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.

Technical status and challenges of shale gas development in Sichuan Basin,China

During the past decade,shale gas developments have changed the energy structure in the US natural gas industry,and the exploration activities for shale gas are also increasing worldwide.According to the papers published in recent years,shale gas resources are quite abundant in China.With the successful experience obtained from North America,many state-of-the-art technologies are brought in and refined for field application.State-owned enterprise,private enterprises and foreign enterprises have all actively participated in the exploitation of shale gas.Compared with US,China faces many more challenges,both geological and above-ground,in the development of shale gas resources.This paper begins with the introduction of shale gas reserve distribution in China and the identified shale gas formation in Sichuan Basin.The following paper reviews the methodology employed in the geophysical prospecting,drilling and completion,and hydraulic fracturing process.Since China is in the early stage of shale gas development,there is a great technical gap between China and North America.Based on literature review,the major challenges faced in the exploration and production process are identified.What presented in this paper should be of particular interest to the personnels involved in shale gas production in China and countries that are about to set foot in shale gas business.It will also be of interest to researchers who are dedicated to developing these technologies to unlock unconventional gas resources in China.