The fissure-block model considered in this paper is sometimes called a dual-porosity model or a naturally fractured reservoir model. Ground water and petroleum literature commonly refer to the pioneering analytical work on this subject by Barenblatt and others (1960) and Warren and Root (1963). Consider flow from primary porosity blocks to secondary porosity fissures but they do not describe the flow within these blocks. Kazemi (1969) presents a finite-difference solution for singlephase flow which does account for flow with in the blocks and Boulton and Streltsova (1977) give exact solutions for this problem.

Nonisothermal, radial flow, fissure-block finite-difference model for geothermal steam reservoirs which was later used to simulate pressure buildup data for a steam well in Larderello, Italy (Moench and Neri, 1979). The model assumed the blocks to be impermeable but capable of conducting heat to the fissures which had been cooled by vaporization. in the present paper the model is revised to account for steam transport and vaporization with in the blocks. account for the longevity of production wells in The Geysers. The blocks, which may be initially saturated with liquid water, are assumed to have low intrinsic permeability and low porosity relative to the fissures.

Results computed with this finite difference model are compared, for isothermal conditions , with the solutions of Boulton and Streltsova(1977) .' Under these conditions the model is similar to that of Kazemi (1969). the blocks from a small amount of uniformly-distributed liquid water it is also possible to apply Boulton and Streltsova's solutions. This is done by allowing for the apparent compressibility of the two-phase fluid mixture in the block. Comparison with Boulton and Streltsova's solutions under two-phase conditions is given in order to verify the finite difference code.

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