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This article focuses on interpretation of well test data from wells completed in naturally fractured reservoirs. Because of the presence of two distinct types of porous media, the assumption of homogeneous behavior is no longer valid in naturally fractured reservoirs. This article discusses two naturally fractured reservoir models, the physics governing fluid flow in these reservoirs and semilog and type curve analysis techniques for well tests in these reservoirs. Naturally fractured reservoirs are characterized by the presence of two distinct types of porous media: matrix and fracture. Because of the different fluid storage and conductivity characteristics of the matrix and fractures, these reservoirs often are called dual-porosity reservoirs.
Jones, Stephen (McMaster University Department of Materials Engineering) | Kish, J. (McMaster University Department of Materials Engineering) | Coley, K. (McMaster University Department of Materials Engineering)
Summary We have analyzed the production performance of a constant-pressure well in a naturally fractured reservoir made up of orthogonal matrix blocks. The fractured reservoir is modeled as a doubleporosity reservoir, in which interporosity flow is represented by an exact analytical transient influx function. Three distinct production modes can be recognized: Modes I, II, and III. In Mode I, the reservoir boundary is seen after flow in the matrix blocks has stabilized. In Mode II, this occurs while flow in the matrix blocks is still in the infinite-acting stage. In Mode III, the reservoir boundary is already seen before the influx from the matrix blocks has effectively set off. The effect of the natural fractures becomes increasingly evident with increasing mode number: from almost absent in Mode I, to significant in Mode II, and to dominant in Mode III. Mode I shows the best production performance, Mode III the worst. Each production mode can be subdivided into a number of distinct flow regimes. The production profiles in each of these regimes and the regime boundaries can be approximated by simple analytical formulas. These formulas may be used for production forecasting and for analyzing historical production decline.