川西中泥盆统观雾山组白云岩储层储集空间类型、成因及演化

Reservoir space type,genesis and evolution of dolomite reservoir in the Guanwushan Formation of Middle Devonian,western Sichuan

川西地区观雾山组白云岩储层储集空间主要为孔洞和裂缝两类。为弄清观雾山组白云岩储层孔洞成因、孔洞充填期次及演化,首先,通过对孔洞型白云岩储层发育规律与沉积相、层序关系的分析,结合第一期白云石胶结物形成与围岩白云石化的先后顺序,认为川西地区观雾山组白云岩储层孔洞为相控准同生岩溶形成;针对孔洞内不同期次白云石和方解石胶结物的包裹体均一温度、碳氧同位素、激光原位U-Pb同位素定年、锶同位素、稀土元素等分析,认为孔洞内胶结物形成于封闭的成岩环境,成岩流体为受下伏碎屑岩地层水加入改造的中泥盆世海水。观雾山组白云岩储层储集空间经历了三个演化阶段:沉积期-白云石化之前的孔洞及裂缝形成阶段、白云石化期间的围岩白云石化及第一期白云石胶结物形成阶段和中—深埋藏成岩期的孔隙定型阶段,其中中—深埋藏阶段是孔隙减少的主要阶段,造成约25%的孔隙损失。

The reservoir space of dolomite reservoirsfromthe Guanwushan Formation in western Sichuan is mainly composed of vugs and fractures. This study aims to understand the genesis, filling stages and evolution of vugs in dolomite reservoirsfromthe Guanwushan Formation. First of all, through the analysis of the relationship between the developmentalrule of vuggy dolomite reservoirs and sedimentary facies and sequence, combined with research on the sequence of dolomite cement which was formed in the first stage and surrounding rock dolomitization, it is proposedthat the vugs in dolomite reservoirs of Guanwushan Formation in Western Sichuan were formed by facies controlled penecontemporaneouskarstification. According to the analysis of inclusion homogenization temperature, carbon and oxygen isotopes, laser in-situ U-Pb isotopic dating, strontium isotopes and rare earth elements of dolomite and calcite cements in different stages in the vugs, it is suggestedthat the cement in the vugs was formed in a closed diagenetic environment, and the diagenetic fluid was the Middle Devonian seawater transformed by the addition of underlying clastic rock formation water. The reservoir space of dolomite reservoirs of the Guanwushan Formation has experienced three evolution stages: the formation stage of vugs and fractures before dolomitization, the formation stage of surrounding rock dolomitization and dolomite cement in the first stage during dolomitization, and the pore setting stage in the middle and deep burial diagenetic stage. The middle and deep burial stage is the main stage of pore reduction, resulting in about 25% pore loss.