Recent developments in completion techniques and stimulation efficiency have allowed many unconventional resource plays to reach economically viable levels. The Bakken/Three Forks play of the Williston basin has rapidly evolved during recent years, and its predominantly successful completion techniques continue to emerge as programs are tailored to geographic areas. As completion intensity increases to facilitate higher early time production returns, so does the need for the critical analysis of production decline rates to meet economic targets.The application of decline curve analysis in unconventional reservoirs, such as the Bakken/Three Forks play in North Dakota, is often problematic because of very long periods of transient flow. This has caused the development of various decline curve relations outside the conventional Arp's equations in an attempt to better explain the transient flow period. Additionally, it has sparked interest in quantifying the uncertainty associated with production and the estimated ultimate recovery (EUR) from these various techniques.The Bakken/Three Forks system is exploited using a large variation of publically reported completion techniques throughout a significant geographic area. Because of the uncertainty in assessing the performance of unconventional wells and the multitude of variables that could affect their production, it is often difficult to determine dominant influencing parameters of completion design. Efficiently implementing optimal completion techniques, provided there is high variability within a continuous horizontal target lithology, is critical because of the large geographic extent of the Williston basin.The focus of this study is to evaluate the completion efficiency of individual wells using decline curve analysis and to quantify uncertainty using this performance metric. A comprehensive completions database of the Bakken/Three Forks play is used to evaluate the expected costs and benefits of various completion designs used throughout the basin. This paper provides examples of stimulation methods optimized to specific regions of the Bakken/Three Forks system using this methodology. Overview of DatabaseTo document the variability in completion design and production throughout the Williston basin Bakken/Three Forks system, a comprehensive database of publically reported completion and production data has been compiled using the North Dakota Industrial Commissions (NDIC) website. In addition to legal information (well name and number, completion date, etc.), the latitude and longitude, target formation, maximum rate, stimulation zones, total treatment fluid, total proppant, completion system, annular isolation, stimulation fluid, primary proppant, and initial production (IP) test choke were recorded. For each well reported, production data was also recorded at various time steps. Because the NDIC reports the number of production days each month, down days were removed from the production data, and linear interpolation was used to obtain production values at 30-da...

Summary Selecting appropriate proppants is an important part of hydraulic-fracture completion design. Proppant selection choices have increased in recent years as regional sands have become the proppant of choice in many liquid-rich shale plays. But are these new proppants the best long-term choices to maximize production? Do they provide the best well economics? The paper presents a brief historical perspective on proppant selection followed by various detailed studies of how different proppant types have performed in various unconventional onshore US basins (Williston, Permian, Eagle Ford, and Powder River), along with economic analyses. As the shale revolution pushed into lower-quality reservoirs, the concept of dimensionless conductivity has pushed our industry to use ever lower-quality materials—away from ceramics and resin-coated proppant to white sand in some Rocky Mountain plays, and more recently from white sand to regional sand in the Permian and Eagle Ford plays. Further, we compare early-to-late-time production response and economics in liquid-rich wells where proppant type changed. The performance of various proppant types and mesh sizes is evaluated using a combination of different techniques, including big-data multivariate statistics, laboratory-conductivity testing, detailed fracture and reservoir modeling, as well as direct well-group comparisons. The results of these techniques are then combined with economic analyses to provide a perspective on proppant-selection criteria. The comparisons are anchored to permeability estimates from production history matching and diagnostic fracture injection tests (DFITs) and thousands of wellsite-proppant-conductivity tests to determine dimensionless conductivity estimates that best approach what is obtained in the field. Dimensionless fracture conductivity is the main driver of well performance because it relates to proppant selection thanks to the inclusion of the relationship of fracture conductivity provided by the proppant relative to the actual flow capacity of the rock (the product of permeability and effective fracture length), which is supported by the production analyses in the paper. The paper shows how much fracture conductivity is adequate for a given effective fracture length and reservoir permeability and then looks at the economics of achieving this “just-good-enough” target conductivity, either through less proppant mass with higher-cost proppants or more proppant mass with lower-cost proppants, as well as mesh-size considerations. This paper does not rely on a single technique for proppant selection but uses a combination of various data sources, analysis techniques, and economic criteria to provide a more holistic approach to proppant selection.

Selecting appropriate proppants is an important part of hydraulic fracture completion design. Proppant selection choices have dramatically increased in recent years as regional sands have become the proppant of choice in many liquid-rich shale plays. But are these new proppants the best long-term choices to maximize production? Do they provide the best well economics? The paper presents a brief historical perspective on proppant selection followed by various detailed studies of how different proppant types have been performing in various unconventional basins (Williston, Permian, Eagle Ford, Powder River and DJ) along with economic analyses. As the shale revolution pushed into lower-quality reservoirs, the concept of dimensionless conductivity has pushed our industry to use ever lower-quality materials – away from ceramics and resin-coated proppant to white sand in some Rocky Mountain plays and more recently from white sand to regional sand in the Permian and Eagle Ford plays. Further, we compare early-to late-time production response and economics in liquid-rich wells where proppant type changed. The performance of various proppant types and mesh sizes is evaluated using a combination of different techniques, including big data multi-variate statistics, lab conductivity testing, detailed fracture and reservoir modeling, as well as direct well group comparisons. The results of these techniques are then combined with economic analyses to provide a perspective on proppant selection criteria. The comparisons are anchored to permeability estimates from production history matching and DFITs and thousands of wellsite proppant conductivity tests to determine dimensionless conductivity estimates that best approach what is obtained in the field. Proppant selection is typically based on crush resistance to stress loading and fracture conductivity under various flow conditions while having the lowest possible cost. However, dimensionless fracture conductivity is the main driver of well performance as it relates to proppant selection since it includes the relationship of fracture conductivity provided by the proppant relative to the actual flow capacity of the rock (the product of permeability and effective fracture length), which is supported by the production analyses in the paper. The paper shows how much fracture conductivity is adequate for a given effective fracture length and reservoir permeability and then looks at the economics of achieving this "just-good -enough" target conductivity, either through less proppant mass with higher-cost proppants or more proppant mass with-lower cost proppants, as well as mesh size considerations. This paper does not rely on a single technique for proppant selection but uses a combination of various data sources, analysis techniques and economic criteria to provide a more holistic approach to proppant selection.