Abstract:

The microscopic test results can reflect abundant oil reservoir information. Currently, there is a growing number of microscopic testing technologies for micro-pores and fractures, but there is still a lack of the understanding of micropores. In order to compare various test techniques, Caoqiao buried hill of Le’an oilfield in Jiyang depression is taken as a typical study case, different fine microscopic specialized test techniques are used to analyze the characteristics of pore and fracture storage spaces, including the composition analysis of micro dissolved hole electron probe, scanning electron microscope, thin slice, and cathodic-luminescence tests. The microscopic characteristics and statistical laws of micro dissolution pores are specifically described. There are some new findings: organic matter, calcite, pyrite, dolomite, gypsum, and other components are found in the electron probe composition of micro dissolution pores of limestone. In thin sections, pores can be found between and inside gravels in limestone oil layers, and there is some calcite at the edges of dissolution pores. The dolomite is mainly composed of inter-granular pores. Through scanning electron microscopy (SEM) analysis, it is found that the crystalline pores of dolomite representing the block are two or more orders of magnitude larger than the dissolution pores of limestone. The brittleness of the rock and whether it is easy to fracture can be inferred through inter-granular pores or dissolution pores; By conducting cathodo-luminescence tests on rock samples, it is possible to distinguish several stages of pore filling materials, which are different in composition. Both SEM and mercury intrusion porosimetry can measure pore-throat sizes. Comparing the two techniques, SEM can measure local nanoscale pore-throat diameter, while mercury intrusion porosimetry can measure the micrometer scale pore-throat radius of a rock sample. From the perspective of application objects, the former is suitable for the pores and throats of minerals, while the latter is more suitable for the comparative research of pores and throats in oil exploitation blocks.

Key words: carbonate rock, micro-dissolved pore, electron probe, SEM, cathodic-luminescence, thin slice, Le’an oilfield