The Sinian-Cambrian formation shale gas exploration and practice in southern margin of Huangling paleo-uplift

The Sinian Doushantuo and the Cambrian Niutitang formations in southern China have a good shale gas resource potential. Although > 20 wells have already been drilled in these formations, the shale gas production has been much lower than expected, due to the high thermal maturity of the rocks and the severely disturbed geological structure of the corresponding area. An industrial gas flow was discovered only in the Weiyuan region. To achieve the shale gas breakthrough of paleo-shale strata, it is necessary to find a shale reservoir with low thermal maturity and weak geological deformation. On the basis of the study on the Weiyuan, Huangling and other paleo-uplifts, a shale gas accumulation mechanism named shale gas accumulating around the edges of paleouplifts was proposed. It has been suggested that the shale gas is usually contained within the slope belt of a paleo-uplift margin characterized by a shallow burial depth, stable structure activity, and a low level of thermal maturity. Taking into account this accumulation mechanism, a large number of wells have been drilled on the southern edge of the Huangling paleo-uplift (western Hubei province). Organic-enriched shales with high shale gas content and low thermal maturity, have been found within the Sinian Doushantuo and the Cambrian Niutitang formations. To tackle the problems deriving from the low exploration level, complex geological structure, low temperature, and low pressure in the region, we proposed and applied innovative fracturing process, new complex fracturing techniques and new recovering technology systems. High and stable shale outputs were obtained from the Niutitang Formation (well Yangye-1HF, HF: Horizontal Well Fracturing) and from the Doushantuo Formation (well Yangye-2HF): 7.83 x 10(4) and 5.53 x 10(4) m(3)/day, respectively. These outputs were achieved following horizontal well section fracturing, which resulted in a significant breakthrough for the production capacity of the low-pressure shale gas reservoir in the complex tectonic region outside of the Sichuan Basin.