Application of GEM elemental logging in shale reservoir sedimentary environment identification

Abstract

BackgroundElement capture logging can be used to determine the elemental contents of rocks in formations.PurposeThis study aims to obtain accurate elemental composition, the content of shale reservoirs and the inaugural parameter well for shale gas in the Cambrian Niutitang Formation of the Baojing Block, located in the Middle Yangtze region of China, with emphasis on the developmental and distributional characteristics of shale gas reservoirs in this formation.MethodsThe shale gas parameter well BY2 was taken as the research object, by interpreting and processing elemental capture logging data, precise elemental compositions of the shale reservoirs were determined. This analysis led to the creation of a comprehensive geochemical index profile for the Niutitang Formation. Additionally, elemental geochemical indicators were used to identify and reconstruct the paleosedimentary environments.ResultsThe analysis results reveal that the predominant elements in the Niutitang Formation's shale are Si, Al, and Fe, accompanied by lower amounts of K, Ca, Mg, and S. The shale features relatively high concentrations of Si, Fe, and S, which contributed to its enhanced fracturing ability. The sedimentation process of this shale can be categorized as active continental margin sedimentation. The source material for the sedimentary rocks is originated from the Kangdian ancient land, located in the northwest. The sedimentation is primarily normal but was influenced by the presence of hydrothermal fluids in the region's active tectonic zone.ConclusionsThe upper section of the Niutitang formation is subject to a dry climate during its depositional period, featuring gentle slope sedimentation at the periphery of a stagnant basin and a lack of oxygen, characterizing with high water salinity, ample land supply, and low water body paleoproductivity this region. Conversely, the lower section is experienced a humid climate and served as a deep-water retention basin, with limited the land supply, but high water salinity and paleoproductivity, leading to the accumulation of organic matter. The aquatic setting is primarily anaerobic, conditions that are conducive to the preservation of organic matter, and provides an optimal sedimentary environment for the generation and concentration of shale gas.

Keywords

• shale reservoir
• element logging
• interpretation and processing
• geochemistry
• depositional environment