深部硬石膏岩盖层地应力测井评价方法

硬石膏岩具有极低的渗透性及良好的压力封闭能力,通常作为大型油气藏的良好区域盖层。塔里木盆地西南部地区古近系地层深部发育较厚的硬石膏岩层。深部硬石膏岩层的地质特征及应力环境相对复杂,对其地应力进行精细测井评价可以为高效钻探提供依据。通过设计三轴力学和声学同步测试实验,模拟地层高应力环境,获取硬石膏岩力学参数。在此基础上,结合地应力实验测试及测井方法,对古近系硬石膏岩层地应力进行测井评价。利用频散校正技术将实验测试的样品高频(1 MHz)波速值转换为测井频率(20 kHz)波速值。建立了古近系硬石膏岩的横波时差及动静态岩石力学参数解释模型。利用改进的Newberry模型对目的层地应力进行了测井评价,整体地应力预测结果的相对误差为5.6%,绝对误差为3.16 MPa,能够满足工程需要。

Log Evaluation Method of Geo-stress in Deep Anhydrite Cap Rock

Anhydrite rock has very low permeability and great pressure sealing ability it is usually used as a good regional cap rock for large oil and gas reservoirs.The deep strata of Paleogene in the southwestern Tarim Basin were developed with thick anhydrite rock formations.The geological characteristics and stress environment of this deep anhydrite rock layer were relatively complex and fine logging evaluation of its geo-stress can provide a basis for efficient drilling.In this paper the triaxial mechanics and acoustic synchronization test experiments were designed to simulate the high stress environment of the formation and obtain the mechanical parameters of anhydrite.On this basis combined with the experimental test of ground stress and logging method the logging stress of the Paleogene anhydrite rock stratum was evaluated.In addition using frequency dispersion correction technology the high frequency(1 MHz)wave velocity value of the sample was converted to the wave velocity value of logging frequency(kHz)and the model of transverse wave time difference and dynamic static rock mechanics parameters of Paleogene anhydrite Rock was established.The improved Newberry model was used to evaluate the geo-stress of the target layer the relative error of the overall geo-stress prediction result was 5.6%and the absolute error was 3.16 MPa which can meet the engineering needs.