Laboratory Study of Gravity Drainage Mechanism in Fractured Carbonate Reservoir-Reinfiltration

摘要

In a well fractured reservoir that has a gas cap, afterrncommencement of production the gas cap expands and therngas-oil contact (GOC) in the fracture system descends. The oilrncontained within the matrix of the gas invaded zone begins torndrain down into the fracture system and into the lower matrixrnblocks, due to the force of gravity. Some of the oil that isrndrained out of the upper matrix blocks can reinfiltrate into thernlower matrix blocks from the top or side surfaces and can flowrndown through the areas of contact between blocks.rnIn this study, data on a set of experiments that center onrnreinfiltration process are presented. The experiments coverrnfully saturated and desaturated blocks in vertical and inclinedrnpositions. The results of our experimental works reveal thatrnthe reinfiltration process depends mainly on the physicalrnproperties of the matrix block, the rate of oil supplied, and therndrainage stage of the block.rnWhen oil is trickled at the top of a desaturated block,rninitially due to an extra capillary pressure gradient therninfiltration rate can be higher than the maximum drainage raternof the block. After some time the rate of the drainagernapproaches that of the infiltration and an almost steady staternflow is established. At this condition, the lower portion of thernblock could drain oil, while the upper portion could be underrninfiltration process.rnWhen the oil is directly supplied on the top of the verticalrnfracture, its crossflow from fracture to the adjacent matrix isrndemonstrated. In other words, under certain conditions thernhigh conductivity vertical fractures are not necessarily thernprimary flow path of the supplied oil.rnThe purpose of this study is to provide a basic understandingrnof reinfiltration process in fractured porous media.