致密砂岩储层成岩作用特征研究及其对储集性能的影响——以鄂尔多斯盆地东部上古生界盒8段天然气储层为例

通过各类薄片显微镜下精细研究与定量统计,利用图像孔喉分析、电镜扫描、阴极发光等多种分析测试手段,对鄂尔多斯盆地东部主力含气层盒8段致密砂岩的岩石学特征、孔隙发育特征及成岩作用特征进行研究,结合成岩演化分析其对盒8段各砂岩储层储集性能的影响。研究表明:盒8段砂岩以岩屑石英砂岩和岩屑砂岩为主,其次是石英砂岩,填隙物以高岭石、硅质和伊利石为主,孔隙类型以次生溶孔为主。储层各砂岩的岩石学特征、孔隙发育状况及其成岩演化过程存在一定的差异。差异性的成岩演化过程导致盒8段各砂岩胶结物成分及其含量不同,并导致各砂岩孔隙结构的不同,后者直接影响砂岩的储集性能。该研究对于探讨不同砂岩类型成岩演化对砂岩储层储集性能的影响具有重要的意义,可为研究区天然气的勘探指明方向。     

鄂尔多斯盆地上古生界层序格架内的成岩作用

鄂尔多斯盆地上古生界主要发育石英砂岩、岩屑砂岩、杂砂岩、“牛毛毡砂岩”、黑色石英砂岩等五种砂岩类型。这些砂岩具有成份成熟度较高、结构成熟度中—低、以正粒序为主、粒级普遍为中粗粒、储层填隙物类型多、含量变化大的特点。经历了三个重要成岩阶段:早成岩压实期—原生孔隙大量破坏损失期，中成岩A期—有机酸溶蚀—次生孔隙发育期，中成岩B期—埋藏压溶再胶结成岩期。在SQ8主要发育压溶、高岭石溶蚀、石英次生加大等成岩作用。SQ11主要发育硅质胶结、碳酸盐胶结成岩作用。成岩相可分为三级五类，即Ⅰ强压溶—石英加大相；Ⅱ压溶—碳酸盐溶蚀—高岭石交代相及溶蚀—弱杂基充填—高岭石交代相；Ⅲ强压实—粘土胶结相及强压实—碳酸盐胶结、交代相。区内储层整体为低孔低渗的致密砂岩储层，以发育次生孔隙为主，包括粒间溶孔、粒内溶孔和高岭石晶间孔，原生孔隙较少保留。通过对沉积砂体展布、储层成岩相类型及储集性能的综合分析，对有利的储层分布区带进行了预测。     

惠州凹陷东部珠海组储层碱性成岩作用及孔隙演化

根据铸体薄片、扫描电镜、粒度分析、X衍射等资料,对惠州凹陷东部珠海组储层的岩石学特征、成岩作用和孔隙演化过程进行分析研究。研究认为,惠州凹陷东部珠海组储层的岩石类型以岩屑砂岩、长石质岩屑砂岩、岩屑质石英砂岩和岩屑质长石砂岩为主,结构成熟度与成分成熟度较低。砂岩埋藏过程中经历了明显的碱性成岩作用:石英的溶蚀与交代、碳酸盐矿物胶结、伊利石和绿泥石的沉淀以及钠长石化等。碱性成岩作用对孔隙的影响包括:石英溶蚀形成次生溶孔、碳酸盐胶结物沉淀损失粒间孔隙、黏土矿物沉淀形成晶间微孔。研究区珠海组主要发育粒内溶孔和粒间溶孔,原生孔隙较少。储层现今处于中成岩阶段A期,早期经历了强烈的压实作用,使其孔隙度由原始孔隙度32.1%降低至8.8%。早成岩阶段为碱性成岩环境,石英溶蚀增孔约0.5%;碳酸盐、硫酸盐、伊利石等胶结物沉淀减孔约2.3%。中成岩阶段A期为酸性成岩环境,硅质、高岭石等胶结物沉淀减孔约1.2%;长石、岩屑等溶蚀增孔约4.3%。最终,储层演化至现今孔隙度10.1%。     

苏里格气田苏西区块上古生界天然气储层特征

从储层的岩石学类型、孔渗特征、孔隙结构类型和储集空间等方面分析苏里格气田苏西区块上古生界天然气储层特征。通过实验室铸体薄片鉴定、岩心物性测试、孔隙图像、扫描电镜以及高压压汞等方法测试研究,结果表明该区上古生界盒8、山1、山2储层以岩屑石英砂岩为主,其次为石英砂岩和岩屑砂岩;储层均属于特低孔超低渗储层;储集空间类型主要为粒间孔、晶间微孔以及粒内溶孔,研究区主要的孔隙结构组合是"溶孔+微孔"型;储层孔喉连通性较差,孔喉连通性较差又直接影响了该区上古生界的储层质量。     

三角洲前缘厚层砂岩孔隙结构及微观渗流特征——以吴仓堡地区长6储层为例

依据薄片、压汞、扫描电镜、物性分析及油水驱替实验资料,对吴仓堡地区三角洲前缘亚相长6厚层砂岩储层的岩石学特征、孔渗特征、孔隙结构特征、成岩作用、微观渗流特征等进行深入研究,分析影响储层储集性能的主控因素。结果表明,受东北物源控制的长6厚层砂岩储层具有成分成熟度中等、结构成熟度较好的特点,储集空间主要为残余粒间孔和粒间溶孔、粒内溶孔,为典型中低孔、特低渗储集层;储层储集性能主要受沉积微相和成岩作用控制。对储层发育影响最大的成岩期位于中成岩A期,中等压实－粘土膜胶结残余粒间孔发育成岩相和弱压实-残余粒间孔+溶蚀孔隙发育成岩相是最有利储层发育的成岩相带。根据微观渗流特征,可划分出4种驱油类型,微观孔隙结构比宏观物性更能反映储层的本质特征。     

松辽盆地白垩系砂岩储集层特征

白垩系砂岩储层是松辽盆地主要的油气层，砂岩成分以石英，长石和岩屑为主，为长石砂岩，岩屑长石砂岩和长石质岩屑砂岩，储层孔隙包括粒间孔，粒内溶孔，铸模孔，胶结物内溶孔，裂缝等，储层孔隙演化经历了早、中、晚等成岩阶段，在中成岩阶段,晚成岩阶段早期和晚期有3次次生孔隙发育，其对储层性质有明显的改善。本区砂岩储集层可分为4个类型，且具有不同的分布规律。     

川东北元坝地区须家河组储层特征与超致密成因探讨

元坝地区须家河组砂岩的致密化程度极高,以超低孔、超低渗储层为主,属于超致密砂岩。本文基于铸体薄片、阴极发光、扫描电镜和物性等资料,在对砂岩的岩石组分、孔隙类型及物性特征分析的基础上,通过与国内外典型致密砂岩对比,揭示研究区砂岩较其他砂岩致密化程度高的原因,分析超致密砂岩的勘探潜能。结果表明,研究区砂岩具有较高的塑性岩屑、碳酸盐岩岩屑和黏土杂基含量;填隙物以黏土杂基和钙质胶结物为主,较强的硅质胶结作用仅发育于石英砂岩中。孔隙多为黏土杂基晶间微孔,喉道呈窄缝状或不发育,孔喉分选差,偏细歪度。砂岩致密化程度高主要有两方面的原因:一是原始组构差,成分成熟度低,含有较高的塑性岩屑、碳酸盐岩岩屑和黏土杂基含量,导致砂岩在早成岩阶段既已经历了很强的压实作用和钙质胶结作用,致密化时间早,溶蚀作用不发育;二是成岩演化阶段高,砂岩经历了中成岩阶段的压溶及进一步的钙质/硅质胶结,使得砂岩超致密化。与国内外典型致密砂岩气藏对比表明,超致密砂岩有效孔隙少,对天然气的富集能力有限。元坝地区须家河组只有孔隙度近于8%(如长石岩屑砂岩)的砂岩才可成为有利的致密气储层。     

鄂尔多斯盆地子洲-清涧地区上古生界山32段储层砂岩成岩作用

鄂尔多斯盆地子洲-清涧地区上古生界山 32段砂岩储层以石英砂岩为主,其次为岩屑质石英砂岩和岩屑砂岩.目前储层正处于晚成岩阶段B期,成岩作用类型包括压实作用、胶结作用、交代作用和溶蚀作用,机械压实作用、压溶作用和自生黏土矿物的胶结作用是低孔低渗储层形成的主要原因,成岩晚期的溶蚀作用大大改善了砂岩储层的储集空间.根据成岩作用的特点,将研究区山 32段划分出5个成岩相:压实压溶相、弱压实-硅质胶结相、弱压实-自生黏土矿物胶结相、弱压实-碳酸盐胶结相、弱压实-溶蚀相.压实压溶相储层物性最差;弱压实-硅质胶结相、弱压实-自生黏土矿物胶结相和弱压实-碳酸盐胶结相储层的孔隙度、渗透率总体也很低;弱压实-溶蚀相储层的储集空间最发育、连通性最好,孔隙类型以粒间孔、粒间溶孔、粒内溶孔为主.     

鄂尔多斯盆地华庆地区延长组长6油层组储层特征

通过对华庆地区长6段岩心铸体薄片及物性资料分析,研究了其岩石学特征、孔隙类型、微观孔隙结构特征、孔渗特征及成岩作用。认为研究区长6储层发育三角洲前缘及深水浊积扇沉积,三角洲前缘水下分流河道和上扇主沟道是储层分布的主要相带,主要发育细粒岩屑长石砂岩及长石砂岩、长石岩屑砂岩;粒间孔及长石溶孔是主要储集空间。孔喉分布表现为小孔微细喉,非均质性强;孔隙度平均为9.5%,渗透率平均为0.38×10-3μm2,为一套低孔低渗-特低渗储层。研究区砂岩埋藏后经历的成岩作用主要有压实作用、胶结作用及溶蚀作用。强烈的压实作用、胶结作用是使孔隙大量消失、物性变差的主要原因;而溶蚀作用,特别是长石、岩屑及浊沸石溶孔在很大程度上改善了储层的储集性能。     

川西坳陷中江气田侏罗系沙溪庙组致密砂岩储层特征及主控因素分析

通过对中江气田沙溪庙组储层的岩石学、物性、储集空间类型、成岩作用等基本特征的研究,明确了本区储层形成的主控因素,建立了优质储层的地质模型,并据此预测出本区优质储层的分布。中江气田沙溪庙组岩石类型以岩屑长石砂岩和长石岩屑砂岩为主,具有富长石的特征。储层平均孔隙度为9.0%,平均渗透率为0.096 m D,属于低孔低渗致密砂岩储层。孔隙类型主要为剩余粒间孔和粒间溶孔,其次为粒内溶孔。储层总体表现出沉积-成岩控储的特征,有利储层的地质模型是:较粗粒度,高长石、低岩屑,低碳酸盐胶结物,不同地区不同层段优质储层的分布均有不同。     

障壁坝砂体储层特征与成岩孔隙定量演化模式 ——以鄂尔多斯盆地延长探区本溪组为例

为明确海陆变迁背景下障壁坝砂体成岩孔隙演化规律,运用岩石薄片、扫描电镜及配套能谱、阴极发光等资料,对延长探区石炭系本溪组障壁成因砂体储集特征与成岩作用进行综合分析,并结合砂岩初始孔隙度恢复模型与薄片孔隙定量分析技术,开展基于埋藏热演化历程的储层孔隙演化参数定量评价,建立该区本溪组障壁坝砂岩孔隙定量演化模式。结果表明:储层砂岩以石英砂岩、岩屑质石英砂岩及岩屑砂岩为主;孔隙度、渗透率平均值分别为4.72%和1.22×10^(-3 )μm^2;储集空间以溶蚀扩大孔、粒内孔、晶间孔为主;现今储层主体已达到晚成岩阶段;砂岩初始孔隙度平均值为38.1%,埋藏至今共经历了四个典型的成岩增/减孔阶段,即P_1～T_2(285～208 Ma)"低地温、快埋藏"的大幅减孔阶段(-30.7%)、T_2～J_3(208～153 Ma)"高地温、缓沉降"的溶蚀增孔阶段(+3.9%)、J_3～K_1(153～96 Ma)"高地温、稳埋深"的减孔定型阶段(-6.6%)、K_1至今(96 Ma～)"低地温、晚隆升"的弱改造阶段。     

Reservoir characteristics and main controlling factors of oil sand in Houba area,northwestern Sichuan Basin,China

Houba oil sand in frontier Longmenshan Mountain is one of the most typically important unconventional resources. The basic reservoir characteristics of oil sand and the main factors affecting reservoir quality were examined in this article based on porosity, permeability, and mercury porosimetry measurements; thin section analyses; SEM observation; and X-ray diffraction analysis. This study shows that the oil-bearing sandstone reservoir is mainly medium?coarse-grained sublitharenite and litharenite. The main pore type is intergranular pores, including residual primary intergranular pores, dissolved intergranular pores, and dissolved intragranular pores; fractures are common in this study area. The quality of sandstone reservoir is of high porosity and high permeability with a high oil saturation of 89.84 %. It is indicated that the main controlling factors of the reservoir in the study area include deposition, diagenesis, and tectonism. Deposition laid a foundation to porosity evolution, and channel sand is the most favorable depositional facies for the reservoir. Diagenetic alterations are the keys to reservoir evolution; dissolution and chlorite coatings cementation play an effective role in the generation and preservation of pores. Compaction, carbonate cementation, and quartz overgrowth cause many damages to the reservoir porosity. Fractures caused by structural breakages can improve the reservoir permeability and they also can provide fluid migration pathways to the late corrosion, which formed a lot of corroded fissures as reservoir and percolation spaces.     

Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area,eastern margin of the Ordos Basin,China

Residual and movable porosity are significant parameters for characterising petrophysical properties, especially in tight reservoirs. Eight tight sandstone samples from the upper Paleozoic gas-bearing strata in the Kangning area, from the eastern margin of the Ordos Basin, were analysed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), petrography, and porosity and permeability tests. The lithology and pore types were identified and classified using petrography and SEM. The residual and movable porosity were obtained with NMR. In addition, NMR was used to visualise pore structure and pore size distribution. The results suggest that the upper Paleozoic sandstones in the study area mainly comprise feldspathic litharenite and litharenite. The sandstone porosity and permeability are low, with means of 5.9% and 0.549 mD, respectively. Four pore types exist in the tight sandstones: residual primary pores, grain dissolution pores, micropores (clay-dominated) and microfractures. The T₂ spectra under water-saturated conditions correlate with pore size and can be used to distinguish small and large pores based on the transverse relaxation time cutoff value of 10 ms, which corresponds to a pore diameter of 0.232 μm. Small pores account for 72% of the pores in the tight sandstones. The continuous bimodal T₂ spectra suggest good connectivity between small and large pores, despite the low porosity and permeability. In this study, the movable porosity of the major tight sandstone gas reservoirs is higher than the residual porosity, which confirms the effective evaluation of movable porosity to tight sandstone reservoirs, based on NMR experiments.     

孔隙结构对低渗-特低渗砂岩储层渗流特征的影响段储层为例——以鄂尔多斯盆地东部上古生界盒8段储层为例

通过铸体薄片显微镜下观察、孔喉图像、毛细管压力、恒速压汞、气水相对渗透率、核磁共振等多种分析实验手段,研究了鄂尔多斯盆地东部上古生界盒8段低孔、低渗-特低渗砂岩储层的微观孔隙结构和渗流特征,探讨了孔隙结构对储层渗流特征的影响。结果表明,孔隙结构特征是影响低孔、低渗-特低渗砂岩储集性能与渗流特征的主要因素。而砂岩的孔隙结构特征主要受砂岩原生矿物组合与成岩演化过程及其产物的控制,盒8段各砂岩类型由于其矿物成分不同导致孔隙结构的差异,也是各砂岩类型储集性能与渗流能力存在差别的直接原因。在孔隙结构参数中,喉道的大小、有效孔隙与喉道的体积及其连通性是决定储层储集与渗流能力的关键。大孔喉对储层渗流能力的贡献更大,中-小孔喉则对储集能力的贡献相对较高。微裂缝是除孔隙结构以外影响砂岩储集性能与渗流特征的重要因素。     

东濮凹陷上古生界石千峰组致密砂岩储层特征

东濮凹陷上古生界石千峰组发育一套厚度较大且具有勘探潜力的河流-湖泊相致密砂岩。采用岩心观察、薄片鉴定、扫描电镜、阴极发光、X衍射全岩及黏土矿物分析等技术手段,对东濮凹陷上古生界石千峰组致密砂岩储层的岩石学特征、物性特征和成岩作用进行了分析。结果表明:储层岩石类型主要为岩屑长石砂岩和长石岩屑砂岩;孔隙度2%~10%,渗透率(0~1)10^-3m²,整体上表现出特低孔超低渗特点;成岩作用主要为压实、压溶、胶结、溶蚀和交代作用。样品古地温、镜质体反射率(R_o,%)和X衍射黏土矿物分析结果进一步证实研究区石千峰组砂岩储层属于中成岩阶段A期。     

鄂尔多斯盆地合水地区长6储层成岩作用与有利成岩相带

鄂尔多斯盆地合水地区长6储层主要为长石岩屑砂岩,平均孔隙度8.68%,平均渗透率0.15×10-3μm2,属于典型的低孔特低渗透储层。储层经历了压实作用、胶结作用、交代作用、溶蚀作用的改造,目前处于晚成岩阶段A期。在成岩作用研究的基础上,通过大量的岩心观察、薄片鉴定、扫描电镜等方法及测井曲线特征研究,进行了单井成岩相分析,进而编制成岩相平面分布图。将研究区辫状河三角洲前缘砂体划分出4个成岩相带:压实相、碳酸盐胶结相、绿泥石膜剩余孔相和绿泥石膜剩余孔—长石溶蚀相。其中,有利储层主要分布在主砂体的绿泥石膜剩余孔相和绿泥石膜剩余孔—长石溶蚀成岩相带上。根据试油资料,处于该有利相带的井一般日产油大于10t/d。     

大牛地气田大18井上古生界致密砂岩储层物性及其成岩主控因素

以大牛地气田大18井上古生界致密砂岩储层为研究对象,利用微观镜下研究手段和储层物性数据等资料,研究了大18井上古生界储层的岩石学特征、孔隙及物性演化特征、致密化成因及优质储层主控因素。分析结果表明:大18井上古生界储层孔隙以次生孔隙为主,包括石英颗粒溶解所形成的粒间溶孔和粒内溶孔、晶间孔,偶见铸模孔和超大孔;储层平均孔隙度为7.1%,平均渗透率为0.34×10-3 μm2,属于低孔低渗储层;压实作用是本区储层致密化的大背景,硅质、钙质及黏土矿物胶结充填孔隙、堵塞孔喉是致密化的主要原因;溶解作用是大18井优质储层形成的主控因素,特别是石英溶解最为发育,而绿泥石环边胶结作用通过增强岩石的抗压实强度、抑制石英次生加大保护原生孔隙,但不能增加储层物性。     

Depositional and Diagenetic Controls on Pore Structure of Tight Gas Sandstone Reservoirs: Evidence from Lower Cretaceous Bashijiqike Formation in Kelasu Thrust Belts,Kuqa Depression in Tarim Basin of West China

Deeply buried Lower Cretaceous Bashijiqike sandstones are important gas exploration targets in the Kelasu thrust belt, Kuqa Depression of Tarim Basin in China. The sandstones are characterized by low porosity, low permeability and strong microscopic heterogeneity due to diagenesis during their geologic history. Mineralogical, petrographic, and geochemical analyses combined with high‐pressure mercury injection analysis have been used to investigate the diagenesis, diagenetic minerals, and their impact on reservoir quality. This article addresses the controls exerted by depositional parameters and diagenetic modifications on pore‐network characteristics (porosity, pore types, sizes, shapes, and distribution), with the aim to unravel the formation mechanisms of this complex pore structures, and to improve the characterization and classification evaluation for the Bashijiqike sandstone reservoirs. The Bashijiqike sandstones are dominated by lithic arkoses and feldspathic litharenite. The pore system consists of intergranular macropores, intergranular micropores, and intragranular pores. Framework grains are generally heavily compacted. Authigenic quartz, authigenic feldspar, clay minerals and carbonates are the major pore‐filling constituents. The pore structure is characterized by small pore radius and poor interconnectivity. Entry pressure reflects the microscopic pore network and macroscopic reservoir property characteristics. Pore structure characteristics are linked to the depositional parameters, type and degree of diagenesis. Clays do not control reservoir pore networks alone, and pores and pore throats are wider in coarser grained sandstones. Entry pressure decreases with the content of the rigid quartz. Compaction and cementation continue to decrease the pore‐throat size, while dissolution enlarges pores and pore‐throats radius. Considerable amounts of microporosity associated with clay minerals and altered grains contribute to the high entry pressure. Comprehensive Coefficient of Diagenesis (CCD), which considers the integrative effect of diagenesis, shows strong statistical correlations with entry pressure. CCD is an integrative modulus of diagenesis and physical property, and generally the higher the values are, the better the pore structure. It is suitable for quantitatively characterizing pore structure in tight gas sandstones. The results of this work can help assess pore‐network characteristics like the Bashijiqike sandstones which had experienced strong diagenetic modifications during their geological history.     

含浊沸石砂岩储层孔隙演化特征及其对储层质量的影响——以鄂尔多斯盆地东南部延长组长101储层为例

鄂尔多斯盆地延长组储层中具有分布极不规律、成因复杂的浊沸石胶结物,其成岩演化特征对储层孔隙的演化有一定影响。为了解盆地含浊沸石砂岩储层的孔隙演化特征,以鄂尔多斯盆地东南部长10₁储层为研究对象,运用铸体薄片、图像粒度分析、扫描电镜手段、X-衍射、包裹体测温等手段,分析了研究区长10₁储层的岩石矿物特征、成岩作用类型,结合埋藏史、热史、生烃史,明确了各成岩事件的形成序列,定性描述、定量分析了各成岩作用下孔隙度的演化模式,并重点刻画了浊沸石在该储层成岩演化中的角色及作用。研究表明：研究区长10₁储层以长石砂岩和岩屑长石砂岩为主,属于典型的低孔低渗储层,储集空间以粒间孔和长石溶孔、浊沸石溶孔等次生溶蚀孔为主。成岩作用类型主要包括压实作用、胶结作用和溶蚀作用,综合判断储层处于中成岩A期。经孔隙定量演化的计算,长10₁储层压实作用、胶结作用是储层致密化的原因,溶蚀作用可有效改善储层物性。储层中浊沸石的差异性成岩演化对储层物性产生了不同影响：早成岩B期呈嵌晶状充填于粒间孔中的浊沸石降低孔隙度的贡献率达27.1%,中成岩A期后随着大量生烃,浊沸石产生的次生孔隙对于孔隙度的增加贡献率为44.1%,总体看浊沸石对长10₁储层起到了改善储层储集性能作用。