Refracturing: Technology and Reservoir Understanding are Giving New Life to Depleted Unconventional Assets

Abstract

Management The unconventional boom that has swept across North America over the past decade is a testament to how game-changing technology combined with expanded knowledge and understanding has transformed the paradigm of hydrocarbon production. Ongoing development of horizontal drilling and completion technologies and sophisticated downhole logging tools have been instrumental in increasing efficiency to make oil and gas shale plays economically viable. Today, more than 70,000 horizontal wells are producing from unconventional resource plays with massive, multistage fracturing campaigns. Over the years, however, operators have learned that reservoir heterogeneity and low-permeability rock present challenges that can limit the potential of unconventional development. Despite the fast pace of technological advances, production log analyses reveal that conventional completion designs, including the practice of placing perforation clusters evenly along the lateral, may not be the best approach to production in these plays. Production logs show that on average, 40% of the perforation clusters in a given lateral are not contributing to production. Unconventional wells also exhibit rapid declines from initial production (IP) rates, sometimes by as much as 60% to 80% during the first year of operation. If early IP rates are not managed, or choked, properly, subsequent steep declines can cause long-term damage to the fracture conductivity. As the industry faces new challenges in the wake of low commodity prices and a slowdown in drilling, it is eyeing a significant new opportunity to take unconventional resource development to the next level: refracturing. While refracturing of the Barnett Shale generated interest in 2008–2009, the development of new diversion technologies is enabling oil and gas operators to once again consider refracturing as an economic alternative to drilling new wells. While producers are still working to understand the mechanisms of unconventional production and how wells behave and flow, they do have a much better understanding of the subsurface than they did in the early days of a play as more wells have been drilled and data collected from these wells are pieced together. At the same time, fracture models for determining optimum treatment designs and technologies that can divert treatments to new unstimulated rock are now available and proven. This enhanced reservoir understanding and access to technology are incentivizing operators to take a second look at refracturing as a feasible and cost-effective alternative to drilling new wells. By reinvigorating existing, often depleted, assets, companies can enhance hydrocarbon recovery while boosting cash flows. A Unique Consortium Refracturing also provides the added benefit of protecting the depleted wells from the negative effects associated with fracture hits when drilling offset wells. Companies historically have encountered production losses from “parent wells” when an infill fracture interferes with the depleted well. By refracturing the depleted wells before fracturing the infill well, operators have successfully prevented these negative impacts and actually experienced improved production from both the infill and depleted wells. In 2014, Schlumberger assembled a team of experienced geoscientists from the hydraulic fracturing and reservoir subsurface disciplines to determine the criteria for developing a workflow to diagnose potential well candidates for refracturing. The team formed a consortium with several of the most active operators in the oil- and liquids-rich Eagle Ford Shale. Members of the consortium are providing the necessary data to define wells, most of them 1 to 4 years old, which would be good refracturing candidates in the play. By joining forces in this unique study, the consortium members are creating a critical mass of data, with the results of the well studies shared among the companies. This has facilitated accelerated learnings and best practices in well candidate selection and refracturing design.