Hydraulic Fracture Reorientation in Primary and Secondary Recovery from Low-Permeability Reservoirs

Abstract

SPE Members Abstract Hydraulic fracture orientation is critical to both primary and secondary oil recovery in low-permeability reservoirs. Incomplete and often overlapping drainage patterns under primary recovery, as well as inefficient sweep and premature water (or steam) breakthrough under secondary recovery are some of the common production problems that often result from hydraulic fracture reorientation. Often, hydraulic fracture orientation is measured on a few wells, and then generalized across the entire field under development. This characterization of regional fracture (stress) orientation is then assumed constant over the development life of the field. A wealth of recent observations have definitively shown that fracture (stress) orientation in low-permeability reservoirs can be profoundly affected by production activities. Hydraulic fracture reorientation has been observed on dozens of staged fracture treatments (in several fields) under both primary and secondary recovery. A summary of collected field data from three extensive field studies is presented. The production impact of fracture reorientation on both primary and secondary recovery schemes is addressed; and strategies are presented which utilize the recent findings for both enhancing primary recovery and mitigating some common problems with secondary recovery. The discussion of reorientation mechanisms is greatly enlightened by recent data which reveals a startling correlation between observed fracture reorientation and indirect measurements of reservoir compaction. Introduction The petroleum industry has long recognized the central role of insitu stress in hydraulic fracture propagation. The insitu stress state controls many aspects of fracture propagation, including: hydraulic fracture geometry and dimensions; near-wellbore fracture tortuosity; and hydraulic fracture orientation. This paper will focus exclusively on the insitu stress state as it affects hydraulic fracture orientation. Realizing the central role that stress state plays. not just in hydraulic fracturing, but also in borehole stability, formation sand control, and wellbore casing damage; the industry has long grappled, often unsuccessfully, with the difficulties of simply determining the insitu reservoir stress state. Added to the difficulty of measuring insitu stress conditions is an additional complication: production activities themselves can significantly perturb the original stress state. This paper documents production induced stress perturbations which lead to changes in hydraulic fracture orientation. The realization that production activities significantly alter the insitu stress state is certainly not new: P. 357