“Extreme utilization” theory and practice in gas storages with complex geological conditions

Based on more than 20-year operation of gas storages with complex geological conditions and a series of research findings, the pressure-bearing dynamics mechanism of geological body is revealed. With the discovery of gas-water flowing law of multi-cycle relative permeability hysteresis and differential utilization in zones, the extreme utilization theory targeting at the maximum amount of stored gas, maximum injection-production capacity and maximum efficiency in space utilization is proposed to support the three-in-one evaluation method of the maximum pressure-bearing capacity of geological body, maximum well production capacity and maximum peak shaving capacity of storage space. This study realizes the full potential of gas storage(storage capacity) at maximum pressure, maximum formation-wellbore coordinate production, optimum well spacing density match with finite-time unsteady flow, and peaking shaving capacity at minimum pressure, achieving perfect balance between security and capacity. Operation in gas storages, such as Hutubi in Xinjiang, Xiangguosi in Xinan, and Shuang6 in Liaohe, proves that extreme utilization theory has promoted high quality development of gas storages in China.

“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.

“Extreme utilization”development of deep shale gas in southern Sichuan Basin,SW China

To efficiently develop deep shale gas in southern Sichuan Basin,under the guidance of“extreme utilization”theory,a basic idea and solutions for deep shale gas development are put forward and applied in practice.In view of multiple influencing factors of shale gas development,low single-well production and marginal profit of wells in this region,the basic idea is to establish“transparent geological body”of the block in concern,evaluate the factors affecting shale gas development through integrated geological-engineering research and optimize the shale gas development of wells in their whole life cycle to balance the relationship between production objectives and development costs.The solutions are as follows:(1)calculate the gold target index and pinpoint the location of horizontal well drilling target,and shale reservoirs are depicted accurately by geophysical and other means to build underground transparent geological body;(2)optimize the drilling and completion process,improve the adaptability of key tools by cooling,reducing density and optimizing the performance of drilling fluid,the“man-made gas reservoir”is built by comprehensively considering the characteristics of in-situ stress and fractures after the development well is drilled;(3)through efficient management,establishment of learning curve and optimization of drainage and production regime,the development quality and efficiency of the well are improved across its whole life cycle,to fulfil“extreme utilization”development of shale gas.The practice shows that the estimated ultimate recovery of single wells in southern Sichuan Basin increase by 10%-20%than last year.