饱和CO_2地层水驱过程中的水-岩相互作用实验

An experimental study on water-rock interaction during water flooding in formations saturated with CO_2

为了研究CO2注入后储层岩性和物性的变化情况,利用室内岩心驱替装置,模拟了地层条件下(100℃,24 MPa)饱和CO2地层水驱过程中的水-岩相互作用,并对CO2注入后,组成储层岩石的矿物溶蚀、溶解和沉淀情况以及渗透率变化的原因进行了研究。通过对实验前后反应液离子成分变化、岩心扫描电镜和全岩X-射线衍射(XRD)资料的分析表明:实验后砂岩岩心中的碳酸盐矿物出现明显的溶解现象,且方解石溶解程度最高,片钠铝石次之,铁白云石最低;反应液中K+质量浓度的变化主要是由碎屑钾长石颗粒溶蚀造成的;实验后有少量的高岭石和中间产物生成,其中间产物的成分主要为C、O、Na、Cl、Al和Si,并有向碳酸盐矿物转变的趋势;新生成的高岭石、中间产物和由碳酸盐胶结物溶解释放出的黏土颗粒一起运移至孔喉,从而堵塞孔隙,降低了岩心渗透率。通过以上实验再现了CO2注入后,短时期内储层岩石中长石和碳酸盐类矿物的溶蚀和溶解过程以及新矿物沉淀情况,并且揭示了储层渗透率变化的原因,从而为CO2的地下捕获机制提供了地球化学依据。

In order to explore the short-term changes in reservoir lithology and physical properties,the process of mineral corrosion,dissolution and precipitiation and the permeability variation of reservoir rocks after CO2 injection,the interation process between CO2-saturated rocks and formation water was studied in detail through core flooding laboratory experiment carried out under simulated reservoir conditions（100℃ and 24 MPa）.Changes in ion compositions of the reaction solution in pre-and post-CO2-flooding experiments as well as core scanning electron microscopic and whole-rock X-ray diffraction（XRD） analyses showed that dissolution and corrosion phenomena of carbonate minerals can be observed after the experiment,among which calcite dissolution is the strongest,followed by dawsonite,while ankerite the weakest.The concentration of K＋ in the reaction solution varies mainly due to the dissolution of detrital K-feldspar grains.A small amount of kaolinite and intermediate products were generated after the experiment.The composition of intermediate products is mainly composed of C,O,Na,Cl,Al and Si,which have a trend to change into carbonate minerals.New minerals（Kaolinite and intermediate products） and the particles released by the dissolution of the carbonate cement were moved to pore throats and blocked the path of pore,which was the main reason that caused the core permeability reduction.The experiment results have reproduced the short-term process of corrosion of feldspar and dissolution of carbonate minerals as well as precipitation of new minerals after CO2 injection,revealed reasons of permeability variation,and provided geochemical evidence for CO2 trapping mechanisms underground.