Modeling ell performance for fractured horizontal gas ells
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In tight gas reservoirs, horizontal wells have been used to increase reservoir contact and hydraulic fracturing has been applied to further extend the contact of the reservoir. Point source solution has been used to describe the flow behavior. The method was advanced to the volumetric sources, and pressure change inside the source was considered. We have developed a method that can predict horizontal well performance, and the model can also be applied for 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 calculation of the semi-analytical response of a rectilinear reservoir with closed outer boundaries. The slab source approach assigns the source 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 of 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 of horizontal wells with uniform flux and infinite conductivity, and fractured wells with uniform flux, finite or infinite conductivity. 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. The examples will be used to illustrate how the model can help to optimize wellbore and fracture design. 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. The results of the study show that in low permeability formation, hydraulic fracturing has more impact on horizontal well performance. 2010, European Association of Geoscientists and Engineers.
