Progress and development directions of stimulation techniques for ultra-deep oil and gas reservoirs

By reviewing the development history of stimulation techniques for deep/ultra-deep oil and gas reservoirs, the new progress in this field in China and abroad has been summed up, including deeper understanding on formation mechanisms of fracture network in deep/ultra-deep oil and gas reservoir, performance improvement of fracturing fluid materials, fine stratification of ultra-deep vertical wells, and mature staged multi-cluster fracturing technique for ultra-deep and highly deviated wells/horizontal wells. In light of the exploration and development trend of ultra-deep oil and gas reservoirs in China, the requirements and technical difficulties in ultra-deep oil and gas reservoir stimulation are discussed: (1) The research and application of integrated geological engineering technology is difficult. (2) The requirements on fracturing materials for stimulation are high. (3) It is difficult to further improve the production in vertical profile of the ultra-deep and hugely thick reservoirs. (4) The requirements on tools and supporting high-pressure equipment on the ground for stimulation are high. (5) It is difficult to achieve efficient stimulation of ultra-deep, high-temperature and high-pressure wells. (6) It is difficult to monitor directly the reservoir stimulation and evaluate the stimulation effect accurately after stimulation. In line with the complex geological characteristics of ultra-deep oil and gas reservoirs in China, seven technical development directions are proposed: (1) To establish systematic new techniques for basic research and evaluation experiments; (2) to strengthen geological research and improve the operational mechanism of integrating geological research and engineering operation; (3) to develop high-efficiency fracturing materials for ultra-deep reservoirs; (4) to research separated layer fracturing technology for ultra-deep and hugely thick reservoirs; (5) to explore fracture-control stimulation technology for ultra-deep horizontal well; (6) to develop direct monitoring technology for hydraulic fractures in ultra-deep oil and gas reservoirs; (7) to develop downhole fracturing tools with high temperature and high pressure tolerance and supporting wellhead equipment able to withstand high pressure.