An Experimental Study of Capillary and Gravity Crossflow Fractured Porous Media

Abstract

SPE Members Abstract Physical phenomena such as capillary, gravity, and viscous cross flow at the interface of two different porous media or in the fracture space between matrix blocks are believed to affect the flow of multiphases. We have not found any reported work on capillary and gravity cross flow in fractured porous media. An experimental and theoretical work has been initiated to understand cross flow in fractured porous media. In this paper, the results of our experimental effort on capillary and gravity crossflow in fractured porous media are presented. Drainage performance of a stack of 12 matrix slabs, three in each row, was measured. The angle between the stack and the vertical direction varied from 0 degrees to 45 degrees. Experiments on a stack of matrix blocks were also conducted to compare the results. The data show that capillary cross flow across side faces of a matrix block is an important flow mechanism. Capillary cross flow enhances drainage performance in fractured porous media. Introduction Fractured reservoirs are comprised of matrix blocks and fractured networks. One may view these reservoirs as the extreme of heterogeneous reservoirs. Physical phenomena such as capillary, gravity, and viscous cross flow at the interface of two different porous media or in the fracture space between the matrix blocks are believed to govern the multiphase flow process. The studies in the literature center around viscous cross flow in layered porous media. Only a few studies have touched upon the subjects of capillary and, gravity cross flow in heterogeneous porous media. We have found no reported work on capillary and gravity cross flow in fractured porous media. Fracture orientation varies from one reservoir to another. Therefore, the significance of capillary and gravity cross flow is reservoir dependent. For naturally fractured reservoirs with heterogeneous rock matrix, capillary and gravity cross flow is believed to play a dominant role in the reservoir performance, even for vertical fractures. In this paper, our experimental work on the drainage performance of an aggregate of matrix blocks (see Fig. 1) to study capillary and gravity cross flow is presented. The results provide a basis for future theoretical studies. EXPERIMENTAL Apparatus - The experimental setup used in this work is similar to the one described in Refs. 5 and 6. In the experiments on the stack of 12 matrix slabs, there was no space between the rock matrix and the glass wall of the core holder. Core Preparation and Properties - In addition to matrix blocks SA, SB, SC, and SD described in Refs. 5, tests with new matrix slabs were carried out in this project. P. 617^