Crossflow in Fractured/Layered Media Incorporating Gravity, Viscous, and Phase Behavior Effects: Part I - Formulation and Features in Layered Media
- B. Dindoruk (Amoco Production Co.) | A. Firoozabadi (Reservoir Engineering Research Institute)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- June 1997
- Document Type
- Journal Paper
- 120 - 135
- 1997. Society of Petroleum Engineers
- 5.3.2 Multiphase Flow, 5.5 Reservoir Simulation, 5.4.2 Gas Injection Methods, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.7.2 Recovery Factors, 5.2.1 Phase Behavior and PVT Measurements
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Crossflow across the interfaces of layered reservoirs, and between matrix blocks and fractures in fractured reservoirs may be very pronounced. The literature emphasizes viscous crossflow, however, crossflow due to gravity even for dip angles of 5 to 15 may be more significant.
In this paper, we present the result of our work on crossflow due to various effects in layered porous media. The examples selected show that most of the oil is first transferred from the low permeability layer to the high permeability layer and then produced.
Crossflow of fluids between a fracture network and rock matrix in fractured reservoirs, and between different layers in layered reservoirs can be very pronounced in certain gas injection schemes. The crossflow could be mainly due to, 1) gravity, 2) capillarity, 3) viscous, and 4) fluid compressibility effects. At high pressures, phase behavior effects reduce surface tension significantly and, therefore, the effect of capillary pressure on crossflow can be neglected.
In our recent work, it was demonstrated that the crossflow of the injected fluid from the fracture to the matrix and the crossflow of the matrix oil to the fracture strongly affect the recovery efficiency. Surprisingly, the crossflow due to gravity is the dominant mechanism for high displacement efficiency for first contact miscible fluid injection in fractured porous media. The investigation of the crossflow process at conditions other than first contact miscibility is one major goal of this work.
In layered reservoirs, similar to fractured reservoirs, crossflow between layers is expected to be important. Due to strong crossflow, one may expect that the recovery from tight layers can be improved. Since the crossflow in both fractured and layered porous media is often a localized phenomenon, reservoir simulators cannot capture its basic features.
In an early paper, Zapata and Lake studied viscous crossflow in layered media for immiscible fluid systems. Pande and Orr also studied viscous crossflow in a two-layer system incorporating transfer of components between gas and liquid phases in the absence of both gravity and volume change due to mixing. In a recent work, Tan and Firoozabadi included the effect of gravity in the study of crossflow between a matrix medium and a fracture medium. In all these studies, the effect of volume change on mixing was neglected. When an injected gas dissolves in the oil phase, the volume of the total system may reduce significantly. The subject of viscous crossflow has received considerable attention. Crossflow due to viscous forces, is generally not very significant. Gravity contribution to crossflow, on the other hand, may be very pronounced for fractured reservoirs, and for layered reservoirs with tilt angles in the range of 5-15 . Phase behavior effects which include component transfer and volume change due to mixing and incorporation of these effects in the crossflow term may also be important.
This study addresses a comprehensive examination of crossflow in fractured and layered media incorporating gravity, compressibility and phase behavior, and viscous effects. In the following, we will first present the problem formulation, and then outline the solution method. The examples of gas injection in a two-layer media will be discussed, and at the end, conclusions will be drawn from the work.
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