海陆过渡相煤系页岩气成藏条件及储层特征——以四川盆地南部龙潭组为例

结合扬子地区海陆过渡相煤系页岩分布与地质特征，以四川盆地南部二叠系龙潭组为例，采用有机碳、Rock-eval热解、显微组分定量、X射线衍射（XRD）、扫描电镜（SEM）、高压压汞、低温气体吸附等多种实验分析方法，对海陆过渡相煤系页岩气成藏条件及储层特征进行了研究。结果表明：海陆过渡相煤系页岩，累计厚度较大，多在100 m以上，而单层厚度较小，一般小于40 m，通常与煤层和致密砂岩甚至与灰岩互层。四川盆地南部海陆过渡相龙潭组煤系页岩有机碳含量较高（TOC含量为0.85%～35.70%，平均6.73%），有机质类型以腐殖型为主（干酪根碳同位素δ13C为-28.0‰～-23.5‰），有机质成熟度达高-过成熟阶段（Ro为1.95%～2.40%，平均2.22%）；页岩中黏土矿物较为发育（20.3%～92.3%，平均61.9%），脆性矿物含量较低（6.3%～65.7%，平均27.7%），页岩储层可压裂性较海相页岩差。龙潭组煤系页岩孔隙度多大于3%，孔隙类型多样，常见粒间孔（含量占29.08%）和溶蚀孔（占30.18%），其次是有机质孔（占16.74%）和粒内孔（占10.56%），还有晶间孔（占4.94%）和微裂缝（占8.5%），为页岩气赋存提供了储集空间；页岩含气性较好，含气量主要介于1.0～3.0 m3/t。

Accumulation conditions and reservoir characteristics of marine-terrigenous facies coal measures shale gas from Longtan Formation in South Sichuan Basin

Combined with the shale distribution and geological characteristics of marine-terrigenous facies coal measures in the Yangtze area，taking the Permian Longtan Formation in South Sichuan Basin as example，the authors investigated the accumulation conditions and the reservoir characteristics of marine-terrigenous facies coal measures shale gas using many experimental methods，such as organic carbon，Rock-eval pyrolysis，maceral identification，X-ray diffraction (XRD)，scanning electron microscope (SEM)，high pressure mercury injection，low temperature gas sorption，etc.The results show that the marine-terrigenous facies coal measures shale has the features of rapid vertical-lateral variation，huge cumulative thickness (mainly over 100 m)，small individual thickness (generally <40 m)，and commonly accompanied with coal bed，limestone and tight sand．The marine-terrigenous facies coal measures shale from Longtan Formation in South Sichuan Basin，which featured with high organic matter abundance (TOC=0.85%-35.70%，average 6.73%)，mainly with humic type organic matter （kerogen δ13C=-28.0‰--23.5‰），high-over thermal evolution level (Ro=1.95%-2.4%，average 2.22%)，rich in clay minerals content（20.3%-92.3%，average 61.9%），and relatively low brittle minerals content (6.3%-65.7%，average 27.7%).The shale reservoir fracturing from Longtan Formation is worse than that of marine shale.The porosity of the Longtan Formation shale in South Sichuan Basin is mainly over 3%.Many types of pores were developed，including intergranular pore (29.08%)，dissolution pore (30.18%)，organic pores (16.74%)，intragranular (10.56%)，inter-crystalline (4.94%) and microfracture (8.5%)，which provide reservoir space for the accumulation of shale gas.Gas generation capability from the Longtan Formation shale is relatively better，and its main gas content can be 1.0-3.0 m3/t.