Geological Characteristics and Pooling Conditions of Terrigenous Mud Oil & Gas in China

Pan, Shuxin ¹; Wang, Tianqi ¹; Wei, Pingsheng ¹; Liu, Caiyan ¹
(1)PetroChina Exploration & Development Research Institute (Northwest), Lanzhou, China.

Lacustrine black mud, widely deposited in terrigenous basins during Mesozoic and Cenozoic, is expected to become a new exploration and development field in China. This article describe the depositional environment, the primary geological and geochemical characteristics of the black mud in China, and its exploration potential and differentia between marine shale and terrigenous mud are analyzed.

Gross thickness of terrigenous black mud ranges from 20 to 1300m with a burial depth of about 300-1500m in different basin. The mudstone mainly consists of clay mineral, and sometimes includes few siltstone. Dark mudstone, light-colored siltstone, and ostracoda mostly formed by interbedded. Total organic carbon(%,TOC) content ranges from 1 to 5%, up to 23%.Vitrinite reflection(%,Ro) ranges from 0.5 to 1.2%. Mud oil&gas systems are of three distinct types: biogenic gas , thermogenic oil and immature oil, although there can also be mixtures of the three gas&oil types. Almost all black mudstone have high pressure in drilling. Studies have shown that hydrocarbon generating pressure-boosting is one of the main factors to generate overpressure. Gas measurement showed obvious abnormity in black mud stone. In additional, multiple types of cracks, such as structural cracks, super-pressure micro-cracks, diagenetic micro-cracks, are developed in mudstone. The cracks are favorable to form fractured mud reservoirs.

There exist significant differences between terrigenous mud and marine shale in the depositional environment, the primary geological and geochemical characteristics.

Through comprehensive evaluation, it is thought that Songliao Basin, Bohai Bay Basin and Ordos Basin etc are favorable target for mud gas &oil exploration. Even in some basins, such as Songliao and Bohai Bay basin, commercial oil &gas production has been received in the mudstone. Mud oil and gas exploration has broad prospects in China.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.