Comparison and integration of experimental methods to characterize the full-range pore features of tight gas sandstone-A case study in Songliao Basin of China

摘要

Pore size distribution (PSD) is a crucial parameter for reserve grading and estimating the productivity of tight oil and gas. The various types and scales of pores in tight reservoirs make any quantification of the PSD with a single experiment incomprehensive; instead, the integration of various techniques is required. This paper present's a case study of the Low Cretaceous tight gas sandstone of the Sorigliao Basin in China that compares and integrates various experimental data to uncover the full-range PSD of tight sandstone with different pore ranges. Scanning electron microscopy (SEM), low-temperature nitrogen adsorption (LTNA), nuclear magnetic resonance (NMR), and rate-controlled porosimetry (RCP)/pressure-controlled porosimetry (PCP) were utilized on the same samples with distinctly different permeabilities and clay contents. For tight sand samples with a high clay content; LTNA can reflect 70% + of pores and reveal the presence of ink-bottle-shaped pores, which leads to deviations between PCP and LTNA results for smaller pores (<20 nm). In comparison, NMR can measure large pores (>200 nm) beyond the range of LTNA but underestimates the-volume of very small pores due to the large echo spacing and larger surface relaxivity of samples. For tight sand samples with a low clay content, the LTNA and RCP results are complementary and can reveal similar to 75% of pores. The left peak of RCP is in excellent agreement with the NMR results, but the right peak shows clear deviations from the NMR results and is similar to SEM images, indicating that RCP overestimates the size of large pores. A new approach for characterizing the full-range PSD by combining NMR and LTNA is established, demonstrating that low clay and high clay tight sand samples contain pores in the main ranges of 0.2-20 tm and 10-300 nm, respectively. Pores are divided into three ranges with dividing diameters of 0.5 mu m and 3 gm, corresponding to relatively smaller inter-crystalline pores (ICPs) in clay and calcite, ICPs in clay and quartz, and residual interparticle pores and dissolution pores. Among these, ICPs in clay dominate. (C) 2016 Elsevier B.V. All rights reserved.