Geological characteristics and developmental achievements of the large presalt carbonate gas fields in the Amu Darya Basin

Abstract

The Amu Darya Basin accounts for one of the most abundant natural gas resources globally, it is the main gas supplier to the Central Asian natural gas pipeline. It also holds potential for the natural gas exploration and development. Within this basin, valuable Jurassic carbonate rocks and gypsum-salt-gas-bearing combinations are developed. These include the presalt transitional Middle and Lower Jurassic coal-bearing source rocks, which provide sufficient gas sources, and the Middle and Upper Jurassic reef-shoal carbonate and gypsum salts, forming an effective reservoir–caprock combination. The unique geological configuration forms optimal accumulation conditions for natural gas in the high-energy sedimentary-facies belt of the carbonate platform which controlled by the coal-bearing gas-generation center and large basement ancient uplift area. Large natural gas fields are mainly distributed in the presalt Jurassic carbonate rocks, driven by high-quality hydrocarbon-generation centers, ancient uplift backgrounds, and ultrathick gypsum-salt rocks. While large gas fields have been discovered in large structural traps at the center of the depressions, exploration potential is still remains in the vast area with a burial depth exceeding 4500 m. These make the basin a key area for further exploration. The Amu Darya Right Bank Block located in the northeast of the basin, which has seen 15 years of rapid and efficient exploration and development by PetroChina, has discovered three gas field groups, each contains 2 billion m3 of gas: the western intraplatform shoal, central gently sloping reef beach, and Eastern thrust structure, fracture-cave-type gas field groups. PetroChina has achieved a production capacity of 14 billion cubic meters. In response to the geological and developmental characteristics of the three gas field groups, tailored development strategies have been formulated. The strategies are based on the integrated concept of geological and developmental engineering. Optimization efforts have been made in well pattern deployment, including highly deviated wells, as well as the design of gas field pressurization engineering. In addition, comprehensive evaluations have been conducted, taking the stable production period, water-avoidance distance, and investment considerations into account. The efforts aim to support the project of transforming the Amu Darya River into a model for the efficient development of the “Belt and Road” energy cooperation project.