Characteristics of the N Gas Reservoir and Controlling Factors of Natural Gas Enrichment in the Right Bank Region of the Amu Darya Basin

The right bank region of the Amu Darya River in Turkmenistan is rich in oil and gas resources in the Middle-Upper Jurassic Callovian-Oxfordian Formation. In recent years, significant achievements have been made in exploration, among which the central N gas field on the right bank of the Amu Darya River has achieved major breakthroughs through rolling exploration. In order to clarify the main controlling factors affecting the high natural gas production in the N gas field, this study systematically analyzed the accumulation elements and natural gas accumulation laws of the Callovian-Oxfordian gas reservoir by combining core macro-micro characteristics, logging, geophysical exploration, and development production data. The research shows that a set of high-quality source rocks with organic carbon content (TOC) of 0.5–2% and maturity (Ro) of 0.8–2.5% was developed in the Middle-Lower Jurassic, laying the material foundation for natural gas enrichment; the grain beach and bioherm (mound) sedimentary facies zones of the Callovian-Oxfordian Formation constitute high-quality reservoirs; the thickness of the Upper Jurassic Kimmeridgian-Tithonian gypsum layer reaches 1400 m, with good sealing performance; the Permian-Jurassic paleostructural highlands and Neogene reverse faults jointly form effective traps; NE-SW and NW-SE high-angle reverse faults not only control the charging of natural gas but also promote the reservoir dissolution during the diagenetic period. Comprehensive analysis shows that the formation of the Jurassic gas reservoir in the N gas field is mainly controlled by inherited paleo-uplifts, Cenozoic reverse faults, and gypsum salt layers. The study clarifies the main controlling factors of high natural gas production in the N gas field, provides theoretical guidance for the exploration of similar reservoirs in the Amu Darya Basin, and expands the exploration field of sub-salt reservoirs.