Abstract
The Ordos Basin is the largest petroliferous basin in China, where the Chang 7 Member shale serves as the major source rock in the basin, with an area of more than 100,000 km2. So far, sedimentary and geochemical characterizations have rarely been conducted on the shale in shallow (< 1000 m) areas in the southeastern part of the basin, but such characterizations can help identify the genesis of organic-rich shale and promote the prediction and recovery of shale oil. In this paper, several outcrop sections of the Chang 7 Member in the Tongchuan area were observed and sampled, and sedimentary and geochemical characterizations were conducted for the well-outcropped YSC section. The study results show that the Chang 7 Member shale is widely distributed laterally with variable thickness. The organic-rich shale is 7–25 m thick in total and exhibits obvious horizontal variation in mineral composition. In the eastern sections, the shale contains organic matter of Type II2–III and is low in thermal maturity, with high clay mineral content, low K-feldspar content, and no pyrite. In the western sections, the shale contains Type II1 organic matter and is low in thermal maturity, with high clay mineral, K-feldspar, and pyrite contents. The YSC section reveals three obvious intervals in vertical mineral composition and organic abundance. The Chang 7 Member organic-rich shale (TOC > 10%) contains mainly sapropelite and liptinite, with Type II kerogen. It is generally characterized by a hydrocarbon potential of more than 70 mg/g, low maturity, and shallow–semideep lacustrine facies. In the western sections, the shale, still in a low maturity stage, has a higher hydrocarbon potential and is optional for shale oil recovery. However, the Chang 7 Member shale in the study area is highly heterogeneous and its shale oil recovery is practical only in the organic-rich intervals.
Highlights
The Ordos Basin is the largest petroleum production basin in China, where the PetroChina Changqing Oilfield Company has produced more than 50 million tonnes of oil and gas each year for the past four consecutive years
Based on available logs and drilling data, the sedimentary and geochemical characterizations were conducted for the well-outcropped YSC section to describe the longitudinal variation of organic-rich shale
Previous studies detected some liberal small-sized folds and minor fault structures locally in the southeastern part of the Ordos Basin, where the burial depth of oil shale generally increases from the southeast to the northwest; constrained by local landforms, the maximum valley-hillside height difference can be more than 200 m (Ren 2008; Li et al 2014)
Summary
The Ordos Basin is the largest petroleum production basin in China, where the PetroChina Changqing Oilfield Company has produced more than 50 million tonnes of oil and gas each year for the past four consecutive years. For the southeastern Ordos Basin, especially the Tongchuan area, a lot of studies have been conducted on shale with respect to sedimentary environment, genesis, distribution, characteristics, and resources (Lu et al 2006; Zhang et al 2006; Li et al 2009; Ren 2008), but no detailed sedimentary and geochemical characterizations have been made of outcrops. The horizontal and vertical sedimentary and geochemical characterizations of organic-rich shale in Chang 7 Member are insufficiently detailed. This has made it difficult to get a better understanding on the formation mechanisms and sedimentary patterns of fine-grained sediments and to select intervals for shale oil production. The sedimentary pattern of the Chang 7 Member shale was established
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call