CO_2-水-方解石相互作用后岩石表观形貌及渗透率变化特征

The Influence of CO_2-water-calcite Interactions on Surface Texture and Permeability of the Calcite

将CO_2注入地下油藏用于驱替原油是减少温室气体的排放及提高原油采收率的一种有效方法。CO_2注入地层后会与地层流体和岩石发生反应,其中岩石组成中的碳酸盐矿物极易与CO_2和水发生反应导致储层岩石物性发生改变。论文以方解石为代表样品,采用X射线衍射仪(XRD),电诱导双等离子体原子排放光谱测定仪(ICP-AES),扫描电镜(SEM)及在5 MPa压力下填砂模型的试验方法进行评价,分别考察了方解石的矿物学性质、CO_2-水-方解石反应前后方解石的表面物性、反应前后溶液的离子浓度变化及方解石填砂模型与CO_2、水反应后渗透率的变化。实验结果表明,与CO_2和水反应后,方解石出现溶蚀现象;反应压力增加,方解石溶蚀现象增加,反应后溶液中Ca^(2+)、HCO_3^-浓度增加;反应温度增加,方解石溶蚀现象增加,反应后溶液中Ca^(2+)、HCO_3^-浓度先增加,后降低;与CO_2和水反应后的方解石/石英砂填砂模型水测渗透率增加。

Injecting CO_2 into underground reservoir to displace oil is a viable means of reducing greenhouse gas emission to the atmosphere and enhancing oil recovery. CO_2 can react with reservoir rock and fluids when injected underground,and it can easily react with carbonates which leads to the physical change of the reservoir rock. Calcite was chose to evaluate the effect of CO_2-water-rock interactions on the characteristics of reservoir rock. The mineralogy of calcite,the surface texture of calcite,the ion concentration in the reacted solution,the permeability of calcite after reacted with injected CO_2 and deionized water was investigated by X-ray diffraction（ XRD）,scanning electronic microscope（ SEM）,inductive coupled plasma-atomic emission spectrometry（ ICP-AES）,and sand-packed model at pressure of 5. 0 MPa. The results showed that the mineral dissolution of calcite would occur when interacting with injected CO_2 and water. With the increase of CO_2 pressure,the surface dissolution of calcite appeared more obvious and Ca^（2＋）、HCO_3^- ion concentration in the solution increased as well. With the increase of reaction temperature,the surface dissolution of calcite also appeared more obvious and Ca^（2＋）、HCO_3^- ion concentration in the solution increased first,then decreased. The mineral dissolution of calcite caused the improvement in water permeability of calcite/quartz sand-packed model.