Exploring the potential of the lacustrine limestone reservoir in the Da’anzhai Member of the Sichuan Basin

Understanding the production dynamics characteristics is crucial in regulating the development potential of tight oil in lacustrine limestone reservoir. However, the development characteristics of oil wells with low production and long-cycles has hindered their commercial development in Da’anzhai Member of Sichuan basin. Here we carried out X-ray diffraction (XRD), focused ion beam scanning electron microscope (FIB-SEM), high-pressure mercury injection, nuclear magnetic resonance (NMR), and nano-CT experiments to study the factors controlling the production characteristics in the Da’anzhai Member in central Sichuan Basin. We found that the lacustrine limestone reservoir contains three types of pores and fractures: non-stratigraphic control, shell control, and matrix control. The lacustrine limestone reservoir developed various pore-throat systems, including along-fracture, dissolution pores, fracture-type pores, and isolated pores. Additionally, the small number, small size, dispersed distribution, and poor connectivity of the pores and throats lead to poor sorting, low mercury saturation, and high displacement pressure. The flow capacity is mainly affected by the size of the mainstream channel, the number of pores and throats, and the development degree of intergranular (interparticle) pores. We further demonstrate at least three types of pore-throat distributions corresponding to at least three types of exploitation model. Our work provides a promising route to evaluate the enormous development potential of tight oil in Sichuan basin.