海拉尔盆地贝尔凹陷火山碎屑岩自生碳酸盐矿物分布及对储层物性的影响

为了查明火山碎屑岩中自生碳酸盐矿物的分布特征及对储层物性的影响,以海拉尔盆地贝尔凹陷火山碎屑岩为研究对象,调查火山碎屑岩中自生碳酸盐矿物的类型,并通过统计50余口探井的碳酸盐含量及储层物性数据,探讨其分布特征及对储层物性的影响。结果表明:海拉尔盆地贝尔凹陷火山碎屑岩中自生碳酸盐矿物主要为方解石和白云石,其次为菱铁矿、片钠铝石和铁白云石;纵向上随着埋藏深度增加出现两个碳酸盐含量高值带,分别出现在1500～1900m和2200～2700m深度,前者主要为以胶结作用为主的连生方解石和显晶方解石及菱铁矿,后者主要为以交代作用为主的晚期方解石、白云石、铁白云石和片钠铝石;湖底扇等分选较差的沉积相为碳酸盐矿物发育的有利相带,扇-辫状河三角洲相为次有利相带;靠近德尔布干深大断裂的井碳酸盐含量要高于远离该断裂的井,且在该断裂附近的德2、德6和德8等井中见片钠铝石自生矿物,这主要因为断层是CO₂逸散的通道,断层处的富CO₂流体能够与围岩反应生成碳酸盐矿物;熔结凝灰岩和凝灰岩中的碳酸盐矿物含量要高于沉凝灰岩、凝灰质砂岩及普通砂岩,这主要因为火山岩及火山碎屑物质中金属离子含量高,易于释放,从而结合CO^2-₃形成碳酸盐矿物;贝尔凹陷内储层孔隙度和渗透率等参数与碳酸盐含量呈负相关关系,说明碳酸盐含量对储层物性主要起破坏作用。

Distribution and Impact on Reservoir Properties of Authigenic Carbonate Minerals in Pyroclastic Rocks of Beier Depression,Hailaer Basin

In order to verify the distribution and impact on reservoir properties of authigenic carbonate minerals in pyroclastic rocks, pyroclastic rocks in Beier Depression of Hailaer Basin were taken as an example; the type of authigenic carbonate minerals were investigated; the distribution and impact on reservoir properties were discussed according to the statistic of carbonate content and reservoir properties for more than 50 wells. The results showed that authigenic carbonate minerals in pyroclastic rocks of Beier Depression, Hailaer Basin were mainly calcite and dolomite, followed by siderite, dawsonite and ankerite; there were two high-value zones of carbonate content vertically, in 1 500-1 900 m and 2 200-2 700 m respectively, and the former mainly contained intergrowth calcite cements, granular calcite cements and siderite, the latter mainly contained late calcite, dolomite, ankerite and dawsonite; the most favorable facies belts for the development of carbonate cements was sublacustrine fan facies,followed by fan-braided fluvial river deltas facies; the carbonate content in wells close Deerbugan deep fault was higher than that in wells away from it, and there were dawsonites in wells De2,De6 and De8 near the fault, mainly because the fault was the channel for CO₂ dispersion and CO₂-rich fluid could react with the surrounding rocks and then the carbonate minerals formed; the carbonate contents in ignimbrite and tuff were higher than that in sedimentary tuff, tuffaceous sandstone and common sandstone, mainly because the contents of metal ions in pyroclastic material were high, and the ions were easy to release, which combined with carbonate ions to form carbonate minerals; the porosity and permeability in Beier Depression were negatively correlated with the content of carbonate.