Unsteady-State Flow Behavior for a Well Near a Natural Fracture

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract A mathematical model was developed to study the transient flow behavior for a well near an infinite conductivity vertical, nonintersecting, natural fracture in an infinite slab reservoir. A slightly compressible fluid was considered. Results when plotted as a function of a dimensionless time follow at ear times a straight line of 1.151 slope characteristic of radial flow. After this radial flow period, the well pressure behavior starts to period, the well pressure behavior starts to be affected by the natural fracture and this causes a negative pseudo-skin factor, which is a function of time, and becomes a constant for large values of time, giving a second 1.151-slope straight line. This pressure behavior is similar to the one predicted by the models of Warren and Root and de Swaan for a uniform naturally fractured reservoir. Results from interference tests, for reservoirs having a natural fracture show that it is impossible to characterize uniquely the reservoir by means of the transient pressure test data alone. An integrated approach or transient pressure test data registered at several observation wells can be used for a unique characterization. From these tests, underestimation or overestimation of the reservoir parameters could result, depending on the location of the observation well relative to the natural fracture. Introduction Considerable amount of information can be found in the literature concerning the pressure transient behavior of hydraulically fractured wells. It is well known that fractures greatly affect the exploration of many reservoirs. Surprisingly, there are few, if any, quantitative data reported in the literature on the effect of vertical or horizontal fractures existing out in the reservoir matrix on the transient well behavior. This problem of fractures not crossing the borehole has been investigated experimentally by Huitt and Ollos. Huskey and Crawford used a potentio-metric model to study the effects of vertical potentio-metric model to study the effects of vertical fractures not crossing the borehole on the steady-state well behavior. Gureghian investigated, by variational methods and a potentiometric model, the effect of fractures in a potentiometric model, the effect of fractures in a confined aquifer on the steady-state flow behavior. He studied both intersecting and nonintersecting fractures. It is believed that natural fractures may exist out in the reservoir and would affect the pressure well behavior. pressure well behavior.