Study Of Mud Lost Mechanism And Loss Prediction Method Of Steeply-folded Structure In X Block Of Myanmer

Myanmer X Block is one of key blocks of SINOPEC oversea strategic exploration and development investment. Most of wells in this block are deep exploration wells which are located in steep structure and have complex formation with a large number of cracks, mud lost was frequently encountered during drilling process. This phenomenon has highered the drilling cost and constrained the development step. It is essential to do the research for formation fracture prediction and analysis, mud lost mechanism and prediction approach. Doing this could provide valuable thereotical basis for drilling parameters design optimization pre-drilling, mud lost prediction and prevention.For the strong geologic stress action and abundant formation fracture existed in steep structure, the paper combined the macro geology mechanical feature with micro rock mechanism, applying finite element analysis theory and using geology, seismic, logging data and drilling report materials, according to Myanmer X Block structure characteristic and history, to establish geology structure model, and then the stress distribution of this structure could be gained based on the determination of the boundary conditions, inversion standard, mechanism properties, loading type, constrain condition and rock mechanical parameters, afterwards, through the rock strength criterion, the formation fracture distribution and fracture parameters could be determined. The analysis result could be helpful for the flow mechanism of the wellbore fluid and the formation fluid in the fracture.Considering the formation fluid invasion, the annuals circulation pressure loss determination method for single phase and multiphase fluid has been studied in this paper, the model of drilling fluid circulation pressure loss determination under two-phase fluid condition has also been established.For the obvious change of the wellbore temperature, drilling fluid properties and density in the deep well, on the basis of the current forecast model of temperature and the drilling fluid density filed in the wellbore of deepwater wells, the law of equivalent static density change of the drilling fluid in wellbore of deepwater well was obtained. The result has shown the impact regular of the different casing program, drilling string assemble and drilling properties to drilling fluid equivalent static density. Mud lost was encountered frequently in X block druing drilling, and the lost type was different, based on this phenomenon, the dynamic pressure balance relationship for different mud lost kinds and the dynamic drilling fluid lost model have been established. The model not only could predict and estimate the mud lost position and properties, but also do the in-situ lost circulation assessment. This approach has provided a new way to solve problems existed in mud lost prediction and assessment pre-drilling.Finally, the application of this method discussed above in the well Yagyi-1 of Myanmer X Block has also been presented; the result was consistent with the actual mud lost statistic report.