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Dynamic variation of fracture width and its effects on drilling fluid lost circulation in fractured vuggy reservoirs |
LI Da qi1, KANG Yi li1, ZENG Yi jin2, LIAN Zhang hua1, DU Chun chao3
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(1.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China;2.Research Institute of Petroleum Engineering, SINOPEC, Beijing 100101, China;3.Northwest Oilfield Company, SINOPEC, Urumqi 830013, China)
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Abstract: |
Based on the geological condition of Tahe Oilfield area 12, a finite element model considering vuggy and drilling fluid losses was established and the fracture width change and its effects on lost circulation were researched by using the model and the drilling practices. The results show that the fracture width is extremely sensitive to the wellbore pressure in fractured vuggy reservoirs, and the fracture width increments will be up to millimeter level under the positive pressure difference of several mega pascal. Drilling fluid losses would make the fracture width become wider and change the fracture morphology accordingly, which increases the difficulty of drilling fluid losses control. The strong stress sensitivity is one of main reasons of lost circulation besides the development of fractured vuggy. Then, precisely managing the wellbore pressure, keeping slightly over balance pressure, and adding millimeter level high acid soluble bridging materials to drilling fluid during drilling the reservoir section can prevent drilling fluid losses. |
Key words: fractured vuggy reservoirs fracture width drilling fluid losses lost circulation control numerical simulation |
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