岩石微观结构CT扫描表征技术研究

CHARACTERIZATION OF ROCK MICROSTRUCTURE USING 3D X-RAY COMPUTED TOMOGRAPHY

岩石微观结构特征研究对非常规油气藏的演化规律、油气赋存状态、运移方式、渗流特征等基础地质问题研究具有重要的科学意义.利用CT扫描技术对油砂、致密砂岩和页岩样品微观结构表征研究,并对比了常规测试方法与CT扫描表征技术的差异性.对比CT扫描法和筛分法测试油砂矿物的粒度分布,两者结果十分接近,矿物颗粒大小分布总体趋势上差异小,但小于96μm的颗粒矿物分布差异性稍大.CT扫描结果显示致密砂岩样品的裂缝比较发育,还发育溶蚀孔隙.由于测试方法和样品大小的差异性,CT扫描获得的孔隙度略大于氦气法孔隙度.微米CT扫描可以表征页岩的层理发育情况,但无法表征内部的微观孔隙结构.与常规测试方法相比,纳米CT扫描表征页岩中有机质和黄铁矿的含量等方面准确性好,但孔隙度测试结果偏小.纳米CT分辨率还不能完全满足表征页岩的微观孔隙结构的要求,同时有机质和孔隙的灰度值差异较小,两者区分难度大,因此纳米CT还无法完全准确表征页岩微观孔隙结构.

The investigation on microstructure of rock is critical to the basic geology research in unconventional oil and gas reservoir, such as evolution, occurrence state of oil and gas, migration patterns and seepage characteristics. The advantages of pore structure characterization by computed tomography（CT） are multi-scale and without damage. The tar sand, tight sand and shale were scanned by the CT, and the results were compared between CT scan characterizations and normal measurements to show that the mineral total components are really close and the size distributions of mineral are overall small difference, and large difference in the mineral size less than 96 μm between CT scan and the sieving method on tar sand. The pore structure of tight sand was observed by the CT images. Due to the different measurements and sample size, the porosity tested by CT scan, is a little more. The layer structure of shale can be found by micro CT images, but the microstructure of pore are not distinguished by the micro CT. Compared with normal methods, the TOC and pyrite mineral are measured by the Nano CT scan, but the porosity test is smaller. It is due to the resolution of Nano CT is not high enough and the grey value between organic matter and pore are not easily separately.