Hydrocarbon Retention and Its Effect on Pore Structure Evolution of Marine Shale Based on Pyrolysis Simulation Experiments

Abstract

Studies on pore structure characterization and its interaction on hydrocarbon retention are the key to understanding shale oil and gas occurrence and accumulation mechanism. To evaluate the evolution of organic pores in marine shales, samples with high organic matter (5.74%) and low thermal maturity (0.67%) were collected from the Neoproterozoic Xiamaling Formation (Pr 3 x) in the Xiahuayuan region, Hebei province, northern China. Samples underwent a thermocompression simulation experiment, and the pore development and pore structure heterogeneity during shale thermal evolution were studied by using multiple techniques, including CO 2 and N 2 physisorption, mercury intrusion porosimetry, and field emission scanning electron microscopy. Meanwhile, the interaction mechanism between pore structure and hydrocarbon retention was revealed by the extraction of residual oil and fractal analyses. Results demonstrated that there is a two-stage interaction relationship between residual hydrocarbons and pore structure: (1) before 400 °C (R o = 1.25%), the pore structure mostly restricts the expulsion of hydrocarbons and (2) after 400 °C, the pore structure is primarily controlled by hydrocarbon expulsion and retention. Mesopores at 2−50 nm in diameters have the greatest effect on hydrocarbon retention, followed by macropores (>50 nm) and micropores (<2 nm). Residual hydrocarbons affect shale porosity by occupying a large amount of mesoporous space in shales, and the effect of pore surface heterogeneity on hydrocarbon retention is greater than that of pore structure heterogeneity. This study provides insights into pore structure evolution of a marine shale along the thermal maturity to further improve the pore development model for effective petroleum production.

Quantifying the Pore Heterogeneity of Alkaline Lake Shale during Hydrous Pyrolysis by Using the Multifractal Method

“…Furthermore, the temperature during pyrolysis plays a critical role in determining the efficiency of hydrocarbon generation and release within shale formations. The release of hydrocarbons in shale induces the production of acidic substances, leading to dissolution processes that significantly impact the development of shale pores [17,18].…”