地面定向井+水力割缝卸压方法高效开发深部煤层气探讨

为了提高深部煤层气储层压降效果,针对深部煤层储层压力大,地应力高,渗透率低等特点,基于切割卸压提高储层渗透率原理,综合矿井下瓦斯抽采实践及地面开发非常规天然气技术方式,提出了地面定向井+水力割缝卸压方法高效开发深部煤层气的方法。地面定向井+水力割缝卸压方法主要包括地面定向钻井和分段水力割缝2个过程。该方法增渗增产原理为:定向井眼和水力缝槽沟通天然裂缝系统,高压水力切割过程中诱导煤层产生裂隙,增加导流通道数量与连通性;水力切割产生的多组缝槽形成卸压空间,利用地应力变化增加裂隙张开度,促进储层压力释放。相比常规水力压裂而言,该方法更有利于形成网格化流体运移通道,扩大煤层卸压范围和卸压程度,强化煤层气解吸扩散。而且,能够避免水力压裂过程中地应力向煤层深部传递以及压裂液注入造成的储层伤害,因而适用深部煤层气储层复杂地质条件下的增产改造。鉴于地面工况条件与矿井下工况条件的差异,提出了地面定向井+水力割缝卸压方法开发深部煤层气需要解决的关键技术问题,包括水力缝槽参数控制,固相颗粒的返排,定向井完井与水力割缝匹配性,以及高压流体传输动力损失。地面定向井+水力割缝卸压方法在非常规天然气开发以及深部煤炭强矿压与瓦斯灾害防治等方面具有应用前景。

Discussion on the efficient exploitation method of deep coalbed methane with pressure relief by ground directional well+hydraulic slotting

In order to improve the efficiency of reservoir pressure relief of deep coalbed methane(CBM),as the deep coal reservoir is characterized by high reservoir pressure,high in-situ stress and low permeability,based on the depressurization principle by cutting to improve reservoir permeability,combining underground gas extraction and surface development of unconventional natural gas technology,the efficient exploitation method of deep CBM development with pressure relief by surface directional well+hydraulic slotting is put forward.The surface directional well+hydraulic slotting methods include two processes of surface directional drilling and staged hy-draulic slotting.The principle of this method for increasing permeability and increasing production is as follows:(1)Directional wellbore and hydraulic slots communicate the natural fracture system,and new fractures can be induced during high-pressure hydraulic slotting,which increase the number and connectivity of migration channels;(2)The pressure relief space is formed by multiple groups of slots,and the fracture opening increases with in-situ stress releasing to accelerate reservoir pressure drop.Compared with conventional hydraulic fracturing,this method is more beneficial to the formation of meshed fluid migration channel,the expansion of coal seam pressure relief range and degree,and the enhancement of CBM desorption and migration.Moreover,this method can avoid reservoir damage caused by crustal stress transfer to the deep coal seam and fracturing fluid injection,which is applicable to the stimulation of deep CBM reservoirs with complex geological conditions.With the consideration of the working conditions of ground and underground,the key technical problems are put forward for the pressure relief method of deep CBM exploitation by ground directional well+hydraulic slotting,including the controlling of hydraulic slot parameters,the flowback of solid phase particles,the matching of directional well completion and hydraulic slotting,as well as the power loss of high-pressure fluid transmission.The pressure relief method of surface directional well+hydraulic slotting stimulation is promising for its application in unconventional natural gas development,prevention and control of high pressure and gas disaster for deep coal,and fluidized intelligent mining of deep coal resources.