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Best selection among crack criterions to sandstone-mudstone formation and its application to fracture penetration ability evaluation |
LU Hu-sheng1,ZHANG Jun-feng2,U Shi-yin3,Z0U Jun4,LIU Ai-wu5
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(1. School of Geosciences in China University of Petroleum, Qingdao 266580, China ;2. Outling Oilfield Developing Company of Qingkai Oilfield, PetroChina, Haixizhou 816400, China;3. Communication Company of Tarim Basin Oilfield of Xinjiang,Korla 841000, China ;4. External Cooperation and Marketing Department of Chuanqing Drilling Engineering Company Limited,PetroChina,Chengdu 610051, China ;5. Exploration and Development Research. Institute of Jianghan Oilfield Company,S!N0PEC,Wuhan 430223, China)
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Abstract: |
Based on the present rock crack criterions,cores observation and rock mechanic tests, a new effective rock failure criterion for interbedded sand and mud stone formation in a certain fractured oil and gas field was developed through the method of mathematical deduction. The penetration degree of fractures in mudstone was evaluated based on the quantitative model between tectonic stress and fracture parameters. The results show that for the compressed conditions, multibowl Kou-lomb-Mohr criterion will be selected to study the formation, but for the tensile conditions,Griffith criterion should be selected. With obvious difference in mechanical properties of sandstone and mudstone, fractures will form in sandstone firstly, then extend into mudstone in vertical direction with variable occurrence. The critical thickness of mudstone is 5 m whether fracture could penetrate the mudstone,and most of fractures will end at the lithologic interface. For the same conditions, the thinner sandstone is easy to generate fractures. When the sandstone thickness reaches 20 m, the thickness variation of sandstone has little influence on fracture's development and penetration degree among mudstone. |
Key words: interbedded sand and mud stone formation tectonic stress fracture density crack criterions |
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