Home to one of the largest North American deposits discovered in the last few decades, the Bakken, spanning 200,000 square miles along the borders of Saskatchewan, North Dakota and Montana is rivaling some of the largest proven reserves. As the use of long horizontal wells and multi-stage fracturing technology has significantly increased productivity and activity in the basin, the challenges associated with infill-completions, depletion and controlled fracture growth must be addressed to ensure efficient and effective practices, encouraging long-term planning without hindering investment.In this paper, models are built to replicate well performance (fracturing and production-numerical & rate-transient) and to understand the impact of key technologies (multi-stage/completion type and multi-laterals) across the basin to demonstrate why completion strategies must be modified based on reservoir quality and stress state. Confusion between the success of sliding sleeves/plug and-perf and what drives the optimal number of stages is also addressed using fracture modeling and production modeling with emphasis on key parameters (fracture length, connectivity, number of fractures) influencing productivity. The recent focus on data acquisition and modeling in the Three Forks has presented a range of challenges and opportunities due to the laminations in this reservoir. Log up-scaling methods and simulator engines were crucial to modeling and thus evaluating propagation behavior. This paper also presents how the use of data gathering (log, routine and specialized core) and modeling has enabled us to understand how in-fill drilling can alter drainage patterns and influence production success.
Since early 2016, commodity prices have been gradually increasing, and the Permian Basin has become the most active basin for unconventional horizontal well development. As the plays in the basin are developed, new infill wells are drilled near pre-existing wells (known as "parent wells"). The impact of pressure depletion caused by adjacent existing producers may have a larger role in the performance of these new infill wells. How the various well spacing impact with the degree of reservoir pressure depletion from parent well is more important than ever for operators to optimize the completion design. Through data analytics and comprehensive fracture/reservoir modeling this paper studies how changes in well spacing and proppant volume in the Spraberry, a main formation in the Permian Basin, will impact new infill well performance. The studies in this paper are focused on the Midland Basin. A public database was used to identify the number of parent and child wells in the Midland basin. Data analysis of production normalized by total proppant and lateral length shows that parent wells outperform infill, or child, wells. To further understand the relationship between parent and child wells, a reservoir dataset for the Spraberry formation was used to build a hydraulic fracture and reservoir simulation model for both the parent well and a two-well infill pad. After production history matching a P50 type well as the parent well, three periods of production depletion were modeled (6 months, 3 years and 5 years) to understand the timing impact on the infill well production. A geomechanical finite-element model (FEM) was then used to quantify the changes to the magnitude and azimuth of the in-situ stresses from the various reservoir depletion scenarios. A two-well infill pad was then simulated into the altered stress field next to the parent well at various spacings between the parent and child wells. A sensitivity was then performed with different stimulation job sizes to understand the volume impact on created complex fracture propagation and total system recovery. This study can help operators understand how well spacing, reservoir depletion, and completion job size impact the infill well performance so they can optimize their infill well completion strategy.
Unconventional completions in North America have seen a paradigm shift in volumes of proppant pumped since 2014. There is a clear noticeable trend in both oil prices and proppant volumes – thanks to low product and service costs that accompanied the oil price crash in early 2015. As the industry continues to recover, operators are reevaluating completion designs to understand if these proppant volumes are beyond what is optimal. This paper analyzes trends in completion sizes and types across all major unconventional oil and gas plays in the US since 2011 and tracks their impact on well productivity. Completion and production data since 2011 from more than 70,000 horizontal wells in seven major basins (Gulf Coast, Permian, Appalachian, Anadarko, Haynesville, Williston and Denver Julesburg basins) and 11 major oil/gas producing formations were analyzed to examine developments in proppant and fluid volumes. Average concentration of proppant per gallon of fluid pumped was used to understand transitional trends in fracturing fluid types with time. Production performance indicators such as First month, Best 3 or Best 12 months of oil and gas production were mapped against completion volumes to evaluate if there are added economic advantages to pumping larger designs. In general, all major basins have seen progressive improvements in average well performance since 2011, with the Permian Basin showing the highest improvement, increasing from an average first-six-months oil production of 25,000 bbl in 2011 to 75,000 bbl in 2017. The Gulf Coast basin, where the Eagle Ford formation is located, has seen a 6-fold increase in proppant volumes pumped per foot of lateral since 2011 while the Permian and Appalachian basins hit peak proppant volumes in 2015 and 2016 respectively. In Permian and Eagleford wells, higher proppant volumes in general have resulted in better production up to a certain concentration. In Williston and Denver basins, most operators are moving away from gelled fluids, and reduced average proppant concentration per fluid volume pumped shows inclination toward hybrid or slickwater designs. While some of these observations are tied to reservoir quality, proppant volumes have begun to peak as operators have either reached an optimal point or are in the process of reducing volumes. Demand for proppant is expected to nearly double by 2020. As oil prices continue to recover, well AFEs continue to increase, despite multiple efforts to improve capital efficiency. The need for enhanced fracture conductivity and extended half-lengths on EURs are been discussed by combining actual observed production data and sensitivities using calibrated production models. The industry is moving toward large-volume slickwater fracturing operations using smaller proppants, but he operating landscape is expected to see a correction when such designs become less economical.
The evolution in oilfield technology to enable the drilling of longer horizontal wells and increased stimulation effectiveness via isolation has resulted in significant productivity gains. The challenges associated with data gathering, increased well count and understanding connectivity of the recently recognized additional reservoir (Three Forks) has generated concerns regarding the development strategy in the Williston Basin. In order to understand a development strategy it is crucial to characterize fracture properties and reservoir properties. A single well model is developed to capture current well performance to understand the impact of the range of fracture geometries and spacing on production performance. Modeling results and fracture pressure data are also presented to demonstrate the effectiveness of fracture initiation techniques, isolation techniques and number of clusters on fracture geometry generation. The paper presents results utilizing single well modeling techniques (using fracture history matching, production history matching and forecasting) to understand and differentiate reservoir quality, reservoir connectivity and completion effectiveness with the aim of understanding the direction in which completion changes must evolve.
It is well accepted by the Oil and Gas industry that approximately 30%-40% of perforations or perforation clusters do not contribute to the production of a multi-stage fracturing stimulated well. Diversion is a common method to maximize the wellbore coverage. The objective of this study is to evaluate and maximize the effect of diversion in multi-cluster horizontal well hydraulic fracturing applications using water hammer profile analysis, step down test and microseismic monitoring. In this study, the authors demonstrated integrated approach for the well stimulation efficiency evaluation. A number of methods have been used for analysis: First, step-down tests after each stage have been used to estimate perforations accepting fluid. Second, innovative method of the high frequency surface pressure record analysis was used to detect diversion. Additionally, microseismic monitoring was used as an independent measurement that allows to validate the results. Eight wells were hydraulically fractured with multiple clusters per stage. Each stage is separated either by frac baffles or plugs. Diverter was pumped to promote more uniform wellbore stimulation. Shut- in procedure was implemented after each diverter step. Signatures of water hammer during shut-in are recorded by high frequency pressure gauge and analyzed in real-time using advanced algorithm from speech processing domain. Locations of clusters receiving fluid were calculated and diversion results are qualified. Microseismic measurements in some of the evaluated wells and step down tests are also performed to qualify the diversion process. All of these measurements were done in real-time and utilized to maximize the number of frac propagations, which will have a positive impact on production. This engineering technique allows the operator to make informed real-time decision based on the effectiveness of inter-stage isolation and diversion. Small footprint high frequency pressure monitoring (HFPM) allows the optimization of cost/BOE ratio.
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