摘要
白云岩储层在全球油气勘探与开发中占有重要地位.白云岩作为一种钙镁碳酸盐矿物,无论在海相、陆相等沉积环境,还是同生、成岩、浅埋藏和深埋藏等成岩过程中均有出现,但在现代海洋沉积中却很少发育.因此,白云岩的成因一直是国内外碳酸盐岩储层研究的难点和热点.研究结果表明:①白云岩的成因可以分为原生和次生两种,巨厚的白云岩地层多由含Mg2+的成岩流体在特定的流体动力学条件下渗透并改造前期石灰岩地层而形成;②依据白云岩形成的环境、流体动力学条件和成岩流体中离子的浓度,将白云岩的成因归纳为 7 种模式:蒸发泵模式、渗透回流模式、混合水模式、海水模式、埋藏模式、热液成因模式和生物成因模式;③白云石化过程对储集空间的发育产生影响,理论模式下,Mg2+的离子半径小于Ca2+,石灰岩转变为白云岩孔隙度通常会增加,但在成岩环境、新生成白云石含量和晶体结构等复杂因素的影响下,白云岩的储集空间并不一定优于石灰岩,通常白云石化过程会提升储层颗粒的抗压能力及渗透率;④优质白云岩储层成因机理表明,原始沉积环境是基础,白云石化是必要条件,白云石化之外的成岩改造是关键因素.
Abstract
Dolomite reservoir occupies a critical position in global oil and gas exploration and development.As a type of calcium magnesium carbonate mineral,dolomite occurs in both marine and continental sedimentary environments,and also in diagenetic processes such as syngenesis,diagenesis,shallow burial,and deep burial.However,it is scarce in modern marine deposits.Therefore,the genesis of dolomite has been a hot point in researches at home and abroad on carbonate reservoir.Study results are as follows:(i)The genesis of dolo-mite can be divided into two types:the original and the secondary.Ultra-thick dolomite formations are mostly originated from the preexisting limestones permeated and reworked by Mg2+-containing diagenetic fluids under specific hydrodynamic conditions.(ii)According to the do-lomite-forming environments,hydrodynamic conditions,and the ion concentration in diagenetic fluids,the genesis of dolomite can be clas-sified as seven models,i.e.,evaporation pump,infiltration reflux,mixed water,seawater,burial,hydrothermal,and biogenic models.(iii)The process of dolomitization impacts the development of reservoir space.Under the theoretical conditions,the ionic radius of Mg2+ is smaller than that of Ca2+,and the porosity often increases when limestone transforms into dolomite.However,under the influence of complex factors such as diagenetic environment,newly generated dolomite content,and crystal structure,the reservoir space of dolomite may not necessarily be better than that of limestone.Usually,the dolomitization process improves the compressive strength and permeability of reservoir parti-cles.(iv)The genetic mechanism of high-quality dolomite reservoir indicates that the original sedimentary environment is the fundamenta-tion,the dolomitization is a necessary condition,and the diagenetic transformation is a key factor.
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