Located in Kelasu Structural Belt in northern Tarim Basin, China, Kelasu Gas Field has mainly pre-salt steep structures in the exploration targets of Cretaceous Bashijiqike and Baxigai Formations. The reservoirs have burial depth ranging from 6000m to 8000m and thickness ranging from 200m to 320m. The formation pressure is 150 MPa and the formation temperature is 190 °C. The reservoirs are typical tight sandstone gas reservoirs with matrix sandstone permeability ranging from 0.001mD to 0.1mD and the porosity ranging from 2% to 8%. The gas reservoirs are very serious in heterogeneity, with fault systems well developed. The distribution of water bodies is complex, and in some of the reservoirs, water invasion occurred fast at the early stage of development, which have serious influence on gas reservoir recovery.
Through years of technical study and deepening understanding of geological characteristics and production performance of gas reservoirs, it has been made clear that the main factors affecting the efficient and economic development of the gas reservoirs are structural style, fault system and water body distribution. Laboratory displacement experiments and numerical simulation about differentiated techniques such as well patterns, well types, multi-stage hydraulic fracturing design and implementation, gas production rate have been carried out to explore the applicable measures for enhancement of recovery efficiency of tight sandstone gas reservoir under high temperature and ultra-high-pressure conditions.
The research results show that the recovery efficiency of the tight gas reservoir has been increased by 10%-15% because of optimum selection of uniform well distribution or Z-shaped well pattern, developed well types with combination of vertical wells, highly deviated wells and horizontal wells, and temporary soft layers plugging and mechanical hard layered fracture network stimulation technology, implementation of annular pressure control and five-sphere integrated production management and control technology including "barrier maintenance, real-time monitoring, anomaly diagnosis, risk assessment and classification administration" to accelerate the fulfillment of fit-for-purpose wellbore life-cycle management and water prevention and sand control measures, and application of different technical strategies including differential gas production rate, etc.