川南地区深层页岩气富集条件差异分析与启示

Analysis and enlightenment of the difference of enrichment conditions for deep shale gas in southern Sichuan Basin

近年来,川南地区上奥陶统五峰组—下志留统龙马溪组页岩气勘探开发逐步向深层领域(埋深3500~4500 m)拓展。已在LZ、DZ2个深层区块取得初步进展,且页岩气勘探开发效果表现不同(前者明显优于后者),其主要与富集条件差异有关。以LZ和DZ区块五峰组—龙马溪组为研究对象,综合利用最新的钻井、录井、测井、地震及分析化验等资料,明确了2个区块富集条件特征、差异性及主控因素。研究表明:①LZ区块在五峰组—龙一1亚段地层厚度、有机质丰度、物性特征、含气性、页岩储层厚度及品质等页岩气富集要素方面均优于DZ区块;②LZ区块在五峰组—龙马溪组形成时期始终位于川南地区深水陆棚相沉积中心,古沉积环境优于DZ区块,古沉积环境的不同造成了2个区块有机质富集和储层规模(厚度、品质)的差异;③DZ区块保存条件明显受断层—天然裂缝系统控制,而LZ区块页岩气的逸散受断层—天然裂缝系统影响较小,压力系数为川南地区最高,保存条件更优。综合研究认为,川南地区LZ、DZ2个深层区块页岩气富集差异性的主控因素为古沉积环境和后期保存条件;在川南地区深层页岩气勘探开发中应秉持“深层领域找深水沉积页岩储层”的理念,华蓥山断裂带南段南侧的断背斜间发育的多个较宽缓向斜构造应是下步深层页岩气勘探的潜在有利区,LZ区块龙一14小层地质条件优越、具备双层立体开发可行性。

In recent years,shale gas exploration and development of O3w-S1l 1 in southern Sichuan Basin have gradually expanded to the deep reservoirs(vertical depth between 3500 m and 4500 m).Preliminary progress have been made in two deep areas,including LZ block and DZ block,and the results of shale gas exploration and development are different(the former is obviously superior to the latter),which is mainly related to the dif⁃ference of enrichment conditions.This article takes Wufeng-Longmaxi formations of LZ block and DZ block as the research objects,and has comprehensively made use of the latest data of drilling,logging,well logging,seismic and experiments,and finally has clarified the characteristics,differences and main controlling factors of enrichment conditions in two blocks.The researches show that:(1)LZ block is superior to DZ block in shale gas enrichment elements,such as formation thickness,organic matter abundance,physical property characteris⁃tics,gas bearing property,as well as the thickness and quality of shale reservoir.(2)During the formation peri⁃od of Wufeng-Longmaxi formations,LZ block was always located in the sedimentary center of deep-water conti⁃nental shelf in southern Sichuan basin,and its paleosedimentary environment was superior to that of DZ block.And the difference of paleosedimentary environment resulted in the difference of organic matter accumulation and reservoir scale(thickness and quality)in the two blocks.(3)The preservation condition of DZ block is obvi⁃ously controlled by fault-natural fracture system,while the shale gas leakage in LZ block is less affected by faultnatural fracture system.The pressure coefficient is the largest in southern Sichuan Basin,and the preservation condition is better.The comprehensive study suggests that,in the two deep areas of LZ block and DZ block in southern Sichuan Basin,the main controlling factors of shale gas enrichment difference are paleosedimentary en⁃vironment and preservation conditions.The concept of"exploring deep-water shale reservoir in the deep area"should be upheld in the exploration and development of deep shale gas in southern Sichuan Basin.Several wide and slow syncline structures which developed among the fault-anticlines in the south side of southern Huaying⁃shan fault-zones should be the potential favorable areas for shale gas exploration in the next stage.And the geo⁃logical conditions of S1l 1-1-4 in LZ block are superior,with the feasibility of three-dimensional development for double-layers.