Leak-Off Mechanism and Pressure Prediction for Shallow Sediments in Deepwater Drilling  

作　　者：TAN Qiang DENG Jingen SUN Jin LIU Wei YU Baohua 

机构地区：[1]State Key Laboratory of Petroleum Resources and Prospecting, ChinaUniversity of Petroleum-Beijing [2]Key Laboratory of Marine Georesources and Prospecting (Hainan Province), Institute of Deep-Sea Science and Engineering, Chinese Academy of Science

出　　处：《Journal of Ocean University of China》2018年第1期65-71,共7页中国海洋大学学报（英文版）

基　　金：supported by the National Basic Research Program (973 Program, No. 2015CB251201);the National Science Foundation Innovative Research Groups (No. 51221003);the Science Foundation of China University of Petroleum, Beijing (No. ZX20150192)

摘　　要：Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS(minimum horizontal principle stress) model and the FIF(fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC(permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling.Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS(minimum horizontal principle stress) model and the FIF(fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC(permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling.

关 键 词：deepwater drilling SHALLOW SEDIMENTS leak-off MECHANISM leak-off PRESSURE 

分 类 号：P7[天文地球—海洋科学]