Combined technology of PCP and nano-CT quantitative characterization of dense oil reservoir pore throat characteristics

Abstract

The size of pore throats in tight oil reservoirs varies from a few tens of nanometers to several hundred micrometers. This complex and diverse microscopic pore throat structure restricts the exploration and development process, affecting the recovery rate. Size, shape, and spatial distribution of pore throats in tight oil reservoirs are revealed in this paper via a scanning electron microscope (SEM), casting thin-sections, high-pressure mercury injection, and Nano-CT. Results show that the pore type of the Chang 7 tight oil reservoir in the Xin’anbian area is mainly divided into three categories: intergranular pores, dissolution pores, and microfractures. Numerous nanoscale pore throats have developed in this area, which greatly contributes to reservoir capacity and seepage. Pore throat distribution on capillary pressure curves of different samples shows that when the threshold pressure is less than 1 Mpa, there are many micron-sized pores with good connectivity and pore throats form a large tubular shape with a throat radius between 3.6 and 1064 nm. When the threshold pressure ranges from 1 to 3 MPa, there are many nanoscale pores with good local connectivity, intragranular dissolution pores develop, and pore throats are in tube bundles and spherical in shape with the throat radius between 3.6−657 nm. When the threshold pressure is greater than 3 MPa, nanoscale microfractures develop and are connected to neighboring small spherical pores, small spherical nanopore spaces become isolated, vertical connectivity is poor, and the throat radius is between 3.6−242 nm.