Abstract: There are few reports in the literature on the effects of linear faults on well test interpretations, especially for linear faults located within combined oil and gas reservoirs. To address this gap, we have constructed a mathematical model for interpreting well tests from infinite formation combined oil and gas reservoirs with two radial zones based on seepage mechanics. Solutions for this model were obtained via Laplace transformations; the principles of image theory and superposition were then used to study the dimensionless bottom hole pressure and pressure derivative curves corresponding to combined oil and gas reservoirs that contain linear faults, along with the factors affecting these curves. The results of this study are as follows:when the distance between a fault and well is less than half the radius of the inner area, the dimensionless pressure derivative curve changes from the 0.5 horizontal line, indicative of an infinite-acting radial flow, to the 1.0 horizontal line, indicative of a faultaffected inner area, and the value that shows the fault's impact on the outer area is the M₁₂ horizontal line. When the distance between a fault and well is more than half the radius of the inner area, the dimensionless pressure derivative curve shifts from the 0.5 horizontal line, corresponding to an infinite-acting radial flow, to the M₁₂/2 horizontal line, which shows the characteristics of the outer area, and the value that is indicative of the fault's impact on the outer area is the M₁₂ horizontal line.

Key words: combined oil and gas reservoirs, well test analysis, pressure dynamics, fault boundaries, image theory