川东北元坝地区须家河组三段钙屑砂岩孔隙类型及地质意义

钙屑砂岩在成因上属于陆源碎屑岩中的一类砂岩，其成分的特殊性决定了埋藏过程中成岩作用、储集空间以及油气产能上的特殊性。结合岩心、普通岩石薄片、铸体薄片、阴极发光、扫描电镜、X衍射数据、压汞数据和物性数据等资料，对川东北元坝西须家河组三段钙屑砂岩的孔隙类型、孔隙定量演化和孔隙有效性等方面进行了系统性分析。结果表明，钙屑砂岩原生孔隙很少，次生孔隙类型主要包括3类：晶间微孔隙、溶蚀型孔隙与裂缝型孔隙。各类孔隙的成因存在差异，晶间微孔主要与钙屑、钙质胶结物的重结晶作用有关，还有一些钙屑晶间微孔来源于母岩的白云岩化。裂缝的成因有两个，贴粒缝是由于钙屑与胶结物重结晶不同步，构造裂缝是由于须三段沉积时期强烈构造运动形成的；研究区钙屑砂岩溶孔发育有限，不能整体改善储层质量，仅形成局部“甜点”；晶间微孔普遍发育，是钙屑砂岩孔隙的主要贡献者，且大部分微孔都是有效孔隙，加上微裂缝的沟通，是天然气的主要储集空间。高钙屑高钙质胶结物含量的地区（如高能的分流河道），由于强烈重结晶提供大量晶间微孔，加上裂缝的沟通，成为须三段的优质储层区，可作为勘探开发的重点。

Pore types and geological significance of calcarenaceous sandstones in the 3rd member of Xujiahe Formation in Yuanba area,Northeastern Sichuan Basin

Calcarenaceous sandstone is a type of sandstone in terrigenous clastic rocks in terms of genesis.The diagenesis in the burial process,reservoir space and hydrocarbon production capacity of calcarenaceous sandstones are determined to be quite special due to its uncommon compositions.Given the observation of the core,common thin sections,casting thin sections,cathode luminescent thin sections,scanning electron photomicrograph,as well as X-ray diffraction data,mercury intrusion data,and physical properties,we made a systematic study on the pore types,as well as quantitative evolution and validity of pores in the calcarenaceous sandstones of the 3rd member of Xujiahe Formation (T₃x₃) in western Yuanba area,Northeastern Sichuan Basin.The results show that there are fewer primary pores in these sandstones,and the secon-dary pores are mainly categorized into three types:intercrystalline micropores,dissolved pores and fractured pores.They are different in terms of genetic mechanism-the formation of intercrystalline micropores are mainly related to the recrystallization of calcareous debris and cements,and some intercrystalline micropores of calcareous debris are a result of the dolomitization of host rocks; while there are two causes for fractures:the intergranular fractures were developed out of unsynchronized recrystallization of calcareous debris and cements,and the structural fractures were formed due to the intense tectonic movements during the deposition of the T₃x₃.In addition,the dissolved pores were less developed and just formed partial "sweet spots",unable to improve the reservoir quality as a whole; while the well-developed intercrystalline pores,most of which are effective,serve as major contributors to the reservoir space of gases in calcarenaceous sandstones,combined with the communication provided by microfractures.Areas with high contents of calcareous debris and calcareous cements (such as high-energy distributary channels) are the high-quality reservoir zones in the T₃x₃,and could be the key areas for exploration and development,since strong recrystallization functions to produce a large number of intercrystalline micropores and the connection provided by fractures is also effective.