【作者】 兰叶芳；

【导师】 黄思静；

【作者基本信息】 成都理工大学 ， 沉积学， 2011， 硕士

【摘要】 本论文以十一五国家科技重大专项专题之一—“鄂尔多斯盆地中生界延长组储层特征研究（2008ZX05001-004-003）”为依托,选取鄂尔多斯盆地姬塬—华庆地区长8油层组自生绿泥石为研究对象,通过薄片分析、全岩及粘土矿物X射线衍射分析、扫描电子显微镜分析、物性分析和压汞分析等手段对自生绿泥石的赋存状态、分布特征、形成机制,及其对储层物性及孔隙结构的影响等进行了探讨,研究主要取得了以下认识:（1）自生绿泥石是鄂尔多斯盆地姬塬—华庆地区长8油层组砂岩中含量最高的自生粘土矿物,主要以孔隙衬里形式存在,常与充填粒间孔隙的自生高岭石共生。（2）根据自生绿泥石的产出方式和赋存状态等特征,对姬塬—华庆地区长8油层组自生绿泥石形成的成岩机制作如下总结:（a）鄂尔多斯盆地姬塬—华庆地区长8油层组砂岩的埋藏前组成中存在较多的中基性火山物质,包括中基性熔岩和火山碎屑物质,这为自生绿泥石的发育提供了重要的物质来源;（b）铁的卸载与姬塬—华庆地区长8油层组沉积相以曲流河三角洲和扇三角洲为主,且长8沉积时期鄂尔多斯盆地的湖水具有一定的盐度有关;（c）自生绿泥石的形成时间大致相当于早成岩阶段早期甚至更早,绿泥石环边沉淀开始的时间应在大多数长石（也包括其它骨架颗粒）溶解之前,在以后的埋藏成岩过程中,这些绿泥石仍然继续定向生长并持续到自生石英沉淀后的成岩阶段;（d）虽然自生绿泥石和高岭石共生,但二者并非同时形成,而是存在时间差,自生绿泥石形成于地温达到60℃—70℃以前,长7烃源层中的有机酸还没有大量排出的成岩时间,当有机酸大量排出后,绿泥石生长停止或减慢,高岭石的沉淀取代绿泥石,成为主要自生矿物。（3）根据姬塬—华庆地区长8油层组作为孔隙衬里的自生绿泥石的形成时间,与孔隙流体介质演化以及和自生高岭石沉淀之间的关系,从以下两个方面讨论自生绿泥石对砂岩孔隙的保护作用:（a）以孔隙衬里方式沉淀的自生绿泥石及其在埋藏成岩过程中的继续生长增加了岩石的机械强度和抗压实能力,该作用使粒间孔隙（原生孔隙为主）不致因压实作用而进一步减少;（b）作为孔隙衬里的自生绿泥石可以通过分隔孔隙水与石英颗粒表面来抑制自生石英胶结物在碎屑颗粒表面成核,由于姬塬—华庆地区长8油层组长石的溶解作用主要发生在有机质热演化形成有机酸的相对较晚的成岩阶段,与之有关的自生石英的沉淀作用发生较晚,这些自生石英对岩石机械强度和抗压实能力的增加有限,因而作为孔隙衬里的自生绿泥石对石英成核的抑制作用是积极的。（4）选取高岭石含量为0,而自生绿泥石含量大于0的102个样品进行自生绿泥石含量与孔隙度—渗透率关系曲线的关系进行了研究,根据具有不同自生绿泥石含量的砂岩样品的孔隙度—渗透率关系方程的特征获得了0.01、0.1、1和10×10^-3μm²渗透率所分别对应的孔隙度,对比研究结果得出以下结论:（a）总的来说,随着砂岩中自生绿泥石含量的增加,要获得相同渗透率所需要的孔隙度是增加的,但对于不同的渗透率区间和不同的自生绿泥石含量,获得相同渗透率所需要的孔隙度增加的幅度是不同的;（b）由于姬塬—华庆地区长8油层组大多数样品（70%左右）的渗透率都介于0.04×10^-3—0.8×10^-3μm²之间,因而获得0.01×10^-3μm²、0.1×10^-3μm²渗透率所对应的孔隙度值的可信程度相对较高;（c）基于自生绿泥石对孔隙度—渗透率关系的影响,在考虑姬塬—华庆地区的孔隙度下限（如进行与孔隙度有关的储量计算或定义渗砂岩）时应考虑自生绿泥石含量的高低。假定以0.1×10^-3μm²的渗透率为参照,对于姬塬—华庆地区长8油层组而言,缺乏自生绿泥石或自生绿泥石含量较低时,可以考虑采用7%—8%的孔隙度下限;当自生绿泥石含量较高时,如自生绿泥石含量为8%—10%或更高的时候,则应该考虑采用9%—10%的孔隙度下限。（5）通过鄂尔多斯盆地姬塬—华庆地区长8油层组10个砂岩样品的薄片分析、X射线衍射分析、扫描电子显微镜分析、物性分析和压汞分析,研究了这些砂岩中自生绿泥石含量与各种孔隙结构参数之间的关系。研究结果表明:（a）在孔隙度变化不大的情况下,随着自生绿泥石含量的增加,砂岩的渗透率降低,排驱压力增加,中值压力增加,与之对应的喉道半径显著减小,同时喉道均值和各种类型喉道的百分数也都显著降低;（b）自生绿泥石含量的增加可以改善喉道分选性和非均质性,但这是牺牲了大喉道的数量来实现的;（c）砂岩中自生绿泥石含量的增加还会显著降低退出效率,这可能说明以孔隙衬里方式存在的自生绿泥石的含量较高时,石油的采收率相对较低;（d）在孔隙度类似的前提下,以孔隙衬里方式产出的自生绿泥石含量的增加,会降低砂岩储层质量并影响烃类开发效果。更多还原

【Abstract】 Based on the major and special project of national science and technology in the Eleventh Five Year Plan -“Reservoir characteristics of mesozoic Yanchang Formation in Ordos Basin”, the occurrence, distribution, formation mechanism of authigenic chlorites and their influences on reservoir properties and pore structure in chang-8 Member of the upper Triassic Yanchang Formation in Jiyuan-Huaqing area, Ordos Basin, were studied by thin section analysis, XRD, SEM, physical property analysis and mercury intrusion analysis and some conclusions are as follows:（1） Authigenic chlorites mainly present in the form of pore-lining cement is with the highest content in authigenic clay minerals, often coexisting with authigenic kaolinite filled in inter-granular pores.（2）According to characteristics of occurrence and distribution, the diagenetic mechanisms of the formation of authigenic chlorites are summarized:（a）Abundant neutral–basic volcanic materials, including neutral–basic lava and pyroclastic materials in sandstones before buried provided important material sources for the development of authigenic chlorites;（b）Unloading of iron was related to meandering river delta and fan delta in Jiyuan-Huaqing area and certain salinity of lake in Ordos Basin during the deposition of chang-8 Member;（c） Authigenic chlorite was formed roughly in early stage of early diagenesis or even earlier. Precipitation of chlorite rim began before the dissolution of the majority of feldspar （also including other skeleton grains）, and the oriented growth of these chlorites during the later diagenetic process lasted until diagenetic stage after the precipitation of authigenic quartz;（d） Authigenic chlorites are associated with kaolinite. However, the formation of the two is not at the same time, but with time difference. Authigenic chlorites formed in the diagenetic time with paleotemperature lower 60℃- 70℃. After a large number of organic acids were discharged, the growth of chlorite ceased or slowed down, and kaolinite was precipitated as the main authigenic mineral.（3）Based on the formation time and its relationships with the evolution of pore fluids and the precipitation of kaolinite, pore-lining authigenic chlorites play an important role in the preservation of porosity in sandstone reservoirs by the following mechanisms:（a） Pore-lining chlorites and their overgrowth during buried diagenesis enhanced the mechanical strength of rocks and the ability of resistant to compaction, so inter-granular pores （mainly primary pores） would not be further reduced due to compaction.（b） Pore-lining chlorites isolate detrital surfaces from contact with pore-water, thus preventing nucleation of authigenic quartz. Due to that dissolution of feldspars occurred in a relatively late diagenetic stage when organic acids were formed by thermal evolution of organic matters, and precipitation of related authigenic quartz occurred later, with limited ability of resistant to compaction, inhibition of nucleation of quartz by the pore-lining chlorite was positive.（4） 102 samples with varied authigenic chlorite content but without kaolinite were selected to study relationships between authigenic chlorite content and porosity -permeability curve. Corresponding porosities for obtaining the permeability of 0.01, 0.1, 1 and 10×10^-3μm² are gained, the following conclusions are reached by comparison of the results:（a）Overall, with the increasing of authigenic chlorite content in sandstones, porosity tends to increase to obtain the same permeability. However, for different ranges of permeability and contents of authigenic chlorites, porosities increase in different degrees to get the same permeability.（b）Because of permeability of most samples （about 70 percent） are between 0.04×10^-3μm² and 0.8×10^-3μm², thus porosities for obtaining the permeability of 0.01×10^-3μm² and 0.1×10^-3μm² are with relatively high credibility.（c） Based on the above principle, when considering the limit of porosity for defining the permeable sandstone or calculating reserves, the content of authigenic chlorite should be considered.（5） The relationship between authigenic chlorite content and the parameters of pore structure was studied on 10 samples. The results are as follows:（a）When sandstone porosity changes little, with increasing authigenic chlorite content, the permeability of the sandstone decreases while drainage pressure and median pressure increase, and the corresponding throat radius decreases obviously; meanwhile, throat mean value and the number of throats in different types also decrease significantly.（b）Although the increasing of authigenic chlorite content would ameliorate the sorting and heterogeneity of throats, the number of large throats would reduce correspondingly.（c） The increasing of authigenic chlorite content would remarkably reduce ejection efficiency, which may indicate that oil recovery may be lower when the content of pore-lining authigenic chlorite is higher in rocks.（d） Increasing pore-lining authigenic chlorites would reduce the quality of sandstone reservoirs and affect hydrocarbon exploitation under the prerequisite of similar porosity.更多还原