Evaluation of horizontal wells with transverse hydraulic fractures in a layered multi-phase reservoir

Abstract

The Upper Bahariyia reservoirs are wide-spread through the Western Desert of Egypt and have significant original oil in-place. Although these reservoirs have been penetrated with numerous wellbores (for developing deeper horizons), they have not been commercially productive with conventional vertical wells. These reservoirs can be characterized as two thin, low permeability layers with no crossflow between them. Productivity of these reservoirs is reduced by gas blocking behavior when attempting to produce below the bubble point pressure. The objective of this work was to investigate the viability of converting existing conventional vertical wells to horizontal wells with multiple transverse fractures. These fractures will not only significantly increase the productivity, but also provide the vertical communication needed between the reservoir layers. Reservoir simulation was used to evaluate various combinations of transverse fractures in horizontal wells. These results were compared with simulation results for conventional vertical wells, with and without vertical fractures. Only infinite conductivity fractures were considered. Early transient behavior as well as pseudosteadystate behavior were simulated. An economical analysis was made for the horizontal wells with multiple transverse fractures. The results show that horizontal wells with transverse fractures appear to make production of the Upper Baharlyla reservoirs economically feasible. In this work, the productivity index has been presented for horizontal wells with various combinations of transverse fractures, producing from the Upper Bahariyia reservoirs. It has been shown that the productivity index of horizontal wells with transverse fractures is mainly affected by the distance between the outermost fractures and not by the number of fractures nor the spacing between them. Between fractures perforations has been shown to have negligible effects on increasing the productivity of horizontal wells with transverse fractures in this reservoir. Also decline type curves are presented, for vertical fractured and horizontal with transverse fractures wells, for future performance prediction and reserves estimates. Although the conclusions of this work were targeted to provide guidelines for selecting a feasible producing technique for the targeted reservoir, these conclusions can be used in similar multiple layered oil reservoirs.