Why high porosity but low-production wells occur in carbonate reservoirs: An explanation from the perspective of pore structure

Abstract

High porosity but low-production wells exist in the Leikoupo Formation in the Sichuan Basin, China. The unclear explanation for this phenomenon has led to the failure of fracture development. We selected 15 cores from the study area based on the oil test data to investigate the cause from the pore structure perspective. The pore structures were studied via a variety of petrophysical experiments, which include conventional physical property analysis, casting thin section, nuclear magnetic resonance technique, and constant-rate mercury injection. The results indicate that the main explanation for the high porosity but low-production wells is that the larger pore-to-throat ratio makes for poor pore connectivity and more large pores and vugs are trapped. Movable fluid saturation can be significantly influenced by microscopic pore structure rather than physical parameters, which is positively affected by throat radius and negatively correlated with the pore-throat radius ratio, relative sorting coefficient, and tortuosity of the throat. The results provide a basis for the exploration of carbonate reservoirs from a microscopic perspective.