渝东北地区巫溪2井五峰组—龙马溪组页岩气储层及含气性特征

为深入研究渝东北巫溪地区五峰组—龙马溪组页岩气储层及含气性特征,以巫溪2井钻井资料为基础,以笔石生物地层作为黑色页岩地层划分对比的"标尺",对富有机质页岩有机地球化学特征、岩石学特征、储集空间类型及特征等进行系统分层研究,并分析其含气性及影响因素。研究结果表明:巫溪2井五峰组—龙马溪组富有机质页岩厚度达89.8 m,笔石序列发育完整连续;有机质类型好、丰度高、热演化程度适中,生烃条件较好;有机质丰度受沉积速率的影响,缓慢的沉积速率有利于黑色笔石页岩有机质的富集;由顶至底硅质含量逐渐增加,黏土矿物含量逐渐减少,脆性逐渐增强;富有机质硅质页岩、黏土质硅质页岩具有"既甜又脆"的特性,为页岩储层发育的优势岩相;纳米孔隙形态多为四边开放平行板状孔,连通性较好;联合孔径分布曲线具有"多峰"特征,主孔位于0.42~0.62nm、3~5nm段;有机质孔、黏土矿物层间孔对总孔容贡献最大,脆性矿物间孔的贡献最小;由顶至底有机质孔隙逐渐增多,黏土矿物层间孔逐渐减少;现场实测岩心含气量最高超过8 m~3/t,含气性受生烃、储集和保存条件的综合控制;凯迪阶沉积期—埃隆阶沉积早期(WF2—LM6带)对应Ⅰ类优质页岩气储层,赫南特阶LM1带为最佳层段,具有"最甜、最脆"的特性,可作为水平井最佳靶体位置"甜点段"。

Reservoirs characteristics and gas-bearing capacity of Wufeng-Longmaxi Formation shale in Well WX-2, northeast Chongqing area

To deeply study the reservoir characteristics and gas-bearing capacity of Wufeng-Longmaxi Formation shale in northeast Chongqing, based on the drilling data of Well WX-2, the graptolite biostratigraphy was taken as the standard ruler for stratigraphic division and comparison in black shale to systematically study the geochemical characteristics, petrography characteristics, reserving space types and features, and gas-bearing capacity of organic rich shale, as well as its controlling factors. The research results show that in Well WX-2, the graptolite biozonations are developed completely and continuously; the organic-rich shale in Wufeng-Longmaxi Formation has a thickness of 89.8 m, characterized by good organic matter type, high abundance of organic matter, moderate thermal evolution degree and favorable hydrocarbon-generation conditions. The abundance of organic matter is influenced by sedimentary rate, and low sedimentary rate is beneficial to the enrichment of organic matter in black graptolite shale. From top to bottom, the siliceous content is gradually increased, while the content of clay minerals is decreasing, leading to the enhanced brittleness. The organic-rich siliceous shale and clayey siliceous shale are characterized by the sweet spot with brittleness, and the dominant lithofacies favorable for the development of shale reservoirs. Nanometer pore morphology is dominated by parallel-plate pores with four sides open and good connectivity. The pore size distribution curve has "multimodal" characteristics, where the dominant pores are located in the sections of 0.42-0.62 nm and 3-5 nm. The organic pores and clay mineral pores make the greatest contribution to total pore volume, while the brittle mineral pores have the least contribution. From top to bottom, organic pores are gradually increased, while clay mineral pores are decreasing. The on-site measured core gas content can exceed 8 m³/t, and the gas-bearing capacity is jointly controlled by hydrocarbon generation, reserving and preservation conditions. The early period of Katian-Aeronian stage (WF2-LM6 biozone) corresponds to Type-I high-quality shale reservoirs, where Hirnantian LM1 biozone (Normalograptus persculptus) is the best "sweet spot" with the highest brittleness as the optimal target position in horizontal wells.