil reservoirs (CN202111535925.2) discloses a fracturing fluid for low-pressure, high-pour-point oil reservoirs, which is composed of the following components by mass percentage: 3-5% heat-generating agent A, 3.5-5.5% heat-generating agent B, 0.5-2% heat-generating reaction catalyst, 0.25-0.5% acid-resistant thickener, 0.2-0.5% crosslinking agent, 0.08-0.15% breaker, and the balance being water, with the sum of the mass percentages of the above components being 100%. The fracturing fluid for low-pressure, high-pour-point oil reservoirs and the fracturing method using it can simultaneously improve crude oil fluidity, increase formation energy, reduce fluid loss, increase single-well production, and enhance the stimulation effect of regional low-pressure, high-pour-point oil reservoirs.

[0003] In a carbon dioxide-enhanced variable displacement mixed injection fracturing method (CN202010302049.8), the carbon dioxide injection amount is determined based on the gas-bearing area of ​​a single well, reservoir geology, and engineering parameters; the total designed discharge rate is kept constant, liquid carbon dioxide is injected according to the carbon dioxide injection amount, and fracturing fluid is injected according to the fracturing parameters; finally, fracturing operation is carried out.

[0004] This article, "Carbon Dioxide Regional Enhanced Volumetric Fracturing Technology for Horizontal Wells in Ordos Basin Shale Oil," addresses the challenges of low reservoir pressure, low fracture network complexity, and water scarcity in the Loess Plateau region of Ordos Basin shale oil. Using the Qingcheng Oilfield shale oil as a case study, physical simulation experiments of slickwater and carbon dioxide fracturing were conducted. High-energy CT was used to monitor the fracture propagation pattern of carbon dioxide fracturing, and the feasibility of forming complex fractures through carbon dioxide fracturing was analyzed. Furthermore, reservoir numerical simulation methods were employed to optimize key parameters for carbon dioxide injection, resulting in a carbon dioxide regional enhanced volumetric fracturing technology suitable for the Qingcheng Oilfield shale oil.

[0005] The three representative methods mentioned above, which aim to increase single-well production by injecting fracturing fluids and media into low-pressure reservoirs to provide formation energy, lack a systematic approach to optimizing fracturing for low-pressure reservoirs and considering reservoir geological characteristics. Therefore, their application is limited. Consequently, there is an urgent need for systematic optimization of key aspects such as fracturing media and methods for low-pressure reservoirs to guide their efficient development. Summary of the Invention

[0006] The present invention aims to address the above-mentioned problems by proposing an optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs.

[0007] The technical solution of this invention is as follows: An optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs is as follows: Preferentially select energy-enhancing media suitable for the target reservoir; Obtain the rock reservoir coefficient for evaluating the geological quality of low-pressure reservoirs; Obtain the rock heterogeneity coefficient for evaluating the engineering quality of low-pressure reservoirs; A comprehensive performance evaluation factor is established that is proportional to the proportion of produced fluid in the horizontal well fracturing section, proportional to the rock reservoir coefficient, and inversely proportional to the rock heterogeneity coefficient. The energy-enhancing fracturing method corresponding to the comprehensive performance evaluation factor > 0.001mD is selected as the preferred energy-enhancing method, thereby achieving optimization of volumetric fracturing in low-pressure reservoirs.

[0008] The calculation process for the comprehensive effect evaluation factor is as follows: CE=R·Q / E (7) Where: CE is the comprehensive effect evaluation factor, mD; R is the rock reservoir coefficient, mD; Q represents the percentage of fluid produced from the fracturing section of the horizontal well, in %; E is the rock heterogeneity coefficient, which is dimensionless.

[0009] The energy-enhancing medium is evaluated by the energy-enhancing coefficient, and the energy-enhancing medium with an energy-enhancing coefficient ≥ 2.0 is the preferred energy-enhancing medium suitable for the target reservoir.

[0010] The specific process of selecting the energy-enhancing medium suitable for the target reservoir is as follows: using the downhole core of the horizontal well fracturing section of the low-pressure reservoir in the tight oil reservoir as the standard rock sample, testing its physical properties and mineral composition, carrying out energy-enhancing experiments with different injection media under reservoir conditions, and calculating the energy-enhancing coefficient; The calculation process for the energy enhancement coefficient is as follows: W = P1 / P0 (1) In the formula: W is the energy gain coefficient, which has no dimension; P1 is the pressure of the standard rock sample after the injection of the energy-enhancing medium, in MPa; P0 is the original formation pressure of the low-pressure reservoir, in MPa; The preferred energy-enhancing medium for the target reservoir is the one with an energy enhancement coefficient ≥ 2.0.

[0011] The calculation process for the rock reservoir coefficient R is as follows: In the formula: k is the permeability, mD; Porosity, %.

[0012] The specific process for obtaining the rock heterogeneity coefficient is as follows: Based on the mineral composition of the standard rock sample and the corresponding mass of each mineral component, the following formula (3) is used. The percentage of different mineral components by mass F was calculated. k ; By using the following formula (4) H = 100 / l (4) The mineral homogeneity coefficient H was calculated. By using the following formula (5) The degree of difference M between different minerals was calculated; By using the following formula (6) The rock heterogeneity coefficient E was calculated. In the formula: l represents the mineral type, species; k represents the different mineral numbers of the standard rock sample, without dimension; M represents the degree of difference between different minerals in the standard rock sample, which is dimensionless; F k The percentage of the mass of mineral of type k in the standard rock sample, expressed as %. m k The mass of different minerals in a standard rock sample is expressed in grams. H is the mineral homogeneity coefficient, which is dimensionless.

[0013] The specific process for selecting the optimal energy-enhancing medium for the target reservoir is as follows: (1) Obtain downhole cores from the horizontal well fracturing section of the low-pressure reservoir in tight oil reservoirs, prepare them into standard rock samples and dry them; test the porosity, permeability, mineral composition and the corresponding mass of each mineral component of the standard rock samples after drying. (2) Conduct energy enhancement experiments with different injection media under reservoir conditions; Saturated crude oil samples were obtained by using standard rock samples of saturated dried crude oil from production wells in the same block and layer. These samples were then loaded into a core holder. The experimental confining pressure was consistent with the formation stress, and the experimental temperature was consistent with the reservoir temperature. After reaching the experimental confining pressure and temperature, the air in the experimental device was purged. Enhancing medium was injected into the core holder until the designed injection volume was reached, at which point the injection was stopped. The pressure of the standard rock sample was measured using a pressure gauge. (3) Calculate the energy enhancement coefficient, and select the energy enhancement medium with an energy enhancement coefficient ≥ 2.0 as the preferred energy enhancement medium suitable for the target reservoir.

[0014] The technical advantages of this invention are as follows: (1) This invention proposes an optimization method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs. First, this invention proposes a systematic optimization method suitable for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs from two aspects: energy-enhancing medium and energy-enhancing method. Second, it is the first to combine the fracturing effect with the geological quality and engineering quality of low-pressure reservoirs, define a new comprehensive effect evaluation factor, and then use the comprehensive effect evaluation factor to evaluate the effect of low-pressure reservoir stimulation, and then select the energy-enhancing method suitable for the characteristics of low-pressure reservoirs. (2) Compared with the current method of evaluating the transformation effect through a large number of indoor core tests and long-term dynamic tests of mine production, the present invention greatly saves testing costs. The calculation method is simple and feasible, and it is also applicable to the volumetric fracturing optimization of similar low-pressure reservoirs. It has good application prospects and provides technical guidance for the efficient development of unconventional low-pressure reservoirs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the apparatus for energy enhancement experiments with different injection media under low reservoir conditions according to the present invention.

[0016] Reference numerals: 1. Constant speed and constant pressure pump; 3. Energy-enhancing medium storage tank; 5. Vacuum pump; 7. Heating jacket; 8. Standard rock sample; 9. Core holder; 10. Pressure gauge; 11. Confining pressure pump. Detailed Implementation

[0017] Example 1 An optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs is as follows: Preferentially select energy-enhancing media suitable for the target reservoir; Obtain the rock reservoir coefficient for evaluating the geological quality of low-pressure reservoirs; Obtain the rock heterogeneity coefficient for evaluating the engineering quality of low-pressure reservoirs; A comprehensive performance evaluation factor is established that is proportional to the proportion of produced fluid in the horizontal well fracturing section, proportional to the rock reservoir coefficient, and inversely proportional to the rock heterogeneity coefficient. The energy-enhancing fracturing method corresponding to the comprehensive performance evaluation factor > 0.001mD is selected as the preferred energy-enhancing method, thereby achieving optimization of volumetric fracturing in low-pressure reservoirs.

[0018] Example 2 Based on Example 1, it also includes: The calculation process for the comprehensive effect evaluation factor is as follows: CE=R·Q / E (7) Where: CE is the comprehensive effect evaluation factor, mD; R is the rock reservoir coefficient, mD; Q represents the percentage of fluid produced from the fracturing section of the horizontal well, in %; E is the rock heterogeneity coefficient, which is dimensionless.

[0019] The energy-enhancing medium is evaluated by the energy-enhancing coefficient, and the energy-enhancing medium with an energy-enhancing coefficient ≥ 2.0 is the preferred energy-enhancing medium suitable for the target reservoir.

[0020] Example 3 Based on Example 2, the following is also included: the specific process of selecting the energy-enhancing medium suitable for the target reservoir is as follows: taking the downhole core of the horizontal well fracturing section of the low-pressure reservoir in the tight oil reservoir as the standard rock sample 8, testing its physical properties and mineral composition, carrying out energy-enhancing experiments with different injection media under reservoir conditions, and calculating the energy-enhancing coefficient; The calculation process for the energy enhancement coefficient is as follows: W = P1 / P0 (1) In the formula: W is the energy gain coefficient, which has no dimension; P1 is the pressure of the standard rock sample 8 after the injection of the energy-enhancing medium, in MPa; P0 is the original formation pressure of the low-pressure reservoir, in MPa; The preferred energy-enhancing medium for the target reservoir is the one with an energy enhancement coefficient ≥ 2.0.

[0021] Example 4 Based on Example 3, the calculation process for the rock reservoir coefficient R is as follows: In the formula: k is the permeability, mD; Porosity, %.

[0022] Example 5 Based on Example 4, the method further includes: the specific process for obtaining the rock heterogeneity coefficient is as follows: Based on the mineral composition of standard rock sample 8 and the corresponding mass of each mineral component, the following formula (3) is used. The percentage of different mineral components by mass F was calculated. k ; By using the following formula (4) H = 100 / l (4) The mineral homogeneity coefficient H was calculated. By using the following formula (5) The degree of difference M between different minerals was calculated; By using the following formula (6) The rock heterogeneity coefficient E was calculated. In the formula: l represents the mineral type, species; k represents the number of the 8 different minerals in the standard rock sample, without dimension; M represents the degree of difference among the 8 different minerals in the standard rock sample, which is dimensionless; F k The percentage of the mass of mineral of type k in standard rock sample 8, %; m k The mass of 8 different minerals in the standard rock sample is given in grams. H is the mineral homogeneity coefficient, which is dimensionless.

[0023] Example 6 Based on Example 5, the process of selecting the optimal energy-enhancing medium for the target reservoir is as follows: (1) Obtain downhole cores from the horizontal well fracturing section of the low-pressure reservoir in tight oil reservoirs, prepare them into standard rock sample 8 and dry them; test the porosity, permeability, mineral composition and the mass of each mineral component of the dried standard rock sample 8. (2) Conduct energy enhancement experiments with different injection media under reservoir conditions; A saturated crude oil sample 8 was obtained by saturating and drying the crude oil from a production well in the same block and layer. The sample was then loaded into a core holder 9. The experimental confining pressure was consistent with the formation stress, and the experimental temperature was consistent with the reservoir temperature. After the experimental confining pressure and temperature were reached, the air in the experimental device was purged. The energy-enhancing medium was injected into the core holder 9 until the designed injection volume was reached. The pressure of the standard rock sample 8 was measured using a pressure gauge 10. (3) Calculate the energy enhancement coefficient, and select the energy enhancement medium with an energy enhancement coefficient ≥ 2.0 as the preferred energy enhancement medium suitable for the target reservoir.

[0024] Specific experimental examples An optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs is as follows: WU1 is a tight oil horizontal well in a key development area of ​​a low-pressure reservoir. The reservoir has a pressure coefficient of 0.67–0.75, classifying it as a typical low-pressure reservoir. The well was developed using horizontal well volumetric fracturing technology. The horizontal section of the well is 1680m long, with 20 fracturing sections designed and numbered Str1–Str20. The low-pressure reservoir where WU1 is located has a temperature of 80℃, a formation stress of 23.5MPa, and an original formation pressure of 17.5MPa.

[0025] Step 1: Select a suitable energy enhancement medium for the target reservoir; The specific process is as follows: (1) Obtain downhole cores of the fracturing section Str1 and fracturing section Str2 in WU1, and make standard rock samples 8 with a diameter of 2.5cm and a length of 5cm, respectively, and number them S1 and S2; place S1 and S2 in a 100℃ oven to dry to constant weight; (2) The porosity of the dried standard rock sample 8 was tested using a helium porosity automatic measuring instrument, and the permeability of the dried standard rock sample 8 was tested using an ultra-low permeability measuring instrument. The test results are shown in Table 1. Table 1. Test results of physical properties of standard rock samples 8 S1 2.5 5 7.2 0.21 S2 2.5 5 5.9 0.09 (3) The mineral composition and the corresponding mass of each mineral component of the dried standard rock sample 8 were tested using an X-ray diffractometer. The mineral components specifically include dolomite, quartz, calcite, feldspar, pyrite and clay. The test results are shown in Table 2. Table 2. Mass test table of mineral composition corresponding to standard rock samples. S1 26.93 107.15 29.09 18.15 1.05 17.63 S2 19.76 76.06 25.91 28.69 2.49 47.09 (4) Conduct energy enhancement experiments with different injection media under reservoir conditions; Using standard rock sample 8, which was saturated and dried from crude oil from a production well in the same block and layer; the experimental temperature was determined to be 80℃, the temperature of the low-pressure reservoir where WU1 is located, and the experimental confining pressure was the formation stress of 23.5MPa; the saturated and dried standard rock sample 8 was placed into the core holder 9, and the heating jacket 7 was used to heat the saturated and dried standard rock sample 8 and the core holder 9 to the experimental temperature of 80℃, and the confining pressure was applied to the experimental confining pressure of 23.5MPa by the confining pressure pump 11; the air in the low-pressure reservoir energy enhancement medium optimization experimental device was emptied by the vacuum pump 5, and the inlet valve of the vacuum pump 5 was closed after the emptying was completed; The energy-enhancing media in this experiment are slickwater and carbon dioxide. The energy-enhancing medium in the energy-enhancing medium storage tank 3 is pumped into the core holder 9 by constant speed and constant pressure pump 1 and pressurized to the original formation pressure of 17.5 MPa; the energy-enhancing medium is pumped into the core holder 9 by constant speed and constant pressure pump 1 at the same injection rate until the experimental injection volume reaches 0.5 times the lithological pore volume. Regarding S1: When the boosting medium is slickwater, the pressure gauge 10 measures the pressure of S1 as 24.7 MPa; When the boosting medium is CO2, the pressure gauge 10 measures the pressure of S1 as 36.8 MPa; For S2: When the boosting medium is slickwater, the pressure gauge 10 measures the pressure of S2 as 21.6 MPa; When the boosting medium is CO2, the pressure gauge 10 measures the pressure of S2 as 35.2 MPa; (5) Calculated using formula (1): When the energy-enhancing medium is slickwater, the energy enhancement coefficient of S1 is 1.4, and the energy enhancement coefficient of S2 is 1.2. When the energizing medium is CO2, the energizing coefficient of S1 is 2.1 and the energizing coefficient of S2 is 2.0. Therefore, CO2 is the preferred energy-enhancing medium for the target reservoir.

[0026] Step 2: Obtain the rock reservoir coefficient for evaluating the geological quality of low-pressure reservoirs; The rock reservoir coefficients of S1 and S2 calculated by formula (2) are 0.015mD and 0.005mD, respectively.

[0027] Step 3: Obtain the rock heterogeneity coefficient for evaluating the engineering quality of low-pressure reservoirs; For the fracturing section Str1, a pre-fracturing enhancement method was adopted, that is, the enhancement medium was injected before the volumetric fracturing and fracture creation stage of the horizontal well; for the fracturing section Str2, a post-fracturing enhancement method was adopted, that is, the enhancement medium was injected after the volumetric fracturing and displacement stage of the horizontal well. The percentage of mineral components F in S1 and S2 is calculated using formula (3). k The calculation results are detailed in Table 3; Table 3. Percentage of different mineral components in standard rock samples (8 samples) Sl 9.88 38.03 12.95 14.34 1.24 23.56 S2 13.46 53.57 14.54 9.07 0.52 8.84 Furthermore, the homogeneity coefficient of the minerals was calculated to be 16.67 using formula (4); Then, the differences between different minerals in S1 and S2 were calculated using formula (5) to be 0.738 and 0.565, respectively; Based on the differences and species distribution of different minerals in S1 and S2, the rock heterogeneity coefficients of the reservoirs containing S1 and S2 were calculated to be 0.60 and 0.70, respectively, using formula (6).

[0028] Step 4: The produced fluid from the horizontal well fracturing section St1 accounts for 10.3%, and the produced fluid from the horizontal well fracturing section St2 accounts for 6.5%.

[0029] Step 5: The comprehensive effect evaluation factor of the fracturing section St1 is calculated to be 0.0025mD and the comprehensive effect evaluation factor of the fracturing section St2 is 0.00046mD using formula (7). The energy-enhancing fracturing method corresponding to the comprehensive effect evaluation factor > 0.001mD is the preferred energy-enhancing method, that is, the energy-enhancing method of WU1 is the preferred pre-energy-enhancing method.

[0030] The present invention has been specifically described above through embodiments. It should be noted that these embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way, nor are they limited to the forms disclosed herein, and should not be construed as excluding other embodiments. Modifications and simple variations made by those skilled in the art that do not depart from the technical concept and scope of the present invention are all within the protection scope of the present invention.

Claims

1. An optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs, characterized in that: The method is as follows: The preferred energy-enhancing medium is one that is suitable for the target reservoir. The energy-enhancing medium is evaluated by its energy enhancement coefficient, and the preferred energy-enhancing medium is one that has an energy enhancement coefficient ≥ 2.

0. Obtain the rock reservoir coefficient for evaluating the geological quality of low-pressure reservoirs; Obtain the rock heterogeneity coefficient for evaluating the engineering quality of low-pressure reservoirs; the specific process for obtaining the rock heterogeneity coefficient is as follows: Based on the mineral composition of the standard rock sample and the corresponding mass of each mineral component, the following formula (3) is used. （3） The percentage of different mineral components by mass F was calculated. k ; By using the following formula (4) H=100 / l （4） The mineral homogeneity coefficient H was calculated. By using the following formula (5) （5） The degree of difference M between different minerals was calculated; By using the following formula (6) （6） The rock heterogeneity coefficient E was calculated. In the formula: l represents the mineral type, species; k represents the different mineral numbers of the standard rock sample, without dimension; M represents the degree of difference between different minerals in the standard rock sample, which is dimensionless; F k The percentage of the mass of mineral type k in the standard rock sample, % m k The mass of different minerals in a standard rock sample is expressed in grams. H is the mineral homogeneity coefficient, which is dimensionless; A comprehensive performance evaluation factor is established that is proportional to the proportion of produced fluid in the horizontal well fracturing section, proportional to the rock reservoir coefficient, and inversely proportional to the rock heterogeneity coefficient. The energy-enhancing fracturing method corresponding to the comprehensive performance evaluation factor > 0.001mD is selected as the preferred energy-enhancing method, thereby achieving optimization of volumetric fracturing in low-pressure reservoirs.

2. The optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs according to claim 1, characterized in that: The calculation process for the comprehensive effect evaluation factor is as follows: CE = R·Q / E (7) Where: CE is the comprehensive effect evaluation factor, mD; R is the rock reservoir coefficient, mD; Q represents the percentage of fluid produced from the fracturing section of the horizontal well, % E is the rock heterogeneity coefficient, which is dimensionless.

3. The optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs according to claim 1, characterized in that: The specific process of selecting the appropriate energy-enhancing medium for the target reservoir is as follows: using the downhole core of the horizontal well fracturing section of the low-pressure reservoir in tight oil reservoir as the standard rock sample, testing its physical properties and mineral composition, carrying out energy-enhancing experiments with different injection media under reservoir conditions, and calculating the energy-enhancing coefficient. The calculation process for the energy enhancement coefficient is as follows: W = P1 / P0 (1) In the formula: W is the energy gain coefficient, which has no dimension; P1 is the pressure of the standard rock sample after the injection of the energy-enhancing medium, in MPa; P0 is the original formation pressure of the low-pressure reservoir, in MPa; The preferred energy-enhancing medium for the target reservoir is the one with an energy enhancement coefficient ≥ 2.

0.

4. The optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs according to claim 2, characterized in that: The calculation process for the rock storage coefficient R is as follows: R=kφ (2) In the formula: k is the permeability, mD; φ represents porosity, in percentages.

5. The optimized method for volumetric fracturing of low-pressure reservoirs in tight oil reservoirs according to claim 3, characterized in that: The specific process for selecting the optimal energy enhancement medium suitable for the target reservoir is as follows: (1) Obtain downhole cores from the horizontal well fracturing section of the low-pressure reservoir in tight oil reservoirs, prepare them into standard rock samples and dry them; test the porosity, permeability, mineral composition and the mass of each mineral component of the standard rock samples after drying. (2) Conduct energy enhancement experiments with different injection media under reservoir conditions; Using standard rock samples of saturated dried crude oil from production wells in the same block and layer, saturated crude oil samples were obtained and loaded into a core holder. The experimental confining pressure was consistent with the formation stress, and the experimental temperature was consistent with the reservoir temperature. After the experimental confining pressure and experimental temperature were reached, the air in the experimental device was purged. The energy-enhancing medium is injected into the core holder until the designed injection volume is reached, and then the pressure of the standard rock sample is measured using a pressure gauge. (3) Calculate the energy enhancement coefficient, and select the energy enhancement medium with an energy enhancement coefficient ≥ 2.0 as the preferred energy enhancement medium suitable for the target reservoir.

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