CN-121413512-B - Unconventional reservoir CO2Intelligent prediction method for phase-mixing drive front edge migration

Abstract

The invention relates to an intelligent prediction method for CO 2 miscible-phase flooding front edge migration of an unconventional reservoir, which comprises the steps of constructing a CO 2 miscible-phase flooding front edge migration prediction dataset considering unconventional reservoir types, constructing a CO 2 mass transportation equation considering injection-production relations, stress sensitivity and starting pressure gradients based on source assembly unit characterization of dynamic injection-production relations, constructing a convection diffusion equation considering CO 2 -rock adsorption effects, constructing a CO 2 miscible-phase flooding front edge migration prediction model, defining a CO 2 miscible-phase flooding front edge based on the prediction model, introducing a pel optimization algorithm to perform fitting optimization on permeability, starting pressure gradients and Langmuir adsorption constants, dynamically optimizing the CO 2 miscible-phase flooding front edge migration prediction model, and realizing intelligent prediction of CO 2 miscible-phase flooding front edge migration. The method can quantitatively and scientifically realize the prediction of the front edge migration in the process of improving the recovery ratio of CO 2 mixed phase flooding.

Inventors

• SHI BOWEN
• ZHONG HUIYING
• MENG FANXIN
• Cao Xiutai
• SUN YUXIN
• LIU HAOQUAN
• SUN JIANZHI

Assignees

• 东北石油大学

Dates

Publication Date

20260508

Application Date

20251219

Claims (7)

1. 1. An intelligent prediction method for the mixed phase drive front edge migration of an unconventional reservoir CO 2 is characterized by comprising the following steps: Step one, constructing a CO 2 miscible flooding front edge migration prediction data set considering unconventional reservoir types; step two, a source assembly unit representation based on a dynamic injection-production relation is used for establishing a CO 2 mass transport equation considering the injection-production relation, stress sensitivity and starting pressure gradient: ; Wherein C m is a mixture compression coefficient, ρ m is a mixture density, ρ g is a CO 2 density, q out is a mixture production rate, x is a displacement distance, t is a displacement time, μ m is a mixture viscosity, k is an absolute permeability, C r is a rock compression coefficient, G is a starting pressure gradient of an unconventional reservoir, p is a reservoir pore pressure, and q in is a CO 2 injection rate; Is porosity; Step three, constructing a convection diffusion equation considering the CO 2 -rock adsorption effect; ; Wherein v g is the seepage speed of CO 2 , and q gout is the extraction speed of CO 2 ; Step four, constructing a CO 2 miscible displacement front migration prediction model, and defining a CO 2 miscible displacement front based on the prediction model, wherein the CO 2 miscible displacement front is regarded as a miscible front when the concentration of dimensionless CO 2 is 0.05; ; Wherein θ is the formation dip angle, C is the concentration of CO 2 , D is the diffusion coefficient of CO 2 , ρ r is the rock density, S max is the maximum adsorption capacity of CO 2 , b is the Langmuir adsorption constant, and k (x, y) is the absolute permeability of the reservoir in the xy direction; And fifthly, introducing a pelican optimization algorithm to perform fitting optimization on the permeability, the starting pressure gradient and the Langmuir adsorption constant, dynamically optimizing a CO 2 miscible-phase drive front edge migration prediction model, and realizing intelligent prediction of CO 2 miscible-phase drive front edge migration.
2. 2. The method for intelligently predicting the CO 2 miscible-phase flooding front edge of the unconventional reservoir according to claim 1 is characterized by comprising the following steps of designing and testing the CO 2 miscible-phase flooding front edge migration characteristics of different types of unconventional reservoir cores based on a CO 2 miscible-phase flooding experiment, constructing a CO 2 miscible-phase flooding front edge migration prediction dataset considering the unconventional reservoir types, and randomly dividing the dataset into a training set, a validation set and a test set in a ratio of 8:1:1 by adopting a leave-out method, wherein the injection speed of the CO 2 miscible-phase flooding experiment is 0.05-3.0 mL/min.
3. 3. The method for intelligently predicting the mixed phase flooding front edge migration of the unconventional reservoir CO 2 according to claim 2, wherein the step two is specifically as follows: Assuming that the CO 2 is completely miscible with crude oil after being injected into the stratum, and the mixture is regarded as a single fluid, respectively introducing a CO 2 injection source term and a mixture extraction sink term, and establishing a CO 2 mass transport equation considering injection-extraction coupling effect: (1) wherein v m is the mixture flow rate; in the fully miscible state, the mixture viscosity was determined using a logarithmic mixing method: (2) wherein mu m is the viscosity of the mixture, x CO2 is the mole fraction of CO 2 in the mixture, mu g is the viscosity of pure CO 2 under the conditions of reservoir temperature and pressure, and mu o is the viscosity of crude oil under the conditions of reservoir temperature and pressure; the miscible density was determined by volume weighted averaging: (3) Wherein m is molar mass, V is molar volume, m g is molar mass of CO 2 , m o is molar mass of crude oil, V g is molar volume of CO 2 under the conditions of reservoir temperature and pressure, and V o is molar volume of crude oil under the conditions of reservoir temperature and pressure; Establishing a mixture seepage equation based on Darcy's law: (4) Wherein p is reservoir pore pressure; In oilfield production dynamics, the essential condition of unconventional crude oil for reservoir stripping is to overcome the initiation pressure gradient, which is introduced into the percolation equation: (5) In actual production, reservoir rock pores have weak compressibility, and a state equation of porosity with pressure is expressed as: (6) Wherein: P 0 is the initial pore pressure; substituting the formula (5) and the formula (6) into the formula (1) to obtain a CO 2 mass transport equation considering injection-production relation, stress sensitivity and starting pressure gradient.
4. 4. The method for intelligently predicting the mixed phase flooding front edge migration of the unconventional reservoir CO 2 according to claim 3, wherein the third step is as follows: In the CO 2 miscible flooding enhanced recovery process, the heterogeneity of reservoir pore structure and mineral composition, wettability distribution together affect the microscopic migration path of CO 2 , which also involves CO 2 -rock adsorption effects, unbalanced diffusion and convective diffusion behavior, therefore, the convective diffusion process of CO 2 in unconventional reservoir porous media is described as: (8) in the actual CO 2 miscible flooding process, the physical adsorption effect of CO 2 and rock is also involved, and an adsorption item is introduced to realize the representation of a complex flow mechanism: (9) Wherein S is the adsorption quantity of CO 2 ; Wherein, the CO 2 adsorption amount is determined according to a Langmuir adsorption model: (10) substituting equation (10) into equation (9) yields a convective diffusion equation that takes into account the CO 2 -rock adsorption effect.
5. 5. The method for intelligently predicting the mixed phase flooding front edge migration of the unconventional reservoir CO 2 according to claim 4, wherein the step four is specifically as follows: And step two, combining with the step three, realizing the description of the forward edge migration law of the CO 2 miscible flooding under the multi-factor coupling effect, and constructing a corresponding prediction model: (12) For unconventional reservoirs, the reservoir is not pure water due to the influence of the earth crust movement, a stratum dip angle exists, the size of the stratum dip angle directly influences the migration path and migration speed of oil gas, the oil gas is easier to migrate along the direction with larger dip angle, and the stratum dip angle is introduced in the formula (12) to obtain the CO 2 miscible phase flooding front edge migration prediction model.
6. 6. The method for intelligently predicting the mixed phase drive front edge migration of the unconventional reservoir CO 2 , which is characterized in that the stratum inclination angle is 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees and 45 degrees.
7. 7. The method for intelligently predicting the mixed phase driving front edge migration of the CO 2 in the unconventional reservoir according to claim 6, wherein the diffusion coefficient of the CO 2 in crude oil is 2.5 multiplied by 10 -6 ~3.0×10 -4 cm 2 /s.

Description

Unconventional reservoir CO 2 miscible flooding front edge migration intelligent prediction method Technical Field The invention relates to a CO 2 mixed phase driving technology in unconventional oil reservoir development, in particular to an intelligent prediction method for the CO 2 mixed phase driving front edge migration of an unconventional oil reservoir. Background The oil gas resource is used as a national strategic energy prop, and is provided with the dual tasks of guaranteeing energy safety and promoting carbon emission reduction. The CO 2 miscible flooding technology is used as an important component of a carbon capturing, utilizing and sealing (CCUS) system, has dual functions of improving the recovery ratio of crude oil and sealing CO 2, and becomes one of key technologies for realizing low-carbon transformation and green development. In recent years, along with the continuous deep exploration and development of unconventional oil and gas resources in China, the new exploration reserves are continuously increased, and the large-scale efficient development of low-grade oil and gas resources is promoted to have important strategic significance for guaranteeing national energy supply. For unconventional oil reservoirs which are difficult to effectively develop by traditional water flooding, the CO 2 miscible phase flooding technology is adopted, so that the crude oil recovery ratio can be remarkably improved, the large-scale sealing and storage of CO 2 can be realized, and the method is the optimal choice for considering economic benefit and environmental benefit at present. A large number of practices at home and abroad show that the CO 2 miscible flooding has remarkable advantages in the aspect of improving the recovery ratio, and gradually becomes a key technology for efficiently developing unconventional oil reservoirs such as compact oil reservoirs, shale reservoirs and the like by supplementing stratum energy, maintaining oil reservoir pressure and delaying yield decrease. Based on multiple action mechanisms such as swelling, extraction, viscosity reduction, diffusion, wettability change and the like, the CO 2 miscible phase flooding can effectively expand the swept volume and improve the oil displacement efficiency, thereby assisting the efficient production and benefit development of unconventional oil reservoirs and providing important technical support for guaranteeing national energy safety and realizing carbon neutralization targets. However, in the process of improving recovery efficiency by CO 2 miscible flooding, the migration behavior of the miscible front is affected by many factors such as reservoir heterogeneity, gravity overburden and starting pressure gradient, which easily causes the miscible front to "finger-in" and "crossflow" phenomena along the water flooding dominant seepage channel. The sweep range of the CO 2 mixed phase flooding is difficult to accurately identify, particularly in the gas channeling stage, the front edge position and the evolution law cannot be effectively characterized, and therefore the oil displacement efficiency is obviously affected. therefore, in the process of improving recovery efficiency by CO 2 miscible flooding, there is a need to deeply reveal the formation and evolution rules of the miscible band, and accurately predict the migration characteristics of the miscible front, that is, quantitatively identify and dynamically monitor the front migration of the CO 2 miscible flooding. In addition, as conventional reservoir development enters the "dual high" stage, unconventional reservoirs, represented by hypotonic, extra hypotonic, tight, and shale reservoirs, have become important successor forces for oil and gas exploration and development. However, the unconventional oil reservoir generally has the characteristics of strong heterogeneity, ultra-low permeability, complex pore structure and the like, so that the seepage, diffusion and miscible processes of CO 2 in the reservoir are more complex, and more severe requirements are put on the reliable prediction of the forward migration of the CO 2 miscible flooding. How to accurately describe the migration law of the mixed phase front of CO 2 in such complex reservoirs becomes a key scientific problem to be solved in order to realize the improvement of recovery efficiency and the inhibition of gas channeling. However, the existing knowledge is based on the core displacement experimental result, and qualitative analysis is carried out on the CO 2 miscible displacement process. Although the method can reveal the migration law and characteristic change of the miscible front to a certain extent, the problem of reliable prediction of the migration law of the CO 2 miscible front cannot be solved under the complex reservoir construction condition and the dynamic injection and production relation, and the scientific design of the CO 2 miscible flooding scheme of an unconventional reservoir is direc