Overpressure Study And Prediction In Hinterland Area Of Junggar Basin

It is a quite universal phenomenon that abnormal high pore fluid pressure (overpressure) occurs in oil gas-bearing basins, overpressure is one of the major earth kinetic reasons of the reservoir formation which is a kind of highly complicated self-organizing phenomenon. From the 1950s, with oil-gas exploration degree increasing, people found that abnormal high pore fluid pressure frequently occurred in the deep of sedimentary basins, which was dangerous to the safety of well drilling engineering and directly causes the increasing of petroleum exploration costs. Ever since then, overpressure causes of its formation and prediction were widely emphasized and strengthened. Presently, hot points in abnormal high pore fluid pressure mostly concentrate on main causes of its formation, its obturated mechanisms, pressure distribution, forecast by physical geographical and geological data, paleo-overpressure and pressure evolution simulation. Studies of pressure compartments and basin-centered gas combine abnormal pressure with petroleum reservoirs and then exploit new exploration fields.This paper studies the causes and distribution of overpressure in hinterland area of Junggar basin and predicts the overpressure of studying area. By the use of geological, well drilling and logging, test and seismic material, the paper discusses the characteristics and origins of the already known overpressure phenomenon in single wells. The corresponding relationship between known overpressure and geological and geographical parameters is built and the main methods of predicting overpressure and influence factors are discussed. Through seismic velocity data to predict deep overpressure by Jason software, analyze overpressure zone's construction and distribute characters, analyze the relationship of overpressure and oil-gas.According to measured pressure data, abnormal high pore fluid pressure universally exists in Junggar Basin. Horizontally, Maqiao, Mobei, Shixi, Shinan, Lunan, Jidong, Xiayan, front zones of southern mountains and Shikeshu Depression, with total area 7 × 10~4km~2, are characterized by similar overpressure distribution. Vertically, overpressure mainly appears in Permian, Triassic and Jurassic stratum with Carboniferous and Tertiary stratum existing some measured value. The range of the depth of overpressure distribution varies greatly and drilling data reveals that overpressure is almost found everywhere below 1500m. Causes of its formation may be due to tectonic extrusion of reverse overriding area or possibly and disequilibrium compaction. Preservation and release of pressure namely pressure obturated validity is mainly related to compaction, diagenesis, and circulation of pressure evolution and tectonic activities.By synthesis analysis of integrating slurry data of drilling, logging and pressure measured data of typical wells with clay mineral data of some wells, we get physical respondent features of over-pressured layers characterized by abnormal high sonic-log values in sandstone, siltstone and mudstone compared to regular sonic-log transmitting trends and obviously unusual lower inspecting resistance quotieties in shale compared to its normal trends, and sonic velocity of individual formations is therefore at a low level in the subsurface. From above discussed results,...