Modeling well performance for fractured horizontal gas wells
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In tight gas reservoirs, horizontal wells have been used to increase reservoir recovery and hydraulic fracturing has been applied to further extend the contact with the reservoir. In the past, many models, analytical or numerical, were developed to describe the flow behavior in horizontal wells with fractures. Source solution is one of analytical/semi-analytical approaches. The source method was advanced from point sources to volumetric source, and pressure change inside fractures was considered in the volumetric source method. We have developed a method that can predict horizontal well performance, and the model can also be applied to fractured horizontal wells. The method solves the problem by superposing a series of slab sources under transient or pseudo-steady state flow conditions. The principle of the method comprises the calculation of semi-analytical response of a rectilinear reservoir with closed outer boundaries. The slab source approach assigns sources a geometry dimension, similar to the volumetric source method; but has the solution similar to the point source method by neglecting the effect of the flow inside the source. When solving the source problem the pressure/flow effect inside source is considered sequentially by superposition principle over multiple sources.The pressure response is integrated over time to provide continuous pressure behavior. Flow effect inside fractures can be studied by dividing the fracture into several segments, and each can be treated as a slab source. The method is validated by comparison with the results of analytical solutions and other commercial software of horizontal wells with uniform flux and infinite conductivity, and fractured wells with uniform flux, finite or infinite conductivity. For multiple fractures in a horizontal well, the method was also compared with some published field data. The method provides an effective tool for horizontal well design and well stimulation design for gas reservoirs.In this paper, we present the details of model development. We use a case study to illustrate how the model can help to optimize wellbore and fracture design by comparing production performances of vertical well, slanted well, horizontal well, and fractured vertical and horizontal wells. The method in this paper is more accurate compared with conventional point-source solution, and can handle the transaction from transient flow to pseudo-steady state flow smoothly. 2014 Elsevier B.V.
