Tectonic Fracture Formation and Distribution in Ultradeep Marine Carbonate Gas Reservoirs: A Case Study of the Maokou Formation in the Jiulongshan Gas Field, Sichuan Basin, Southwest China

Abstract

Tectonic fractures are the key factors affecting hydrocarbon migration and accumulation in ultradeep marine carbonate gas reservoirs. Taking the Maokou Formation in the Jiulongshan Gas Field as an example, tectonic fracture formation and distribution are quantitatively characterized by the outcrops, cores, Fullbore Formation MicroImager (FMI) imaging logging, acoustic emission experiments, fluid inclusion experiments, and burial–thermal evolution history analysis. The formation stage of the tectonic fractures in the study area can generally be divided into three stages: the Indosinian stage, the early middle Yanshanian stage, and the late Yanshanian–Himalayan stage. The key stages are the early middle Yanshanian stage and the late Yanshanian–Himalayan stage. According to the theory of tectonic geomechanics, the evolution pattern of different stages of tectonic fractures and faults in the Maokou Formation is established. The finite element method was used to simulate the three-dimensional paleotectonic stress field during the key stages of fracture formation, and a rock failure criterion (η) was used to quantitatively predict the development and distribution of the tectonic fracture. In the early middle Yanshanian stage, the fracture degree was relatively small, and the highly fractured areas were mainly concentrated in the areas near the northern fault zone and the high part of the anticline, with the highest rock failure proximity of 1.118. In the late Yanshanian–early Himalayan stage, the highly fractured areas are distributed in the northeast and northwest, near the E–W fault rupture zone, the high parts of the Jiulongshan and Tadongping areas, and the local tectonic high parts. The degree of rock failure mainly concentrated between 0.890 and 1.127. There is a good positive correlation between the fracture density and the degree of rock failure.

Geological Characteristics and Controlling Factors of Enrichment of Deep Shale Gas in the East Weiyuan–North Rongchang Area, Sichuan Basin, China

“…Fractures are important reservoir spaces and migration channels of shale gas, playing an important role in the accumulation, preservation, exploration, and development of shale gas (Li et al, 2019c;Li et al, 2020;Li H. et al, 2021;Li 2021). Investigation of the Lower Paleozoic marine shale gas in the Sichuan Basin and its surrounding areas shows that marine shale has a good material foundation, and gas-bearing can almost be observed in each drilling.…”

“…et al, 2020Xu F. S. et al, 2021;Xi et al, 2021a, Xi et al, 2021b. Previous studies have made great progress in understanding the geological characteristics of shale reservoirs; defined the geochemical characteristics, mineralogical characteristics, and reservoir space characteristics of the reservoirs; found that the sedimentary environment, organic matter (OM), clay minerals, brittle minerals, and fractures are the main controlling factors of shale reservoir yields; and formed a comprehensive research system for shale reservoirs (Chen et al, 2016;Li et al, 2019c;Chen S. L. et al, 2020;Li et al, 2020;Liu et al, 2020;Chen et al, 2021a;Chen et al, 2021b;Liu J. et al, 2021;Sun, 2021). However, these research results and conclusions apply mainly to shallow shale gas with a burial depth of less than 3,500 m. Due to the influence of sedimentation, diagenesis, and tectonism, deep shale gas reservoirs have higher contents of brittle minerals, more developed natural fractures, and more complex pore evolution, resulting in different shale geological characteristics and controlling factors for shale gas enrichment and yield (Yin et al, 2019;Chen F. et al, 2020;Chai et al, 2020;Xu and Gao, 2020;Yin and Wu, 2020;Zhou et al, 2020;Song et al, 2021;Tabatabaei 2021).…”

Development Characteristics and Finite Element Simulation of Fractures in Tight Oil Sandstone Reservoirs of Yanchang Formation in Western Ordos Basin

“…The collection cost of conventional logging data is much cheaper than other data, so it is widely used in reservoir exploration and evaluation (Jiang et al, 2017;Liu et al, 2019;Santosh and Feng., 2020;Yoshida and Santosh., 2020;He et al, 2021;Huang et al, 2021). However, the logging response is a comprehensive reflection of the various characteristics of the rock, and it is easily affected by factors such as fillings, mud, and dissolution (Mardia et al, 2007;Laubach et al, 2009;Sun et al, 2014;Hu et al, 2020;Li et al, 2020;Kang., 2021). Therefore, it is very difficult to directly use conventional logging curves to identify fractures.…”

Genetic Mechanism of Pyrite in the Shale of the Longmaxi Formation and Its Influence on the Pore Structure: A Case Study of the Changning Area, South Sichuan Basin of SW China

“…The contribution of pyrite developed in shale to the pore system is now widely accepted (Li et al, 2019;Li et al, 2020;Liu et al, 2022), but there are still some disputes about its porosity development degree and the importance of pores related to pyrite. The contribution of pore development characteristics related to the pyrite of a shale reservoir cannot be quantified .…”