Research on gas content and its influencing factors of shale gas of the Lower Cambrian Niutitang Formation in Well Guidudi 1, southern Guizhou Depression

This paper is the result of shale gas geological survey engineering.

Objective The Niutitang Formation of the Lower Cambrian in the southwestern margin of the Xuefeng Uplift is currently a key area for shale gas exploration in the Upper Yangtze region. This study aims to identify the accumulation conditions and gas-bearing properties of shale gas in the Niutitang Formation of the research area, and to clarify the main controlling factors for shale gas enrichment.

Methods Based on the newly deployed drilling and testing analysis data of Well Guidudi 1, the petrological characteristics, organic geochemical characteristics, reservoir physical properties, reservoir space types and gas bearing properties of organic shale in the Niutitang Formation have been thoroughly studied. The main controlling factors and differences in shale gas accumulation in the first and third sections of the Niutitang Formation have been compared and analyzed.

Results (1) The mineral composition of the shales in the Niutitang Formation Section 1 is mainly brittle minerals, accounting for 66.14%. The contents of clay minerals, brittle minerals, and carbonate minerals of the shales in the Niutitang Formation Section 3 are balanced, accounting for 36.45%, 33.09%, and 30.45%, respectively; (2) The average TOC value of the shale in the Niutitang Formation Section 1 is 4.71%, and the organic matter type belongs to type I, with an average Ro value of 3.59%. The average TOC value of the shale in the Niutitang Formation Section 3 is 2.20%, and the organic matter type belongs to type I, with an average Ro value of 3.18%; (3) Five types of reservoir spaces are identified, including intragranular dissolved pores, intergranular pores, intergranular pores, organic pores, and microcracks. The Niutitang Formation Section 1 is mainly composed of organic pores, intergranular pores, and microcracks, while the Niutitang Formation Section 3 is mainly composed of intragranular dissolved pores; (4) The average total gas content analyzed on site in the Niutitang Formation Section 3 is 1.03 m³/t. The average total gas content analyzed on site in the Niutitang Formation Section 1 is 0.22 m³/t.

Conclusions By comparing the accumulation conditions and gas content of shale gas in the first and third sections of the Niutitang Formation, it is found that the accumulation of shale gas in the Niutitang Formation Section 1 is mainly influenced by conditions such as organic matter abundance, mineral composition, and pore structure. The gas content is positively correlated with organic carbon content and detrital mineral content. The accumulation of shale gas in the Niutitang Formation Section 3 is mainly influenced by conditions such as mineral composition and storage space, and the gas content is positively correlated with carbonate mineral content.