Strategies to Minimize Frac Spacing and Stimulate Natural Fractures in Horizontal Completions

Abstract

AbstractThe opening of a propped transverse fracture in horizontal wells causes a reorientation of stresses in its neighborhood, which in turn affects the direction of propagation of subsequent fractures. This phenomenon, often referred to as stress shadowing, can negatively impact the efficiency of each frac stage. By mapping the angle of stress reorientation and the horizontal deviatoric stress in multi-fractured horizontal wells, we offer some insight on the completion designs that will (a) minimize induced fracture spacing without compromising the efficiency of each frac stage and (b) effectively stimulate natural fractures in the vicinity of the created fracture.The rapid development of shale gas in North America can be tied to the combination of horizontal drilling and multi-stage fracturing. The spacing between fractures and perforation clusters as well as the ability to stimulate the fractures naturally present in the rock are thought to be major factors in the success of horizontal completions in shale gas reservoirs. The understanding and quantification of the mechanical stress interference generated during the stimulation of horizontal wells is crucial to improving reservoir drainage in shale gas reservoirsTransverse fractures initiated from a horizontal well may deviate toward or away from the previous fracture depending on the mechanical properties of the reservoir rock, fracture spacing, and the orientation of the previous fracture. Using a numerical model allowing non-transverse fractures (those that deviate from the orthogonal path), we show that some induced fractures propagate into previously stimulated areas during the consecutive fracturing of a Barnett shale well, thus decreasing the reservoir drainage efficiency of the frac treatment. The observed net pressure trend matches field observations during fracturing and microseismic measurements.The alternate sequencing of transverse fractures as well as multi-lateral completions were recognized to be effective ways to enhance natural fracture stimulation, by allowing fracture stages to experience a smaller stress contrast during propagation. More importantly, it is shown that net fracturing pressure data measured in the field can be used to detect mechanical interference between multiple transverse fractures and optimize fracture spacing for a specific well.