Shiyou shiyan dizhi (Mar 2021)
Formation conditions of shale oil and favorable targets in the second member of Paleogene Funing Formation in Qintong Sag, Subei Basin
Abstract
The favorable targets of shale oil exploration were optimized based on the analyses of hydrocarbon generation, reservoir conditions and oil content of the shale sections in the second member of Paleogene Funing Formation in the Qintong Sag, Subei Basin. Some favorable zones were predicted according to the properties of lithology, pressure and fractures. The mud shale with an organic carbon content (TOC) greater than 1.0% is widespread in the second member of Funing Formation with the thickness distributed between 160-260 m. The Ro values vary from 0.5% to 1.1%, indicating a wide maturity range. The organic matter type is good, and the organic microscopic maceral is dominated with algae, which provides a substantial potential for generation of shale oil. The average porosity of the second member of Funing Formation is 8.9%. Dissolved pores, clay minerals and carbonate intercrystalline pores act as main reservoir spaces. For the laminar marls and silty mudstones, micro-fractures were well developed, which controlled the permeability of the reservoir. From the third to the fifth section of the second member of Funing Formation, the content of brittle minerals distributed between 62%-65%, mainly composed with quartz, calcite and dolomite. The free hydrocarbon content (S1) showed a range of 0.1-2.7 mg/g, with an average value of 0.54 mg/g, referring the most favorable layers for shale oil exploration of the sections mentioned above. The shale oil in the second member of Funing Formation in the study area was mainly types Ⅱ and Ⅲ. It has also been indicated that the Shiyan and Chujialou deep depressions are the most favorable areas for silty mudstone and marl reservoirs, while the eastern slope is favorable for tuff mudstone shale reservoirs.
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