FRACTURING HORIZONTAL WELLS IN GAS RESERVOIRS

The fracturing of horizontal wells has recently gained wide acceptance as a viable completion option to maximize the return on investment. This is especially true in the case of tight gas formations. Horizontal wells have unique rock mechanics and operational aspects that affect fracture creation and propagation and control fracture orientation with respect to the horizontal well. The fracture orientation greatly affects the productivity and well testing aspects of the fractured horizontal wells. Depending on stress orientation relative to the wellbore, the fractures may be transverse or longitudinal. This paper presents a model for fractured horizontal wells operating under constant pressure conditions. This condition is most suitable for producing tight gas reservoirs. The model considers the presence of either transverse or longitudinal fractures. In this paper, we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented. The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points-of-view is presented. Also included is a short discussion of field examples. Because performance of a highly conductive longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outer fractures outperform the inner fractures. However, in most practical cases, more than two fractures are necessary to efficiently produce the reservoir. A simplified economic analysis supports this conclusion.