The paper illustrates, using a field example, how well test data can be used to evaluate matrix block size and fissure volume in fissured reservoirs. The method is based on type-curve analysis with a recently published type-curve for double porosity reservoirs, published type-curve for double porosity reservoirs, and is applied to two tests on the same well, performed at a few years interval, with reservoir pressure above and below the bubble point, respectively. Detailed analysis of the two tests is presented, that yields consistent values for fissuration parameters, w and X, although pressure behavior during the tests is very different. Interpretation results were used as inputs to a numerical reservoir simulator, which was then calibrated against actual performance history to yield the size of the matrix blocks. The result was in excellent agreement with that obtained from X, and with available geological information.Introduction. Naturally fissured reservoirs are recognized as major contributors to the world oil reserves. As a result, they have been the subject of many studies over the last twenty years.Although several fissured reservoir models have been presented in the literature, field examples to support presented in the literature, field examples to support these models are scarce. In fact, there still is some debate on fissured reservoir behavior, and consequently, on the ability of well tests to provide specific information on fissure parameters, such as spacing and porosity. The general feeling appears to be that fissured reservoir behavior is too complex and too averse to be analyzed in a systematic and unique way.In this paper, field data from two different tests on the same well in a fissured reservoir are analyzed with the help of a recently published type-curve.It is shown that, although the well behavior was very different in the two tests, the same model could be used for analysis, and provided values of the parameters that were consistent with reservoir parameters that were consistent with reservoir information obtained from other sources.INTERPRETATION MODELS FOR FISSURED RESERVOIRSDIRECT PROBLEM. The direct problem (i.e., predicting the pressure behavior of a fissured reservoir from the knowledge of pertinent reservoir parameters) has been investigated by many different authors. Most of them, however, used the same basic model to describe a fissured reservoir, and their solutions only differed by the nature of fissure-matrix interaction, the boundary conditions included in the model, and the computation techniques employed.Fissured formations are commonly represented by a double porosity reservoir (i.e. a reservoir with two porous regions of distinctly different porosities and permeabilities). One region (the porosities and permeabilities). One region (the fissures) has a high conductivity, and carries the reservoir fluid to the well, whereas the other region (the blocks) has a low conductivity and feeds the fluid only to the fissures.Parameters necessary to describe a fissured reservoir are the same as those used for homogeneous reservoirs, plus two specific ones, namely.(1)and(2)In Eqs 1 and 2, subscript f refers to the fissure system, m to the matrix and (f+m) to the total reservoir.