摘要
水岩相互作用是成岩矿物演化和地层水离子变化之间的桥梁,两者通过水岩反应达到水岩体系的平衡,呈现出此消彼长的关系,并留下了水岩相互作用的证据。本文通过川西坳陷中段须家河组储层成岩矿物的微观特征以及地层水离子地球化学特征等的综合分析,对其水岩相互作用机制及概念模式进行了探讨,认为研究区须家河组二段(简称须二段)和须家河组四段(简称须四段)不同的水岩体系、围岩基质及地层水背景是造成两者水岩作用机制存在差异的根本原因。由于较大的K+/H+活度比,须二段长石得到有效保存;须四段长石缺失的最重要原因是其本身的物源较为贫长石,同时,低K+/H+活度比导致长石溶蚀进一步降低了其中的长石含量。长石的溶解、自生矿物的沉淀和黏土矿物的转化主要受长石溶蚀—离子(K+)迁移性—伊利石化三元体系中最慢反应进程控制。碳酸盐胶结物的碳氧同位素分析表明须四段的水岩体系更为开放,酸性流体数量大于须二段,须二段缺少有机CO2记录,推测与酸性流体数量较少、烃源岩为海相灰质泥页岩及构造抬升剥蚀有关,CO2运移分馏的影响较小。在此基础上,分别建立了铝硅酸盐和碳酸盐水岩作用概念模式,认为泥页岩并不是水岩体系中的封闭性因素,相反是水岩体系的第一开放对象,泥页岩(煤层)同时是物质提供者和接受者,是整个水岩体系不可或缺的部分。
Water-rock interaction acts as a bridge between the diagenetic mineral evolution and formation water ion change, through which minerals and formation water keep the water-rock system equilibrious, taking on a reciprocal relationship between them and giving proof of water-rock interaction. The present paper discussed the mechanism and conceptual model of water-rock interaction by comprehensive- ly investigating microcosmic characteristics of minerals and chemical characteristics of formation water in Xujiahe Formation of the study area, the result showed that different water-rock systems, host-rock matrices and backgrounds of formation water are the key reason for the difference in water-rock interaction mechanism between member 2 and 4 of Xujiahe Formation. Feldspar in Member 2 of Xujiahe Formation is effectively preserved due to a higher K ＋/H ＋ activity ratio, while the feldspar-depleted material source is the most signifi- cant reason for the absence of feldspar in Member 4 of Xujiahe Formation, moreover, the dissolution of feldspar caused by a lower K＋ / H＋ activity ratio can also result in the lower concentration of feldspar. Feldspar dissolution, authigenic mineral precipitation and clay mineral transformation are controlled mainly by the slowest reaction process in the ternary system of feldspar corrosion, ionic migration （K＋ ） and illitization. Carbon and oxygen isotopes of carbonate cements indicated that Member 4 has an open water-rock system because of more acidic fluid than Member 2. The lack of organic CO2 in Member 2 of Xujiahe Formation was supposed to be related with less a- cidic fluid, marine lime argillutite as a source rock and the denudation caused by tectonic uplift, and to be less affected by the fractionation of CO2 migration. Based on these, we established conceptual models of water-rock interaction for aluminosilicate and carbonate rocks, respectively. Argillutite was proposed not to be a sealing factor but the first open object in a water-rock system, moreover, some argil- lutite（coal bed）, as a material contributor and receiver, was thought indispensable in a whole water-rock system.
出处
《石油学报》
EI
CAS
CSCD
北大核心
2013年第1期47-58,共12页
Acta Petrolei Sinica
基金
国家自然科学基金项目(No.41172119)
油气藏地质及开发工程国家重点实验室基金项目(PLC201101)资助
关键词
地层水
储层
水岩相互作用
须家河组
川西坳陷
formation water
reservoir
water-rock interaction
Xujiahe Formation
western Sichuan depression
