CN-122021261-A - Numerical simulation method for flowback of front fracturing stuffy well in consideration of reservoir damage

CN122021261ACN 122021261 ACN122021261 ACN 122021261ACN-122021261-A

Abstract

The invention discloses a numerical simulation method for flowback of a pre-fracturing stuffy well considering reservoir damage, and belongs to the technical field of reservoir reconstruction in petroleum development. The method comprises the steps of obtaining initial parameters of a target oil reservoir, carrying out fracturing fracture expansion simulation, constructing an embedded discrete fracture grid based on fracture morphology obtained through simulation, determining a functional relation between a reservoir damage coefficient and water saturation according to experimental results, establishing a reservoir parameter dynamic calculation model, constructing a mass conservation equation and carrying out differential dispersion to obtain a numerical discrete solution model, carrying out iterative solution on the model, dynamically updating reservoir physical parameters at each time step, and finally obtaining a pressure field, a saturation field and crude oil yield prediction in the whole fracturing process. The method solves the problem that the conventional numerical simulation cannot dynamically reflect the damage to the reservoir caused by the invasion of the fracturing fluid, realizes the accurate simulation of the full-cycle process of pre-fracturing-well-flowback, and provides a reliable tool for fracturing optimization and productivity prediction.

Inventors

LI LEI
Hou Zihan
SU YULIANG
DU SHUJIE
WU XUELING
CHEN YUETONG
HU YICHEN

Assignees

中国石油大学(华东)

Dates

Publication Date: 20260512
Application Date: 20260105

Claims (7)

1. A numerical simulation method for flowback of a pre-fracturing stuffy well considering reservoir damage is characterized by comprising the following steps: S1, acquiring initial parameters of a target oil reservoir, performing fracturing fracture expansion simulation, and constructing an embedded discrete fracture grid based on fracture morphology obtained by simulation; S2, determining a functional relation description equation between a reservoir damage coefficient and reservoir water saturation based on experimental results of a reservoir damage rule; S3, establishing a reservoir parameter dynamic calculation model considering a reservoir injury mechanism based on the reservoir injury coefficient, wherein the dynamic calculation model at least comprises a permeability calculation model for dynamically correcting the reservoir permeability; S4, constructing a mass conservation equation of the reservoir fluid according to the reservoir parameter dynamic calculation model, and carrying out differential discretization on the mass conservation equation to obtain a numerical discrete solving model; And S5, carrying out iterative solution on the numerical discrete solution model based on initial physical parameters, solving to obtain a pressure field and a saturation field of the reservoir at the current moment in each time step, updating the reservoir damage coefficient according to the functional relation in S2 by utilizing the saturation field at the current moment, dynamically correcting the physical parameters of the reservoir at the next time step by using the dynamic calculation model in S3, and calculating the crude oil yield of the reservoir based on the pressure field and the saturation field obtained by iterative solution.
2. The numerical simulation method for flowback of pre-fracturing vaulting well taking reservoir damage into consideration as claimed in claim 1, wherein in S2, the reservoir damage coefficient is as follows Saturation with reservoir water The functional relation description equation between them is: where a and b are coefficients obtained based on regression of experimental data.
3. The numerical simulation method for flowback of a pre-fracturing stuffy well taking reservoir damage into consideration as set forth in claim 1, wherein in S3, the permeability calculation model is: , wherein, Represents the fracture permeability at the current time, The fracture permeability at the previous time is indicated, Representing the reservoir damage coefficient at the current time.
4. The method for modeling a flowback of a pre-fractured tight well taking into account reservoir damage according to claim 1, wherein in S3, the reservoir parameter dynamic calculation model further comprises a capillary force correction model, and the expression is as follows: , wherein, For the current capillary force, For an initial maximum capillary force, In order to tie up the water saturation, For the current water saturation level, Is a dimensionless parameter of pore size distribution.
5. The numerical simulation method for flowback of a pre-fracturing stuffy well taking reservoir damage into consideration as set forth in claim 1, wherein in S4, the reservoir fluid is an oil-water two-phase fluid, and the constructed oil phase mass conservation equation is as follows: ; the constructed conservation equation of water phase mass is: ; Wherein, the In order to achieve a degree of porosity, the porous material, 、 The water volume coefficients are respectively the oil volume coefficient, 、 Respectively the water and the oil are respectively used for sealing, 、 The saturation of oil and water respectively, 、 The permeability of oil and water is respectively that of water, 、 The viscosity of the oil and the water are respectively, 、 The pressure of the oil and the water phase are respectively, For the force of the capillary tube, 、 The source sink items of the oil and water phases respectively, ∇ represent gradient operators.
6. The method for simulating the flowback of the pre-fracturing stuffy well taking reservoir damage into consideration as recited in claim 1, wherein in S1, the initial parameters comprise a geological model, a well track, a fracturing construction design parameter, reservoir initial physical parameters and fluid data, and the fracturing fracture expansion simulation is performed based on the geomechanical model and a fracturing program to obtain fracture parameters including fracture geometry and flow conductivity spatial distribution.
7. The numerical simulation method for flowback of pre-fracturing well in consideration of reservoir damage according to claim 1, wherein the method is specifically applied to simulation of a CO2 pre-fracturing-well-flowback process for predicting CO2 sweep range, reservoir pressure field evolution and crude oil viscosity change in the process.

Description

Numerical simulation method for flowback of front fracturing stuffy well in consideration of reservoir damage Technical Field The invention belongs to the technical field of reservoir transformation in petroleum development, and particularly relates to a numerical simulation method for flowback of a pre-fracturing stuffy well in consideration of reservoir damage. Background Efficient development of unconventional reservoirs such as tight reservoirs is highly dependent on hydraulic fracturing techniques. The process typically includes three stages of pre-fluid (possibly containing CO2, active water, etc.) injection, shut-in, and open-well flowback. Fracturing fluids (including pad fluids) invade the reservoir matrix under high pressure, on the one hand, displacing crude oil by imbibition and on the other hand, also cause damage to the reservoir by physical and chemical actions such as water lock, solid phase invasion, clay swelling, etc., resulting in significant permeability decline. Studies have shown that reservoir damage caused by fracturing fluid invasion can reduce permeability by 30% -50%, with the dramatic increase in capillary resistance caused by the water lock effect being the core mechanism. In the micro-nano pore throat of a tight reservoir, capillary force can reach megapascal level, and crude oil flow is seriously hindered. At present, numerical simulation research on the whole fracturing process has obvious defects. Conventional black oil models or component models generally consider reservoir physical parameters (such as permeability, capillary force) as static constants and cannot characterize the parameter time-varying effects caused by fracturing fluid loss, imbibition and damage. While the advanced discrete fracture model can finely describe a complex fracture network, the properties of the fracture and the matrix are also statically assigned, and the dynamic evolution rule of the physical properties of the matrix-fracture system caused by fluid interaction in different stages of fracturing injection, well closing and flowback is ignored. The static assumption causes deviation between the simulation result and the actual production dynamic, and the accurate pre-measurement of the post-pressure productivity and the optimization of the flowback system are difficult. In the prior art, part of research focuses on prediction of fracturing fluid loss or fracture propagation simulation, for example, some patent documents disclose fluid loss analysis methods based on embedded discrete fracture models or flowback design methods considering imbibition. However, these methods are either used only for process parameter optimization or fail to quantify the dynamic damage effects of fracturing fluid invasion on reservoir properties and couple into full-cycle seepage simulation, lacking a solution to deeply fuse experimentally obtained damage laws with full-flow numerical simulation. Therefore, there is a need to develop a novel numerical simulation method, which can embed a reservoir damage mechanism represented in a laboratory into a whole process numerical simulation from fracturing to flowback in a dynamic and quantifiable manner, so as to more truly reflect reservoir physical property changes and realize accurate productivity prediction and process optimization. Disclosure of Invention Aiming at the defects of the prior art, the invention aims to solve the key technical problem that the physical parameters (such as permeability and capillary force) of the reservoir caused by the invasion of the fracturing fluid cannot be reflected dynamically in the whole process of fracturing simulation by the traditional numerical simulation method. The invention provides a numerical simulation method for flowback of a pre-fracturing closed well considering reservoir damage, which can comprehensively consider seepage and suction and reservoir damage mechanisms at different stages of fracturing injection-well-closing-flowback, realize high-precision numerical simulation of the whole period of reservoir fracturing and accurately describe the influence of dynamic change of reservoir physical properties on fluid distribution and final yield in a fracture network. In order to achieve the above purpose, the present invention adopts the following technical scheme: A numerical simulation method for flowback of a pre-fracturing stuffy well considering reservoir damage comprises the following steps: S1, acquiring initial parameters of a target oil reservoir, performing fracturing fracture expansion simulation, and constructing an embedded discrete fracture grid based on fracture morphology obtained by simulation; S2, determining a functional relation description equation between a reservoir damage coefficient and reservoir water saturation based on experimental results of a reservoir damage rule; S3, establishing a reservoir parameter dynamic calculation model considering a reservoir injury mechanism based on the reservoi