Method for determining pollution radius of injection well of sewage containing polymer

Abstract

The present application relates to a kind of methods for determining the pollution radius of poly-containing sewage injection well.The method is mainly used to solve the problems of poor pertinence, high cost, long construction period and unsuitability for poly-containing sewage injection well in conventional methods for determining reservoir pollution radius.The method is characterized by the following steps:a, recording the current injection pressure, injection rate, stable injection pressure and injection rate of poly-containing sewage injection well;c, performing backflow water operation on poly-containing sewage injection well, and calculating the average water discharge rate;d, closing the well to restore pressure, recording the initial pressure, and recording the wellhead pressure data over time until the pressure stabilizes;plotting the pressure recovery curve;e, obtaining the pressure and time of the intersection point of the curve segment and the straight line segment in the pressure recovery curve, and calculating the pollution radius.The method is simple to operate, has low construction cost and is highly targeted for single well.

Description

Technical Field

[0001] This invention relates to the field of oil production engineering technology, and in particular to a method for determining the pollution radius of polymer-containing wastewater reinjection wells. Background Technology

[0002] Currently, the reinjection of polymer-containing wastewater into wells for unclogging is an effective measure for reducing pressure and increasing injection volume, and it has been applied in oilfields. However, many technical problems still exist in determining the reservoir contamination radius. For example, in the Changyuan old area of ​​Daqing Oilfield, the waterflooding development targets are mainly the Sa, Pu, and Gao oil layers. Due to the reinjection of polymer-containing wastewater, the formation is severely blocked, with a deep degree of contamination and great difficulty in remediation. Conventional methods for determining the reservoir contamination radius mainly include physical simulation and well test analysis. The physical simulation method uses artificial cores to simulate the damage degree and radius of each component in polymer-containing wastewater to reservoirs with different permeability, establishes a numerical model, analyzes the contamination of different components of blockage in the water injection section of the block, and calculates the contamination radius based on the blockage law of the core. However, natural reservoirs have the characteristic of heterogeneity, and the simulation results deviate from reality, making this method less targeted. The well test analysis method uses well test interpretation to obtain the bottom hole pressure, performs data analysis and interpretation, obtains relevant oil layer interpretation parameters, and calculates the contamination radius. This method requires well test operations, which are costly and have a long construction period. Current methods for determining the pollution radius, developed in conjunction with actual field conditions, are highly applicable to specific regions but require complex and diverse parameters, incur high costs for parameter acquisition, and produce significant calculation errors. Furthermore, they are not suitable for polymer-containing wastewater reinjection wells. Therefore, there is an urgent need for a pollution radius determination method that is simple to operate, has low construction costs, is highly specific to individual wells, and is applicable to polymer-containing wastewater reinjection wells. Summary of the Invention

[0003] The technical problem to be solved by this invention is to overcome the problems of conventional methods for determining the reservoir contamination radius in the prior art, which have poor targeting, high cost, long construction period and are not applicable to polymer-containing wastewater reinjection wells. Instead, this invention provides a method for determining the contamination radius of polymer-containing wastewater reinjection wells. This method calculates the contamination radius by monitoring the variable discharge injection data and the discharge volume and pressure data after the return water operation of the polymer-containing wastewater reinjection well. The method is simple to operate, has low construction cost, and is highly targeted to a single well, making it suitable for determining the contamination radius of polymer-containing wastewater reinjection wells.

[0004] The present invention solves its problem through the following technical solution: a method for determining the pollution radius of a polymer-containing wastewater reinjection well, comprising the following steps: a. For the polymer-containing wastewater reinjection well, obtain the current injection pressure P1 and injection discharge Q1; b. Conduct a half-discharge injection test on the polymer-containing wastewater reinjection well to obtain the stable injection pressure P2 and injection discharge Q2; c. Perform backflow operation on the polymer-containing wastewater reinjection well to obtain the backflow volume Q. t The water discharge time t is used to determine the water discharge volume Q. t The average water discharge rate q0 is obtained by considering the water discharge time t. d. Close the reinjection well for the polymer-containing wastewater to restore pressure and obtain the initial pressure P. wf The wellhead pressure data is acquired over time until the pressure stabilizes; a pressure recovery curve is plotted based on the acquired wellhead pressure data over time. e. Based on the obtained pressure recovery curve, plot the data at the intersection of the straight line segment and the curved line segment of the pressure recovery curve using pressure and time points to obtain the pressure P at the intersection of the curved line segment and the straight line segment in the pressure recovery curve. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s ; f. Calculate the epidermal coefficient S based on the data obtained in steps c to e; g. Based on the data obtained in steps a to e and the calculated skin coefficient S, calculate the water phase permeability value K of the contaminated zone. s and pollution radius r s .

[0005] Furthermore, the method for calculating the average water discharge rate q0 in step c is as follows: Water discharge volume Q t The ratio of the average water discharge rate to the water discharge time t is the average water discharge rate q0.

[0006] Furthermore, based on the obtained pressure recovery curve, the pressure P at the intersection of the curve segment and the straight line segment in the pressure recovery curve is obtained. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s The methods include: The pressure recovery curve includes a curved segment at the beginning and a straight segment at the end. By plotting the data at the intersection of the straight and curved segments of the pressure recovery curve, pressure and time points are obtained, and the pressure P at the intersection of the curved and straight segments of the pressure recovery curve is acquired. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s .

[0007] Furthermore, the skin coefficient S in step f is calculated using the pressure drop well test analysis formula (1): S = 1.1515 × {(P ws -P wf ) / m-[log(Kt s / φμC t r w 2 )+log(t / (t+ts ))+0.91]} (1) Where: m = 2.12 × 10 -3 ×q0×μ×B0 / KH (2) Where: μ—injected fluid viscosity, mPa·s; K—Water permeability of the oil reservoir, μm 2 ; H—perforation thickness, m; r w —Wellbore radius, m; φ—porosity, % C t —Comprehensive compression coefficient, MPa -1 B0—Volume index, m 3 / m 3 ; t — time to expel water, h; P wf —Initial pressure after well shut-in, MPa; P ws —Pressure at the intersection of the curved segment and the straight segment in the pressure recovery curve, in MPa; t s —The time (h) at the intersection of the curved segment and the straight segment in the pressure recovery curve; q0 — Average water discharge rate before well shut-in, m 3 / h; S—epidermal coefficient; m — slope of the curve.

[0008] Further, the calculation step involves determining the water phase permeability value K in the contaminated zone. s and pollution radius r s : Adopting the piecewise equation of contaminated planar radial flow (3): (P2-P1) / (Q2-Q1)=μ / 2πKH×ln(r / r S )+μ / 2πK S H×ln(r) S / r w (3) In the formula: P1—Current injection pressure, MPa P2—Stable injection pressure when displacement is halved, MPa Q1—Current injection displacement, m 3 / h Q2—Half the injection displacement, m 3 / h r—Liquid supply radius, m Ks—Average water permeability of the contaminated zone in the oil reservoir, in μm2 r s —Pollution radius, m.

[0009] Further, the calculation step involves determining the water phase permeability value K in the contaminated zone. s and pollution radius r s : Using the epidermal coefficient formula (4): S=(K / K S -1)×lnr S / r w (4) Where: S—epidermal coefficient.

[0010] Furthermore, the piecewise equation (3) for the contaminated planar radial flow is combined with the skin coefficient formula (4) to calculate the permeability value K of the aqueous phase in the contaminated zone. s and pollution radius r s .

[0011] Compared with the above-mentioned background technology, the present invention has the following beneficial effects: This invention provides a method for determining the pollution radius of polymer-containing wastewater reinjection wells, which has the following advantages: 1) This invention uses actual contaminated target wells as the research object, obtains the required experimental data through field testing, and uses formulas to derive and calculate parameters such as contamination radius and skin coefficient. This method is highly targeted and has high measurement accuracy. 2) This invention is easy to operate. On-site testing requires only one pump truck and one tanker truck. The construction cycle is 0.5 days, and the pollution radius can be calculated on the same day, which greatly improves efficiency. 3) This invention uses a fixed tubing string method, requiring only 2,000 yuan for a single well test, resulting in low construction costs and the potential for large-scale promotion and application.

[0012] This method can economically and efficiently measure the pollution radius of polymer-containing wastewater reinjection wells, guide the design of unblocking agent dosage, and is simple to operate, with low construction costs, strong single-well targeting, and no need for tubing string operation. It is suitable for determining the pollution radius of polymer-containing wastewater reinjection wells. Attached Figure Description

[0013] Appendix Figure 1 This is a curve showing the relationship between injection pressure and injection rate in well L according to an embodiment of the present invention; Appendix Figure 2 This is a curve showing the relationship between the water output of well L and time in an embodiment of the present invention; Appendix Figure 3 This is the pressure recovery curve of well L in an embodiment of the present invention. Detailed Implementation

[0014] The invention will be further explained below with reference to the diagrams: The method for determining the pollution radius of the polymer-containing wastewater reinjection well includes the following steps: a. For the polymer-containing wastewater reinjection well, obtain the current injection pressure P1 and injection discharge Q1; b. Conduct a half-discharge injection test on the polymer-containing wastewater reinjection well to obtain the stable injection pressure P2 and injection discharge Q2; c. Perform backflow operation on the polymer-containing wastewater reinjection well to obtain the backflow volume Q. t The water discharge time t is used to determine the water discharge volume Q. t Calculate the discharge volume Q based on the discharge time t. t The ratio of the average water discharge rate to the water discharge time t is the average water discharge rate q0. d. Close the reinjection well for the polymer-containing wastewater to restore pressure and obtain the initial pressure P. wf The wellhead pressure data was acquired over time until the pressure stabilized; a pressure recovery curve was plotted based on the acquired wellhead pressure data over time. e. Based on the obtained pressure recovery curve, plot the data at the intersection of the straight line segment and the curved line segment of the pressure recovery curve using pressure and time points to obtain the pressure P at the intersection of the curved line segment and the straight line segment in the pressure recovery curve. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s ; f. Calculate the epidermal coefficient S based on the data obtained in steps c to e; Calculate the skin coefficient S in step f using formula 1 for pressure drop well test analysis: S = 1.1515 × {(P ws -P wf ) / m-[log(Kt s / φμC t r w 2 )+log(t / (t+t s ))+0.91]}(1) Where: m = 2.12 × 10 -3 ×q0×μ×B0 / KH (2) Where: μ—injected fluid viscosity, mPa·s K—Water permeability of the oil reservoir, μm 2 H—Perforation thickness, m r w —Wellbore radius, m φ—porosity, % C t —Comprehensive compression coefficient, MPa -1 B0—Volume index, m 3 / m3 t — time to expel water, h P wf —Initial pressure after well shut-in, MPa P ws —Pressure at the intersection of the curved segment and the straight segment in the pressure recovery curve, in MPa t s —The time (h) at the intersection of the curved segment and the straight segment in the pressure recovery curve. q0 — Average water discharge rate before well shut-in, m 3 / h S—Epidermal coefficient m — slope of the curve.

[0015] g. Based on the data obtained in steps a to e and the calculated skin coefficient S, calculate the water phase permeability value K of the contaminated zone. s and pollution radius r s .

[0016] Calculation steps: g - water phase permeability value K in the contaminated zone s and pollution radius r s The piecewise equation (3) and skin coefficient formula (4) for contaminated planar radial flow are as follows: (P2-P1) / (Q2-Q1)=μ / 2πKH×ln(r / r S )+μ / 2πK S H×ln(r) S / r w (3) S=(K / K S -1)×ln(r S / r w (4) By combining the piecewise equation (3) for the contaminated planar radial flow with the skin coefficient formula (4), the permeability value K of the water phase in the contaminated zone is calculated. s and pollution radius r s . Example

[0017] The specific steps for determining the pollution radius of polymer-containing wastewater reinjection wells using this invention are as follows: A method for determining the pollution radius of well L in a polymer-containing wastewater reinjection block of Daqing Oilfield. Well L is an under-injection well in Daqing Oilfield caused by the reinjection of polymer-containing wastewater. The perforation thickness H of the well is 23.8 meters, the porosity φ is 24%, and the water phase permeability K of the oil reservoir is 74.2 μm. 2 Before the measures were implemented, the water injection pressure was 12.8 MPa, and the injection displacement was 0.46 m³ / s. 3 / h, after adjustment, the stable injection pressure is 12.2MPa, and the injection displacement is 0.23m³ / h. 3 / h, reservoir overall compressibility coefficient C t 1.6×10 -3 MPa -1 The volume factor B of the injected water is 1m. 3 / m 3 The contamination radius of the well was determined according to the following steps: a. such as Figure 1 As shown, the current injection pressure P1 and injection discharge rate Q1 of the polymer-containing wastewater reinjection well are 12.8 MPa and 0.46 m³, respectively. 3 / h; b, such as Figure 1 As shown, a half-discharge test was conducted on the polymer-containing wastewater reinjection well, and the stable injection pressure P2 and injection discharge rate Q2 were recorded as 12.4 MPa and 0.23 m³ / h, respectively. 3 / h; c. For example Figure 2 As shown, a backflow operation was performed on the polymer-containing wastewater reinjection well, and the backflow volume Q was recorded. t With the water discharge time t, 12m 3 The average water discharge rate q0 (m) was calculated over 0.4 h. 3 / h); d. Shut down the well and restore pressure, such as Figure 3 As shown, record the initial pressure P. wf The pressure was set at 10.1 MPa, and wellhead pressure data were recorded over time until the pressure stabilized; a pressure recovery curve was then generated. e. Utilize the pressure recovery curve, such as Figure 3 As shown, pressure and time points are plotted on the data at the intersection of the straight line segment and the curved line segment to obtain the pressure P at the intersection of the curved line segment and the straight line segment in the pressure recovery curve. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s The values ​​were 12.0 MPa and 0.3 h, respectively.

[0018] The skin coefficient, contamination radius, and water phase permeability of the contaminated zone, S=4.05, were calculated using the following formula. s =4.2m, K s =27.4 * 10 -3 *μm 2 ; Joint formula: (1) m = 2.12 × 10 -3 ×q0×μ×B0 / KH (2) S = 1.1515 × {(P ws -P wf ) / m-[log(Kt s / φμC t r w2 )+log(t / (t+t s ))+0.91]} (3) (P2-P1) / (Q2-Q1)=μ / 2πKH×ln (r / r S )+μ / 2πK S H×ln(r) S / r w ) (4) S=(K / K S -1)×ln(r S / r w ) Combining the above formulas (1)-(4): The value of m in equation (1) can be obtained from the data obtained through testing; In equation (2), let the constant a = 1.1515 × {(P ws -P wf ), constant b = log(Kt) s / φμC t r w 2 )+log(t / (t+t s ))+0.91 The simplified equation (2) is: S = a / m + b In equation (2), S can be calculated from the data obtained through testing; In equation (3), let the constant be c = 2πHK[(P2-P1) / (Q2-Q1)] / μ The simplified equation (3) is: c = ln(r / r) S )+K / K S ×ln(r) S / r w ) With equation (4) S=(K / K S -1)×ln(r S / r w Solve the system of equations simultaneously; there are two unknowns, K. S、 r S K can be obtained from two equations. S、 r S value.

[0019] Continuing with the solution above: Simplified equation: Let K / K S =x,r S / r w =y, then r / r S = r w / r S * r / rw Let r / r w =d; The simplified equation (3) by substitution is: c = ln(d / y) + x * ln(y) Equation (4) is: S = (x-1) * ln(y) Substituting x from equation (4) into equation (3), we get: Equation (3): c=lnd-lny+((S+lny) / lny )*lny=lnd+S; This embodiment serves as an application example, yielding S and K. S、 r s The value is: S=4.05; K s =27.4 * 10 -3 * μm 2 ;r s =4.2m.

[0020] in: Inherent parameters of the formation: μ—viscosity of the injected fluid, mPa·s; K—Water permeability of the oil reservoir, μm 2 H—perforation thickness, m; r—Liquid supply radius, m; r w —Wellbore radius, m; φ—porosity, % C t —Comprehensive compression coefficient, MPa -1 ; B0—Volume index, m 3 / m 3 ; Test-obtained parameters: P1—Current injection pressure, MPa; P2—Stable injection pressure at half displacement, MPa; Q1—Current injection displacement, m 3 / h; Q2—Half the injection displacement, m 3 / h; Q t —Water discharge volume, m 3 ; t — time to expel water, h; P wf —Initial pressure after well shut-in, MPa; P ws —Pressure at the intersection of the curved segment and the straight segment in the pressure recovery curve, in MPa; t s —The time (h) at the intersection of the curved segment and the straight segment in the pressure recovery curve; q0 — Average water discharge rate before well shut-in, m 3 / h; In the above method, steps a, b, and c involve equipment including pump trucks, tank trucks, pipelines, and flow meters, requiring the flow meters to have an accuracy higher than 0.01m. 3 Step d involves a digital electronic pressure gauge with an accuracy higher than 0.01 MPa. In this embodiment, on-site testing requires only one pump truck and one tanker truck, with a construction period of 0.5 days. The pollution radius calculation is completed on the same day, significantly improving efficiency. This invention adopts a stationary tubing method, requiring only 2,000 yuan for single-well testing, resulting in low construction costs and the potential for large-scale application.

Claims

1. A method for determining the pollution radius of a polymer-containing wastewater reinjection well, characterized in that: a. For the polymer-containing wastewater reinjection well, obtain the current injection pressure P1 and injection discharge Q1; b. Conduct a half-discharge injection test on the polymer-containing wastewater reinjection well to obtain the stable injection pressure P2 and injection discharge Q2; c. Perform backflow operation on the polymer-containing wastewater reinjection well to obtain the backflow volume Q. t The water discharge time t is used to determine the water discharge volume Q. t The average water discharge rate is obtained by considering the water discharge time t. d. Close the reinjection well for the polymer-containing wastewater to restore pressure and obtain the initial pressure P. wf The wellhead pressure data is acquired over time until the pressure stabilizes; a pressure recovery curve is plotted based on the acquired wellhead pressure data over time. e. Based on the obtained pressure recovery curve, plot the data at the intersection of the straight line segment and the curved line segment of the pressure recovery curve using pressure and time points to obtain the pressure P at the intersection of the curved line segment and the straight line segment in the pressure recovery curve. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s ; f. Calculate the epidermal coefficient S based on the data obtained in steps c to e; g. Based on the data obtained in steps a to e and the calculated skin coefficient S, calculate the water phase permeability value K of the contaminated zone. s and pollution radius r s ; The skin coefficient S in step f is calculated using the pressure drop well test analysis formula (1): S=1.1515×{(P ws -P wf ) / m-[log(Kt s / φμC t r w 2 )+log(t / (t+t s ))+0.91]}(1) Where: m = 2.12 × 10 -3 ×q0×μ×B0 / KH (2) Where: μ—injected fluid viscosity, mPa·s; K—Water permeability of the oil reservoir, μm 2 ; H—perforation thickness, m; r w — Wellhead radius, m; φ—porosity, % C t —Comprehensive compression coefficient, MPa -1 ; B0—Volume index, m 3 / m 3 ; t — time to expel water, h; P wf —Initial pressure after well shut-in, MPa; P ws —Pressure at the intersection of the curved segment and the straight segment in the pressure recovery curve, in MPa; t s —The time (h) at the intersection of the curved segment and the straight segment in the pressure recovery curve; q0 — Average water discharge rate before well shut-in, m 3 / h; S—epidermal coefficient; m—slope of the curve; Calculation steps: g - water phase permeability value K in the contaminated zone s and pollution radius r s : Adopting the piecewise equation of contaminated planar radial flow (3): (P2-P1) / (Q2-Q1)=μ / 2πKH×ln(r / r S )+μ / 2πK S H×ln(r S / r w ) (3) In the formula: P1—Current injection pressure, MPa; P2—Stable injection pressure at half displacement, MPa; Q1—Current injection displacement, m 3 / h; Q2—Half the injection displacement, m 3 / h; Ks—Average water permeability of the contaminated zone in the oil reservoir, in μm 2 ; r—Liquid supply radius, m; r s —Pollution radius, m; r w — Wellhead radius, m; Calculation steps: g - water phase permeability value K in the contaminated zone s and pollution radius r s : Using the epidermal coefficient formula (4): S=(K / K S -1)×ln(r S / r w )…(4); Combine the piecewise equation (3) for the contaminated planar radial flow with the skin coefficient formula (4) to calculate the permeability value K of the water phase in the contaminated zone. s and pollution radius r s .

2. The method for determining the pollution radius of a polymer-containing wastewater reinjection well according to claim 1, characterized in that: Step c: Calculation method for average water discharge rate q0: Water discharge volume Q t The ratio of the average water discharge rate to the discharge time t is the average water discharge rate q. 0。 3. The method for determining the pollution radius of a polymer-containing wastewater reinjection well according to claim 1, characterized in that: Based on the obtained pressure recovery curve, obtain the pressure P at the intersection point of the curve segment and the straight line segment in the pressure recovery curve. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s The methods include: The pressure recovery curve includes a curved segment at the beginning and a straight segment at the end. By plotting the data at the intersection of the straight and curved segments of the pressure recovery curve, pressure and time points are obtained, and the pressure P at the intersection of the curved and straight segments of the pressure recovery curve is acquired. ws The time t at the intersection of the curved segment and the straight segment in the pressure recovery curve s。

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