Abstract
The North American success of unconventional oil development from marine shales has inspired the global liquid-rich shale (LRS) exploration and production trend. Resource evaluation and screening are always important for emerging shale basins. In contrast to North America, 95% of the LRS resources in China are found within lacustrine shales. Songliao, Ordos, Junggar and Bohai Bay basin are the four major lacustrine oil basins in which LRS plays are claimed and considered to be of huge resource in China. Lacustrine system differs from marine systems in many aspects with high impact on the LRS commercial development. Adopted from the classic Darcy’s law, resource potential, flow ability and drive energy are the three key factors influencing estimated ultimate recovery (EUR). Unlike routine in-place volume driven play assessment, this paper presents a multi-component EUR driven evaluation and screening that has been applied to the four major lacustrine basins in China. 1) Compared with ocean, lake usually developed in a confined area which result in the thick shale pack (more than 100m in most cases). However, in some basin, single layers with high total organic content (TOC) is thin and their distribution is disrupted by low TOC mud rocks, which would impact play resource potential. 2) Regarding the difference in kerogen type between marine and lacustrine shales, it was observed that Type I dominated lacustrine shales have a lower HC conversion rate than Type II kerogens for a given maturity, indicating that a higher maturity would be essential to achieving better fluid properties. These higher maturities tend to be found more toward the basin centers, that are often characterized by deeper burial and increased clay content. As deeper burial and higher clay content can lead to increased drilling and completion (fracability) challenges that may be costly, so a careful balance must be achieved when seeking higher maturity. 3) Considering of heterogeneity of lacustrine system, highly frequented alternation among different lithologies were observed in some lacustrine plays. The high stress contrast between different lithologies would consume energy of hydraulic fracture and impact the fracture growth.
