川西龙门山前雷口坡组四段白云岩储层胶结物对早期孔隙的影响

Cement characteristics and effects on dolomite reservoir pores in the fourth member of Leikoupo Formation, Longmen Mountain front, western Sichuan Basin

利用薄片、阴极发光、探针微量元素、激光碳氧同位素及包裹体测温等资料,在龙门山前中三叠统雷口坡组四段上亚段白云岩储层中主要识别出3期5种胶结物,在对不同期次和不同种类胶结物特征及分布特征研究的基础上,结合胶结物的发育程度,还原了胶结物对龙门山前雷四上亚段不同类型白云岩储层孔隙演化的影响过程。研究认为:第一期浅埋藏白云石胶结物形成是藻类白云岩储层孔隙破坏的主要阶段,但这期胶结物产生后对残余孔隙起支撑作用,有利于大量早期孔隙保存;在第一期胶结物充填基础上叠加第二期表生期渗流砂充填,破坏部分藻类白云岩早期残余孔隙;第三期再埋藏含铁嵌晶方解石胶结是晶粒白云岩储层孔隙破坏的主要原因,在藻类白云岩储层中,该期胶结物不均匀分布进一步加剧了储层非均质性,但这期胶结物的产生受到烃类和油气充注的抑制,因此早期残余孔隙在漫长的再埋藏阶段得到较好保存。

Based on the analysis of thin sections, cathode luminescence, electron probe, laser carbon, oxygen isotopes and inclusion thermometry, three periods including five cement types were observed in the dolomite reservoir of the 4th member of the Leikoupo Formation in Longmen Mountain front. Distribution characteristics and development degree indicated a reduction of the influencing process on pore cements. Phase 1 cement is dolomite. Its deposition is the main stage that leads to the porosity decline of the blue green algae agglutinate dolomite. However, after the cementation, the residual porosity has some supporting protection, and a large number of early pores are preserved. Phase 2 cement is the vadose silt that causes reservoir inhomogeneity of the blue green algae agglutinate dolomite. Phase 3 cement is the ferric calcite. These late diagenetic products generally filled in the pores of micritic-silty dolomite to further reduce the reservoir porosity, but this cement was inhibited by the organic acid. Therefore primary pores are well preserved in the long reburial stage.