Distribution and genesis of secondary pores in Paleogene clastic reservoirs of Beidagang structural belt in the Huanghua depression

Abstract

The distribution and genesis of secondary pores in Paleogene clastic reservoirs of Beidagang structural belt in the Huanghua depression have been systematically studied. We investigated sedimentary facies and carried out a comprehensive analysis of the vast amount of data from casting thin sections, scanning electron microscope and physical data. Then we analyzed the pore types, pore evolution, distribution and genesis of secondary pores in our study area and discussed the factors controlling the distribution of secondary pores. The results show that pores in the study area are largely composed of intergranular dissolution pores and constituent dissolved pores. Three secondary pore zones were developed in the study area at depths of 2800∼3400 m, 3600∼4200 m and 4500∼4800 m. Secondary pores have been formed mainly because carbonate cement, feldspar, clastic debris and other plastic substances were dissolved by organic acid, released during the evolution of organic matter and acid water formed by CO 2. The development and distribution of secondary pores are vertically controlled by the maturity time of source rocks and horizontally by the distribution of acid water. As well, this distribution was affected by the sedimentary facies belt and the development of fault zones.