Strata Uplift Controlled Deep Shale Gas Accumulation Modes: A Case Study from the Weiyuan Block, Sichuan Basin

Abstract

Shale gas exploration and development is regarded as one of the vital areas in which breakthroughs are urgently needed. The Longmaxi Formation shale in the Weiyuan Block was considered a case study. Based on the analysis of the physical evolution, burial history, thermal history, as well as hydrocarbon generation history of the Longmaxi Formation shales, the impact of uplift amplitude on the shale gas reservoirs, the shale gas transport pattern and direction in the adjustment stage, and the shale gas enrichment pattern are discussed in this study. The results from this study showed that (1) the Weiyuan Block could reach the maximum burial depth in the Late Middle Cretaceous, and then there was uplifting and erosion of the strata, with an erosion amount of 2000–4200 m. (2) The migration of shale gas is mostly contributed by Darcy flow and slippage flow. In addition, Darcy flow contributed to larger migration, which is about 100 times that of slippage flow. Darcy flow occurs in about 13.7% of the pores in the Longmaxi Formation shale. (3) The enrichment of shale gas can be significantly impacted by the uplift amplitude. The gas reservoirs with uplift amplitudes higher than 3000 m and lower than 3000 m differ significantly in terms of their physical characteristics, pressure coefficients, and gas concentrations. (4) The Longmaxi Formation shale gas reservoirs can be separated into five categories based on the uplift amplitudes, migration characteristics, and pressure coefficients: a lost gas reservoir, an enriched gas reservoir, a gas reservoir first enrichment and then loss, a gas reservoir first loss and then enrichment, and a supply gas reservoir. Although the supply gas reservoir occupies the largest area, the enriched gas reservoir is the key zone for analysis, as well as the development of the Longmaxi Formation shale gas in the Weiyuan Block.

Mechanism of Wettability and Pore Water Occurrence State in Overmaturity Shale: A Case Study of Longmaxi Formation Shale in South Sichuan Basin, China

“…(a) Structural unit of Sichuan Basin. (b) Stratigraphic histogram of Sichuan Basin (modified after ref ).…”

Genesis, Identification Method, and Exploration Potential Evaluation of Marine Low-Resistivity Shale Gas Reservoirs

“…Within the first section of the Longmaxi Formation, there are two subsections: the first subsection and the second subsection. The first subsection can be further divided into four sublayers (Figure b). ,, Due to its high organic matter abundance and porosity characteristics, the S 1 l 1 1 1 sublayer to S 1 l 1 1 3 sublayer interval is frequently utilized as the main shale gas production layer …”

Pore Structure and Migration Ability of Deep Shale Reservoirs in the Southern Sichuan Basin

“…The formula for calculating Kn can be obtained by referring to reference [20]. Since the migration ability of Darcy flow is 100 times that of slip flow and 10,000 to 1,000,000 times that of Fickian diffusion [20,21], we consider that if more than 1% of the pore volume in the samples satisfies Darcy flow, it can be approximately considered as satisfying Darcy's law.…”

“…However, these models primarily consider small pore sizes, neglecting the contributions of macropores and fractures to shale gas migration. Recent studies have discovered five distinct migration types for shale gas in bedding fractures and matrix pores, namely Darcy flow, slip flow, Fickian diffusion, Knudsen diffusion, and adsorptiondesorption diffusion [19][20][21]. These migration types significantly influence the enrichment level and determine favorable areas within shale gas reservoirs, exerting control over the direction and intensity of shale gas migration [20][21][22].…”

“…Pore structure parameters, including pore volume, specific surface area, pore size, and their distribution patterns, are of significant importance in studying the occurrence state, desorption diffusion, and permeability of shale gas [25][26][27][28][29]. Among these parameters, pore volume determines the migration space for shale gas, while pore size governs its migration mode and capacity [20][21][22]. In addition, the complexity of the pore system also affects the migration efficiency of shale gas.…”