Abstract

The Vaca Muerta shale oil play in Argentina's Neuquén Basin is expected to make a large contribution to Argentina's hydrocarbon production in the future. In 2013, the U.S. Energy Information Administration estimated that the Vaca Muerta had technically recoverable reserves of 308 Tcf gas and 16 billion bbl of oil and condensate, making it the third largest shale oil reservoir in the world at that time. Wintershall Energia has been active in the Neuquén Basin since 1994. In 2014, it acquired a controlling interest in the Aguada Federal block with an intention to exploit the Vaca Muerta oil shale occurrence within that block. At the outset of its development program, Wintershall decided to incorporate microseismic monitoring to help understand completions in the Vaca Muerta. Monitoring of the completion of vertical well AF.x-1 was accomplished with a surface array. The goal of the monitoring was to inform later decisions on horizontal wellbore direction, wellbore and stage spacing, and landing depth. Results of the surface array monitoring were also used in the design of a permanent buried array intended to monitor subsequent development wells. The buried array was installed in September 2016 and consists of 126 stations spread at an interval distance of approximately 500 m over an area of roughly 5 by 7 km. Each station has geophones placed over a depth range of 20 to 50 m subsurface. The first two horizontal development wells in the project, AF.x-4h and AF.x-9h, were completed in late December 2016 and early January 2017. The second set of two wells, AF.x-3h and AF.x-7h, was completed from May to June 2017. The 4h and the 7h were landed in the upper Middle Vaca Muerta while the 9h and 3h were drilled about 100 m deeper, landing still in the Middle Vaca Muerta. The lateral length of each well was approximately 1000 m, and each was completed with 11 plug-and-perf stages. Stage length and interval were varied along the wells to test various completion strategies. The completions of all four wells were successfully monitored using the buried array. These microseismic data provide a detailed description of the fracture network created by the treatments. Focal mechanisms determined for the detected events have been used to understand the stress distribution in the reservoir and to further refine the completion parameters for future development wells.

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