Method for determining injection allocation rate of pressure drive in water injection well

Abstract

The present invention provides a method for determining the pressure drive injection allocation volume of an injection well, including: Step 1, calculating the relationship between the injection volume and the formation pressure recovery using the material balance equation; Step 2, drawing a chart of the formation pressure drop variation at different injection-production ratios based on Step 1; Step 3, drawing a profile of the inter-well pressure variation before pressure drive; Step 4, determining the ultimate easy-flow radius of the water well and the ultimate oil drainage radius of the oil well during pressure drive; Step 5, drawing a schematic diagram of the water drive swept area between the oil well and the water well during pressure drive, and calculating the maximum water drive front swept radius corresponding to the establishment of an effective displacement relationship using the fluid connection method; Step 6, calculating the pore volume within the water drive swept radius using the ellipsoid model to determine the pressure drive injection volume; Step 7, comparing and optimizing the pressure drive water volume calculated in Step 6 with the material balance method to determine the appropriate displacement radius and pressure drive injection allocation volume. This method determines the pressure drive injection front and thus the pressure drive injection volume according to the seepage characteristics of low-permeability reservoirs and in combination with the inter-well pressure variation characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield development, and particularly to a method for determining the injection volume of pressure drive in injection wells. Background Technique

[0002] For waterflooding developed oilfields, especially water injection developed oilfields, how to determine a reasonable injection allocation plan and make full use of water injection to supplement energy and expand the swept area of waterflooding is the key to improving the recovery factor of oil reservoirs.

[0003] In conventional waterflooding developed oilfields, the injection allocation method for injection wells generally determines the required water injection volume for each small layer in the well area based on the energy maintenance requirements of each small layer in a certain injection-production well area, with production determining injection. Referring to the calculation method of the injection volume allocated to each small layer of the injection well, the theoretical injection volume of each water well in the injection-production well area is calculated, Q / SH1020 0529-2017, Design Method for Geological Injection Allocation Plan of Injection Wells (5.5.1). This method first calculates the injection volume allocated to each small layer of the injection well, splits the production according to the production allocation of the development plan, the process technology level, the stratified test data of the oil wells in the well area, and the stratified flow coefficient to determine the liquid production volume of each small layer, determines the injection-production ratio according to the reasonable injection-production pressure requirements of different oil reservoirs, thereby determining the water injection volume of the small layer, and then determines the injection volume allocated to each small layer of each water well in the injection-production well area. The injection volumes of each small layer are added to obtain the injection volume of the layer section, and the injection volumes of the layer sections are added to obtain the total well injection volume. This method is based on the principle of balanced displacement between oil and water wells and calculates the injection volume based on the injection pressure being lower than the fracture pressure. It is not suitable for calculating the injection volume in the case of large displacement water injection, i.e., pressure drive injection mode, when the injection pressure is higher than the fracture pressure.

[0004] Another method for determining the water injection volume of water wells is the material balance method. By using the formula derivation of the material balance equation, the relationship between the injection-production ratio and the total formation pressure drop and liquid production volume is determined, and a relationship chart of formation pressure and annual liquid production volume under different injection-production ratios of the oilfield (unit) is made, thereby determining the reasonable injection-production ratio and injection volume. (Application of Material Balance Equation in Determining Reasonable Injection-Production Ratio of Oilfield, Journal Name: Inner Mongolia Petrochemical Industry, Editor-in-Chief: Qiqige, Publishing House: Inner Mongolia Petrochemical Industry, Time: 22nd Issue in 2012).

[0005]

[0006] K 1 = NC t B oi

[0007] K 1 : represents the elastic productivity, ×10 4 m 3 / MPa;

[0008] K 2 : represents the water influx coefficient, ×104 m 3 / (a·MPa);

[0009] △P: represents the total formation pressure drop, MPa;

[0010] Q L : represents the annual liquid production, ×10 4 t;

[0011] Ct: represents the comprehensive compressibility of the rock, Mpa -1 ;

[0012] Boi: represents the oil volume factor, m 3 / m 3 ;

[0013] N: represents the geological reserves, ×10 4 m 3 ;

[0014] IPR: represents the injection-production ratio;

[0015] Main steps: First, consider two states of having edge-bottom water invasion and no edge-bottom water invasion, and calculate the water invasion coefficient. In actual development, the proportion of ineffective water injection needs to be considered to determine the relationship between formation pressure drop and different injection-production ratios and different liquid production rates, obtain the linear relationship curve between the injection-production ratio IPR and the formation pressure drop under the unit liquid production rate, and finally obtain the reasonable injection-production ratio and the allocated injection volume of the well group or block.

[0016] However, this method has deficiencies. First, the formula is applicable to elastic water drive oil reservoirs, matrix pore throats and fracture reservoirs under conventional water injection conditions (below the fracture pressure); second, the elastic productivity is related to the comprehensive compressibility of the rock, and the selection of these parameters is complex and difficult to accurately obtain; third, the calculation errors of the water invasion volume and water invasion coefficient of the edge-bottom water are relatively large; fourth, indoor experimental studies show that during pressure drive, microfractures will be generated, causing fracture propagation, an increase in matrix pore pressure, an increase in pore throat size, an increase in the number of connected pores and throats, and the reservoir porosity will increase by 2-3%, and the permeability will increase significantly. Therefore, it is not very suitable to calculate the allocated injection volume of water wells only by the material balance method under high-pressure drive with large displacement exceeding the fracture pressure.

[0017] The allocation of injection volume for injection wells can also be calculated using reservoir numerical simulation technology, which can provide relatively accurate quantitative guidance and can be achieved under conventional water injection conditions. However, when injecting water above the formation fracture pressure, the underground oil-water seepage law changes, and the current mathematical model of reservoir numerical simulation is obviously not applicable.

[0018] In the Chinese patent application with the application number: CN201510142060.1, it involves a method for vectorized production and injection allocation in an offshore oilfield. This method for vectorized production and injection allocation in an offshore oilfield includes: Step 1, calculating the directional flow rate between oil wells and water wells, and determining the displacement breakthrough coefficient; Step 2, through the analysis of remaining oil between oil wells and water wells, obtaining the boundary value for judging whether the displacement is balanced by the displacement breakthrough coefficient; Step 3, dividing the actual displacement situation into multiple modes according to the boundary of the displacement breakthrough coefficient; and Step 4, for each mode, establishing a method for vectorized production and injection allocation to achieve the maximum displacement balance of the reservoir under the condition of multi-well interference in the offshore area.

[0019] In the Chinese patent application with the application number: CN201611113552.9, it involves a method for drawing an injection-production capacity chart considering non-Darcy flow. This method includes the following steps: (1) Extracting core samples from the target block, testing the starting pressure gradient, and obtaining the characteristic expression of the starting pressure gradient; (2) Collecting basic reservoir data and calculating the starting pressure gradient; (3) Modifying the productivity calculation model for fractured vertical wells in low-permeability reservoirs, and obtaining the correction factor of the productivity formula through regression training; (4) Setting the parameter change interval, conducting sensitivity analysis, and completing the drawing of the productivity chart; (5) Calculating the balanced water absorption index of the injection well, setting different injection-production ratios, and completing the drawing of the injection pressure chart.

[0020] In the Chinese patent application with the application number: CN201510276011.7, it involves a method for reservoir water injection, which relates to the technical field of reservoir water injection development. The method includes: taking the injection allocation volume of the central injection well as the dependent variable and the liquid production volume of each production well as the independent variable, establishing a multiple regression model, conducting multiple regression calculations, and determining the single-well injection allocation volume of the injection well; determining the gravity segregation influence coefficient and the water-oil mobility ratio of the reservoir through geological data and reservoir data; according to the gravity segregation influence coefficient and the water-oil mobility ratio of the reservoir, determining the gravity segregation degree value corresponding to the gravity segregation influence coefficient and the water-oil mobility ratio of the reservoir on a pre-set gravity segregation chart; determining the theoretical minimum perforation thickness according to the single-well meter water absorption index, the maximum bottom-hole pressure of the injection well, the formation pressure, and the single-well injection allocation volume; determining the perforation thickness according to the reservoir thickness, the theoretical minimum perforation thickness, and the gravity segregation degree value, and injecting water into the injection well.

[0021] The above existing technologies are quite different from the present invention and fail to solve the technical problems we want to address. Pressure drive is a new type of water injection technology with large displacement, ultra-high pressure, and rapid injection. During pressure drive, the injection pressure increases, the pressure difference between oil wells and water wells enlarges, and the ultimate drainage radius at the oil well end increases accordingly. Affected by the pressure drive fractures, there is a significant risk of water channeling. There is currently no relevant data or literature on how to accurately calculate the reasonable pressure drive injection volume for well groups and well areas under a formation fracture pressure higher than the formation fracture pressure to ensure a reasonable recovery of formation pressure while reducing the risk of water channeling. Therefore, a new technology for pressure drive water injection is needed, which is fast and convenient to apply and can accurately calculate the pressure drive injection volume. For this reason, we have invented a new method for determining the pressure drive injection volume of injection wells. Summary of the Invention

[0022] The objective of the present invention is to provide a method for determining the pressure drive water injection front and thus the pressure drive injection volume according to the seepage characteristics of low-permeability reservoirs and in combination with the pressure change characteristics between oil wells and water wells.

[0023] The objective of the present invention can be achieved by the following technical measures: A method for determining the pressure drive injection volume of injection wells, which includes:

[0024] Step 1: Calculate the relationship between the injection volume and the formation pressure recovery using the material balance equation;

[0025] Step 2: Based on Step 1, draw the formation pressure drop change chart under different injection-production ratios;

[0026] Step 3: Draw the pressure change profile between wells before pressure drive;

[0027] Step 4: Determine the limit easy flow radius of the water well and the limit drainage radius of the oil well during pressure drive;

[0028] Step 5: Draw a schematic diagram of the water drive sweep range between oil wells and water wells during pressure drive, and use the fluid connection method to calculate the maximum water drive front sweep radius corresponding to the established effective displacement relationship;

[0029] Step 6: Calculate the pore volume within the maximum water drive sweep radius using the ellipsoid model to determine the limit pressure drive injection volume;

[0030] Step 7: Compare and optimize the pressure drive water volume calculated in Step 6 with the material balance method to determine the appropriate displacement radius and pressure drive injection volume.

[0031] The objective of the present invention can also be achieved by the following technical measures:

[0032] In Step 1, based on the material balance equations for natural water drive and artificial water injection elastic drive in an unsaturated reservoir:

[0033] N p Bo = NB oi C t ΔP + (W i + W e - W p )B w (Equation 1)

[0034] Wherein:

[0035] N: Geological reserves, ×10 4 m 3 ; Np: Cumulative oil production, ×10 4 m 3 ;

[0036] Wp: Cumulative water production, ×10 4 m 3 ; Wi: Cumulative water injection, ×10 4 m 3 ;

[0037] We: Cumulative natural water influx, ×10 4 m 3 ; Swc: Irreducible water saturation, decimal;

[0038] Boi: Oil formation volume factor at initial pressure; Bo: Oil formation volume factor at pressure P;

[0039] Bw: Water formation volume factor, m 3 / m 3 ; Cw: Water compressibility, Mpa -1 ;

[0040] Cf: Pore compressibility, Mpa -1 ; Co: Oil compressibility, Mpa -1 ;

[0041] Ct: Rock comprehensive compressibility, Mpa -1 ; ΔP: Formation pressure drop, MPa;

[0042] Assume that the water formation volume factor Bw = 1.0

[0043] Equation 1 is transformed into:

[0044] We = N p B o - NB oi C t ΔP - Wi + Wp (Equation 3)

[0045] Known elastic productivity: K1 = NC t B oi

[0046] Cumulative produced fluid: WL = N p B o +W p

[0047] Formula 3 is transformed into: We = WL - Wi - K 1 △P (Equation 4)

[0048] For a reservoir without bottom water and edge water, the water influx is 0, that is, We = 0;

[0049] Formula 4 is transformed into:

[0050] Wi = K 1 △P + WL (Equation 5)

[0051] Differentiate with respect to time:

[0052]

[0053] The known injection-production ratio IPR:

[0054]

[0055] That is

[0056]

[0057] Formula 6 can be transformed into:

[0058] That is:

[0059]

[0060] Represents the total pressure drop per unit time, Represents the cumulative produced fluid volume per unit time

[0061] Represents the cumulative injection water volume per unit time.

[0062] In Step 1, use Formula 7 to plot the variation of formation pressure drop under different injection-production ratios for fixed-rate production, so as to calculate the relationship between the pressure-driven injection water volume per unit time and the formation pressure change.

[0063] In Step 3, due to the characteristics of low-permeability reservoirs, such as large seepage resistance and obvious starting pressure gradient, the pressure between oil wells and water wells can be divided into an easy-flow area and a blocking-flow area. During conventional water injection, due to the high starting pressure, poor water absorption in water wells, it is difficult to establish an effective displacement relationship between oil wells and water wells, and there is a large blocking-flow area. During pressure drive, the injection pressure increases, exceeding the formation fracture pressure, generating microfractures, the matrix pore pressure rises, the pore throat size increases, and the number of connected pores and throats increases, promoting water absorption in the low-permeability zone of small pores. An effective displacement relationship is gradually established between oil wells and water wells, and a new pressure balance cross-section and balance point are formed. As the injection volume increases, the pressure balance point will move towards the oil well end. When the water drive front reaches within the ultimate drainage radius of the oil well, water flooding and water channeling phenomena occur in the oil well.

[0064] In Step 4, in the well group implementing pressure drive, an oil well and water well displacement expression related to permeability and original oil properties is established according to the principle of seepage mechanics.

[0065] Considering that the oil well and water well are homogeneous media and the flow is radial during production:

[0066]

[0067] Where:

[0068] Q: Oil production or water injection volume, m 3 / d; K: Effective permeability of the oil reservoir, 10 -3 μm 2 ;

[0069] H: Effective thickness of the production layer, m; μ: Fluid viscosity, mPa·s;

[0070] B o : Formation volume factor of crude oil at pressure P; △P: Formation pressure drop (MPa);

[0071] R: Supply radius, m; r: Wellbore radius of the oil well, m;

[0072] Assuming that the flow rate or injection volume is constant, the formation thickness H, and the wellbore radius r of the oil well are all specific values, then the logarithm lnR of the seepage radius of the oil well and the injection supply radius of the water injection well are both proportional to △P and k / μ. Under this condition, the formula for the ultimate radius of flow of the oil well and water well is derived:

[0073]

[0074] Pe: Formation pressure, Mpa; Pw: Bottom-hole flowing pressure, MPa;

[0075] When it is a water injection well in Equation 9, r 极限 is the ultimate easy-flow radius of the water injection well under different permeabilities and crude oil viscosities at a certain specific water injection pressure difference; when it is an oil well in Equation 9, r极限 is the ultimate drainage radius of the oil well at a certain specific production pressure difference with different permeabilities and crude oil viscosities;

[0076] During pressure drive, as the injection pressure increases, the bottom-hole pressure of the water well exceeds the formation fracture pressure, generating micro-fractures and triggering fracture propagation, forming a production fracture network in the near-wellbore area, and significantly increasing the reservoir permeability; compared with conventional water injection, during pressure drive, the pressure difference between the water well and the oil well increases, and the ultimate easy-flow radius of the water well and the ultimate drainage radius of the oil well will increase. Affected by fractures, there is a greater risk of water channeling.

[0077] In step 5, the injection-production well spacing is the sum of the ultimate easy-flow radius of the water well, the ultimate drainage radius of the oil well, and the blocking distance between the water well and the oil well;

[0078] The injection-production well spacing D = the ultimate easy-flow radius Rw + the blocking distance Rc + the ultimate drainage radius Ro

[0079] Compared with conventional water injection, after pressure drive, the ultimate easy-flow radius of the water well and the ultimate drainage radius of the oil well increase. Therefore, the blocking distance will decrease; to establish an effective displacement relationship between the water well and the oil well, the pressure drive sweep radius should be greater than the ultimate easy-flow radius and less than the sum of the blocking distance and the ultimate easy-flow radius, that is, Rw < the pressure drive sweep radius < Rc + Rw; combined with the on-site practice of pressure drive, it is more reasonable that the water drive sweep radius reaches 1 / 3 - 2 / 3 of the blocking area, and it is considered that 1 / 2 of the blocking area is the best;

[0080] Therefore, the maximum pressure drive sweep radius is

[0081]

[0082] K: effective permeability of the oil reservoir, 10 -3 μm 2 ; μ: fluid viscosity, mPa.s;

[0083] Pe: formation pressure, Mpa; Pw: bottom-hole flowing pressure, MPa.

[0084] In step 6, since during pressure drive, injection is carried out at a pressure exceeding the formation fracture pressure, micro-fractures will form in the near-wellbore area, triggering fracture branching and propagation, forming a large number of fracture network zones, and the pore-throat size of the matrix reservoir increases, and the number of connected pores and throats increases, and the porosity and storage capacity of the reservoir are correspondingly improved. Through indoor core simulation pressure drive injection experiments, the porosity is increased by 2 - 3%, and the fracture network improves the storage capacity by 8% - 15%. Therefore, the coefficient of the method for calculating the pore volume by the ellipsoid method to obtain the pressure drive injection volume is corrected, and the value is 1.1 - 1.18;

[0085] Therefore, the maximum pressure drive injection volume:

[0086]

[0087] β: Correction coefficient, 1.1 - 1.18; Φ: Porosity, %

[0088] H: Reservoir thickness, m; F: Fracture bandwidth of fracturing in the reference well area

[0089] Rmax: Maximum sweep radius of pressure drive

[0090] In step 7, compare the maximum pressure drive injection volume calculated in step 6 with the injection volume required for pressure drive when the formation pressure coefficient calculated by the material balance method in steps 1 - 2 is restored to 1.0 - 1.2, and optimize the injection volume allocation for pressure drive where the water drive sweep radius is within the range of 1 / 3 - 2 / 3 of the distance in the flow - blocking area, achieving the purpose of reasonably restoring the formation pressure while expanding the water drive sweep range and reducing the risk of water channeling.

[0091] The method for determining the injection volume allocation for pressure drive in this invention is further combined based on the basic theory of seepage mechanics, material balance theory, and a new pressure drive injection mode. According to the seepage characteristics of low - permeability reservoirs and combined with the pressure change characteristics between oil and water wells, a method for determining the pressure drive injection front and thus the pressure drive injection volume is established. Compared with the prior art, this invention has derived a set of formulas for predicting the relationship between formation pressure recovery and pressure drive injection volume through the material balance equation, drawn the charts of formation pressure recovery under different injection - production ratios, determined the maximum, reasonable, and optimal sweep ranges of pressure drive by combining the fluid connection method, determined the injection volume for different sweep ranges using the ellipsoid model, compared and optimized the pressure drive injection volume measured by the material balance method and the fluid connection method. While reasonably restoring the formation pressure, it expands the water drive sweep range and reduces the risk of water flooding and water channeling, filling the gap that there is no relevant technical data support for the design of pressure drive injection volume allocation. After implementing the pressure drive by this method, the formation pressure continuously rises, effectively expanding the water drive sweep range, reducing the risk of water channeling, and increasing the seeing - effect rate of the pressure drive well group to over 82%, with obvious production - increasing effects. Brief Description of the Drawings

[0092] Figure 1 It is a flowchart of a specific embodiment of the method for determining the injection volume allocation for pressure drive of this invention;

[0093] Figure 2 It is a schematic diagram of formation pressure drop change under different injection - production ratios with a fixed liquid production rate of this invention;

[0094] Figure 3 It is a schematic diagram of the pressure change between wells during conventional water injection, pressure drive water injection, and water flooding of this invention;

[0095] Figure 4 It is a schematic diagram of the maximum water drive wave radius of pressure drive of this invention;

[0096] Figure 5 It is a schematic diagram of the water drive front sweep pattern of groundwater drive of this invention;

[0097] Figure 6 Schematic diagram of the formation pore volume calculation model within the pressure drive sweep range of the present invention;

[0098] Figure 7 Schematic diagram of the formation pressure drop change curve under different injection-production ratios during fixed liquid production in a specific embodiment of the present invention;

[0099] Figure 8 Schematic diagram of the pressure profile between oil and water wells in a specific embodiment of the present invention;

[0100] Figure 9 Schematic diagram of the permeability contour map, easy flow radius, and ultimate drainage radius of a well group in a specific embodiment of the present invention;

[0101] Figure 10 Schematic diagram of the pressure drive injection water volume under different water drive front sweep radii in a specific embodiment of the present invention;

[0102] Figure 11 Schematic diagram of the daily production curve of a well group after pressure drive water injection in a specific embodiment of the present invention;

[0103] Figure 12 The shown figure is the injection-production well pattern diagram of a specific embodiment of the present invention;

[0104] Figure 13 Schematic diagram of the curve of the formation pressure drop changing with time under different injection-production ratios during fixed liquid production in a well area in a specific embodiment of the present invention;

[0105] Figure 14 Schematic diagram of the pressure profile between Well L13-X62 and Well L13-X64 in a specific embodiment of the present invention;

[0106] Figure 15 Schematic diagram of the ultimate easy flow radius and ultimate drainage radius of Well Group L13-X62 and L13-X63 in a specific embodiment of the present invention;

[0107] Figure 16 Schematic diagram of the pressure drive injection water volume corresponding to different pressure drive and water drive sweep radii of Well L13-X62 in a specific embodiment of the present invention;

[0108] Figure 17 Schematic diagram of the pressure drive injection water volume corresponding to different pressure drive and water drive sweep radii of Well L13-X63 in a specific embodiment of the present invention;

[0109] Figure 18 Verification diagram of the application effect of a specific embodiment of the present invention in the L13-X63 well area;

[0110] Figure 19Injection-production well pattern diagram in a specific embodiment of the present invention;

[0111] Figure 20 In a specific embodiment of the present invention, it is a curve graph showing the change of formation pressure drop with time under different injection-production ratios during fixed liquid production in the S106-8 well area;

[0112] Figure 21 In a specific embodiment of the present invention, it is a schematic diagram of the inter-well pressure profile between Well S106-8 and Well S106-7;

[0113] Figure 22 In a specific embodiment of the present invention, it is a schematic diagram of the limit easy-flow radius and limit drainage radius of the S106-8 well group;

[0114] Figure 23 In a specific embodiment of the present invention, it is a schematic diagram of the pressure drive injection water volume corresponding to different pressure drive water flooding swept radii in S106-8;

[0115] Figure 24 In a specific embodiment of the present invention, it is a verification diagram of the field application effect in the S106-8 well area. Detailed implementation manners

[0116] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0117] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0118] The method for determining the pressure drive injection volume of an injection well in the present invention includes the following steps:

[0119] Step 1, calculate the relationship between the injection volume and the formation pressure recovery using the material balance equation;

[0120] Calculate the relationship between the injection volume and the formation pressure recovery according to the material balance equation;

[0121] The natural water drive and artificial water injection elastic drive material balance equations for an undersaturated oil reservoir (Pi > Pb) are known:

[0122] N p B o = NB oi Ct △P+(W i +W e -W p )B w (Equation 1)

[0123] Wherein:

[0124] N: Geological reserves, ×10 4 m 3 ; Np: Cumulative oil production, ×10 4 m 3 ;

[0125] Wp: Cumulative water production, ×10 4 m 3 ; Wi: Cumulative water injection, ×10 4 m 3 ;

[0126] We: Cumulative natural water influx, ×10 4 m 3 ; Swc: Irreducible water saturation, decimal;

[0127] Boi: Formation volume factor of crude oil at initial pressure; Bo: Formation volume factor of crude oil at pressure P;

[0128] Bw: Formation volume factor of water, m 3 / m 3 ; Cw: Compressibility of water, Mpa -1 ;

[0129] Cf: Compressibility of pore space, Mpa -1 ; Co: Compressibility of crude oil, Mpa -1 ;

[0130] Ct: Total compressibility of rock, Mpa -1 ; △P: Formation pressure drop, MPa;

[0131] Assume the formation volume factor of water Bw = 1.0

[0132] Equation 1 is transformed into:

[0133] We = N p B o -NB oi C t △P - Wi + Wp (Equation 3)

[0134] Known elastic productivity: K1 = NC t B oi

[0135] Cumulative produced fluid: WL = N pB o +W p

[0136] Equation 3 is transformed into: We = WL - Wi - K 1 △P (Equation 4)

[0137] For a bottom - water - free reservoir, the water influx We = 0, that is, We = 0;

[0138] Equation 4 is transformed into:

[0139] Wi = K 1 △P + WL (Equation 5)

[0140] Differentiate with respect to time:

[0141]

[0142] The known injection - production ratio IPR:

[0143]

[0144] That is

[0145]

[0146] Equation 6 can be transformed into:

[0147] That is:

[0148]

[0149] Represents the total pressure drop per unit time, Represents the cumulative liquid production per unit time

[0150] Represents the cumulative injection volume per unit time.

[0151] Step 2, based on Step 1, draw the formation pressure drop variation chart under different injection - production ratios, as Figure 2 shown. It can be known from Figure 2 that the current formation pressure drop in a certain well area is 14.5 Mpa. If the injection volume with an injection - production ratio of 21 is adopted, the formation pressure drop will decrease from 14.5 Mpa to 3.5 Mpa in 3 months. If the injection volume with an injection - production ratio of 3 is adopted, it will take 24 months to reduce the formation pressure drop from 14.5 Mpa to 3.5 Mpa; Use Equation 7 to draw the variation of the formation pressure drop under different injection - production ratios for fixed - liquid production, so as to calculate the relationship between the pressure - driven injection volume per unit time and the formation pressure change.

[0152] Step 3, analyze the displacement relationship between oil wells and water wells according to the production dynamic data of oil wells and water wells, and draw the pressure change profile between wells before pressure - driven;

[0153] Analyze the displacement relationship between oil wells and water wells based on the production dynamic data of oil wells and water wells, and draw the pressure change profile between wells before pressure displacement. Due to the influence of the boundary layer effect in low-permeability reservoirs, which is characterized by large seepage resistance and obvious starting pressure gradient, the seepage area between oil wells and water wells is divided into an easy-flow area and a blocking area, as Figure 3 shown. From Figure 3 it can be seen that during conventional water injection, due to the high starting pressure, poor water absorption in water wells, it is difficult to establish an effective displacement relationship between oil wells and water wells, and the blocking area between wells is relatively large. During pressure displacement, the injection pressure increases, exceeding the formation fracture pressure, generating micro-fractures, the matrix pore pressure rises, the pore throat size increases, and the number of connected pores and throats increases, promoting water absorption in the low-permeability zone of small pores. An effective displacement relationship is gradually established between oil wells and water wells, and the blocking area decreases or even disappears, and a new pressure balance section and balance point are formed. As the injection volume increases, the pressure balance point will move towards the oil well end. When the water drive front reaches within the ultimate drainage radius of the oil well, water flooding and water channeling phenomena occur in the oil well.

[0154] Step 4, determine the ultimate easy-flow radius of the water well and the ultimate drainage radius of the oil well during pressure displacement. In the well group where pressure displacement is implemented, establish an oil-water well displacement expression related to permeability and crude oil properties based on the principle of seepage mechanics.

[0155] Considering that the oil well and water well are homogeneous media and the flow is radial during production:

[0156]

[0157] Among them:

[0158] Q: Oil production or water injection volume, m 3 / d; K: Effective permeability of the oil layer, 10 -3 μm 2 ;

[0159] H: Effective thickness of the production layer, m; μ: Fluid viscosity, mPa·s;

[0160] B o : Formation volume factor of crude oil at pressure P; △P: Formation pressure drop (MPa);

[0161] R: Supply radius, m; r: Wellbore radius of the oil well, m;

[0162] Assuming that the flow rate or injection volume is constant, the formation thickness H and the wellbore radius r of the oil well are all specific values, then the logarithm lnR of the seepage radius of the oil well and the injection supply radius of the injection well are both proportional to △P and k / μ. Under this condition, the formula for the ultimate radius of oil-water well flow is derived:

[0163]

[0164] In formula 9, when the water injection well is 极限 is the limiting easy flow radius of the water injection well with different permeabilities and crude oil viscosities under a certain injection pressure difference; when it is an oil well, r 极限 It is the limiting oil leakage radius of an oil well with different permeabilities and crude oil viscosities under a certain production pressure difference.

[0165] During pressure drive, the injection pressure increases, the bottom hole pressure of the water well exceeds the formation fracture pressure, fine cracks are generated and crack expansion is triggered, a fracture network is produced in the near-well area, and the reservoir permeability is greatly improved. Compared with conventional water injection, the pressure difference between oil and water wells increases during pressure drive, the water well limit easy flow radius and the oil well limit oil leakage radius will increase, and under the influence of cracks, there is a greater risk of water channeling.

[0166] Step 5, draw a schematic diagram of the water drive sweep range between oil and water wells during pressure drive, and use the fluid connection method to calculate the corresponding maximum water drive front sweep radius after the effective displacement relationship is established;

[0167] Draw a schematic diagram of the water drive range during pressure drive, such as Figure 4 As shown in the figure, the maximum water drive front sweep radius is determined by the fluid connection method. The larger the pressure drive water injection sweep radius, the better. If the sweep radius is too large, the water drive front will easily reach the bottom of the oil well, causing water flooding and water channeling. If the water drive front sweep radius is too small, the flow resistance area will be large, the starting pressure gradient will be large, the pressure drop loss will be serious, and it will be difficult to establish an effective displacement pressure difference between the oil and water wells. The study shows that the maximum water drive front sweep radius of the pressure drive cannot exceed the limit oil discharge radius of the oil well, otherwise the oil well will show water flooding and water channeling.

[0168] Figure 4 Schematic diagram of the maximum water drive wave radius of the pressure drive of the present invention. The injection-production well spacing is the sum of the water well's limit easy flow radius, the oil well's limit oil leakage radius and the flow resistance distance between the oil and water wells.

[0169] Injection-production well spacing D = limit easy flow radius Rw + flow blocking distance Rc + limit oil leakage radius Ro

[0170] Compared with conventional water injection, the limit easy flow radius of water wells and the limit oil discharge radius of oil wells increase after pressure drive, so the blocking distance will decrease. To establish an effective displacement relationship between oil and water wells, the pressure drive sweep radius should be greater than the limit easy flow radius and less than the sum of the blocking distance and the limit easy flow radius, that is, Rw < pressure drive sweep radius <Rc+Rw。结合压驱现场实践,水驱波及半径到达阻流区的 1 / 3-2 / 3较为合理,认为位于阻流区的1 / 2为最佳。

[0171] Therefore, the maximum sweep radius of pressure drive is

[0172]

[0173] Step 6, using the ellipsoid model to calculate the pore volume within the water drive wave radius to determine the pressure drive water injection volume;

[0174] Affected by the heterogeneity between and within reservoir layers, the water flooding front does not present a concentric circle-like balanced diffusion during pressure-driven water injection. Combining the fracturing ellipsoid seepage theory, numerical simulation and indoor experimental research, the water injection front presents an ellipsoid-like shape, such as Figure 5 As shown. Figure 5 It can be seen that, when the water well is injected, the water flooding range between the oil and water wells presents a certain angle, and the overall shape is elliptical. Therefore, the ellipsoid method is used to calculate the pore volume within the maximum pressure drive displacement radius to obtain the maximum pressure drive water injection volume, so as to avoid water flooding and water channeling after pressure drive. Figure 6 As shown in the figure, the long axis radius Rmax of the ellipsoid is the maximum water drive sweep radius, the short axis radius F can refer to the bandwidth of the simulated pressure drive fracture, and the longitudinal axis radius H / 2 refers to half of the effective thickness of the reservoir. During pressure drive, the super-formation fracture pressure is injected, and fine fractures will form in the near-wellbore area, which will cause fracture branching and expansion, forming a large number of fracture network belts. In addition, the pore throat size of the matrix reservoir increases, the number of connected pores and throats increases, and the porosity and storage capacity of the reservoir are correspondingly improved. Through indoor core simulation pressure drive injection experiments, the porosity is increased by 2-3%, and the fracture network improves the storage capacity by 8%-15%. Therefore, the coefficient correction is made to the method of calculating the pore volume by the ellipsoid method to obtain the pressure drive water injection volume, and the value is 1.1-1.18.

[0175] Therefore, the maximum water injection volume for pressure drive is:

[0176]

[0177] β: correction factor, 1.1-1.18 Φ: porosity, %

[0178] H: reservoir thickness, m; F: reference simulation pressure-driven fracture bandwidth

[0179] Step 7: Compare the pressure drive water volume calculated in step 6 with the material balance method to optimize and determine the appropriate displacement radius and pressure drive water injection volume.

[0180] The maximum pressure drive water injection volume calculated in step 6 is compared with the pressure drive water injection volume required when the formation pressure coefficient is restored to 1.0-1.2 calculated by the material balance method in step 1-2, and the pressure drive water injection volume with a water drive sweep radius within the range of 1 / 3-2 / 3 of the distance to the blocking area is preferably selected, so as to achieve the purpose of reasonably restoring the formation pressure while expanding the water drive sweep range and reducing the risk of water breakthrough.

[0181] The following are several specific embodiments of the present invention.

[0182] Example 1: (The water volume calculated by material balance method is less than the minimum reasonable pressure drive water injection volume)

[0183] In a specific embodiment 1 of applying the present invention, as Figure 1 shown, Figure 1 This is a flowchart of a specific embodiment of a new method for designing the injection allocation volume of a water injection well in the present invention.

[0184] Step 101: Establish an expression relationship between the formation pressure drop, liquid production volume, water injection volume, and injection-production ratio within a certain time period according to the material balance equation;

[0185]

[0186] Step 102: Draw a schematic diagram of the change of the formation pressure drop with time at different injection-production ratios when the annual liquid production volume is fixed according to Equation 1. The higher the injection-production ratio, the faster the formation pressure recovers, and the shorter the water injection time to reach the same pressure. The water injection volume under the ideal formation pressure can be calculated based on the liquid production volume and the injection-production ratio.

[0187] Figure 7 The following shows an injection-production well pattern diagram of a specific embodiment of the present invention, Figure 8 and the following shows the curve of the change of the formation pressure drop with time at different injection-production ratios during the fixed liquid production of Well Group N35-42. Before the implementation of pressure drive in the well group, the formation pressure was 16.4 MPa. It is designed that the formation pressure coefficient will recover to 1.2, i.e., 35.9 MPa, after pressure drive. The predicted annual liquid production volume after pressure drive is 0.77×10 4 t. Under the condition of material balance, the pressure drive water injection volume of 3.53×10 4 m 3 .

[0188] Step 103: Analyze the displacement relationship between oil wells and water wells based on the dynamic production data of oil wells and water wells and the historical water injection effectiveness, and draw a cross-section of the pressure change between wells.

[0189] Figure 9 The following is a schematic diagram of the pressure profile between Well N35-42 and Well N35-X7, which is a specific embodiment of the present invention. The daily liquid production of each well in Well Group N35-42 is 1.5 t / d, the daily oil production of each well is 1.2 t / d, and the daily injection of each well is 13.4 m 3 / d. The long-term water injection effect of the water wells is poor, and the oil wells have not seen any effect. It is considered that there is no effective displacement relationship between the oil wells and water wells, and there is a large flow resistance distance between the oil wells and water wells.

[0190] Step 104: Calculate the limit easy-flow radius of the water wells in Well Group N35-42 and the limit oil drainage radius of the corresponding oil wells according to Equation 2.

[0191]

[0192] The limit easy-flow radius of N35-42 before pressure drive is calculated to be 66 m by Formula 2, and the limit oil drainage radii of N35-X7, N35-X6, N35-X41, N35-43, and N35-5-X4 are 48.3 m, 62.1 m, 27.6 m, 46.1 m, and 19.8 m respectively.

[0193] Step 105: Draw a schematic diagram of the water drive swept area of the well group based on the limit easy-flow radius and the limit oil drainage radius, and determine the maximum water drive front swept radius.

[0194] Figure 7 This is a specific embodiment of the present invention, showing the schematic diagrams of the limit easy-flow radius and the limit oil drainage radius of the N35-42 well group. Since the historical fracture direction of N35-X7 has the smallest matrix well spacing from the water well N35-42, the maximum pressure drive displacement radius is determined by N35-42 and N35-X7 wells. During pressure drive, due to the increase in injection pressure and the larger injection-production pressure difference, the limit easy-flow radius of the water well and the limit oil drainage radius of the oil well become larger. The limit easy-flow radius of N35-42 after pressure drive is calculated to be 122 m, and the limit oil drainage radius of N35-X7 well is 122 m. The blocking distance between the two wells is 96 m. Then, the maximum displacement radius = injection-production well spacing 360 m - limit oil drainage radius 122 m = 218 m. The reasonable water drive swept radius is located at 1 / 3 - 2 / 3 of the blocking area, that is, 154 m - 186 m, and the best water drive swept radius at 1 / 2 of the blocking area is 170 m.

[0195] Step 106: Calculate the pore volume within the maximum pressure drive displacement radius, the reasonable pressure drive displacement radius, and the best water drive swept radius of the well group in the embodiment according to the ellipsoid method model, and obtain the corresponding pressure drive injection volume.

[0196] Figure 10 This is a specific embodiment of the present invention, showing the schematic diagram of the pressure drive injection volume corresponding to different pressure drive and water drive swept radii. The maximum pressure drive displacement radius of the N35-42 well group is 218 m, and the corresponding injection volume is 5.67×10 4 m 3 ³, the reasonable pressure drive injection volume range is 154 m - 186 m, and the corresponding injection volume is 4.01 - 4.84×10 4 m 3 ³, the best pressure drive swept radius is 170 m, and the corresponding injection volume is 4.42×10 4 m 3 ³.

[0197] Step 107: Compare the maximum pressure drive injection volume calculated in Step 106 with the injection volume required for pressure drive when the formation pressure coefficient is restored to 1.2 by the material balance method in Step 102. The injection volume for pressure drive measured by the material balance method for the N35-42 well group is 3.53×10 4 m 3Less than the injection water volume limit of pressure drive water channeling of 5.67×10 4 m 3 , and further optimize and select the optimal injection water volume of 4.42×10 4 m 3 .

[0198] Figure 11 This is the verification diagram of the application effect of a specific embodiment of the present invention in the N35-42 well group. According to this method, the pressure drive injection water volume design is optimized, the water drive swept range is expanded, and the risk of water channeling is reduced. After the pressure drive of the N35-42 well group, the production capacity is increased to nearly 3 times, and the water cut of the well group is stable, verifying the correctness and practicability of this method.

[0199] Example 2: (Measuring the water volume by the material balance method within the reasonable pressure drive injection water volume range)

[0200] In the specific embodiment 2 of applying the present invention, Figure 1 This is the flowchart of a specific embodiment of the new method for designing the pressure drive injection water volume of the injection well of the present invention.

[0201] Step 101, establish the relationship expression between the formation pressure drop, liquid production volume, injection water volume, and injection-production ratio within a certain time period according to the material balance equation of formula 1;

[0202] Step 102, draw the schematic diagram of the change of the formation pressure drop with time at different injection-production ratios when the annual liquid production volume is constant according to formula 1.

[0203] Figure 12 The following shows the injection-production well pattern diagram of a specific embodiment of the present invention, Figure 13 The following shows the curve of the change of the formation pressure drop with time at different injection-production ratios during the fixed liquid production in the L13-X63 well area. Before the pressure drive of the well group, the formation pressure is 23.6 MPa, the total formation pressure drop is 25.16 Mpa. After the design of the pressure drive, the formation pressure coefficient is restored to 1.2, that is, 38.9 MPa. The pressure drive injection water volume measured by the material balance method is 3.4×10 4 m 3 .

[0204] Step 103, analyze the displacement relationship between oil wells and water wells according to the dynamic production data of oil wells and water wells and the historical water injection effectiveness, and draw the cross-section of the pressure change between wells.

[0205] Figure 14 This is a specific embodiment of the present invention, the schematic diagram of the pressure profile between the L13-X62 well and the L13-X64 well. In the L13-X63 well area, the daily liquid production per well is 2.5 t / d, the daily oil production per well is 2.0 t / d, the daily injection per well is 5.5 m3 / d. The water wells have poor long-term water absorption, and the oil wells have low liquid production and low energy. It is considered that there is no effective displacement relationship between the oil wells and water wells, and there is a large blocking distance between the oil wells and water wells.

[0206] Step 104: Calculate the ultimate easy-flow radius of the water wells in the L13-X63 well area of the example according to Equation 2 and the ultimate oil drainage radius of the corresponding oil wells.

[0207] The ultimate easy-flow radii of L13-X62 and L13-X63 before pressure drive are calculated to be 78.2 m and 59.6 m respectively by Formula 2, and the ultimate oil drainage radii of L13-X60, L13-X61, L13-X64, L13-X65, and L13-X66 are 58.2 m, 23.6 m, 84.4 m, 55.2 m, and 111.0 m respectively.

[0208] Step 105: Draw a schematic diagram of the water flooding sweep area of the well group according to the ultimate easy-flow radius and the ultimate oil drainage radius, and determine the maximum water flooding front sweep radius.

[0209] Figure 15 This is a specific implementation example of the present invention, which is a schematic diagram of the ultimate easy-flow radius and the ultimate oil drainage radius of the L13-X62 and L13-X63 well groups. Since the historical fracture direction of L13-X64 is the closest to the matrix well spacing between the water well L13-X62, the maximum pressure drive displacement radius of L13-X62 is determined by L13-X62 and L13-X64 wells. Similarly, the maximum pressure drive displacement radius of L13-X63 is determined by L13-X63 and L13-X65 wells. During pressure drive, due to the increase in injection pressure and the increase in the injection-production pressure difference, the ultimate easy-flow radius of the water well and the ultimate oil drainage radius of the oil well become larger. The ultimate easy-flow radii of L13-X62 and L13-X63 after pressure drive are calculated to be 113.7 m and 73.4 m respectively, the ultimate oil drainage radii of L13-X64 and L13-X65 wells are 104.3 m and 68.2 m respectively, the blocking distance between L13-X62 and L13-X64 is 42 m, and the blocking distance between L13-X63 and L13-X65 is 158.4 m. Then, the maximum displacement radii of L13-X62 and L13-X63 are 155.7 m and 231.8 m respectively, the reasonable water flooding sweep radii of L13-X62 and L13-X63 are 127.7 m - 141.7 m and 126.2 - 179 m respectively, and the optimal displacement radii of L13-X62 and L13-X63 wells are 134.7 m and 152.6 m respectively.

[0210] Step 106: Calculate the pore volume within the maximum pressure drive displacement radius, the reasonable pressure drive displacement radius, and the optimal water flooding sweep radius of the well group in the example according to the ellipsoid method model, and obtain the corresponding pressure drive injection volume.

[0211] Figure 16A specific embodiment of the present invention, a schematic diagram of the pressure drive injection volume corresponding to different pressure drive water drive sweep radii of L13-X62. The maximum pressure drive displacement radius of the L13-X62 well group is 155.7 m, and the corresponding injection volume is 2.5×10 4 m 3 , the reasonable pressure drive injection volume range is 127.7 m - 141.7 m, and the corresponding injection volume is 2.1 - 2.5×10 4 m 3 , the best pressure drive sweep radius is 134.7 m, and the corresponding injection volume is 2.2×10 4 m 3 .

[0212] Figure 17 A specific embodiment of the present invention, a schematic diagram of the pressure drive injection volume corresponding to different pressure drive water drive sweep radii of L13-X63. The maximum pressure drive displacement radius of the L13-X63 well group is 231.8 m, and the corresponding injection volume is 2.5×10 4 m 3 , the reasonable pressure drive injection volume range is 126.2 m - 179 m, and the corresponding injection volume is 1.3 - 1.9×10 4 m 3 , the best pressure drive sweep radius is 152.6 m, and the corresponding injection volume is 1.6×10 4 m 3 .

[0213] Step 107 compares the maximum pressure drive injection volume calculated in step 106 with the injection volume required when the formation pressure coefficient calculated by the material balance method in step 102 is restored to 1.2, that is, 38.9 Mpa. The pressure drive injection volume measured by the material balance method in the L13-X63 well area is 3.4×10 4 m 3 , the reasonable pressure drive injection volume calculated by the fluid connection method for the well area is 3.4×10 4 m 3 - 4.2×10 4 m 3 , the maximum pressure drive injection volume is 5.0×10 4 m 3 . Considering that the pressure drive water volume measured by the material balance method has reached the reasonable pressure drive water volume range, and the oil wells in the well area are put into production by the imitation horizontal well fracturing method, in order to avoid linear water channeling in the fracture, the pressure drive injection volume of 3.4×10 4 m 3 measured by the material balance method is preferably selected, where the pressure drive injection volume of L13-X62 is 2.1×10 4 m 3 , the pressure drive injection volume of L13-X62 is 1.3×10 4 m 3 .

[0214] Figure 18 This is the verification diagram of the application effect of a specific embodiment of the present invention in the L13-X63 well area. According to this method, the injection water volume design of pressure drive is optimized. After the pressure drive water injection in the well area is 3.4×10 4 m 3 , the daily oil production increases from 9.2 t / d to 17.9 t / d, the water cut of the well group is stable, and the cumulative oil increment is 1976 t, indicating that this method has good guiding significance.

[0215] Example 3: (The water volume calculated by the material balance method is greater than the maximum pressure drive injection water volume)

[0216] In the application of the specific Example 3 of the present invention, Figure 1 This is the flow chart of a specific embodiment of the new method for designing the pressure drive injection volume of injection wells of the present invention.

[0217] Step 101: Establish the relationship expression between the formation pressure drop, liquid production volume, injection water volume, and injection-production ratio within a certain time period according to the material balance equation of Formula 1;

[0218] Step 102: Draw the schematic diagram of the change of formation pressure drop with time at different injection-production ratios when the annual liquid production volume is constant according to Formula 1.

[0219] Figure 19 The following shows the injection-production well pattern diagram of a specific embodiment of the present invention, Figure 20 The following shows the curve of the change of formation pressure drop with time at different injection-production ratios during the fixed liquid production in the S106-8 well area. Before the implementation of pressure drive in the well group, the formation pressure is 25.5 MPa, the total formation pressure drop is 18.89 Mpa. It is designed that the formation pressure coefficient is restored to 1.0, that is, 34.1 MPa after pressure drive. The pressure drive injection water volume calculated by the material balance method is 4.5×10 4 m 3 .

[0220] Step 103: Analyze the displacement relationship between oil wells and water wells based on the dynamic production data of oil wells and water wells and the historical water injection effectiveness, and draw the cross-section of the pressure change between wells.

[0221] Figure 21 The following is a schematic diagram of the pressure profile between wells of a specific embodiment of the present invention, the S106-8 well and the S106-7 well. In the B106-8 well area, the daily liquid production per well is 3.8 t / d, the daily oil production per well is 1.3 t / d, the daily injection per well is 11.5 m3 / d, and it is difficult to inject and produce. The blocking distance between oil wells and water wells is relatively large.

[0222] Step 104: Calculate the limit easy flow radius of the water wells in the S106-8 well area of the embodiment and the limit oil drainage radius of the corresponding oil wells according to Formula 2.

[0223] The limit easy - flow radius before pressure drive of S106 - 8 is calculated as 90.36 m by Formula 2, and the limit oil - drainage radii of S106 - 2, S106 - 7, S106 - 4, and S106 - X9 are 67.8 m, 49.3 m, 73.3 m, and 54.5 m respectively.

[0224] Step 105: Draw a schematic diagram of the water - drive swept area of the well group according to the limit easy - flow radius and the limit oil - drainage radius, and determine the maximum water - drive front swept radius.

[0225] Figure 22 For a specific embodiment of the present invention, it is a schematic diagram of the limit easy - flow radius and the limit oil - drainage radius of the S106 - 8 well group. Since the historical fracturing crack direction of S106 - 4 has the smallest matrix well spacing from the water well S106 - 8, the maximum pressure - drive displacement radius is determined by S106 - 4 and S106 - 8. During pressure drive, the limit easy - flow radius of the water well and the limit oil - drainage radius of the oil well become larger. The limit easy - flow radius of S106 - 8 after pressure drive is calculated as 131.4 m, the limit oil - drainage radius of S106 - 4 well is 104.8 m, and the blocking distance between S106 - 8 and S106 - 4 is 113.8 m. Then, the maximum displacement radius of S106 - 8 is 245.2 m, the reasonable water - drive swept radius is 169.3 - 207.2 m, and the best displacement radius is 188.3 m.

[0226] Step 106: Calculate the pore volume within the maximum pressure - drive displacement radius, the reasonable pressure - drive displacement radius, and the best water - drive swept radius of the well group in the embodiment according to the ellipsoid - method model, and obtain the corresponding pressure - drive injection volume.

[0227] Figure 23 For a specific embodiment of the present invention, it is a schematic diagram of the pressure - drive injection volume corresponding to different pressure - drive and water - drive swept radii of S106 - 8. The maximum pressure - drive displacement radius of the S106 - 8 well group is 245.2 m, and the corresponding injection volume is 4.2×10 4 m 3 ³, the reasonable pressure - drive injection volume range is 169.3 m - 207.2 m, and the corresponding injection volume is 2.9 - 3.5×10 4 m 3 ³, the best pressure - drive swept radius is 188.3 m, and the corresponding injection volume is 3.2×10 4 m 3 ³.

[0228] Step 107: Compare the maximum pressure - drive injection volume calculated in Step 106 with the injection volume required when the formation pressure coefficient is restored to 1.0 (i.e., 34.1 Mpa) by the material - balance method in Step 102. The pressure - drive injection volume measured by the material - balance method in the S106 - 8 well area is 4.5×10 4 m 3 ³, and the reasonable pressure - drive injection volume of the well area calculated by the fluid - connection method is 2.9×104 m 3 -3.5×10 4 m 3 , the maximum pressure-driven injection volume is 4.2×10 4 m 3 . Considering that the pressure-driven water volume measured by the material balance method is greater than the injection volume measured by the maximum pressure-driven wave radius, water channeling may occur. It is preferable to select the pressure-driven injection volume of 3.5×10 4 m 3 .

[0229] Figure 24 This is the verification diagram of the application effect of a specific embodiment of the present invention in the S106-8 well area. According to this method, the pressure-driven injection volume design is optimized. After the pressure-driven water injection in the well area is 3.5×10 4 m 3 , the production capacity doubles and the water cut of the well group is stable, indicating that this method has good guiding significance.

[0230] Compared with the prior art, the present invention derives a set of formulas for predicting the relationship between formation pressure recovery and pressure-driven injection volume through the material balance equation, draws the charts of formation pressure recovery under different injection-production ratios, determines the maximum, reasonable, and optimal swept ranges of pressure drive by combining the fluid connection method, determines the injection volume in different swept ranges using the ellipsoid model, compares and optimizes the pressure-driven injection volume measured by the material balance method and the fluid connection method, expands the waterflooding swept range while reasonably restoring the formation pressure and reduces the risk of water flooding and water channeling, making up for the blank that there is no relevant technical data support for the design of pressure-driven injection volume. This method has been applied in multiple well groups in the Xianhe Oil Production Plant of Shengli Oilfield. After implementing pressure drive, the formation pressure continues to rise, effectively expanding the waterflooding swept range, reducing the risk of water channeling, and the seeing efficiency of the pressure-driven well group has increased to more than 82%, with obvious production increase effect.

[0231] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0232] Except for the technical features described in the specification, the rest are well-known technologies to those skilled in the art.

Claims

1. Method for determining injection allocation rate for pressure drive in injection wells Characterized in that The method for determining injection allocation rate for pressure drive in injection wells includes Step 1: Calculate the relationship between injection volume and formation pressure recovery using the material balance equation Step 2: Based on Step 1, draw the formation pressure drop change charts at different injection-production ratios Step 3: Draw the pressure change profile between wells before pressure drive Step 4: Determine the ultimate easy-flow radius of the water well and the ultimate oil drainage radius of the oil well during pressure drive Step 5: Draw a schematic diagram of the water drive sweep range between the oil well and the water well during pressure drive, and calculate the maximum water drive front sweep radius corresponding to the establishment of an effective displacement relationship using the fluid connection method Step 6: Calculate the pore volume within the maximum water drive sweep radius using the ellipsoid model to determine the ultimate pressure drive injection volume Step 7: Compare and optimize the pressure drive water volume calculated in Step 6 with the material balance method to determine the appropriate displacement radius and injection allocation rate for pressure drive In Step 1, based on the material balance equation of natural water drive and artificial water injection elastic drive in an unsaturated oil reservoir N p B o = NB oi C t △P+(W i +W e -W p )B w (Equation 1) Wherein: N: Geological reserves, ×10 4 m 3 ; Np: Cumulative oil production, ×10 4 m 3 ; Wp: Cumulative water production, ×10 4 m 3 ; Wi: Cumulative water injection, ×10 4 m 3 ; We: Cumulative natural water influx, ×10 4 m 3 ; Swc: Irreducible water saturation, fraction; Boi: Formation volume factor of crude oil at original pressure; Bo: Formation volume factor of crude oil at pressure P Bw: Coefficient of water volume, m 3 / m 3 ; Cw: Coefficient of water compressibility, Mpa -1 Cf: Compressibility coefficient of pores, Mpa -1 Co: Compressibility coefficient of crude oil, Mpa -1 Ct: Comprehensive compressibility coefficient of rock, Mpa -1 △P: Formation pressure drop, MPa; Assume the formation volume factor of water Bw = 1.0 Formula 1 is transformed into We = N p B o -NB oi C t △P - Wi + Wp (Equation 3) Known elastic yield: K1 = NC t B oi Cumulative produced fluid: WL = N p B o +W p Equation 3 is transformed into: We = WL - Wi - K 1 △P (Equation 4) For an oil reservoir without bottom water and edge water, the water influx volume is 0, i.e., We = 0 Formula 4 is transformed into Wi = K 1 △P + WL (Equation 5) Differentiate with respect to time: Given the injection-production ratio IPR That is Formula 6 can be transformed into That is represents the total pressure drop per unit time, represents the cumulative liquid production per unit time Indicates the cumulative water injection volume per unit time; In Step 1, use Formula 7 to plot the formation pressure drop changes at different injection-production ratios for fixed production, so as to calculate the relationship between the injection volume for pressure drive per unit time and the formation pressure change 2. The method for determining injection allocation rate for pressure drive in injection wells according to claim 1 Characterized in that In Step 3, due to the characteristics of large seepage resistance and obvious starting pressure gradient in low-permeability oil reservoirs, the pressure between the oil well and the water well can be divided into an easy-flow area and a resistance-flow area; during conventional water injection, due to the high starting pressure, poor water absorption in the water well, it is difficult to establish an effective displacement relationship between the oil well and the water well, and there is a large resistance-flow area; during pressure drive, the injection pressure increases, exceeding the formation fracture pressure, generating micro-fractures, the matrix pore pressure rises, the pore throat size increases, and the number of connected pores and throats increases, promoting water absorption in the small-pore low-permeability zone, gradually establishing an effective displacement relationship between the oil well and the water well, and forming a new pressure balance section and balance point. As the injection volume increases, the pressure balance point will move towards the oil well end. When the water drive front reaches within the ultimate oil drainage radius of the oil well, water flooding and water channeling phenomena occur in the oil well 3. The method for determining injection allocation rate for pressure drive in injection wells according to claim 1 Characterized in that In Step 4, in the well group where pressure drive is implemented, establish an oil-water well displacement expression related to permeability and crude oil properties based on the principles of seepage mechanics Considering that the oil well and the water well are homogeneous media and radial flow occurs during production Where Q: Oil production or water injection rate, m 3 / d; K: Effective permeability of oil reservoir, 10 -3 μm 2 ; H: Effective thickness of the production layer, m; μ: Fluid viscosity, mPa.s B o : Formation volume factor of crude oil at pressure P; △P: Formation pressure drop (MPa); R: Supply radius, m; r: Wellbore radius of the oil well, m Assume that the flow rate or injection volume is constant, the formation thickness H and the wellbore radius r of the oil well are all specific values. Then, the logarithm lnR of the seepage radius of the oil well and the injection supply radius of the injection well are both proportional to △P and k / μ. Under this condition, the formula for the ultimate radius of oil-water well flow is derived Pe: Formation pressure, Mpa; Pw: Bottom hole flowing pressure, MPa When it is an injection well in Equation 9, r 极限 is the critical flow radius of an injection well with different permeabilities and crude oil viscosities under a certain injection pressure differential; when it is a production well in Equation 9, r 极限 is the critical drainage radius of a production well with different permeabilities and crude oil viscosities under a certain production pressure differential; During pressure drive, the injection pressure increases, and the bottom-hole pressure of the water well exceeds the formation fracture pressure, generating micro-fractures and triggering fracture propagation, forming a production fracture network in the near-wellbore area, and significantly increasing the reservoir permeability. Compared with conventional water injection, during pressure drive, the pressure difference between the water well and the oil well increases, and the ultimate easy-flow radius of the water well and the ultimate oil drainage radius of the oil well will increase. Affected by fractures, there is a greater risk of water channeling.

4. The method for determining the pressure drive injection allocation volume of an injection well according to claim 1, characterized in that, in step 5, the injection-production well spacing is the sum of the ultimate easy-flow radius of the water well, the ultimate oil drainage radius of the oil well, and the blocking distance between the water well and the oil well; The injection-production well spacing D = ultimate easy-flow radius Rw + blocking distance Rc + ultimate oil drainage radius Ro Compared with conventional water injection, the ultimate easy-flow radius of the water well and the ultimate oil drainage radius increase after pressure drive. Therefore, the blocking distance will decrease. To establish an effective displacement relationship between the water well and the oil well, the pressure drive sweep radius should be greater than the ultimate easy-flow radius and less than the sum of the blocking distance and the ultimate easy-flow radius, that is, Rw < pressure drive sweep radius < Rc + Rw; Combining with the on-site practice of pressure drive, it is more reasonable for the water drive sweep radius to reach 1 / 3 - 2 / 3 of the blocking area, and it is considered that 1 / 2 of the blocking area is the best; Therefore, the maximum pressure drive sweep radius is K: Effective permeability of the oil reservoir, 10 -3 μm 2 ; μ: fluid viscosity, mPa·s; Pe: formation pressure, Mpa; Pw: bottom-hole flowing pressure, MPa.

5. The method for determining the pressure drive injection allocation volume of an injection well according to claim 1, characterized in that, in step 6, since during pressure drive, injection is carried out at a pressure exceeding the formation fracture pressure, micro-fractures will form in the near-wellbore area, triggering fracture branching and propagation, forming a large number of fracture network zones, and the pore throat size of the matrix reservoir increases, and the number of connected pores and throats increases, and the porosity and storage capacity of the reservoir are correspondingly improved. Through indoor core simulation pressure drive injection experiments, the porosity is increased by 2 - 3%, and the fracture network improves the storage capacity by 8% - 15%; Therefore, the method for calculating the pore volume by the ellipsoid method to obtain the pressure drive injection volume is corrected by a coefficient, and the value is 1.1 - 1.18; Therefore, the maximum pressure drive injection volume: β: correction coefficient, 1.1 - 1.18 Φ: porosity, % H: reservoir thickness, m; F: fracture bandwidth of the reference well area for fracturing Rmax: maximum pressure drive sweep radius.

6. The method for determining the pressure drive injection allocation volume of an injection well according to claim 1, characterized in that, in step 7, compare the maximum pressure drive injection volume calculated in step 6 with the injection volume required for pressure drive when the formation pressure coefficient calculated by the material balance method in steps 1 - 2 is restored to 1.0 - 1.2, and the pressure drive injection allocation volume within the range of 1 / 3 - 2 / 3 of the distance of the water drive sweep radius in the blocking area achieves the purpose of reasonably restoring the formation pressure while expanding the water drive sweep range and reducing the risk of water channeling.

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