“Extreme utilization”development theory of unconventional natural gas

In the process of unconventional natural gas development practice,the"extreme utilization"concept that focuses on"continuously breaking through the limit of development technology"is gradually formed,and supports the scale benefit exploration of unconventional gas in China.On this basis,the development theory of"extreme utilization"is proposed,its theoretical connotation together with development technologies of unconventional natural gas are clarified.The theoretical connotation is that,aiming at"extreme gas reservoirs","extreme techniques"are utilized to build subsurface connected bodies,expand the discharge area,and enlarge the production range,to obtain the maximum single-well production,extreme recovery,and eventually achieve the"extreme effect"of production.The series of development technologies include micro/nano-scale reservoir evaluation,"sweet spot"prediction,unconventional percolation theory and production capacity evaluation,optimization of grid well pattern,optimal-fast drilling and volume fracturing,and working regulation optimization and"integrated"organizing system.The"extreme utilization"development theory has been successfully applied in the development of unconventional gas reservoirs such as Sulige tight gas,South Sichuan shale gas,and Qinshui coalbed methane.Such practices demonstrate that,the"extreme utilization"development theory has effectively promoted the development of unconventional gas industry in China,and can provide theoretical guidance for effective development of other potential unconventional and difficult-to-recovery resources.

Effect of proppant pumping schedule on the proppant placement for supercritical CO_(2) fracturing

Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the proppant-transport behavior of CO_(2)is required to better apply this technique in the engineering field.In the present paper,we adopted a coupled Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels.Previous experiments were first simulated to benchmark the CFD-EDM approach,and then various pumping schedules and injection parameters(injection location,multi-concentration injection order,multi-density injection order and injection temperature)were investigated to determine the placement characteristics of proppant.Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture.The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration.Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent.Decreasing the initial injection temperature of supercritical CO_(2)slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO_(2)in carrying proppant.

Sustainable development index of shale gas exploitation in China, the UK, and the US

While shale gas could complement the world's natural gas supply,its environmental tradeoffs and sustainability potential should be cautiously assessed before using it to satisfy future energy needs.Shale gas development in China is still in its infancy but has been progressing by the Central Government at a fast pace nowadays.Advanced experience from North America would greatly benefit sustainable design and decision-making for energy development in China.However,the lack of consistency concerning internal and external parameters among previous investigations does not allow an integrated impact comparison among shale gas-rich countries.Herein,we applied a meta-analysis to harmonize environmental tradeoff data through a comprehensive literature review.Greenhouse gas emission,water consumption,and energy demand were selected as environmental tradeoff indicators during shale gas production.Data harmonization suggested that environmental tradeoffs ranged from 5.6 to 37.4 g CO_(2)-eq,11.0-119.7 mL water,and 0.027-0.127 MJ energy to produce 1 MJ shale gas worldwide.Furthermore,sustainable development indexes(SDIs)for shale gas exploitation in China were analyzed and compared to the United States and the United Kingdom by considering environment,economy,and social demand through an analytic hierarchy process.The United States and China elicit higher SDIs than the United Kingdom,indicating higher feasibility for shale gas exploitation.Although China has relatively low scores in the environmental aspect,large reservoirs and high future market demand make Chinese shale gas favorable in the social demand aspect.Region-specific SDI characteristics identified among representative countries could improve the sustainability potential of regional development and global energy supply.