Abstract

Abstract The purpose of this study is to introduce a new three-linear flow model for capturing the dynamic behavior of water flooding with different fracture occurrences in carbonate reservoirs. Low-angle and high-angle fractures with different occurrences are usually developed in carbonate reservoirs. It is difficult to simulate the water injection development process and the law of water flooding is unclear, due to the large variation of the fracture dip. Based on the characteristics of water flooding displacement streamlines in fractured cores with different occurrences, the matrix is discretized into a number of one-dimensional linear subregions, and the channeling effect between each subregion is considered in this paper. The fractures are divided into the same number of fracture cells along with the matrix subregion, and the conduction effect between the fracture cells is considered. The fractured core injection-production system is divided into three areas of linear flow: The injected fluid flows horizontally and linearly from the matrix area at the inlet end of the core to the fracture and then linearly diverts from the fracture area. Finally, the matrix area at the outlet end of the core also presents a horizontal linear flow pattern. Thus, a trilinear flow model for water flooding oil in fractured cores with different occurrences is established. The modified BL equation is used to construct the matrix water-flooding analytical solution, and the fracture system establishes a finite-volume numerical solution, forming a high-efficiency semianalytical solution method for water-flooding BL-CVF. Compared with traditional numerical simulation methods, the accuracy is over 86%, the model is easy to construct, and the calculation efficiency is high. In addition, it can flexibly portray cracks at any dip angle, calculate various indicators of water flooding, and simulate the pressure field and saturation field, with great application effect. The research results show that the greater the fracture dip angle, the higher the oil displacement efficiency. When the fracture dip angle is above 45°, the fracture occurrence has almost no effect on the oil displacement efficiency. The water breakthrough time of through fractures is earlier than that of nonthrough fractures, and the oil displacement efficiency and injection pressure are more significantly affected by the fracture permeability. With the increase of fracture permeability, the oil displacement efficiency and the injection pressure of perforated fractured cores dropped drastically. The findings of this study can help for better understanding of the water drive law and optimizing its parameters in cores with different fracture occurrences. The three-linear flow model has strong adaptability and can accurately solve low-permeability reservoirs and high-angle fractures, but there are some errors for high-permeability reservoirs with long fractures.

Highlights

  • Carbonate reservoirs have various types of fractures with different occurrences—mainly concentrated in high-angle fractures and low-angle fractures, which have a great impact on oilfield water injection development

  • Drid and Tiab [3] established a water-gas alternating (WAG) flooding model based on the BL equation, which broadened the scope of application of the BL equation

  • The BL equation is used to establish the matrix flow analytical solution, and the finite volume method is used to establish the numerical solution of fracture flow which has formed a BL-CVF hybrid high-efficiency solution method for water flooding oil, with high calculation accuracy; it can realize the calculation of water flooding indicators under any fracture occurrence and key seepage parameters and can realize the water flooding oil saturation field, and the simulation of the pressure field provides a new method for water flooding in carbonate reservoirs

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Summary

Introduction

Carbonate reservoirs have various types of fractures with different occurrences—mainly concentrated in high-angle fractures and low-angle fractures, which have a great impact on oilfield water injection development. The BL equation is used to establish the matrix flow analytical solution, and the finite volume method is used to establish the numerical solution of fracture flow which has formed a BL-CVF hybrid high-efficiency solution method for water flooding oil, with high calculation accuracy; it can realize the calculation of water flooding indicators under any fracture occurrence and key seepage parameters and can realize the water flooding oil saturation field, and the simulation of the pressure field provides a new method for water flooding in carbonate reservoirs. The main innovation of this paper is the establishment of a semianalytical model suitable for exploring the dynamic law of water flooding in cores with different fracture occurrences. The semianalytical model in this paper can more accurately describe any occurrence of fractures and realize the exploration of core water flooding rules

Physical Model and Assumptions
Mathematical Model of Water Flooding Trilinear Flow
Semianalytical Solution Based on BL-CVF
Model Verification and Analysis
Water Flooding Characteristics and Production Law
Findings
Summary and Conclusions
Full Text
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