赤水林滩场地区龙马溪组页岩气勘探潜力分析

Exploration potential of shale gas in Longmaxi Formation, Lintanchang area, Chishui area

四川盆地是中国页岩气增储上产的主阵地,随着盆内深层页岩气开发建产规模的推进,上奥陶统五峰组—下志留统龙马溪组页岩气勘探转向盆缘复杂构造区,位于该盆地东南缘的贵州赤水探区林滩场构造为其典型代表。LY1HF、LY3HF井的成功实施证实了林滩场具备良好的页岩气形成条件,但也反映了该区构造特征及保存条件复杂。为了落实页岩气有利区,通过对已钻井的评估分析,基于页岩气形成条件分析,重点对该地区构造特征和保存条件进行了深化研究。研究结果表明:①研究区龙马溪组深水陆棚相优质页岩厚度较大,有机碳丰度高、孔隙度高、含气量高,具有页岩气富集的良好地质条件;②林滩场是受推覆断层控制的推覆断背斜,保存条件具分区差异性,其中盆缘正向复杂构造区沿地层上倾方向有逆冲断层阻隔是有利的保存条件;③综合考虑龙马溪组泥页岩发育程度、埋深、保存和开发等条件,优选出南1、北1区为该区龙马溪组页岩气勘探的Ⅰ类有利区,勘探开发潜力较大。

Sichuan Basin is the main battlefield to increase shale gas reserves and production in China. As the development and productivity construction are advanced in its deep shale gas, the shale gas exploration in Wufeng Formation –Longmaxi Formation has shifted to complex structures along basin margin, whose representative is Lintanchang structure of Chishui exploration area in southeastern basin margin. Furthermore, successfully drilling in LY1HF and LY3HF wells proves formation conditions of shale gas in Lintanchang structure and also reveals complex structural characteristics and preservation conditions in Chishui exploration area. To ascertain favorable belts for shale gas, a few wells were evaluated and analyzed. Then, both structural characteristics and preservation conditions were summed up on the basis of formation conditions of shale gas. Results show that(1) in the study area, quality shale of deepwater continental shelf facies in Longmaxi Formation is thicker with high organic carbon abundance, porosity and gas content, providing right conditions for shale gas enrichment;(2) in Lintanchang structure as a nappe fault anticline controlled by nappe faults, preservation conditions are different in different zones. In the complex positive structure belt along basin margin, thrust faults serve as barriers in the updip direction through strata to offer favorable preservation;and(3) taking into consideration the development degree, burial depth, preservation and development conditions of shale in Longmaxi Formation, Nan 1 and Bei 1 belts can be selected as I-type favorable exploration belts of shale gas in Longmaxi Formation, Lintanchang structure of Chishui area, owing to their huge exploration and development potential.