Shale gas reservoir-forming conditions and exploration prospecting in the Cambrian Hetang Formation of southwestern Zhejiang and northeastern Jiangxi Province

This paper is the result of oil and gas exploration engineering.

Objective The dark shale of the Cambrian Hetang Formation widely occurred in southwestern Zhejiang and northeastern Jiangxi is the key target of shale gas exploration in the Lower Yangtze region. However, due to the present low exploration level of this interval, understanding of the shale gas accumulation conditions is still insufficient.

Methods Based on the analysis of geological background, organic geochemical indicators and field stratigraphic outcrop investigation of the dark shale, the shale gas resource potential is evaluated and the favorable areas are optimized.

Results The dark shale ranges from 35 to 200 meters in thickness with an average of over 50 meters in Jiangshan-Changshan area and is characterized by medium to high content of organic matter (TOC ranging from 1.48% to 23.53%) and high to over maturity (Ro ranging from 2.01% to 3.0%). The organic matters are highly and over highly matured. Abundant micropores and microfractures were observed in the shales, indicating the high quality shale reservoirs. The isothermal adsorption experiment shows that the carbonaceous shale has strong adsorption ability, which reaches 5.93 kg/t on average.

Conclusions It is suggested that the region of Jiangshan-Changshan area in western Zhejiang is favorable for shale gas exploration on the basis of relatively low thermal evolution of organic matter and stable stratigraphic structure preservation conditions.