Lateral Percolation and Its Effect on Shale Gas Accumulation on the Basis of Complex Tectonic Background

Abstract

As a result of complex tectonic background, shale gas in China exhibits differential enrichment. Choosing a favorable exploration target accurately is a crucial problem to be solved. In this study, the tests show that there is a superior transportation pathway within shale layer. Gas in the shale layer percolates much more in the direction parallel to the plane. Therefore, the accumulation pattern of shale gas indicates a complex tectonic background. Gas in the lower part of the structure diffuses and percolates in the vertical direction into the surrounding rock. Most gas percolates towards the high part of the structure in the direction parallel to the plane. When the shale was exposed, gas percolated along the parallel direction into the air. In the case of fracture development, if there is a reverse fault, gas would be enriched in the footwall. However, if there is an unsealed fault, it would become a pathway for gas migration. The above accumulation pattern was proved in several Areas. Also, this research presented a basis of evaluation units division. According to the buried depth, fractures, and structural position, Xiuwu Basin was divided into five evaluation units and Unit A3 is the most favorable exploration target.

Effect of Hydrothermal Activity on Organic Matter Enrichment of Shale: A Case Study of the Upper Ordovician and the Lower Silurian in the Lower Yangtze, South China

“…According to previous research [33,34,[66][67][68], well X is located in the southern part of the Lower Yangtze, which is described as a deep-water shelf controlled by a foreland basin in the Late Ordovician and Early Silurian. The southern part of the Lower Yangtze generally transformed from shallow-water shelf into onshore and ancient land northwestwards, while the Cathaysia plate in the south changed dramatically from shallow-water shelf into and ancient land [34,35,67,68].…”

“…Yuan et al [31] and Wang et al [32] used difference of elements accumulation in deposition processes, applying the indicators Ca/(Ca + Fe) and Ti/Al for the characterization of different sedimentary environments and changes in water depth. Zhang et al [33][34][35] proposed a sequence division method for shale by lithology, well logging, and outcrop data, using U/Th as the principle index, Ca/(Ca + Fe) and Ti/Al as supporting indices.…”

“…Holdaway and Clayton [61] defined no-terrigenous siliceous minerals as excess silicon, and proposed a quantitative calculation method. In addition, based on large amount of statistics, Wedepohl [62], Adachi et al [63], and Yamamoto [64] proposed an Al-Fe-Mn method to identify the genesis of excess silicon (hydrothermal or biologic origin) widely applied under pelagic settings [33][34][35]60,65]. All these techniques help to reveal the influence of sedimentary environments on organic matter enrichment.…”

A Cause Analysis of the High-Content Nitrogen and Low-Content Hydrocarbon in Shale Gas: A Case Study of the Early Cambrian in Xiuwu Basin, Yangtze Region

“…This makes further study on shale gas accumulation mechanism urgent to be carried out [8,9]. Explorations on the accumulation mechanisms of shale gas have been carried out by previous works, including shale heterogeneity [10][11][12], shale pore connectivity [13][14][15][16], shale sedimentary environments [17], and structural styles [18,19]. However, compared with North America, the Paleozoic marine shale in South China experienced a more complex, multistage tectonic and thermal evolution.…”

Division of shale sequences and prediction of the favorable shale gas intervals: an example of the Lower Cambrian of Yangtze Region in Xiuwu Basin

“…Sequence stratigraphy has been successfully applied to the exploration of clastic and carbonate reservoirs since proposed nearly four decades ago [12][13][14][15][16][17][18]. However, the traditional sequence stratigraphy is based on the passive continental margins, with either carbonate or clastic sedimentary rocks.…”