This hydraulic fracture stimulation case study in the Mancos Shale, Piceance Basin used real-time microseismic imaging to evaluate and guide changes to diversion strategies. The objective was to identify and improve hydraulic fracture development of three neighboring, horizontal, and parallel wells.
Black Hills Exploration and Production, Inc. (BHEP) hydraulically fractured three wells using a plug-and-perforate completion technique. All injection stages used the same treatment fluids and proppant types and differed by perforation schemes and diversion strategies. Diversion strategies included combinations of ball sealers and clean fluid sweeps (i.e., fluid without proppant), separating proppant-laden, ramped segments. Stages included one, two, or three proppant segments. The study included microseismic imaging, which acquired data using two deep geophone arrays in nearby wells. The microseismic data were processed during active injections (i.e., in real time). Following each stage, the on-site engineers compared the microseismic event distributions before and after diverters to evaluate diversion effectiveness. Differing microseismic distributions (e.g., changes in shape, azimuth, extent, etc.) combined with bottomhole pressure responses (e.g., increases and breakdowns) indicated successful diversion. Based on design, successful diversion strategies were repeated.
Normally, an on-site engineer assesses diversion success using only the bottomhole pressure response. For this project, the assessment was substantially enhanced by combining bottomhole pressure response with microseismic imaging. As a result of this strengthened assessment, the on-site engineers concluded two main results during the study: (1) ball sealers separating proppant segments led to successful diversion and (2) a clean fluid sweep or a second set of ball sealers separating three proppant segments was less effective than two proppant segments. After identifying these findings, the engineers changed subsequent stages to include one set of ball sealers separating two proppant segments.
In this study, reducing the number of proppant segments: (1) increased the stages per day by 10% and (2) increased the proppant load per fluid volume by 7%. In addition to these increased operational efficiencies and cost savings, this diversion evaluation and real-time changes improved perforation cluster efficiency (percentage of producing perforation clusters). For the three wells studied, production logs showed 3–24% greater perforation cluster efficiency than other local wells without diversion.