应用ICT技术研究致密砂岩气藏储集层裂缝特征

Application of Industrial Computed Tomography(ICT) to Research of Fractured Tight Sandstone Gas Reservoirs

塔里木盆地某气田下白垩统巴什基奇克组储集层属于典型的低渗裂缝性砂岩储集层,由于经历构造运动期次多、埋藏深度大、夹层发育,储集层裂缝演化发育规律复杂.目前常用的裂缝描述方法（包括医用CT）存在精度低、定量评价效果差等不足.利用ICT层析扫描成像技术（工业CT）对该气田低渗裂缝性砂岩岩心内部裂缝进行了精细扫描成像,在此基础上对裂缝形态特征、产状、充填特征、空间组合和裂缝成因分类进行了系统研究.研究结果指出,研究区裂缝以高角度构造缝为主,可划分为张性缝、剪切缝和多期混合缝,裂缝形态有直线型、折线型、复杂网状、穗状和帚状等类型,首次发现裂缝发育复杂的“多层充填结构”,ICT扫描裂缝孔隙度主要为0.01％～0.04％.

The Lower Cretaceous Bashijiqike reservoirs in a gasfield of Kuqa depression in Tarim basin belong to a typical low-permeability and fractured tight sandstone reservoir. Their fractures have complex origin and evolution history due to a multistage tectonic movements experience, large burial depth and many interbeds. The fractures in them not only play an important role in oil and gas migration as the main effective pathway, but also a significant impact factor on the reservoir stimulation by hydraulic fracturing. The main methods （including medical CT） for fractures description or characterization have disadvantages of low identification precision and poor quantitative assessment effect. In this paper, ICT （Industrial Computed Tomography） technique is used to scan and image the inner fractures in core samples from the fractured tight sandstone reservoirs in this gasfield, based on which the systematically study is carried out on the shape, occurrence, filling feature, spatial combination and origin classification of the fractures. The result shows that the fractures occurred in this study area are dominated by high-angle tectonic fractures, including extension one, shear one and multistage mixed one given by mechanism analysis. The type of fractures can be divided into linear, broken line, complicated network, wheat-like and broom-like ones. And the lots of fractures have complex ＂multi-layer filling structure＂ that is discovered for the first time. The porosity of fractures in these reservoirs by the ICT analvsis mainly ranges from 0.01% to 0.04%.