| Borehole wall stability problem often happen in drilling engineering which is a very complicated problem. W12 oilfield group is located in the west of the south China sea of beibu gulf basin, the region is often met in drilling operation in the near future of borehole wall instability affects drilling speed, lead to the low operation time, high cost, seriously affect the progress of exploration and development of drilling and completion, and affect the final comprehensive economic benefits.W12 oilfield group is the development of new fields planned new multiple platform development, has developed dozens of Wells. Throughout the early stage of the adjoining well drilling operation situation, combined with the current drilling program, summing up the field of operation difficulties are as follows:fault, crack development, rock hydration, prone to collapse; Well depth is larger: the average of depth is more than three thousand meters; More than four kilometers have seneral well; Maximum depth reaches nearly five kilometers, resulting in long open hole section, increased the wall rock of soaking time; Multi-port well pressure coefficient of the average, the mud weight is high, easy to leakage formation; Poor drillability, results in the decrease of the mechanical drilling rate, increase the exposure time of open hole; well track is complex, including high Angle long oblique section, prone to other complex situations. These complex have caused great difficulties on the optimal selection of optimization of hole structure.In this paper, aiming at the existing problem of W12 oilfield group, use the data of logging, geology and drilling and well completion, through a lot of research work, combined with drilling engineering difficulties in the study area and formation characteristics, conducting W12 oilfield group of borehole wall stability and well bore structure optimization research. By establishing the calculation model of formation pore pressure, the use of geological, logging, drilling, logging, testing data, combined with oil field geology, determine the longitudinal distribution of formation pore pressure, the further research of formation pore pressure transverse distribution. Through the experiment of stratum collapsed cycle are analyzed and predicted, so the cycle of hole collapse and drilling fluid system and the relationship between density of drilling fluid. According to the W12 oilfield group of formation pore pressure and fracture pressure and collapse pressure distribution in strata pressure leakage, collapse and economic to drill ends layer for the principle, identify the wellblock single-well reasonable casing program. In the process of study mainly solve these following problems:(1) oilfield group of faults, fracture development, rock hydration, generally speaking, the early stage of the borehole wall instability is serious, need to figure out the causes of borehole wall instability and horizon, detect the horizon prone to leakage, and precise calculation of formation pressure, and obtain the corresponding pressure profile recommended safe mud density window, so that choose the appropriate when homework mud weight and performance.(2) Through indoor mechanics experiment of rock mechanics parameter, According to the region of rock for determination of in-situ stress tests and in-situ stress profile, study on sidewall stability in the region(3) oilfield group drilling hole depth is larger, part of the well drilling in poor drillability of formation, and track complex, open hole long exposure time, so we need to estimate collapse period, get naked eye exposure time limit data, provide basic data for casing program design.(4) the formation of three pressure calculation result and the result of the collapse cycle analysis, optimize the ODP recommended hole structure, the aim is to reduce the complicated situation, reduce the operation cost. |
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