| Lost circulation is one of the most serious situations affecting drilling operation safety. The occurrence of lost circulation not only can bring damage to the drilling engineering, but also can cause borehole collapse, blowout and pipe-sticking accidents. If the lost circulation couldn’t be handled in time, it will make some or all well sections scrap. Thus, there will be difficult to exploit oil and gas resources.The first regional exploration well of the Yalu River basin was Lincan 1. It was drilled in October of the year 2012. Since then it has occurred lost circulation many times and caused serious economical losses. Based on the field data and stratum situation analysis, we made a conclusion that the porosity and fracture of basalt caused malignant leakage of upper strata, while void and micro-fracture caused small or medium leakage of lower strata. We took measures to solve this leakage problem. Adopting bridge blinding and sealing slurry can solve the lost circulation of upper strata. To solve the lower strata leakage, we adopted the method of bridge blinding. Finally we formulate the implementation scheme of drilling fluid and plugging measures, and guide the field construction.A mathematical model for Herschel-Bulkley [yield-power-law(YPL)] drilling-fluid losses in naturally fractured formations is presented.The study of the effect of fluid rheology on mud losses con-vinced us that use of LCMs is not the only way of reducing mud losses. LCMs may result in permanent damage of productive fractured zones. The use of LCM in conjunction with rheology adjustment is recommended as a better way of mitigating fluid losses. From the quantitative analysis of field data on the basis of the provided model, estimates of the fracture width can be obtained. This is valuable information for designing sealing treatments and other potential cures for lost circulation. The model provides an effective tool for characterizing naturally fractured reservoirs along with well-completion strategies. |
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