Research on the differential tectonic-thermal evolution of Longmaxi shale in the southern Sichuan Basin

Abstract

The southern Sichuan Basin in China holds abundant shale gas resources; however, the shale gas bearing property shows great differences due to the multiple stages of tectonic transformation. The key to revealing the shale gas differential enrichment mechanism is to explore the thermal evolution characteristics during tectonic evolution. Therefore, taking the Luzhou and Changning blocks as an example, which have obvious differences in tectonic evolution, the organic geochemical conditions of Longmaxi shale were firstly compared with the test data. Then, the thermal evolution characteristics under the background differential tectonic uplift-erosion were recovered using basin modeling techniques. The results showed that the two blocks contain similar organic geochemical conditions of the Longmaxi shale. Moreover, the hydrocarbon generation condition in Luzhou Block is greater than that in the Changning Block. Influenced by the differential tectonic evolution, the study area experienced a complex burial history and the formation of multiple unconformities. As a result, the present burial depth of Longmaxi Formation in the Luzhou Block is significantly greater than that in the Changning Block. The thermal evolution history of Longmaxi shale in the study area could be divided into three stages, including a low-temperature stage from Caledonian to Hercynian, a middle-temperature stage from Hercynian to Indosinian, and a high-temperature stage from Yanshanian to Himalayan. In addition, it was found that the Himalayan period is the main stage resulting in the differential gas bearing property of Longmaxi shale in the southern Sichuan area. Under the differential structural modification, the peak time of hydrocarbon generation in the Luzhou Block occurred earlier and the conversion rate was slightly higher than that in the Changning Block.

Variational Reservoir Characteristics of the Wufeng–Longmaxi Formation from Different Sedimentary Region and Its Implications in Southeastern Sichuan Basin, China

“…On the basis of the kerogen-type classification standard of TI, 38 the TI results show that the organic matter type of shale in the YC-LL1 well is type I, while that in the YC-LL2 well and YC-LL3 well is type I or type II 1 (Figure 9). Therefore, based on the comprehensive analysis of δ 13 C and TI, it could be speculated that the organic type of samples from the YC-LL1 well is type I with a higher hydrocarbon generation potential than II 1 , while that from the YC-LL2 well and YC-LL3 well is type I or type II 1 .…”

“…When shale is regarded as a hydrocarbon source rock, it can be demonstrated that the higher the organic matter content of hydrocarbon source rocks, the higher the natural gas content generated. , Therefore, when evaluating the hydrocarbon generation capacity of shale, that is, a kind of hydrocarbon source rock, the geochemical characteristics of the hydrocarbon source rock including organic matter abundance, organic matter type, and degree of organic matter evolution need to be involved . Switching to the perspective of being a hydrocarbon reservoir formation, with the successful exploitation of shale gas in North America, such as the Barnet, Marcellus, and Woodford shales, , shale gas in China also has received much attention from sedimentologists. − Especially, the Wufeng–Longmaxi shale (i.e., from the upper Ordovician Wufeng to the lower Silurian Longmaxi formation) is currently the key stratum for commercial shale gas exploration and development in the whole Sichuan Basin and its periphery, represented by the southeast Sichuan Basin. ,− …”

Forward modeling of P- and S-waves response of fractures intersected with horizontal wells in tight reservoirs

“…With the vigorous development of unconventional reservoir exploration and development (Ozkan et al, 2009;Sayed et al, 2017;Dang et al, 2022;Zhao et al, 2023), horizontal well has been widely used for its effectively connecting with reservoirs and expanding oil production area (Joshi, 1991;Soliman and Boonen, 1996;Qun et al, 2022). Exploration and development practice has shown that fractures are key factors for deep gas development.…”

Multi-Scale and Multi-Dimensional Imaging of Mineral Matrix Pore-Fracture Networks in Lower-Thermal-Maturity Lacustrine Shale: Examples from the Paleogene Shahejie Formation, Bohai Bay Basin

“…The rising demand of hydrocarbons as a clean and green energy source has caused the study of unconventional oil and gas resources. − The unconventional mudrocks have received renewed research focus for over two decades because of their emergence as the source and reservoir for shale oil and shale gas (mudrocks include mudstones and shales). − Major shale oil plays include the Shahejie, Kongdian, Qingshankou, Yanchang, Fengcheng, and Lucaogou shales in China ,, and the Bakken, Woodford, Eagle Ford formations in North America. − Shale gas plays consist of the Wufeng-Longmaxi, Qiongzhusi, Shanxi-Taiyuan, and Yanchang shales in China − and the Lewis, Antrim, New Albany, Ohio, Barnett, Marcellus, Haynesville, and Fayetteville formations in North America. ,− ,, …”