川南地区二叠系茅口组一段瘤状灰岩储层成因

The genesis of nodular limestone reservoirs of the first period of Maokou Formation of Permian in southern Sichuan Basin

大石1井、义和1井、焦石1井、潼探1井相继在四川盆地中二叠统茅口组一段钻获工业气流,展示了良好的天然气勘探潜力。但由于前期对该套储层成因的研究不够深入,仍存在约束该类型气藏勘探的问题。为此,通过岩心观察、薄片鉴定,结合扫描电镜、氮气吸附脱附、稀土元素、微量元素和能谱实验,取得了3项成果认识:(1)川南地区茅一段瘤状灰岩储层主要发育在泥灰岩中,为一套低孔低渗裂缝—孔隙型致密碳酸盐岩储层,储集空间类型多样,滑石孔缝对储层贡献最大;(2)滑石主要由成岩期海泡石转化而来,海泡石中的硅元素来源于中二叠世同沉积期断裂热液,镁元素来源于束缚孔隙海水及亚稳定矿物的转化释放;(3)埋藏过程中,海泡石受压力、温度、埋藏时间和成熟度影响,结构转变为滑石,由于脱水和硅质的析出,晶体体积变小,形成大规模滑石化成岩孔缝,为储层发育奠定了基础。成果认识对川南地区茅口组一段瘤状灰岩气藏勘探提供了有力地质支撑,对油气勘探具有较好的现实指导意义。

Industrial natural gas flows have been gained from the wells penetrated in the nodular limestone,shows a good potential for natural gas exploration.In the early stage,the research on the formation of this reservoir is not in-depth enough,which restricts the exploration of this type of gas reservoir.Based on core observation,thin section authentication,combined with the results of scanning electron microscope,nitrogen adsorption and desorption,rare earth elements,trace elements and energy spectrum analysis,three achievements were gained.The results show that the reservoirs mostly exist in the argillaceous limestone matrix,which is a set of tight carbonate fracture-pore reservoir with low porosity and low permeability.The reservoir space is complex and the talc diagenetic shrinkage fissure is the greatest contribution storage space to the reservoir.Talc is mainly transformed from sepiolite during diagenesis,the silicon element in sepiolite comes from the fault hydrothermal fluid of Maokou Formation in the same sedimentary period,and magnesium comes from bound pore water and conversion release of a metastable mineral.Sepiolite transforms into talc under the influence of pressure,temperature,buried time and grade of maturity during burial.Due to dehydration and silica precipitation,the crystal gets smaller,which formed large-scale of talc diagenetic shrinkage fissure that lays the material foundation for reservoir.Research results provide strong geological support for the nodular gas pool exploration of the first member of Maokou Formation of Permian in southern Sichuan Basin.It has a good guiding significance for oil and gas exploration.