Application of laplace transform in well test interpretation - an example of tahe oilfield cavity-fractured reservoirs in tarim basin

The oil and gas distribution is controlled by some factors in the cavity-fractured reservoirs, such as multiple reservoir formation, different epigenetic transformation induced destroys, heterogeneity of the reservoir space and so on, which lead to difference in hydrocarbon migration and accumulation and the extremely uneven distribution of reservoir properties. Constrained by the model, conventional analytical solution of well test analysis theory cannot meet such needs to solve the seepage in the cavity-fractured reservoirs. A new well test interpretation model of wells drilled in cavity was presented in the paper and a corresponding mathematical model was built up, Laplace transform and Stehfest reverser method was used to solve the model. The influences of inter-porosity flow coefficient and size of cavity to the bottom pressure response were analyzed, obtained the rules: when the size of cavity is constant, the smaller inter-porosity flow coefficient is, the later the seepage stage will emerge, the size of inter-porosity flow coefficient only affects the duration of early curve; when the size of inter-porosity flow coefficient is constant, the smaller the cavity is, the more obvious seepage stage will reflect. Early curve parallel to the different sizes cavity, the smaller cavity is, the larger the intercept will be. Well test interpretation method for wells drilled in cavity of cavity-fractured reservoirs was presented, practical software was developed. Finally, the new well test model was used to analysis one well test data in Tahe Reservoir and the explanation of well test accorded with the result of geological model and drilling data.