Petroleum Science >2017, Issue 4: 720-730 DOI: https://doi.org/10.1007/s12182-017-0182-1
Fracture gradient prediction: an overview and an improved method Open Access
文章信息
作者:Jincai Zhang and Shang-Xian Yin
作者单位:
Geomech Energy, Houston, TX, USA; North China Institute of Science and Technology, Yanjiao, Beijing 101601, China; Present Address: Sinopec Tech, Houston, TX, USA and North China Institute of Science and Technology, Yanjiao, Beijing 101601, China
投稿时间:2017-09-02
引用方式:Zhang, J. & Yin, SX. Pet. Sci. (2017) 14: 720. https://doi.org/10.1007/s12182-017-0182-1
文章摘要
Abstract The fracture gradient is a critical parameter for drilling mud weight design in the energy industry. A new method in fracture gradient prediction is proposed based on analyzing worldwide leak-off test (LOT) data in offshore drilling. Current fracture gradient prediction methods are also reviewed and compared to the proposed method. We analyze more than 200 LOT data in several offshore petroleum basins and find that the fracture gradient depends not only on the overburden stress and pore pressure, but also on the depth. The data indicate that the effective stress coefficient is higher at a shallower depth than that at a deeper depth in the shale formations. Based on this finding, a depth-dependent effective stress coefficient is proposed and applied for fracture gradient prediction. In some petroleum basins, many wells need to be drilled through long sections of salt formations to reach hydrocarbon reservoirs. The fracture gradient in salt formations is very different from that in other sedimentary rocks. Leak-off test data in the salt formations are investigated, and a fracture gradient prediction method is proposed. Case applications are examined to compare different fracture gradient methods and validate the proposed methods. The reasons why the LOT value is higher than its overburden gradient are also explained.
关键词
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Keywords Fracture gradient prediction, Leak-off test, Breakdown pressure, Mud loss, Fracture gradient in salt