Abstract:

Suibin depression is one of secondary tectonic units in the western Sanjiang Basin. As an unique sedimentary basin in Mesozoic, which developed marine and marine-continental transitional formations in the northeast China, conventional oil-gas breakthrough has not been made. So the study of unconventional oil-gas geology is of great importance. The Chengzihe-Muleng coal-bearing formation organic-rich shale in the Lower Cretaceous, the Mesozoic, are the main source rock in these areas. By analysis of the distribution, geochemical indicators, reservoir characteristics and gas-bearing of the Lower Cretaceous shale in Suibin depression, the results indicate that the Lower Cretaceous dark shale is broadly distributed (＞2,000 km²) and extents widely in large thickness (＞1,000 m) with a high TOC content (＞1.3%), a high thermal maturation (1.19%) influenced by the local volcanic activity, and typeⅡ₂-Ⅲ kerogens. The shale reservoir has high brittle mineral content with a large proportion of the quartz and feldspar content, which indicates that the shale can be well fractured. Additionally, the abnormal responses of gasbearing shale on well logging also indicate that it is qualified for the geological conditions to accumulate shale gas. Compared with the main parameters of North American marine and China marine or lacustrine shale, the favorable area of shale gas exploration in Suibin depression is located in the northern of PuyangNandalinzi sag and the southern of Jixian-Dongrong. And Chengzihe Formation shale may be the most favorable layers for shale gas exploration, followed by Muleng Formation shale, with a huge resource potential of shale gas.

Key words: shale gas, continental shale, geological condition, the Lower Cretaceous, Suibin depression, Sanjiang Basin