Development and technology status of energy storage in depleted gas reservoirs

Utilizing energy storage in depleted oil and gas reservoirs can improve productivity while reducing power costs and is one of the best ways to achieve synergistic development of"Carbon Peak–Carbon Neutral"and"Underground Resource Utiliza-tion".Starting from the development of Compressed Air Energy Storage(CAES)technology,the site selection of CAES in depleted gas and oil reservoirs,the evolution mechanism of reservoir dynamic sealing,and the high-flow CAES and injection technology are summarized.It focuses on analyzing the characteristics,key equipment,reservoir construction,application scenarios and cost analysis of CAES projects,and sorting out the technical key points and existing difficulties.The devel-opment trend of CAES technology is proposed,and the future development path is scrutinized to provide reference for the research of CAES projects in depleted oil and gas reservoirs.

Large-Scale Carbon Dioxide Storage in Salt Caverns:Evaluation of Operation,Safety,and Potential in China

Underground salt cavern CO_(2) storage(SCCS)offers the dual benefits of enabling extensive CO_(2) storage and facilitating the utilization of CO_(2) resources while contributing the regulation of the carbon market.Its economic and operational advantages over traditional carbon capture,utilization,and storage(CCUS)projects make SCCS a more cost-effective and flexible option.Despite the widespread use of salt caverns for storing various substances,differences exist between SCCS and traditional salt cavern energy storage in terms of gas-tightness,carbon injection,brine extraction control,long-term carbon storage stability,and site selection criteria.These distinctions stem from the unique phase change characteristics of CO_(2) and the application scenarios of SCCS.Therefore,targeted and forward-looking scientific research on SCCS is imperative.This paper introduces the implementation principles and application scenarios of SCCS,emphasizing its connections with carbon emissions,carbon utilization,and renewable energy peak shaving.It delves into the operational characteristics and economic advantages of SCCS compared with other CCUS methods,and addresses associated scientific challenges.In this paper,we establish a pressure equation for carbon injection and brine extraction,that considers the phase change characteristics of CO_(2),and we analyze the pressure during carbon injection.By comparing the viscosities of CO_(2) and other gases,SCCS’s excellent sealing performance is demonstrated.Building on this,we develop a long-term stability evaluation model and associated indices,which analyze the impact of the injection speed and minimum operating pressure on stability.Field countermeasures to ensure stability are proposed.Site selection criteria for SCCS are established,preliminary salt mine sites suitable for SCCS are identified in China,and an initial estimate of achievable carbon storage scale in China is made at over 51.8-77.7 million tons,utilizing only 20%-30%volume of abandoned salt caverns.This paper addresses key scientific and engineering challenges facing SCCS and determines crucial technical parameters,such as the operating pressure,burial depth,and storage scale,and it offers essential guidance for implementing SCCS projects in China.

New design method of unequal taper thread(UTT)pairs and its application in API NC38 thread improvement

API standard threads are the most commonly used thread configurations for drill pipe joints in the petroleum industry.Recently with the increasing application of horizontal wells and extended-reach wells in drilling engineering,drill pipe joint threads are subjected to complex loads,and drill pipe joint thread breakage accidents occur frequently.The API NC38 threaded pair used in the SU36-8-4H2 well suffered a fracture accident.Macroscopic analysis found that the fracture sites were located near the root of the first engagement pin-thread where the stress was greatest.Therefore,it is necessary to find an alternative method to reduce the largest stress of NC38 threads.Then,a new design method of unequal taper thread(UTT)pairs is proposed that the taper of pin thread,slightly smaller than the taper of matched-box thread,is not equal to one of box-thread.In the UTT pairs of API NC38 thread,the taper of box thread is kept as the standard taper of 1:6,but the taper of pin thread is,respectively,1:6.1(UTT-I),1:6.2(UTT-Ⅱ),1:6.3(UTT-Ⅲ)and 1:6.4(UTT-IV).The 3D finite element models of four UTT pairs and one standard pair based on NC38 thread were developed,and the mechanical properties of five thread pairs bearing such typical working loads as torque,axial compression,axial tension,bending moment,internal and external pressure,were analyzed.The results show that four UTT pairs are superior to the standard pair of API NC38,and UTT-Ⅲ has the most performance in all of four UTT pairs.Compared with the standard pair of API NC38,UTT-Ⅲ pair can improve the bearing capacity such as torsion strength,compression strength,tensile strength,bending strength,strength against internal and external pressure,by 24.8%,13.2%,22%,9.99%and 14.2%,respectively.The new design method of UTT pair enhances the bearing capacity of API NC38 thread,and has been applied in Changqing Drilling Company of CNPC Chuanqing Drilling Engineering Company Limited.The UTT-thread pair method is not only applicable for API series threads to improve the connection performance,but also suitable for various non-API taper connection threads to promote existing working ability such as air tightness,stress corrosion resistance,fatigue resistance et al.