鄂尔多斯南部上古生界泥岩突破压力测井解释及区域预测

LOGGING INTERPRETATION AND REGIONAL PREDICTION OF MUDSTONE BREAKTHROUGH PRESSURES IN THE UPPER PALEOZOIC,SOUTH ORDOS BASIN

突破压力是泥质盖层封闭性能评价的关键参数,通过岩心实测数据与测井参数的相关分析,建立了声波时差与突破压力的关系,并依据此关系研究了鄂尔多斯盆地南部地区上古生界泥岩突破压力的垂向和平面分布规律。结果表明,突破压力西高东低、北高南低,且东西向压力差异显著。中二叠世早期开始,盆地南部湖相分布广泛,沉积速率快,泥质含量高,晚三叠世—早侏罗世盆地快速沉降,上石盒子组泥岩在叠加压实过程中排液受阻,发育异常高压,突破压力总体表现较低。下石盒子组沉积期及其以前,突破压力高值沿庆阳、延安及宜川呈弧形展布,低值沿南西向分布,从上石盒子时期开始,突破压力低压值的分布方向由研究区的南西向逐渐变化为南东向,高值则由东部和东北部迁移到西部及西南部。

The breakthrough pressure is the key parameter in evaluating the sealing capabilities of mudstone caprock. Through the cor-relation analysis of measured core pressures and logging data, the equation between the acoustic transit time and the breakthrough pres-sure was established and, on such a basis, the vertical and plane variation characteristics of mudstone breakthrough pressures in the Upper Paleozoic of south Ordos Basin were studied. The result showed that pressure values in the west and north areas were higher than those in the south and east, and pressure differences in the east-west direction were remarkable. Due to high deposition rate and clay content in the wide lake facies developed from early Middle Permian and rapid subsidence of basin from Late Triassic to Early Juassic, liquid discharge of mudstone in the Upper Shihezi Formation was blocked during the overlying compaction that caused abnormal high pressures and relatively low breakthrough pressures. Before and during the deposition of Lower Dhihezi Formation, high breakthrough pressures were distributed in arc along Qingyang, Yanan and Yichuan, low pressures were in the SW direction of the study area, while from the Upper Shihezi Formation period, low pressure distribution direction changed gradually southeastward and high pressures trans-ferred from the east and northeast of the study area to the west and southwest.