As the length of a horizontal well is increased, its drainage area also increases. Productivity of a long horizontal well is no longer proportional to the well length because increase in the length of horizontal production section also causes frictional losses in the wellbore. However, no reliable standards are currently available that take into account quantitatively the parameters necessary for the calculation of productivity index in long horizontal well.

A new approach of the specific productivity index is proposed to predict the production rate considering friction losses in long production section under inflow conditions. This paper specifically describes model development, solution and the simulation results for the production of a long horizontal well with the specific productivity index. This specific productivity index is derived by assuming steady-state flow of a slightly compressible fluid in an anisotropic formation. The influence of wellbore damage near the horizontal wellbore is also considered in the model. The sensitivity study of the various parameters affecting productivity is performed and the results are analyzed quantitatively. The study shows that there is a critical point, where rate of friction pressure is suddenly increased and productivity index is decreased abruptly with increase in horizontal well length beyond this point. This critical point is the tangent point on which friction losses should be considered for production estimation. The model facilitates determination of the new horizontal productivity index considering friction losses in long horizontal wells.

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