渤中凹陷CFD18-2油田高岭石胶结作用及其对储层物性的影响

Kaolinite Cementation and Its Influences on Reservoir Properties in CFD18-2 Oilfield in Bozhong Sag

为探究成岩作用过程中所形成的次生黏土矿物对储层物性的影响,借助偏光显微镜及扫描电镜的镜下分析,并结合储层物性等数据,对渤中凹陷附近沙垒田凸起东南部CFD18-2油田东三段高岭石的特征、类型、成因及其对储层物性的影响进行了研究。研究结果表明:1)研究区高岭石为有机酸溶蚀长石形成的自生高岭石,呈现典型的"手风琴状"及"蠕虫状",常充填于粒间孔、长石次生溶孔及碳酸盐胶结物溶孔中并形成良好的晶间孔隙。2)研究区主要发育两期高岭石,第一期主要充填于早期碳酸盐胶结物溶孔中,呈微小"蠕虫状";第二期充填于铁方解石与铁白云石胶结物溶孔中,部分高岭石具碱性溶蚀特征,且第二期高岭石与晚期伊利石共生。3)研究区东三段储层具备一定的渗流能力,使长石溶蚀形成的"副产物"被流体带走;但在破坏性成岩作用下,储层渗流能力会逐渐变差,最终使得"副产物"堆积于孔隙,降低储层物性。4)高岭石及同期硅质胶结物对储层物性的影响是一把"双刃剑",当高岭石及硅质的体积分数低于6.81%时,长石溶蚀有利于改善储层物性;当高岭石及硅质的体积分数高于6.81%时,则不利于储层物性的改善。

Kaolinite is a common aluminum-rich silicate clay mineral in sandstone reservoirs. It usually fills in the pore-throat of reservoirs. Its appearance generally indicates the dissolution of feldspars and the formation of secondary pores. The authors studied the characteristics, types, origin of the kaolinite through analyzing the data of polarizing microscope, scanning electron microscope, and the physical properties of the reservoir in the third member of Dongying Formation (Ed3) of CFD18-2 oil field in the southeastern part of Shaleitian uplift in Bozhong Sag. The results reveal that:1) The kaolinite of the study area is authigenic kaolinite formed by feldspar dissolution by organic acid. The authigenic kaolinite shows typical "accordion" and "worm" shapes, and is often filled in intergranular pores, feldspar secondary dissolution pores, and carbonate cement dissolution pores, forming good inter-crystalline pores. 2) Two phases of kaolinite are developed in the study area. The first phase of kaolinite is mainly filled in the dissolution pores of early carbonate cement, showing a tiny "worm" shape;the second phase of kaolinite is filled in the dissolution pores of ferrocalcite and ankerite cements, some kaolinite have the characteristics of alkaline dissolution, and the second phase of kaolinite is symbiotic with late illite. 3) The reservoir in the third member of Dongying Formation has a certain ability to seep, so that the "byproducts" formed by feldspar dissolution can be taken away by the fluid. However, under the action of destructive diagenesis, the seepage ability of the reservoir will gradually deteriorate, eventually causing "byproducts" to accumulate in the pores and reduce the physical properties of the reservoir. 4) The effect of kaolinite and siliceous cement on reservoir properties are "double-edged sword". When the content of kaolinite and siliceous material is low, dissolution of feldspar is beneficial to improving the physical properties of reservoirs;while the high content of kaolinite and siliceous is not conducive to the improvement of reservoir quality.