Analysis of Recovery Mechanisms for Naturally Fractured Gas-Condensate Reservoirs

摘要

The study of depletion performance of naturally-fracturedrnreservoirs has gained wide interest in the petroleum industryrnduring the last few decades and poses a challenge for thernreservoir modeler. The presence of a retrograde gas-condensaternfluid incorporates an additional layer of complexity to thernperformance of this class of reservoirs. Upon depletion, reservoirrnpressure may fall below the dew-point of the hydrocarbonrnmixture which results in liquid condensation at reservoirrnconditions. In the case of fractured gas-condensate reservoirs,rncondensate will first appear in the high-conductivity channelsrnsupplied by the fracture network and around the external edgesrnof the matrix blocks which are the zones prone to fasterrndepletion. Even though fracture condensate may havernconsiderable mobility, that is not the case for the liquid formedrnat the external portions of the matrix. Its presence will hinder thernflow of hydrocarbons from the inner portions of the matrixrnblocks and severely obstruct their recovery. This impairmentrnbecomes quite severe for the case of tight, naturally fracturedrnreservoirs where matrix permeabilities may be less than 0.1 md.rnSince the bulk of hydrocarbon storage resides inside the matrix,rnit is critical to answer the question whether this trapped gas hasrnbeen irreversibly lost or not. It is believed that the interplay ofrnDarcian-type flow and Fickian-type flow (multi-mechanisticrnflow) is the key to answering the questions about depletionrnperformance and ultimate recovery in these reservoirs. Thisrnstudy investigates the recovery mechanisms from a single matrixrnblock surrounded by an orthogonal matrix network, as thernfundamental building block for the full-scale system. In thisrnwork, we show the dominant flow processes and recoveryrnmechanisms taking place in naturally-fractured gas-condensaternreservoirs and describe the depletion performance of thesernsystems, which provides guidance for the development andrnanalysis of this class of reservoirs.