蜀南-渝西地区中二叠统茅一段灰质源岩气储层特征及主控因素--以DB1井为例

Characteristics and main controlling factors of the limy source rock gas reservoir in the first member of the Middle Permian Maokou Formation in the southern Sichuan and western Chongqing area:a case study of well DB 1

四川盆地中二叠统茅口组是天然气的重要产层,近期浙江油田分公司在渝西大安探区DB1井茅一段“眼皮眼球”灰岩的灰质源岩气储层中,直井试气获得42000 m3/d、水平井(DB1H井)试气初产55.6×104 m3/d以上的工业气流,实现了蜀南—渝西泥质灰岩非常规天然气勘探突破,展示了该区良好的勘探前景。四川盆地茅一段眼皮眼球灰岩具有自生自储特征,连续稳定展布,且热演化成熟度高,中缓坡相带纯灰岩不具有水敏和酸敏特性,以碳酸盐脆性矿物为主,易于酸化压力开发,因此开展富有机质灰岩储层特征及主控因素研究意义重大。以DB1井为例,研究茅一段岩石学、沉积学及储层特征,发现沉积于水体较震荡、生物发育的中缓坡相带、主体为深灰—灰黑色富有机质的泥晶灰岩储层物性较好,总体上茅一c亚段好于茅一a亚段,眼皮灰岩大孔发育程度高于眼球灰岩,微孔发育程度差别不大。茅一段主要储集空间类型有溶蚀孔、裂缝、黏土矿物孔缝和有机质孔,黏土矿物(主要是滑石)和有机质内的孔隙主要分布于眼皮灰岩中;沉积过程与成岩作用是控制茅一段眼皮、眼球灰岩储层发育的主要因素,中缓坡沉积相带控制了富有机质纯泥晶生屑灰岩储层的发育特征和区域展布,成岩作用和断裂、断溶作用影响灰岩储层储集性能的改善,并成为富集高产的主因。渝西DB1井区“黑茅口”富有机质的茅一段直井、水平井突破商业气流获得稳定高产,表明茅一段灰质源岩气成藏赋存条件好,具有自生自储为主+局部构造带短距离聚集的2种成藏模式以及气藏连续型展布、资源规模大的特征,茅一段灰质源岩气“连续型气藏”勘探潜力大,将成为四川盆地重要的潜在勘探新层系。

The Middle Permian Maokou Formation in the Sichuan Basin is an important natural gas payzone.Recently,Zhejiang Oilfield Company of CNPC obtained industrial gas flow of vertical well test 42×103 m^(3)/d and horizontal well(well DB 1H)test 556×10^(3) m^(3)/d in the limy source rock gas reservoir of eyelid and eyeball⁃shaped limestone in the first member of the Maokou Formation in well DB 1,Da’an exploration area,western Chongqing.A breakthrough has been made in the unconventional gas exploration of argillaceous limestone in the southern Sichuan and western Chongqing area,showing good exploration prospects in this area.The eyelid and eyeball⁃shaped limestone in the first member of the Maokou Formation in the Sichuan Basin has the characteris⁃tics of self⁃generation and self⁃storage,continuous and stable distribution and high thermal maturity.The lime⁃stone of central gentle slope facies shows no water sensitivity or acid sensitivity,and is dominated by carbonate brittle minerals,which is ideal for acid⁃fracturing development.It is of great significance to study the characteris⁃tics and main controlling factors of the organic rich limestone reservoir.Taking well DB 1 as an example,this paper carried out a study on the petrology,sedimentology and reservoir characteristics of the first member of the Maokou Formation,and it is found that,deposited on the central gentle slope with frequent water activity and abundant organism,the dark gray to black micrite with high organic matter content has good physical properties.In general,submember c has better physical properties than submember a.The development degree of macro⁃pores in eyelid⁃shaped limestone is higher than that in eyeball⁃shaped limestone,and the development degree of micropores is not much different.The main pore types of the first member of the Maokou Formation include disso⁃lution pores,fractures,clay mineral apertures and organic pores.The pores in clay minerals(mainly talc)and organic matters are mainly distributed in the eyelid⁃shaped limestone.Depositional process and diagenesis are the main factors controlling the development of the eyelid and eyeball⁃shaped limestone reservoirs.The central gentle slope facies controls the development and distribution features of the organic⁃rich micrites.Diagenesis as well as fracture and dissolution effects improve the reservoir capacity of limestone,which is critical for hydrocarbon accu⁃mulation.Stable and high yield commercial gas flow was obtained in the vertical wells and horizontal wells in the first member of the Maokou Formation which has high organic matter content in well DB 1 block in the western Chongqing area,indicating that the accumulation and occurrence conditions of limestone source rock gas are good in the first member of the Maokou Formation.It has two kinds of accumulation modes with self⁃generation and self⁃storage dominance and short distance aggregation of local structural bands,and has the characteristics of continuous distribution of gas reservoir and large resource scale.The continuous gas reservoir:in the limestone source rock in the first member of the Maokou Formation has great exploration potential,which will become an important exploration target with good potential in the Sichuan Basin.