Ultra-low permeability reservoir water drive front edge calculation method
By establishing a flow splitting equation and similar principle conversion that considers capillary force and start-up pressure gradient, combined with the Berkeley equation, the problem of low prediction accuracy of water-drive leading edge velocity in ultra-low permeability reservoirs is solved, and fast and accurate water-drive front Fraction position prediction provides theoretical support for water injection development.
Patent Information
- Application Number
- CN202411347779.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-26
- Publication Date
- 2024-12-31
AI Technical Summary
Traditional methods fail to consider capillary force and starting pressure gradient when determining the water-driving leading edge velocity of ultra-low permeability reservoirs, resulting in low prediction accuracy and the use of tracer monitoring methods has the disadvantage of high testing costs and long cycles.
Establish a flow split equation that considers capillary force and start-up pressure gradient, use the J function obtained from the mercury impression experiment to invert the capillary force and water saturation correlation function, combine the results of the phase permeation experiment, convert the capillary pressure through similar principles, and combine it with the Berkeley equation , calculate the saturation of the leading edge of the water drive and the water phase flow rate.
It realizes rapid prediction of the advancement position of the water-drive leading edge, provides theoretical methods for adjusting water injection development technical policies, improves prediction accuracy and reduces costs.
Smart Images
Figure CN119226669A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of oil and gas field development and relates to a new method for calculating the water drive front of an ultra-low permeability oil reservoir. Background Art
[0002] Water flooding is the most important technical means to supplement formation energy and improve oilfield recovery in ultra-low permeability reservoirs. Mastering the water injection dynamics and clarifying the water flooding front velocity are of great significance for guiding the optimization of water injection parameters and adjusting development plans. Ultra-low permeability reservoirs have small pore throats, a starting pressure gradient, and strong capillary forces. The traditional theoretical method of determining the water flooding front velocity does not consider the effects of capillary forces and starting pressure gradients, and the prediction accuracy is low; the method of using tracer monitoring to determine the water flooding front velocity faces the disadvantages of high testing costs and long cycles;
[0003] Therefore, it is urgent to establish a new method for calculating the water flooding front of ultra-low permeability reservoirs. The present invention establishes a partial flow equation considering capillary force and starting pressure gradient, uses the J function obtained by mercury injection experiment, inverts the capillary force and water saturation related function, realizes the conversion of capillary pressure under reservoir conditions according to the similarity principle, calculates the partial flow equation considering capillary force in combination with the phase permeability experiment results, determines the saturation of the water flooding front considering capillary force and starting pressure gradient, and establishes a new method for calculating the water flooding front of ultra-low permeability reservoirs in combination with the Berkeley equation. Summary of the invention
[0004] The present invention aims to solve the above problems. By establishing a partial flow equation considering capillary force and starting pressure gradient, the J function obtained by mercury injection experiment is used to invert the capillary force and water saturation correlation function. According to the similarity principle, the conversion of capillary pressure under reservoir conditions is realized. Combined with the results of phase permeability experiment, the partial flow equation considering capillary force is calculated, the saturation of water drive front considering capillary force and starting pressure gradient is determined, and combined with the Berkeley equation, a new water drive front calculation method for ultra-low permeability reservoirs is established.
[0005] The technical solution of the present invention is: A method for calculating the water flooding front of an ultra-low permeability reservoir is as follows: Step 1: Establish the flow equation considering capillary force and starting pressure gradient; Step 2: Obtain the J function of the reservoir to be tested, invert the capillary force under mercury injection conditions, convert it into the capillary force under reservoir conditions, substitute it into the fractional flow equation considering the capillary force and the starting pressure gradient, and then obtain the water phase fractional flow considering the capillary force and the starting pressure gradient; Step 3: Calculate the water phase fraction flow rate taking into account the capillary force and the starting pressure gradient, and determine the saturation at the water flooding front and the partial derivative of the water phase fraction flow rate at the water flooding front; Step 4: Combine the Berkeley-Levert equation to determine the water flooding front at different times.
[0006] The specific process of step 1 is as follows: According to the oil-water two-phase motion equation, the flow rate equation considering capillary force is established: The equation of motion for the oil phase is: (1) Where: is the oil phase flow rate, in m 3 / s; is the absolute permeability, in mD; is the relative permeability of the oil phase, dimensionless; is the viscosity of the oil phase, in mPa.s; is the oil phase pressure, in MPa; is the fluid seepage distance, in m; is the oil phase starting pressure gradient, in MPa / m; The equation of motion for the water phase is: (2) Where: is the water phase flow rate, in m 3 / s; is the relative permeability of water phase, dimensionless; is the viscosity of the water phase, in mPa.s; is the water phase pressure, in MPa; is the water phase starting pressure gradient, in MPa / m; According to the definition of capillary force, we get: (3) Where: is the capillary force, the unit is MPa; Formula (1) combined with formula (3) yields: (4) The total fluid flow rate is: (5) Where: is the total flow rate of the fluid, in m 3 / s; The water phase fraction flow rate in the fluid and the oil phase fraction flow rate in the fluid are: ; ; (6) Where: is the fractional flow rate of water phase in the fluid, dimensionless; is the oil phase fraction flow rate in the fluid, dimensionless; Combining equations (1), (2), (3) and (6), we get: (7) Combination , transforming formula (7) into: (8) Formula (8) is transformed into: (9) Where: is the water saturation, dimensionless.
[0007] The specific process of step 2 is as follows: The capillary force under mercury injection condition is obtained by inverting the J function of the measured reservoir : (10) Where: is the capillary force under mercury injection conditions, in MPa; is the J function of the reservoir to be measured, dimensionless; is the gas-mercury interfacial tension, in N / m; is the wetting angle under mercury intrusion conditions, in degrees; is the porosity, dimensionless; is the bound water saturation, dimensionless; , b is a constant coefficient, dimensionless; obtained by fitting the J function of the reservoir to be measured; According to the principle of similarity transformation, the capillary force under mercury injection condition is Converted to reservoir condition capillary force: (11) Where: is the capillary force under reservoir conditions, in MPa; is the oil-water interfacial tension, in N / m; is the reservoir condition wetting angle, in degrees; Substituting equation (11) into equation (9), we can obtain the water phase fraction flow rate considering the capillary force and the starting pressure gradient: (12) Where: It is the water phase fraction flow rate that takes into account the capillary force and the starting pressure gradient, and is dimensionless.
[0008] The specific process of step 3 is as follows: Over bound water saturation Water phase fractional flow rate considering capillary force and starting pressure gradient along a point Draw a tangent line to obtain the water flooding front saturation considering the capillary force and the starting pressure gradient and the partial derivative of the water phase fractional flow rate at the water flooding front considering the capillary force and the starting pressure gradient .
[0009] The specific process of step 4 is as follows: (13) Where: is the distance from the center of the injection well to the water drive front, in meters; is the daily water injection volume, in m 3 / d; is the water injection time, in d; is the oil layer thickness, in m; is the wellbore radius, m.
[0010] The J function of the oil reservoir to be tested is obtained through mercury injection experiment.
[0011] The technical effects of the present invention are: The invention establishes a fractional flow equation considering the capillary force and the starting pressure gradient, utilizes the J function of the oil reservoir to be measured, inverts the capillary force under mercury injection conditions, converts the capillary force under mercury injection conditions into the capillary force under reservoir conditions according to the similarity conversion principle, and then obtains the water phase fractional flow considering the capillary force and the starting pressure gradient, calculates the water drive front saturation and the partial derivative of the water phase fractional flow at the water drive front; combines with the Berkeley-Levert equation, determines the water drive front at different times; the invention can quickly predict the advancing position of the water drive front, and provides a theoretical method for adjusting the technical policy of water injection development. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 It is the J function of the oil reservoir to be tested in the specific experimental example of the present invention.
[0013] Figure 2 It is the phase permeability curve of the specific experimental example of the present invention.
[0014] Figure 3It is the water phase fraction flow rate without considering the capillary force and the starting pressure gradient in the specific experimental examples of the present invention and the water phase fraction flow rate considering the capillary force and the starting pressure gradient.
[0015] Figure 4 The different water injection times of the specific experimental examples of the present invention The curve of the front position of the lower water flooding changing with the injection volume. DETAILED DESCRIPTION
[0016] A method for calculating the water flooding front of an ultra-low permeability reservoir is as follows: Step 1: Process the data of coring and mercury injection experiments in the block to obtain the J function of the reservoir to be tested and fit it to get the constant term and b ; Then we can obtain the capillary force under mercury injection condition ; Step 2: Obtain relevant parameters of the reservoir to be tested through the phase permeability curve, and then obtain the water phase fraction flow rate considering the capillary force and the starting pressure gradient; Step 3: Over-Imposed Water Saturation Draw a tangent line along the water phase fraction flow considering the capillary force and the starting pressure gradient to obtain the water flooding front saturation considering the capillary force and the starting pressure gradient. , and the partial derivative of the water phase fractional flow rate at the water flooding front considering the capillary force and the starting pressure gradient ; Step 4: According to formula (13), plot the curve of the water flooding front position versus injection volume at different injection times t.
[0017] Specific experimental example: Chang 6 reservoir in Ordos Basin
[0018] The Chang 6 oil layer in the Ordos Basin is a typical ultra-low permeability oil reservoir. Taking the Chang 6 reservoir in the Huaziping block of Xingzichuan as an example, the specific method of determining the water drive front by using the present invention is specifically described.
[0019] A method for calculating the water flooding front of an ultra-low permeability reservoir is as follows: Step 1: Data processing is performed on the coring and mercury injection test data of the block to obtain the J function of the oil layer, see Figure 1 ; Fit the constant term =0.5514, b =1.6628; then the capillary force under mercury injection condition It is expressed as: ; Step 2: The phase permeability characteristic curve of the study area is shown in Figure 2 ; Immune water saturation is 0.34; oil-water interfacial tension The interfacial tension between air and mercury is 0.025N / m. The wetting angle under mercury intrusion conditions is 0.48N / m. The wetting angle is 160°, the reservoir condition The oil phase viscosity is 30° 2.5mPa.s; water phase viscosity 1 mPa.s; oil phase starting pressure gradient 0.198MPa / m; water phase starting pressure gradient is 0.333MPa / m; when the seepage is stable, the outlet end velocity is equal to the injection velocity. 0.00012m / s; The water phase flow rates without considering the capillary force and the starting pressure gradient and considering the capillary force and the starting pressure gradient are plotted respectively. Figure 3 ; Step 3: Over-Imposed Water Saturation The water phase fraction flow rate without considering the capillary force and the starting pressure gradient is drawn as a tangent line to obtain the water flooding front saturation without considering the capillary force and the starting pressure gradient. , and the partial derivative of the water phase fractional flow rate at the water flooding front without considering the capillary force and the starting pressure gradient ; Over bound water saturation Draw a tangent line along the water phase fraction flow considering the capillary force and the starting pressure gradient to obtain the water flooding front saturation considering the capillary force and the starting pressure gradient. , and the partial derivative of the water phase fractional flow rate at the water flooding front considering the capillary force and the starting pressure gradient ; Depend on Figure 3 It can be seen that the water flooding front saturation without considering the capillary force and the starting pressure gradient Water flooding front saturation considering capillary force and starting pressure gradient is basically equal, about 0.542; then the partial derivative of the water phase fraction flow rate at the water flooding front without considering the capillary force and the starting pressure gradient is obtained is about 3.24, considering the capillary force and the starting pressure gradient, the partial derivative of the water phase fractional flow at the water flooding front About 3.65; Step 4: According to formula (13), the daily injection volume 20m 3 / d, cumulative injection volume 4000 m 3 , oil layer thickness 4m, porosity is 0.106; plot different water injection times The curve of the front position of the lower water flooding changing with the injection volume is shown in Figure 4 It can be seen that in water-wet reservoirs, considering the influence of capillary force and starting pressure gradient, the water drive front is located farther and the water drive advancement speed is faster.
Claims
1. A method for calculating the water flooding front in an ultra-low permeability reservoir, characterized in that: Here’s how: Step 1: Establish the flow equation considering capillary force and starting pressure gradient; Step 2: Obtain the J function of the reservoir to be tested, invert the capillary force under mercury injection conditions, convert it into the capillary force under reservoir conditions, substitute it into the fractional flow equation considering the capillary force and the starting pressure gradient, and then obtain the water phase fractional flow considering the capillary force and the starting pressure gradient; Step 3: Calculate the water phase fraction flow rate taking into account the capillary force and the starting pressure gradient, and determine the saturation at the water flooding front and the partial derivative of the water phase fraction flow rate at the water flooding front; Step 4: Combine the Berkeley-Levert equation to determine the water flooding front at different times.
2. The method for calculating the water flooding front of an ultra-low permeability reservoir according to claim 1, characterized in that: The specific process of step 1 is as follows: According to the oil-water two-phase motion equation, the flow distribution equation considering capillary force is established: The equation of motion for the oil phase is: （1） Where: is the oil phase flow rate, in m 3 / s; is the absolute permeability, in mD; is the relative permeability of the oil phase, dimensionless; is the viscosity of the oil phase, in mPa.s; is the oil phase pressure, in MPa; is the fluid seepage distance, in m; is the oil phase starting pressure gradient, in MPa / m; The equation of motion for the water phase is: （2） Where: is the water phase flow rate, in m 3 / s; is the relative permeability of water phase, dimensionless; is the viscosity of the water phase, in mPa.s; is the water phase pressure, in MPa; is the water phase starting pressure gradient, in MPa / m; According to the definition of capillary force, we get: （3） Where: is the capillary force, the unit is MPa; Formula (1) combined with formula (3) yields: （4） The total fluid flow rate is: （5） Where: is the total flow rate of the fluid, in m 3 / s; The water phase fraction flow rate in the fluid and the oil phase fraction flow rate in the fluid are: ； ；（6） Where: is the fractional flow rate of water phase in the fluid, dimensionless; is the oil phase fraction flow rate in the fluid, dimensionless; Combining equations (1), (2), (3) and (6), we get: （7） Combination , transforming formula (7) into: （8） Formula (8) is transformed into: （9） Where: is the water saturation, dimensionless.
3. The method for calculating the water flooding front of an ultra-low permeability reservoir according to claim 2, characterized in that: The specific process of step 2 is: The capillary force under mercury injection condition is obtained by inverting the J function of the measured reservoir : （10） Where: is the capillary force under mercury injection conditions, in MPa; is the J function of the reservoir to be measured, dimensionless; is the gas-mercury interfacial tension, in N / m; is the wetting angle under mercury intrusion conditions, in degrees; is the porosity, dimensionless; is the bound water saturation, dimensionless; , b is a constant coefficient, dimensionless; It is obtained by fitting the J function of the reservoir to be tested; According to the principle of similarity transformation, the capillary force under mercury injection condition is Converted to reservoir condition capillary force: （11） Where: is the capillary force under reservoir conditions, in MPa; is the oil-water interfacial tension, in N / m; is the reservoir condition wetting angle, in degrees; Substituting equation (11) into equation (9), we can obtain the water phase fraction flow rate considering the capillary force and the starting pressure gradient: （12） Where: It is the water phase fraction flow rate that takes into account the capillary force and the starting pressure gradient, and is dimensionless.
4. The method for calculating the water flooding front of an ultra-low permeability reservoir according to claim 3, characterized in that: The specific process of step 3 is as follows: Over bound water saturation Water phase fractional flow rate considering capillary force and starting pressure gradient along a point Draw a tangent line to obtain the water flooding front saturation considering the capillary force and the starting pressure gradient and the partial derivative of the water phase fractional flow rate at the water flooding front considering the capillary force and the starting pressure gradient .
5. The method for calculating the water flooding front of an ultra-low permeability reservoir according to claim 4, characterized in that: The specific process of step 4 is as follows: （13） Where: is the distance from the center of the injection well to the water drive front, in meters; is the daily water injection volume, in m 3 / d; is the water injection time, in d; is the oil layer thickness, in m; is the wellbore radius, m.
6. The method for calculating the water flooding front of an ultra-low permeability reservoir according to claim 1, characterized in that: The J function of the oil reservoir to be tested is obtained through mercury injection experiment.