初论塔里木盆地砂岩储层中SiO2的溶蚀类型及其机理

根据显微镜观察,塔里木盆地砂岩储层中SiO₂溶蚀分为石英颗粒边缘溶蚀、次生加大边溶蚀和交代溶蚀。通过对石英颗粒和加大边溶蚀特征及其与粘土矿物组合、与碳酸盐胶结、与古油藏破坏以及现今油田水中Si离子含量等关系的综合研究,这些SiO₂溶蚀可能存在两种机理:碱性环境下的SiO₂溶蚀和有机酸(烃类微生物降解产生的有机酸以及有机质成熟产生的有机酸)引起的SiO₂溶蚀。第一种溶蚀类型较普遍,但程度微弱;第二种溶蚀类型主要发生在古油藏破坏和有机质成熟过程中,这种溶蚀较强烈但很局限。SiO₂的溶蚀作用可以为油气提供一定量的储集空间,这对于深埋的时代较老的志留-泥盆系储层具有重要意义。在古油藏中尽管烃类已经充注储层孔隙,但只要孔隙中存在有机酸或碱性孔隙水,SiO₂的溶蚀和石英次生加大的胶结等作用仍可进行。

AN APPROACH TO CATEGORIES AND MECHANISMS OF SiO2 DISSOLUTION IN SANDSTONE RESERVOIRS IN THE TARIM BASIN

By microscopic observation, dissolutions of SiO2 of sandstone reservoirs in the Tarim Basin could be divided into 3 types: quartze grain rim dissolution, overgrowth dissolution and replacement dissolution. Based on the integrated studies to the characteristics of dissolutions, clay mineral combination, carbonate cementation, paleo-oil reservoir breaking down and present Si4 contents in the oilfield water, two kinds of dissolution mechanism of SiO2 were proposed in this paper. The first kind of dissolution would be brought about by the alkaline water, which was widespread but very feeble. The secondary dissolution would be caused by the organic acids from the decomposition of micro-organism to the hydrocarbon, which happened under the paleo-oil reservoir breaking and hydrocarbon suffered the decomposition, or by the organic acids originated from the maturing of the organism matters. This kind of dissolution was not as widespread as the dissolution by alkaline water, but relatively stronger in the sandstones. The dissolution of SiO2 provided certain porosity for hydrocarbons, which must be very important for the deep buried reservoirs, for example, the Silurian and Devonian (Donghe) sandstones. Although the reservoir pores were fulled by hydrocarbon in the paleo-oil pool, only there existed organic acids or alkaline water in the pores, the diagenesis such as dissolution and cementation or replacement still kept on strongly.