番禺低隆起珠海组砂岩碳酸盐胶结特征及其对储层物性的影响
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摘要
为了深化珠江口盆地番禺低隆起的油气地质特征认识,针对碎屑砂岩储层中碳酸盐胶结物发育特征、胶结机制及其对储层物性的影响等问题,采用孔渗分析、薄片鉴定、扫描电镜及X射线衍射等测试手段,对该区珠海组储层砂岩开展了系统的成岩作用研究。结果表明:该区发育同生成岩期、早成岩阶段A期及晚成岩阶段A_1期共3期碳酸盐胶结;同生成岩期发育基底式胶结的方解石及铁白云石,与该时期孔隙流体在弱碱性成岩环境中过饱和析出有关;早成岩阶段A期发育孔隙式胶结的方解石、铁白云石及菱铁矿,该期胶结物质来源包括生物化石骨架颗粒溶解、铝硅酸盐矿物水化作用及早期残余孔隙流体等;晚成岩阶段A_1期发育少量孔隙式胶结的方解石及铁白云石,该阶段末期成岩环境逐步转变为弱碱性—碱性,在较大埋深、较高温压条件下,强烈的水-岩反应释放出Ca~(2+),Fe~(2+)及Mg~(2+)等离子并进入孔隙流体,导致末期方解石及铁白云石过饱和析出;碳酸盐胶结是导致研究区储层物性变差的主要原因之一,早期方解石及铁白云石包裹碎屑颗粒,充填粒间孔隙,极大地破坏了储层物性,中期孔隙式胶结的方解石、铁白云石及菱铁矿进一步缩减了孔隙空间,晚期碳酸盐胶结见方解石及铁白云石充填粒间孔隙并交代碎屑颗粒,使砂岩进一步致密化。研究结果可为该区有利区带预测及勘探目标评价提供依据。
Based on a series of testing method of porosity & permeability measurements,mercury porosimetry measurements,thin section analyses,SEM observations and X-ray diffraction(XRD)analysis,diagenetic features and reservoir property of marine sandstones acquired from Zhuhai Formation in Panyu low-uplift of Pearl River Mouth Basin were analyzed. The results show that three stages of carbonate cements were identified in the studied reservoir sandstones,which was present by calcite and ferro-dolomite in syn-diagenesis,calcite,ferrodolomite and siderite in eodiagenesis,and a small amount of calcite and ferro-dolomite in A stage of eodiagenesis. Early calcite and ferro-dolomite precipitated basally within pore spaces formed supersaturated pore fluid in alkaline environment early in diagenetic history. The second stage of carbonate cements were characterized by porous cementation,and their sources include dissolution of bio-clasts,hydration of Aluminum silicate minerals,and residual pore fluid. In A_1 stage of meso-diagenesis,diagenetic environment has been transformed into alkaline when acid fluid was exhausted. The third stage of carbonate cements precipitated when abundant Ca~(2+),Mn~(2+),Fe~(2+)and Mg~(2+) were dissolved and entered into pore fluid in relatively deeper burial depth,higher temperature and pressure. Carbonate cement is one of the most important factors that caused great loss of reservoir property in the studied reservoir sandstones,showing that the higher content of carbonate cements occurred,the poorer of the reservoir property is. Most obviously,early carbonate cements occurred basally and highly reduced reservoir property. The second stage of carbonate cements generally were featured by porous cementation and blocked the pore spaces. Late carbonate cements generally have a low content,but occurred as replacements of detrital grains or pore fillings in intergranular pores and dissolution pores,which caused further densification of reservoir sandstones. The results can provide a basis for the prediction of favorable zones and the evaluation of exploration targets in this area.
Based on a series of testing method of porosity & permeability measurements,mercury porosimetry measurements,thin section analyses,SEM observations and X-ray diffraction(XRD)analysis,diagenetic features and reservoir property of marine sandstones acquired from Zhuhai Formation in Panyu low-uplift of Pearl River Mouth Basin were analyzed. The results show that three stages of carbonate cements were identified in the studied reservoir sandstones,which was present by calcite and ferro-dolomite in syn-diagenesis,calcite,ferrodolomite and siderite in eodiagenesis,and a small amount of calcite and ferro-dolomite in A stage of eodiagenesis. Early calcite and ferro-dolomite precipitated basally within pore spaces formed supersaturated pore fluid in alkaline environment early in diagenetic history. The second stage of carbonate cements were characterized by porous cementation,and their sources include dissolution of bio-clasts,hydration of Aluminum silicate minerals,and residual pore fluid. In A_1 stage of meso-diagenesis,diagenetic environment has been transformed into alkaline when acid fluid was exhausted. The third stage of carbonate cements precipitated when abundant Ca~(2+),Mn~(2+),Fe~(2+)and Mg~(2+) were dissolved and entered into pore fluid in relatively deeper burial depth,higher temperature and pressure. Carbonate cement is one of the most important factors that caused great loss of reservoir property in the studied reservoir sandstones,showing that the higher content of carbonate cements occurred,the poorer of the reservoir property is. Most obviously,early carbonate cements occurred basally and highly reduced reservoir property. The second stage of carbonate cements generally were featured by porous cementation and blocked the pore spaces. Late carbonate cements generally have a low content,but occurred as replacements of detrital grains or pore fillings in intergranular pores and dissolution pores,which caused further densification of reservoir sandstones. The results can provide a basis for the prediction of favorable zones and the evaluation of exploration targets in this area.
引文
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