大牛地气田石英次生加大特征及其对储层物性的影响

以大牛地气田太原组、山西组和下石盒子组致密砂岩储层为研究对象,依据石英次生加大的点状式、环边式和多期式形貌,结合流体包裹体均一温度,将石英次生加大分为3期,其中第Ⅱ期在本区发育数量最多,含有一定量的有机包裹体,第Ⅰ期和第Ⅲ期见石英溶解现象。随石英次生加大期次的增加,加大边的宽度逐渐增大,对应的储层物性逐渐变差,但第Ⅲ期对应的孔隙度较前两期明显偏高。当大牛地气田的硅质胶结物含量大于3%时,将以孔隙充填为主,在第Ⅲ期石英次生加大之后,砂岩储层已完全致密化。在整体致密的背景下,碱性溶解作用形成的石英溶解型孔隙,为大牛地气田提供了大量的储集空间,是太原组二段次生孔隙的主要成因。

Characteristics and its effect on reservoir physical property of quartz overgrowth at Daniudi Gas Field

The tight sandstone reservoirs from the Taiyuan, Shanxi and Xiashihezi Formations of the Daniudi Gas Field were studied. In view of the punctate type, zonary structure and multistage morphology of quartz overgrowth, and combined with the homogenization temperature fluid inclusions, the quartz overgrowth were divided into three stages, among which the stage Ⅱ was most developed and contained some organic inclusions. Quartz solution was found in the stages Ⅰ and Ⅲ. The corresponding reservoir physical property gradually became poor with the increasing stage of quartz overgrowth and the increasing width of enlargement margin; however, the porosity of the stage Ⅲ was obviously higher than that of the previous two stages. Pore filling was dominant when the content of siliceous cement was over 3% at the Daniudi Gas Field. After the quartz overgrowth in the stage Ⅲ, sandstone reservoirs were densified completely. Under the whole compact background, alkalinity dissolution resulted in pores of quartz solution type, which offered reservoir space for the Daniudi Gas Field, and was the main cause for secondary pores in the second member of the Taiyuan Formation.