Double-medium oil reservoir stepped fracture capacity expansion reservoir transformation method

Abstract

The invention relates to the technical field of volcanic rock oil reservoir development methods, in particular to a double-medium oil reservoir stepped crack expansion reservoir transformation method which comprises the steps of processing evaluation index data of volcanic rock with a certain storage-production ratio, constructing an evaluation index weight vector and an evaluation index membership matrix, and calculating a stepped expansion potential index according to the evaluation index weight vector and the evaluation index membership matrix. The method comprises the following steps: preferably selecting a perforation interval for expansion transformation according to a calculation result, determining parameters such as reasonable construction displacement of the perforation interval in combination with inter-well rock mass conditions, increasing subsequent expansion step by step, controlling fracture height and fracture length excessive extension, increasing the number of fractures, increasing the complexity of the fractures, and analyzing pressure drop during each fracture expansion shut-in period. Therefore, the seepage state is judged to evaluate the crack expansion operation effect. According to the method, stepped crack expansion fracturing is carried out on the optimized interval, the crack height is effectively controlled, a complex micro-crack net is formed, the production degree of a carboniferous oil layer, especially a thin-difference layer and an interlayer and inter-well oil-water relation complex oil layer is improved, and the volcanic rock development effect and recovery efficiency are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of volcanic rock reservoir development methods, and is a dual-medium reservoir stepped fracture expansion reservoir reconstruction method. Background Art

[0002] Conventional development of volcanic rock reservoirs has no effective production capacity, and fracturing is generally used for production. Conventional fracturing production faces the following problems: ① Conventional fracturing uses large-scale one-time fracturing. Under the induction of micro-cracks, long cracks that connect natural fractures are generally formed; high production can be achieved in areas with relatively developed natural fractures, while the production in micro-developed areas or undeveloped areas is relatively low; therefore, conventional fracturing is prone to low-yield wells when natural fractures are not clearly characterized; ② Carboniferous reservoirs are usually accompanied by edge and bottom water. Conventional fracturing uses high displacement, high sand volume, and high liquid volume. Therefore, the avoidance height during conventional fracturing is above 60m, making some reservoirs difficult to mobilize. At the same time, this high-displacement fracturing operation mode is also prone to fracturing interference between wells and layers, affecting the production of new and old wells. For this type of dual-medium reservoirs with active edge and bottom water, corresponding reservoir transformation measures need to be taken to increase production.

[0003] The Chinese patent document with the authorization number CN115163022 B discloses "A method for systematic expansion for optimizing oil well production and transformation areas", which proposes to use permeability, skin coefficient, recovery degree and average reservoir pressure as the evaluation index matrix, establishes an expansion and transformation index model to guide scientific area selection, and conducts systematic reservoir expansion for the selected areas to form large-scale complex micro-fractures, communicate the connectivity between injection and production well networks, and improve oil well recovery. The evaluation index system is implemented on a regional basis, and no evaluation and optimization is carried out for reservoirs that meet the system expansion conditions. The reservoir heterogeneity of the oil reservoir leads to differences in single well reservoirs. If the expansion and transformation index of the entire area is used to evaluate the transformation potential of a single well, it cannot provide a reference basis for the optimization of the perforation layer of a single well. The Chinese patent document with the authorization number CN111271043B discloses "A method for increasing production by expanding and reforming geostress in oil and gas wells", and proposes a method for expanding geostress in a single well. This method focuses on the geomechanical parameters of the reservoir, such as the three-dimensional principal stress, permeability, reservoir pressure, and fracture fluid efficiency, to constrain the scale of reservoir transformation, forming a large-volume, high-porosity, and high-permeability expansion zone, thereby improving the permeability of the rock mass and achieving the purpose of increasing production and injection. The patent as a whole focuses on the process of fine fracturing, and does not conduct research on the value and optimization of specific fracturing parameters. The Chinese patent document with the publication number CN115659566A discloses "An integrated design method for fracturing and energy enhancement of old wells". In view of the insufficient formation energy of old wells in tight reservoirs, the optimal absorption and well suffocation time and the reasonable energy enhancement injection amount optimization chart are designed, but no research is conducted on the evaluation and optimization of reservoir sections. The Chinese patent document with publication number CN112832731A discloses "A method for micro-fracturing of oil well reservoirs in long horizontal sections", which discloses a method for micro-fracturing of oil well reservoirs in long horizontal sections. This method is only for micro-fracturing transformation of single wells with multiple sections, and no optimization is performed on the transformed wells. How to select the transformation area is an important factor affecting the success of the overall transformation. At present, there is no special optimization rule. Only a very small number of experienced experts can make reasonable judgments, but the success rate cannot be guaranteed. If the area selection is unreasonable, a lot of manpower and material resources will be wasted at best, and the oil well will be damaged at worst, making the development of the oil well more difficult. Summary of the invention

[0004] The present invention provides a dual-medium reservoir stepped fracture expansion reservoir reconstruction method, which overcomes the deficiencies of the above-mentioned prior art and can effectively solve the technical problem of poor overall development effect caused by water channeling and fracturing interference problems in conventional reservoir reconstruction.

[0005] The technical solution of the present invention is achieved through the following measures: A dual-medium reservoir stepped fracture expansion reservoir reconstruction method, comprising the following steps:

[0006] (1) Select independent volcanic rock bodies with relatively low production levels and relatively clear oil-water relationships, and determine the range of the reserve-production ratio of the volcanic rock bodies; the reserve-production ratio should be greater than 20.

[0007] (2) Collect oil well data in the selected volcanic rock bodies, including stratigraphic data, dynamic production data of oil wells, conventional logging curves, effective thickness of oil layers, oil saturation, porosity, and fracture index; use the oil well data in the volcanic rock bodies to calculate the geological reserves and reserve-production ratio of the rock bodies; select rock bodies with a reserve-production ratio greater than 20 to conduct reservoir potential evaluation research;

[0008] (3) Determine the evaluation index of the volcanic reservoir, which includes porosity, oil saturation, oil layer thickness, permeability, and fracture index. According to the importance of each evaluation index, construct a weight judgment orthogonal matrix A=(a ij ) n×n ;

[0009] (4) Take the geometric mean of the column vectors of matrix A:

[0010]

[0011] Calculate the proportion to judge the consistency of the orthogonal matrix. After meeting the consistency requirements, calculate the weight of each evaluation index and establish the weight vector calculation formula:

[0012]

[0013] Form the evaluation index weight vector ω=(ω 1 ,ω 2 ,ω 3 ,ω 4 ,ω 5 ) T ;

[0014] (5) Each evaluation index is dimensionless and then normalized: Get the evaluation index membership matrix L = (L" 1 , L" 2 , L" 3 , L" 4 , L" 5 ),

[0015] The step-by-step expansion potential index is calculated according to the following formula:

[0016] R=ω×L

[0017] In the formula, R is the step expansion potential index, ω is the index weight vector, and L is the evaluation index membership matrix; the larger the R value, the greater the reservoir transformation potential, and the perforated layer section for expansion and transformation is selected according to the calculation results;

[0018] (6) Determine the well selection principle based on the inter-well rock mass connectivity, well spacing, reservoir span, completion structure, and plane fault development;

[0019] (7) Determine the appropriate construction displacement of the perforated layer to achieve the purpose of controlling the fracture length, collect the fracture pressure of the same layer in the selected well or the same layer in the adjacent well, and conduct formation testing to obtain data such as the maximum construction pressure, maximum construction displacement, shear stress, and fracture extension displacement;

[0020] (8) Multiple rounds of transformation combined with pre- and post-test processes, alternately injecting "clean water + nano oil-displacing agent (nanocellulose, polyethylene glycol, etc.) + small-particle proppant" and selectively injecting temporary plugging agent (when the pressure drop is too high), dynamically adjusting the construction parameters, and performing double logarithmic curve analysis through fracturing software, can observe the existence of impermeable boundary flow state (restriction / matrix flow), linear flow (fracture flow) and bilinear flow state in the formation seepage flow stage, and the transition between each stage; control the fracture height and fracture length so that they do not communicate with adjacent well layers or upper and lower water layers, so that small-particle proppant (quartz sand, temporary plugging agent is added when necessary) can quickly bridge and plug the shear fracture neck, increase the net pressure in the fracture, use the pressure pulse in the fracture to open new fractures, and promote the complexity of near-well fractures;

[0021] In step (8), the conditions for forming cracks are related to the ground stress and its distribution, the mechanical properties of the rock, the properties of the stepped crack expansion fluid and the injection method. The underground rock is in a three-dimensional pressure state, and the stress of a certain unit body of the underground rock is the vertical principal stress and the two-dimensional horizontal principal stress. In the process of the crack extending forward, as the crack grows, the friction resistance in the crack increases, and the net pressure at the front end of the crack gradually decreases. When the net pressure is lower than the tensile strength of the crack, the crack no longer extends forward. If the crack expansion fluid is continuously pumped, the crack height will only increase. The crack height can be controlled by optimizing the design and construction scale, while reducing the friction resistance of the fracturing fluid and increasing the net pressure at the front end of the crack.

[0022] The filtration rate of the step-type fracture expansion fluid has a significant impact on the fracture height, and the filtration coefficient of the step-type fracture expansion fluid affects the fracture size. Designing a reasonable amount of step-type fracture expansion fluid to extend the fracture can effectively control the fracture height and length; when the pressure drop and filtration loss are large during the expansion construction process, it can be adjusted by adding temporary plugging agents; when the pressure drop and filtration loss are large during the expansion construction process, it can be adjusted by adding temporary plugging agents; low-concentration sand addition is used during construction, so that small-particle proppant can quickly bridge and plug at the neck of the shear fracture, increase the net pressure in the fracture, use the pressure pulse in the fracture to open new fractures, and promote the complexity of near-well fractures; the pressure rises rapidly after the bridge plugging, indicating that the amount of sand added is sufficient and the pump should be stopped and the sand addition should be stopped. The pressure derivative curve of the double logarithmic curve is used as a diagnostic curve to analyze the pressure drop during each fracture expansion and well shut-in period. The pressure drop analysis uses interpretation software and selects the model of wellbore reservoir + skin coefficient + homogeneous composite reservoir + infinite boundary for typical curve analysis, analyzes the changes in fracture height and fracture length, compares the stress field of the longitudinal profile of the formation, and increases or decreases the scale of the next step of construction.

[0023] (9) Through multiple expansion steps, the excessive extension of fracture height and fracture length is controlled, the number of fractures is increased, and the complexity of fractures is increased. The pressure derivative curve of the double logarithmic curve is used as a diagnostic curve to analyze the pressure drop during each fracture expansion and well shut-in period. The pressure drop analysis uses interpretation software (well testing software). In the software, a model of wellbore reservoir + skin coefficient + homogeneous composite reservoir + infinite boundary is selected for typical curve analysis to judge the seepage state and evaluate the effect of fracture expansion operation.

[0024] In step (9), the conditions for forming cracks are related to the injection method, etc. During the forward extension of the cracks, the horizontal stress difference in both directions is large. If the crack expansion fluid is continuously pumped, it will only increase the original crack height and length, or form an open crack. The crack height and length need to be controlled by increasing the number of step-type crack expansion times. When the first crack is closed, a higher pressure is required to open the crack again. After increasing the net pressure of the wellbore, a new crack will be opened. Designing multiple expansion steps can control the excessive extension of the crack height and length, increase the number of cracks, increase the complexity of the cracks, and improve the production increase effect of step-type crack expansion. In actual construction, according to the pressure drop curve analysis results and the fracturing software fitting, the permeability change value before and after the transformation is compared, and the number of step increases is increased or decreased.

[0025] The following are further optimizations and / or improvements to the above technical solutions:

[0026] Preferably, in the above step (4), when the consistency of the weight judgment orthogonal matrix is ​​judged as R<0.1, the consistency judgment is satisfied, and the formula is R=C / RI, wherein,

[0027] RI is a constant value.

[0028] Preferably, in the above step (5), the evaluation indicators are porosity, oil saturation, oil layer thickness, permeability, and fracture index, respectively. According to the reservoir parameter characteristics of the oil reservoir, the porosity (5% to 15%), oil saturation (35% to 80%), oil layer thickness (1m to 15m), permeability (0.01mD to 5mD), and fracture index (0.08 to 1.5) are used. The dimensionless processing formula of the evaluation indicators is:

[0029] L'=(LL min ) / (L max -L min ).

[0030] Preferably, in the above step (6), the rock mass between wells is not connected, the span of the perforation section from the oil and water layer is more than 25m (ordinary fracturing requires a span of more than 60m), the thickness of a single layer can be perforated is between 10m and 25m, and the perforation span is less than 30m; a sufficient distance is required from adjacent wells to avoid production / pressure interference, and the bottom hole spacing is preferably greater than 150m; avoid selecting wells with bottom holes close to faults or reservoir boundaries; the completion structure is from a vertical well to a well with an inclination of less than 30 degrees.

[0031] Preferably, in the above step (7), the construction displacement is the main factor affecting the fracture height. A reasonable design of the construction displacement can control the extension pressure in the fracture and prevent the net pressure in the fracture from being too high and the fracture height from passing through the interlayer. When designing a step-type fracture expansion scheme, firstly, the fracture pressure of the same layer in the well or the fracture pressure of the same layer in the adjacent well should be calculated by the formation fracture pressure calculation formula:

[0032] P f =G f ×H f

[0033] Where P f is the formation fracture pressure, MPa; G f is the formation fracture pressure gradient, MPa / m; H f is the vertical height of the middle of the oil layer, m; clarify the fracture pressure of the target layer section of the well construction, and then conduct formation testing through increasing displacement, make the relationship curve between displacement and construction oil pressure and casing pressure during the test process, and determine the fracture extension pressure (FEP) and extension rate (FER) through the inflection point; use the pressure drop test data after stopping the pump to perform double logarithmic analysis of time and pressure difference to determine the fracture closure pressure, time to reach radial flow, and formation permeability; the pressure corresponding to the reasonable construction displacement value should be greater than the shear stress but not higher than the fracture pressure.

[0034] The present invention adopts a dual-medium reservoir stepped fracture expansion reservoir reconstruction method, which is applicable to independent volcanic rock bodies with relatively low production degree and relatively clear oil-water relationship. It establishes a volcanic rock reservoir stepped expansion potential evaluation model, eliminates interference from human factors, scientifically selects wells and layers, and improves the efficiency of reservoir reconstruction; establishes a design method for stepped expansion fracturing parameters, performs stepped fracture expansion fracturing in preferred layers, effectively controls fracture height, forms a complex micro-crack network, improves the production degree of Carboniferous oil layers, especially thin and poor layers and oil layers with complex oil-water relationships between layers and wells, and effectively improves the development effect and recovery rate of volcanic rocks.

[0035] The present invention aims at wells with poor reservoirs and insufficient water avoidance height. By shearing and expanding the capacity, three-dimensional support is achieved to manufacture complex seam networks, and a low displacement (0.5m 3 / min to 2.0m 3 / min), low sand adding strength (0.15m 3 / m to 0.3m 3 / m), clean (dirty) water carrying sand, and fine formation testing to accurately control the construction displacement. Applied to volcanic rock reservoirs with complex oil-water relationships, the use of stepped fracture expansion technology has greatly increased the production of low-quality volcanic rocks in response to problems such as poor physical properties and insufficient water avoidance height. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Attached Figure 1 Schematic diagram of the principle of stepped crack expansion technology.

[0037] Attached Figure 2 This is the formation test map of Well 3.

[0038] Attached Figure 3 This is the fitting diagram for the No. 3 formation test.

[0039] Attached Figure 4 This is the first round of construction drawings for Well No. 3.

[0040] Attached Figure 5 This is the pressure drop analysis diagram for the first round of construction work in Well No. 3.

[0041] Attached Figure 6 This is the second round of construction drawings for Well No. 3.

[0042] Attached Figure 7 This is the pressure drop analysis diagram for the second round of construction work in Well No. 3.

[0043] Attached Figure 8 This is the second formation test map of Well 3.

[0044] Attached Figure 9 This is the formation test fitting diagram for the second formation test of Well 3. DETAILED DESCRIPTION

[0045] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0046] The step-type fracture expansion technology of the present invention is based on the geomechanical characteristics of low-permeability brittle strata. It uses a low-rate, low-displacement, and continuous cycle method to cause shear expansion, shear slip, rock rotation, stress change, stratum yield, and other phenomena to form a complex fracture network. It changes from the traditional use of normal stress to the use of shear stress, and from the rapid formation of linear fractures to the slow creation of complex fracture networks ( Figure 1 ).

[0047] When considered in conjunction with the accompanying drawings, the present invention can be more completely and better understood and many of the attendant advantages thereof can be easily known by referring to the detailed description below, but the drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation on the present invention.

[0048] The present invention will be further described below in conjunction with embodiments:

[0049] Embodiment: This embodiment is a specific example of a stepped fracture expansion reservoir reconstruction method for a volcanic rock reservoir in Xinjiang Oilfield, which includes the following operations:

[0050] 1. Collect geological stratification data of the target reservoir, including well logging data of oil wells, result data of reservoir logging interpretation, including porosity, oil saturation, permeability, oil layer thickness, fracture index, proved reserve calculation parameters of each rock mass in the target reservoir, cumulative oil production of each rock mass, water content and other development index data. Combined with the current development stage and development mode of the reservoir, determine that the reserve-production ratio of the target reservoir rock mass is greater than 20, select rock masses with greater potential to carry out system expansion reservoir reconstruction, select the overflow phase rock mass of well CH3035, compare and explain the 14 oil wells in the rock mass, and give the calculation process of the reservoir section of each oil well:

[0051] 2. The evaluation indicators of stepped fracture expansion reservoir transformation are porosity, permeability, oil saturation, oil layer thickness, and fracture index. Each indicator is assigned a value according to its importance (equal importance is 1, slightly important is 3, and strong importance is 5, and so on). The importance of each evaluation indicator is shown in Table 1. The orthogonal matrix A = (a ij ) n×n

[0052] Table 1 Importance of each evaluation index

[0053]

[0054] 3. Calculate the weight of each column vector of matrix A according to the geometric average to determine the consistency of the orthogonal matrix. After meeting the consistency requirements, calculate the weight of each evaluation index and establish the weight vector calculation formula:

[0055] The weights of each evaluation index are shown in Table 2.

[0056] Table 2 Weights of each evaluation index

[0057]

[0058] The evaluation index weight ω={0.0594, 0.1956, 0.0946, 0.4439} is obtained.

[0059] 4. According to the reservoir parameter characteristics of the Carboniferous oil reservoir in the CH302 well area, porosity (5% to 15%), oil saturation (35% to 80%), oil layer thickness (1m to 15m), permeability (0.01mD to 5mD), and fracture index (0.08 to 1.5), the evaluation indicators are dimensionless, and each evaluation indicator is dimensionless and then normalized:

[0060] (1) Porosity:

[0061] (2) Oil saturation:

[0062] (3) Oil layer thickness:

[0063] (4) Permeability:

[0064] (5) Crack index:

[0065] In the above formulas (1) to (5), X: variable, y: independent variable;

[0066] 5. Obtain the evaluation index membership matrix L = (L" 1 , L" 2 , L" 3 , L" 4 , L" 5 ), the step expansion potential index R = ω × L, the step expansion potential index (potential index) is shown in Table 3, and the perforated layer section for expansion and transformation is selected according to the calculation results.

[0067] Table 3 Step-by-step expansion potential index

[0068] Serial number φ K So h Fracture index Potential index 1 0.17 0.03 0.22 0.23 0.35 0.241 2 0.27 0.06 0.24 0.14 0.29 0.207 3 0.31 0.08 0.34 0.10 0.17 0.163 4 0.30 0.07 0.31 0.13 0.19 0.173 5 0.29 0.05 0.47 0.09 0.09 0.133 6 0.34 0.12 0.13 0.34 0.07 0.156 7 0.19 0.09 0.22 0.23 0.27 0.218 8 0.31 0.08 0.35 0.16 0.10 0.144 9 0.32 0.08 0.33 0.11 0.15 0.157 10 0.31 0.06 0.25 0.26 0.11 0.158 11 0.27 0.04 0.24 0.31 0.13 0.171 12 0.30 0.12 0.27 0.28 0.03 0.138 13 0.30 0.08 0.21 0.29 0.11 0.165 14 0.32 0.06 0.28 0.18 0.17 0.167

[0069] 6. Combined with the geological characteristics of the study area, establish the principle of well selection for stepped fracture expansion

[0070] ① Understand the oil-water relationship and select low-production oil layers;

[0071] ② The rock mass between wells is not connected, and the span of the perforated well section from the oil and water layer is more than 25m (ordinary fracturing requires a span of more than 60m);

[0072] ③ The perforation thickness of a single layer is 10m-25m, and the perforation span is less than 30m;

[0073] ④ There are micro-cracks in the stratum, with obvious ground stress difference and low fracture extension and displacement;

[0074] ⑤ The completion structure is from a vertical well to a well with an inclination of less than 30 degrees;

[0075] ⑥ There needs to be sufficient distance from adjacent wells to avoid production / pressure interference. It is best if the bottom hole distance is greater than 150m;

[0076] ⑦ Avoid selecting wells whose bottom is close to faults or reservoir boundaries.

[0077] 7. Combined with the expansion and transformation potential index and the well selection principle, Well No. 3 is preferred for step-by-step fracture expansion. The first step is to calculate the fracture pressure of the well. Well No. 3 needs to carry out step-by-step fracture expansion transformation in the well section from 2558.0 to 2582.5 m. Since this well has not been transformed in the early stage and there is no bottom fracture pressure data, the formation fracture pressure calculation formula is referenced according to the early fracturing results of adjacent wells: P f =G f ×H f

[0078] The formation breakdown pressure gradient is referenced to the adjacent well CF0615. The breakdown pressure at the middle depth of 2509.5m in the oil layer of CF0615 is 46MPa. Therefore, the formation breakdown pressure gradient is calculated to be approximately 0.018MPa / m.

[0079] The formation breakdown pressure of Well CF0635 can be calculated using the formation breakdown pressure calculation formula:

[0080] P f =G f ×H f =0.018×2571.75=46.3MPa

[0081] Therefore, during the formation testing phase, the construction pressure should not be greater than 46.35MPa.

[0082] 8. Conduct formation testing. After connecting the surface pipeline, use a pump truck to conduct formation testing. Test by increasing the displacement steadily. Each displacement is maintained for 10-15 minutes. After obtaining the construction second data, stop the construction and shut down the well until the wellhead pressure drops to zero. Figure 2 shown.

[0083] During the first absorbency test, the pumping rate was maintained at 0.47 m / min. 3 , the wellhead pressure value is 16.43MPa. The pump injection volume is 44.16 cubic meters. After the test is successfully completed, the well is shut in for 3.93 hours to diffuse the pressure and collect the pressure drop data. After shutting in for 3.93 hours, the wellhead pressure is 1.59MPa.

[0084] The data was fitted by the fracturing software using the field construction data. The casing pressure (CP) and wellhead pressure (WHP) were monitored during the test, and the data analysis was based on the wellhead pressure. A pressure inflection point was found in the first step-by-step test analysis (reference Figure 3 ),

[0085] Fracture extension pressure (FEP): 14.8MPa

[0086] Crack extension rate (FER): 0.5m 3 / min

[0087] Calculated rupture gradient: 15.8 kPa / m

[0088] The test was successfully completed. The well was shut down for 16.05 hours to diffuse the pressure and collect the pressure drop data. The instantaneous pump stop pressure value was 14.60MPa. After shutting down the well for 16.05 hours, the pressure dropped to 3.75MPa. Figure 3 As shown in the figure, the shear stress (also known as extension pressure) is 14.8MPa through the transformation of the linear slope of the data. The corresponding displacement is 0.5m 3 / min, so the minimum pressure during the formal construction of the stepped fracture expansion in Well CF0635 is 14.8MPa, and the maximum pressure should not exceed 46.35MPa.

[0089] 9. Implement step-by-step expansion. After the construction pressure is determined, select the appropriate pressure for construction. Add oil displacement agent (nanocellulose) to the clean water to increase the fluidity of the crude oil formation and reduce the surface tension to increase the oil production of low permeability reservoirs. The mass addition ratio of the oil displacement agent is 0.2%.

[0090] The first round of crack expansion operation ( Figure 4 The process includes three stages of continuous plugging and sand expansion. During this expansion process, the wellhead pressure was maintained between 27.08MPa and 38.65MPa, and the average pumping displacement was 1.04m 3 / min to 1.75m 3 / min. The injection volume of the expansion pump in this round was about 478.65 cubic meters. The pressure rose rapidly after each round of bridge plugging, indicating that the amount of sand added was sufficient and the pump should be stopped to stop adding sand. A total of 1.04 cubic meters of 40 / 70 mesh (sand) quartz sand was added, and the mixing ratio was 0.98% to 1.4% by volume (dry sand volume). After the first round of operation, the well was shut down for 19.12 hours to diffuse the pressure. After 19.12 hours, the pressure dropped to 3.57MPa.

[0091] By analyzing the pressure drop of the first round of construction results ( Figure 5 The improvement of the conductivity produced by this round of measures is not very obvious. The interpreted permeability of the near-wellbore zone is about 45mD to 65mD, and the interpreted permeability of the far-wellbore zone (late stage) is about 14mD. Combined with the pressure drop analysis of each stage, different seepage states are shown overall. After three stages of expansion, the seepage state changed from the initial weak linear flow and boundary impermeability conditions to radial flow in the near-wellbore zone and linear flow in the far-wellbore zone. Fracture fluidity: After this round of expansion operations, the early stage to the transition stage showed obvious fracture linear flow. It was found that the formation was not fully transformed at this time, so the transformation construction continued.

[0092] The second round of crack expansion operation (reference Figure 6 ) includes two stages of slugging sand. During the expansion process, the average injection rate was about 1.46m 3 / min, the wellhead pressure is 32.70MPa; in the high-displacement stage, the average injection rate is about 1.80m 3 / min, the average wellhead pressure value is between 40.20MPa and 40.23MPa. The total amount of produced water used in the whole expansion process is 225.96 cubic meters, and 0.86 cubic meters of 40 / 70 mesh (sand) quartz sand is added in this round, and the mixing sand ratio is 1.13-1.49% by volume. After the second round of operation, the well was shut in for 16.62 hours to diffuse the pressure, and the pressure dropped to 3.41MPa.

[0093] By analyzing the pressure drop of the second round of construction results ( Figure 7), compared with the first round, the second round of fracture expansion did not change the formation conductivity significantly, and the interpreted permeability of the near-wellbore area was about 40mD to 45mD. The slightly decreased interpreted permeability was mainly due to the failure to complete the 4th and 5th section fracture expansion measures. The seepage difference in the far-wellbore area was not large, and the interpreted permeability was about 11mD. In general, the near-wellbore area showed radial flow, and the far-well area showed linear seepage conditions. The seepage state showed that dual seepage conditions of matrix and fractures were developed in the area. Fracture fluidity: This round of expansion operations gradually created linear flow in the fractures. This phenomenon indicates that a certain extended leakage area was formed in the surrounding formations. The overall effect of the measures reflected the formation of a complex fracture network transformation area. Since it was judged that the transformation had been sufficient, the construction was stopped after another formation test (such as Figure 8 shown).

[0094] The maximum pump rate for this formation test was 1.75 m / min. 3 , a total of 104.04m 3 Produced water. After the pumping was completed, the well was shut in for 22.52 hours to diffuse the pressure. The instantaneous shut-in pressure was 18.29 MPa. The minimum shut-in pressure was 3.43 MPa. During the test, the casing pressure (CP) and wellhead pressure (WHP) were monitored, and the data analysis was based on the wellhead pressure. The analysis of the fourth step-up test showed that there was a pressure inflection point (reference Figure 9 ):

[0095] Fracture extension pressure (FEP): 15.6MPa

[0096] Crack extension rate (FER): 0.62m 3 / min

[0097] Calculated rupture gradient: 16.1 kPa / m.

[0098] The dual-medium reservoir step-type fracture expansion reservoir reconstruction method of the present invention is a set of step-type expansion reservoir reconstruction parameter optimization design method, which optimizes reservoir reconstruction parameters, realizes low-displacement injection, effectively reduces the risk of crosstalk, and improves the production utilization rate of oil layers with poor reservoir conditions and the utilization rate of reservoirs with close inter-well and inter-layer water. The indoor research parameters are closely combined with field tests, further enriching and improving the reservoir evaluation technology theory of volcanic rock reservoirs.

[0099] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. A dual-medium reservoir stepped fracture expansion reservoir reconstruction method, Features The steps include: (1) Select independent volcanic rock bodies with relatively low production levels and relatively clear oil-water relationships, and determine the range of the reserve-production ratio of the volcanic rock bodies; (2) Collect oil well data in the selected volcanic rock bodies, including stratigraphic data, dynamic production data of oil wells, conventional logging curves, effective thickness of oil layers, oil saturation, porosity, and fracture index; use the oil well data in the volcanic rock bodies to calculate the geological reserves and reserve-production ratio of the rock bodies; select rock bodies with a reserve-production ratio greater than 20 to conduct reservoir potential evaluation research; (3) Determine the evaluation index of the volcanic rock reservoir, the evaluation index includes: porosity, oil saturation, oil layer thickness, permeability, fracture index, according to the importance of each evaluation index, construct a weight judgment orthogonal matrix A = (aij)n × n; (4) Take the geometric mean of the column vectors of matrix A: Calculate the proportion to judge the consistency of the orthogonal matrix. After meeting the consistency requirements, calculate the weight of each evaluation index and establish the weight vector calculation formula: Form the evaluation index weight vector ω=(ω 1 ,ω 2 ,ω 3 ,ω 4 ,ω 5 ) T ; (5) Each evaluation index is dimensionless and then normalized: Get the evaluation index membership matrix L = (L" 1 , L" 2 , L" 3 , L" 4 , L" 5 ), The step-by-step expansion potential index is calculated according to the following formula: R=ω×L In the formula, R is the step expansion potential index, ω is the index weight vector, L is the evaluation index membership matrix, and the perforated layer section for expansion and transformation is selected according to the calculation results; (6) Determine the well selection principle based on the inter-well rock mass connectivity, well spacing, reservoir span, completion structure, and plane fault development; (7) Determine the appropriate construction displacement of the perforated layer to achieve the purpose of controlling the fracture length, collect the fracture pressure of the same layer in the selected well or the same layer in the adjacent well, and conduct formation testing to obtain the maximum construction pressure, maximum construction displacement, shear stress, and fracture extension displacement data; (8) Multiple rounds of transformation combined with pre- and post-test processes, alternately injecting clean water, nano-displacement agents and small-particle proppants, and selectively injecting temporary plugging agents, dynamically adjusting construction parameters, and performing double logarithmic curve analysis through fracturing software to observe the formation seepage flow stage and the transition between each stage; controlling the fracture height and fracture length so that they do not connect to adjacent well layers or upper and lower water layers, so that small-particle proppants or temporary plugging agents can quickly bridge and plug the shear fracture neck, increase the net pressure in the fracture, and use the pressure pulse in the fracture to open new fractures and promote the complexity of near-well fractures; (9) Through multiple expansion steps, the excessive extension of fracture height and fracture length is controlled, the number of fractures is increased, and the complexity of fractures is increased. The pressure derivative curve of the double logarithmic curve is used as a diagnostic curve to analyze the pressure drop during each fracture expansion and well shut-in period. The pressure drop analysis uses interpretation software to determine the seepage state and evaluate the effect of fracture expansion operations.

2. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 1, Features In step (4), when the consistency of the weight judgment orthogonal matrix is ​​judged to be R<0.1, the consistency judgment is satisfied, and the formula is R=C / RI, where: RI is a constant value.

3. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 1 or 2, Features In step (5), the evaluation indicators are porosity, oil saturation, oil layer thickness, permeability, and fracture index, and the dimensionless processing formula of the evaluation indicators is: The (LL) min ) / (L max -L min ) 4. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 1 or 2, Features In step (6), the rock mass between wells is not connected, the span of the perforation section from the oil and water layer is more than 25m, the thickness of a single layer can be perforated is between 10m and 25m, and the perforation span is less than 30m; the distance from the bottom of the adjacent well is greater than 150m; avoid selecting wells with bottoms close to faults or reservoir boundaries; the completion structure is a vertical well to a well with an inclination of less than 30 degrees.

5. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 3, Features In step (6), the rock mass between wells is not connected, the span of the perforation section from the oil and water layer is more than 25m, the thickness of a single layer can be perforated is between 10m and 25m, and the perforation span is less than 30m; the distance from the bottom of the adjacent well is greater than 150m; avoid selecting wells with bottoms close to faults or reservoir boundaries; the completion structure is a vertical well to a well with an inclination of less than 30 degrees.

6. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 1 or 2, Features In step (7), the formation fracture pressure is calculated by the formula: P f =G f ×H f Where P f is the formation fracture pressure, MPa; G f is the formation fracture pressure gradient, MPa / m; H f is the vertical height of the middle of the oil layer, m; clarify the fracture pressure of the target layer section of the well construction, and then conduct formation testing through increasing displacement, make a relationship curve between displacement and construction oil pressure and casing pressure during the test process, and determine the extension pressure and extension rate of the fracture through the inflection point; use the pressure drop test data after stopping the pump to perform a double logarithmic analysis of time and pressure difference to determine the closure pressure of the fracture, the time to reach radial flow, and the formation permeability; the pressure corresponding to a reasonable construction displacement value should be greater than the shear stress but not higher than the fracture pressure.

7. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 3, Features In step (7), the formation fracture pressure is calculated by the formula: P f =G f ×H f Where, Pf is the formation fracture pressure, MPa; G f is the formation fracture pressure gradient, MPa / m; Hf is the vertical height of the middle of the oil layer, m; the fracture pressure of the target layer section of the well construction is clarified, and then the formation test is required to increase the displacement, and the relationship curve between the displacement and the construction oil pressure and casing pressure during the test process is made, and the extension pressure and extension rate of the fracture are determined by the inflection point; the double logarithmic analysis of time and pressure difference is performed on the pressure drop test data after stopping the pump to determine the closure pressure of the fracture, the time to reach radial flow, and the formation permeability; the pressure corresponding to the reasonable construction displacement value should be greater than the shear stress but not higher than the fracture pressure.

8. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 4, Features In step (7), the formation fracture pressure is calculated by the formula: P f =G f ×H f Where P f is the formation fracture pressure, MPa; G f is the formation fracture pressure gradient, MPa / m; H f is the vertical height of the middle of the oil layer, m; clarify the fracture pressure of the target layer section of the well construction, and then conduct formation testing through increasing displacement, make a relationship curve between the displacement and construction oil pressure and casing pressure during the test process, and determine the extension pressure and extension rate of the fracture through the inflection point; use the pressure drop test data after stopping the pump to perform a double logarithmic analysis of time and pressure difference to determine the closure pressure of the fracture, the time to reach radial flow, and the formation permeability; the pressure corresponding to a reasonable construction displacement value should be greater than the shear stress but not higher than the fracture pressure.

9. The dual-medium reservoir stepped fracture expansion reservoir reconstruction method according to claim 5, Features In step (7), the formation fracture pressure is calculated by the formula: P f =G f ×H f Where P f is the formation fracture pressure, MPa; G f is the formation fracture pressure gradient, MPa / m; H f is the vertical height of the middle of the oil layer, m; clarify the fracture pressure of the target layer section of the well construction, and then conduct formation testing through increasing displacement, make a relationship curve between the displacement and construction oil pressure and casing pressure during the test process, and determine the extension pressure and extension rate of the fracture through the inflection point; use the pressure drop test data after stopping the pump to perform a double logarithmic analysis of time and pressure difference to determine the closure pressure of the fracture, the time to reach radial flow, and the formation permeability; the pressure corresponding to a reasonable construction displacement value should be greater than the shear stress but not higher than the fracture pressure.

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