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 esp ecially true in the case of tight gas formations. Horizontal wells have unique rock mechanics and operational aspects that af fect fracture creation and propagation and control fracture orientation wit h respect to the horizontal well. It has been well documented that fracture orientation greatly affects the productivity and well testing aspects of t he 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 transvers e or longitudinal fractures. In this paper, we examine the factors involved in determining the optimum n umber 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 pr esented. The performance of a longitudinal fracture is examined and compared to a fr actured vertical well and a transverse-fractured horizontal well. A compari son of longitudinal versus transverse fractures from reservoir and operatio nal points of view is presented. Also included is a short discussion of fie ld 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 hi gh degree of confidence. This approximation is valid for moderate to high d imensionless conductivity. In the case of transverse fractures, the outer f ractures 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.