近年来,中国石化借鉴非常规天然气思路,加强川东地区二叠系天然气勘探,在涪陵焦石坝及其邻区多口井茅口组一段获得工业气流,揭示了该区茅一段天然气勘探的良好前景。通过对焦石坝地区茅口组一段碳酸盐岩层序地层及沉积特征、生烃条件、储层微观孔隙结构特征、含气性进行系统分析,结果表明:①茅一段可分为2个四级沉积旋回和8个小层,主要发育灰泥灰岩、泥晶灰岩、瘤状灰泥灰岩、瘤状泥晶灰岩4种岩性;②茅一段TOC（总有机碳含量）平均含量介于0.75 %~0.87 %,整体上属于中等有机质丰度的碳酸盐岩烃源岩,泥晶灰岩、瘤状泥晶灰岩有机质丰度相对较低,灰泥灰岩、瘤状灰泥灰岩有机质丰度相对较高,有机质类型以Ⅰ型为主、Ⅱ型为辅;R_o（镜质体反射率）介于1.71 %~2.18 %,平均1.97 %,处于高—过成熟度阶段;③茅一段整体为特低孔、特低渗储层,局部层位表现出裂缝性储层特点,储集空间以有机质孔、黏土矿物成岩收缩缝和矿物颗粒粒缘缝为主,碳酸盐矿物溶蚀孔次之,孔径分布以介孔和大孔为主;④茅一段天然气组分以甲烷为主,重烃含量较低,为典型的干气,δ¹³C₁介于-31.25 ‰~-31.12 ‰,δ¹³C₂介于-35.28 ‰~-31.23 ‰,δ¹³C₃介于-34.87 ‰~-34.66 ‰,为典型的油型气,烷烃系列碳同位素发生反转,呈现出δ¹³C₁>δ¹³C₂>δ¹³C₃特征,揭示茅一段天然气为高过成熟阶段的烃源岩干酪根裂解气与早期形成的液态烃裂解成气的混合产物;⑤茅口组一段具有自生自储的特点,为一套介于页岩储层与裂缝性储层之间的特殊碳酸盐岩储层,需要借鉴页岩气勘探思路,加强甜点层段评价和适应性工程工艺技术攻关,促进天然气的规模上产和效益开发。

In recent years, Sinopec has used the unconventional natural gas idea to strengthen the Permian natural gas exploration in eastern Sichuan and obtained industrial gas flow in the first member of Maokou Formation of several wells in Jiaoshiba of Fuling and its adjacent area, revealing a good prospect for natural gas exploration. In this paper, the sequence stratigraphy, sedimentary characteristics, hydrocarbon generation conditions, micro pore structure characteristics and gas bearing property of Mao-1 Member in Jiaoshiba area are systematically analyzed. The results show that: ① Mao-1 member can be divided into two fourth-order sedimentary cycles and eight small layers, which mainly develops four kinds of lithology such as Limestone, micritic limestone, nodular limestone and nodular micritic limestone. ② The average TOC of the Mao-1 Member ranges from 0.75 % to 0.87 %, which on the whole, belongs to carbonate source rock with medium organic matter abundance. The organic matter abundance of micritic limestone and nodular micritic limestone is relatively low, while the organic matter abundance of limestone and nodular limestone is relatively high. The type of organic matter is mainly type I and supplemented by type Ⅱ. R_o ranges from 1.71 % to 2.18 %, with an average of 1.97 %. ③ The Mao-1 Member is an ultra-low porosity and permeability reservoir, and the local layers show the characteristics of fractured reservoir. The reservoir space is mainly composed of organic pores, diagenetic contraction fissures of clay minerals, and grain margin fractures of mineral particles, followed by dissolution pores of carbonate minerals. Moreover, the pore size distribution is mainly mesoporous and macroporous. ④ The natural gas of Mao-1 member is mainly composed of methane with low heavy hydrocarbon content, which is typical dry gas; δ ¹³C₁ ranged from -31.25 ‰ to -31.12‰, δ¹³C₂ is between -35.28 ‰ and -31.23 ‰, δ¹³C₃ is between -34.87 ‰ and -34.66 ‰, which is a typical oil type gas. The carbon isotope of alkane series is reversed, showing a trend of change δ¹³C₁>δ¹³C₂>δ¹³C_3. According to the characteristics, the natural gas from Mao-1 Member is the mixture of kerogen cracking gas and liquid hydrocarbon cracking gas. ⑤ Mao-1 Member has the characteristics of self-generated and self-reservoired, which is a set of special carbonate reservoir between shale reservoir and fractured reservoir. It is necessary to learn from shale gas exploration experience, strengthen sweet spot interval evaluation and adaptive engineering technology research, and promote the large scale production and benefit development of natural gas.