Abstract
Abstract The northern Guizhou area, located near the southwestern margin of the Yangtze Block, is a promising area for shale gas exploration and development. The Lower Silurian Shiniulan Formation as a new discovery stratum of natural gas marks an exciting breakthrough in natural gas exploration in northern Guizhou area. Based on several field investigations and samples analyses, the lithology and fracture characteristics were systematically analyzed in the lower Shiniulan Formation, and the reservoir specificity and its influence on natural gas accumulation were determined. The characteristics of the relatively fractures and lithology assemblages were identified as key factors controlling the natural gas accumulation. The lower Shiniulan Formation is deposited as calcareous shale and marlstone with frequent centimeter-scale interlayers. This is reflective of a shallow sea shelf strata with decreasing sedimentary rhythm and gradual weakening of sedimentary changes and developed calcareous shale and marlstone with frequent centimeter scale interlayer changes. The gas reservoir is dominated by calcareous mudstone, controlled by the interbedded rock association (calcareous mudstone and limestone), characterized by the raw-storage and the accumulation-reservoir interbedded system. The reservoir is located in the central part of the syncline and is characterized by strong sealing of the stratum, large proportion of free gas, and high abnormal pressure. The Lower Shiniulan Formation is formed between the shale layer with horizontal fractures and dense limestone with underdeveloped fractures. Among them, the shale section generally develops diagenetic shrinkage fractures, which provide good storage space for natural gas and act as the main body of natural gas. The pore sizes in limestone (2.8 nm) are significantly smaller than those in mudstone (7.5 nm), which results in a good capping and preservation of shale gas. This paper reports on results that are of significance for supplementing the theory of unconventional natural gas accumulation and guiding shale gas exploration in similar areas.
Highlights
Along with the rapid development of the economy, the consumption of oil and gas resources is increasing
This paper reports on results that are of significance for supplementing the theory of unconventional natural gas accumulation and guiding shale gas exploration in similar areas
Anchang syncline in the northern Guizhou Province is located in the southwestern margin of the Yangtze Block, south of the Sichuan Basin (Figure 1)
Summary
Along with the rapid development of the economy, the consumption of oil and gas resources is increasing. The Silurian Longmaxi and the Upper Ordovician Wufeng Formations are important target layers of high-yield natural gas in the Sichuan Basin and are the main strata in which exploration and development progress have been achieved [15,16,17,57,65]. Studies of these strata have shown that high yield of shale gas has become. Combining the observations with the statistics of the developed fracture and reservoir physical properties, the main factors affecting gas accumulation were investigated
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