New Semianalytic Technique to Determine Horizontal Well Productivity Index in Fractured Reservoirs.

Simplified analytical relations derived for homogeneous formations are usually applied for the determination of the productivity of horizontal wells, regardless of the presence of heterogeneities in the reservoir. Furthermore, complex well architectures and the wealth of completion options currently available can not be properly taken into account, because the well trajectory can only be schematized as a single horizontal wellbore. However, the use of numerical reservoir simulators to reliably forecast the productivity of horizontal wells draining heterogeneous reservoirs may be time-prohibitive or not feasible due to lack of sufficiently detailed information, especially during the appraisal phase or the early stages of production. A new semi-analytic technique is proposed in this paper to solve the inflow equations in an approximate yet reliable manner. The solution to 3-dimensional problems of single-phase flow into a horizontal well, taking into account friction in the wellbore, is provided for both single-layer reservoirs and reservoirs comprising two interfering layers. The method has been extended also to describe the fluid flow when the well intercepts one or more fractures. The presented technique allows very fast calculation of the well productivity in oil and gas reservoirs, offering great flexibility in the placement and architecture of the wells. The method has been applied to two field cases for which the well productivity under pseudo steady-state conditions was measured. One of these is a 200-m long horizontal well draining an isotropic carbonatic reservoir and intersected by a natural low-conductivity fracture. The other is a similar well, intercepting a natural high-conductivity fault, but the oil-bearing formation is anisotropic. Good correspondence was found between the actual productivity and the predictions obtained by application of the proposed semi-analytic technique.