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Energies 2017, 10(11), 1820;

Moderate Collapse in a Shale Cap of a Nearly Depleted Reservoir

College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil & Gas Reservoirs, Xi’an Shiyou University, Xi’an 710065, China
Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX 78712, USA
Authors to whom correspondence should be addressed.
Academic Editor: Mehrdad Massoudi
Received: 29 September 2017 / Revised: 6 November 2017 / Accepted: 8 November 2017 / Published: 9 November 2017
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Reservoir depletion will cause the safe equivalent circulation density (ECD) operating window of drilling fluids to narrow, or even disappear. Previous studies have proposed a set of two specific casings at the top and bottom of the depleted reservoir, respectively, or conducted wellbore strengthening to increase fracture pressure, but these will cause a waste of time and costs, or differential pressure sticking. Aiming at resolving this problem, a novel concept and evaluation method of moderate collapse in the shale cap was developed and case calculations were performed. The results show that the degree of collapse is different for wells drilled in different types of fault regimes, and it can be controlled by optimizing the well trajectory. The collapse pressure within the shale cap was decreased due to reservoir depletion, and when a certain degree of collapse was acceptable, the collapse pressure can be even lower and a safe operating window will appear which can be beneficial to optimizing the casing program and drilling design. The research results provide a theoretical basis and new design idea for successfully and economically drilling into new untapped reservoirs in deeper horizons through depleted zones in the future. View Full-Text
Keywords: reservoir depletion; moderate collapse; shale cap; safe operating window reservoir depletion; moderate collapse; shale cap; safe operating window

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Zhao, K.; Han, J.; Dou, L.; Feng, Y. Moderate Collapse in a Shale Cap of a Nearly Depleted Reservoir. Energies 2017, 10, 1820.

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