孝泉—新场—合兴场地区须家河组砂岩储层中自生矿物研究.doc

孝泉新场合兴场地区须家河组砂岩储层中自生矿物研究 【中文摘要】综合运用薄片分析、电镜扫描、X射线衍射分析以及碳、氧同位素地球化学分析等手段,对川西凹陷中段孝泉-新场-合兴场地区须家河组砂岩储层中的自生矿物进行含量、类型、分布规律的分析研究,探讨其形成机制及成岩过程中对储层的影响,为猜测和评估储层质量奠定基础。须家河组的主要储集层为须2段和须4段,砂岩储层中的自生矿物类型主要为自生粘土矿物、自生碳酸盐胶结物及自生硅质矿物。须家河组储层砂岩中的自生粘土矿物以自生的绿泥石和高岭石为主。绿泥石含量的均匀值为0.21,主要以孔隙衬里方式产出。纵向分布上,须2、须4段均有自生绿泥石分布,但其含量大于2的样品只出现在须2段,物质来源可能与埋躲前组成中铁镁暗色矿物的存在和数目有关。平面分布上,孝-新-合地区偏北东方向的钻井中自生绿泥石含量较高,可能与龙门山北段须家河组砂岩中有更高的岩屑有关。须家河组大多数的白生绿泥石的沉淀作用是在较早的成岩阶段发生的,大多数须4段的粘土包膜比须2段更薄,其沉淀主要的时间与须2段类似,开始于较早的成岩阶段,略早于须4段长石的溶解时间。绿泥石环边能明显进步岩石的机械强度和抗压实能力,并在埋躲成岩过程中继续生长,且对石英的胶结作用具有一定的抑制作用,不仅使砂岩的原生孔隙得以保存,同时也使由长石等骨架颗粒溶解形成的此时次生孔隙得以保存。须家河组砂岩储层中自生高岭石含量较低,为0.29,纵向分布具有明显的地层专属性,基本上只分布在须家河组第4段顶部或紧靠项部的砂岩中,这些高岭石可能是层序中某些特殊界而或其四周的产物,并可能是这些特殊界而的标志矿物。X射线衍射结果表明砂岩中的高岭石基本都是自天生因,主要与长石等硅铝酸盐的溶解有关。从储层演化的角度来说,高岭石通常是长石溶解和次生孔隙发育的指示矿物。碳酸盐胶结物均匀含量高达6.02,占胶结物总量的84,是该区域中自生矿物中含量最多的。碳酸盐胶结物的主要类型包括方解石、白云石、铁方解石和铁白云石。纵向分布上,须2、须4两个砂岩段碳酸盐胶结物总量没有实质性差别,但须3、须5两个泥岩段的碳酸盐胶结物含量均匀值分别高于对应的砂岩段。白云石胶结物的含量以下部地层段较高,须2段白云石胶结物含量均匀值明显高于须4段,而须3段白云石胶结物的含量的均匀值明显高于须5段;方解石胶结物的纵向变化趋势则与白云石相反,须4段方解石胶结物含量的均匀值明显高于须2段,须5段方解石胶结物含量的均匀值则明显高于须3段。须2段白云石胶结物是在相对浅埋躲的条件下沉淀的,由于它们具有很高的沉淀温度据氧同位素分析,同时岩石的负胶结物孔隙度也很低。据其碳同位素分析,其物质来源中可能存在海相物质来源。结合氧同位素分析,须4段的方解石胶结物可能是在相对浅埋躲的较早成岩阶段沉淀的,由于它们具有比较低的沉淀温度;据碳同位素分析,其物质来源可能与长石的溶解作用有关。相当数目的碳酸盐胶结物的物质来源还与粘土矿物的转化有关。该区域砂岩储层中硅质矿物的总量总体上较低,均匀值为0.90。大多数自生硅质矿物以围绕碎屑石英边沿生长的方式存在,加大部分常由多个具相同光性方位的石英组成,这些石英终极连接成一个大的晶体形成加大边并堵塞一部分孔隙,但仍有相当数目的硅质矿物以分散的微晶形式存在于长石溶解形成的次生孔隙中,说明长石溶解是硅质矿物的重要物质来源之一。硅质矿物在分布上受到地层段的控制,从须2段到须5段,砂岩中的硅质矿物从须2段的1.42明显减少到须5段的0.13。与须4段相比,须2段的长石溶解量明显减少,次生孔隙的尽对值和相对值都明显较低,薄片观察表明,一些样品中完全没有长石溶解,但石英却普遍次生加大。因此须2段硅质矿物对储层的影响主要是负面的,须4段的硅质胶结作用是在相对较早期的成岩阶段发生的,不会对储层有明显的负面影响。; 【Abstract】 The analyses of authigenic minerals content、type and distribution regular in Xujiahe ation sandstone reservoir of the middle section of Western Sichuan Sag are based on Thin-section analysis、Scanning electron microscope、X-ray Diffraction、Carbon and oxygen isotope analyses.The analyses lay a foundation for discussing the ation mechanism and the influence to reservoir,forcasting and assessing the quality of the reservoir.XujiaheⅡandⅣare the main reservoir,authigenic clay minerals、authigenic carbonate cements and authigenic siliceous cements are the main type of authigenic minerals in sandstone reservoir.Authigenic minerals in Xujiahe ation contains mainly Chlorite and Kaolinite.The average content of chlorite is 0.21,and it exist as pore-lining cements.Chlorite distribute both in the XujiaheⅡandⅣvertically,but the samples that contain chlorite more than 2only found in XujiaheⅡ,the provenance may be relevant with dark-colored ferromagnesian mineral.On plain distribution,the well drillings which lean to north-east contain more chlorite,maybe it\s caused by higher cuttings in North of Xujiahe ation.Most of the authigenic chlorite deposit at earlier diagenetic stage,and most clay coatings in XujiaheⅣare more thin than XujiaheⅡ,which deposit at early stage as XujiaheⅡ,earlier than the dissolution of feldspar.Authigenic Kaolinite has low content 0.29of sandstone reservoir in Xujiahe ation.Kaolinite\s distribution is influenced obviouslly by strata,it distribute only in sandstone of the top of XujiaheⅣor near the top.Maybe these Kaolinite is the product of some particular stratic inte***ce or near the inte***ce,and may be the index mineral of these particular inte***ce.The research result of X-ray Diffraction show that almost all the kaolinite in sandstone is authigenetic,which dominanted by dissolution of aluminosilicate,such as feldspar.From the angle of reservoir evolution,kaolinite is the index mineral of feldspar\s dissolution and secondary porosity\s development.The average content of carbonate cementsthe most abundant authigenic minerals this areaaccess to 6.02,which occupy 84of all the cements.Carbonate has four main typescalcite、dolomite、forrocalcite and ankerite.The two sandstone member,XujiaheⅡandⅣcontain the carbonate cements,which don\t have much difference on vertically distribution,but the average content of XujiaheⅢandⅤmudstone memberis higher than sandstone member accordantly.The lower strata has higher domomite cements content,the average content of dolomite in XujiaheⅡis higher than XujiaheⅣobviously,and the average content of dolomite in XujiaheⅢis higher than XujiaheⅤ.But the tendency of calcite cements is converse with dolomite vertically,the average content of calcite XujiaheⅣin is higher than XujiaheⅡ,and the average content of calcite in XujiaheⅤis higher than XujiaheⅢobviouslly.Dolomite cements in XujiaheⅡdeposit at shallow burial depth,cause they have higher deposition temperatureaccording to oxygen isotope analysis,and the value of minus cement porosity is very low.Based on carbonate isotope analysis,marine provenance may one the reason that dolomite ing.Combine with the oxygen isotope analysis,the calcite cements in XujiaheⅣmay deposit at early diagenetic stage,for they have lower depostion temperature.By carbonate isotope analysis,maybe the calcite is relavent with dissolution of feldspar.Most the calcite\s provenace may be relavent with the conversion of clay minerals.The authigenic seliceous cements in the sandstone reservoir is low,the average content is 0.90.Most the authigenic seliceous cements present around the periphery of detrital quartz,the widen section is composed with several quartz which have the same optic orientation.Finally,these quartz connect as a big crystal and the quartz overgrowth to block up some of the pore space,but quantitative seliceous cements present in secondary porosity as microlite after the dissolution.it conclude that feldspar\s dissolution is the one of most important provenance of seliceous cements.The distribution of seliceous cements are controlled by strata obviouslly,the content of XujiaheⅡis 1.42and it decrease to 0.13of XujiaheⅤ.Compare with XujiaheⅣ,the feldspar\s dissolution decrease apparently,both the absolute magnitude and relative magnitude of XujiaheⅡare very low.The thin-section analysis show some samples don\t have the dissolution of feldspar completely,but the quartz overgrow generally.So the seliceous cements in XujiaheⅡhave destructive infulence,while the seliceous cemented at earlier diagenetic stage,they don\t play obviously destructive influence to reservoir.