核磁共振冻融法表征非常规油气储层孔隙的适用性

核磁共振冻融法是当前非常规油气储层孔隙分布研究的一个热点技术,但因这类孔隙分布与成因复杂,使得该方法的适用性和准确性仍不很确定,是领域研究的难点。为加深对此的认识,采用核磁共振冻融法,结合相对传统的压汞法、氮气吸附法以及核磁共振T2法,分别对页岩、煤、致密砂岩3类端元非常规储层样品进行了孔径分布特征测试对比研究。结果表明,核磁共振冻融法在表征非常规储层纳米孔隙分布特征方面具有很好的适用性和准确性,但样品和实验条件也在一定程度上影响着测试精度,如制样大小、探针液体的KGibbs-Thomson(KGT)、冻融损伤以及金属矿物(黄铁矿)的含量等。因此实际分析中需根据研究对象选择合适颗粒大小的样品进行测定,需首先计算得出适合待测样品的KGT,需要探索新的探针液体,而因大多数非常规储层样品中的黄铁矿含量较低(10%),所以测试结果仍能够比较完整定量地刻画孔隙。核磁共振冻融法对于表征非常规储层孔隙很有潜力,其适用性和准确性还需进一步探索。

Application of nuclear magnetic resonance cryoporometry in unconventional reservoir rocks

Currently, Nuclear magnetic resonance(NMR) cryoporometry is a hotspot technology for studying the pore distribution of unconventional hydrocarbon reservoir. But due to the complex distribution and genesis of such pores, the applicability and accuracy of this method is still uncertain, which is the difficulty in this field study. To deepen this understanding, NMR cryoporometry is used in combination with relatively traditional mercury porosimetry, nitrogen adsorption method and nuclear magnetic resonance method, so as to perform a comparative study on the pore distribution characteristic test of three types of end-member unconventional reservoir samples including shale, coal and tight sandstone. The results show that NMR cryoporometry has good applicability and accuracy in characterizing the nanopore distribution features of unconventional reservoirs, but the test precision, such as sample size, K_{Gibbs-Thomson}(K_GT) of probe liquid, freezing-thawing damage and metallic mineral (pyrite)content, is also influenced by the samples and experiment conditions to some extent. Thus, in a practical analysis, the samples with suitable grain size should be selected for measurement according to research object. Firstly, it is required to calculate the K_GT of the samples to be tested and explore the new probe liquid. However, because of the lower pyrite content (<10%)in most unconventional reservoir samples, the test results can still characterize the pores in a relative complete and quantitative way. NMR cryoporometry has a great potential for characterizing unconventional reservoir pores, and its applicability and accuracy are still to be explored further.