致密天然气砂岩储层:成因和讨论

致密天然气砂岩储层具有高的毛管压力和束缚水饱和度,孔隙类型以次生孔隙为主.根据致密成因可以将致密砂岩储层划分为4种类型:1)由自生粘土矿物的大量沉淀所形成的致密砂岩储层;2)由胶结物的晶出改变原生孔隙形成的致密砂岩储层;3)高含量塑性碎屑因压实作用形成的致密砂岩储层;4)粒间孔隙被碎屑沉积时的泥质充填形成的致密砂岩储层.有关致密砂岩储层次生孔隙的成因有多种理论,但是由于致密砂岩储层的复杂性,没有一种理论可以将所有的孔隙成因完全解释清楚,因此次生孔隙的成因机制仍然存在争议.尽管致密砂岩储层经历了复杂的成岩演化历史,成岩作用对储层的致密化起决定作用,然而沉积环境依然是控制致密砂岩储层形成的基本因素.深入了解沉积环境和成岩作用对致密砂岩储层的共同作用,有助于对致密天然气砂岩储层的预测和评价.     

四川盆地上三叠统砂岩成岩作用及其对孔隙的控制

四川盆地上三叠统不仅是一个含煤层系,也是一个有良好前景的含油(气)组合,已在多处获得工业油、气井(藏)。储集岩主要是须家河组的须二段和须四段的砂岩,其次是须三段、须五段和小塘子组的砂岩。近6000块砂岩物性分析,平均孔隙度6.8%,渗透率0.7毫达西,通常小于1毫达西。对某气田70余块砂岩所做的压汞分析,平均孔喉直径0.566微米。显然,它们主要属于细-微毛细管孔隙类型。何以形成如此低的孔、渗性呢?与其沉积环境和成岩作用有关。     

榆林-神木地区上古生界盒8段及山2段气层的成岩作用和成岩相

榆林-神木地区上古生界盒8段和山2段储集岩以石英砂岩、岩屑砂岩和岩屑质石英砂岩为主,成岩作用类型包括压实作用、胶结作用、交代蚀变作用、重结晶作用和溶蚀作用。砂岩经历了早期成岩阶段A,B期和晚期成岩阶段A₁,A₂和B期的成岩演化过程。压实作用和胶结作用是砂岩孔隙度降低的主要原因,分别造成22%和15%的原生孔隙丧失。砂岩中粘土矿物晶间微孔隙占总孔隙的60%以上,是砂岩的主要储集空间;溶解作用形成的次生孔隙在一定程度上改善了砂岩的储集性能;构造裂隙孔对砂岩储集性能的改善不明显。研究区发育6种不同成因类型的成岩相带,其中石英加大胶结组合孔隙相和自生粘土衬边胶结溶蚀孔相是最有利的天然气储集相带,二者的叠加和改造部位是气藏发育的最有利地带;粘土杂基充填微孔相和自生粘土胶结晶间孔相是较有利的成岩储集相带;杂基蚀变水云母充填压实紧密相和钙质胶结交代致密相不利于孔隙的发育和天然气的储集。     

Effects of composition, texture and diagenesis on porosity, permeability and oil recovery in a sandstone reservoir

Relationship among depositional texture, composition, diagenesis, porosity, permeability, initial water saturations and residual oil saturations have been investigated in a set of sandstone samples from a North American oil reservor. Pointcount, compositional and textural data obtained from thin sections were used.Grain size, sorting and mineralogy are closely interrelated. As grain size increases, sorting decreases and the proportion of readily soluble detrial grains increases.The type and extent of diagenetic alteration is related to grain size. Silica cement as overgrowths is more common in finer-grained sandstones with abundant monocrystalline quartz, whereas carbonate cement is more common in coarsergrained sandstones. Carbonate dissolution is extensive in some intervals in the reservoir.Sandstone samples were subdivided into tow subgroups in which relationshiops among grain size, porosity and permeability are significantly different: Sandstones with less than 13% porosity are strongly influenced by carbonate cement which controls porosity and permeability, independently of variations of grain size and sorting. Sandstones having porosity greater than 13% have undergone extensive carbonate dissolution, and coarse-grained sandstones have more secondary porosity than the finer-grained due to dissolution of unstable constituents. Both porosity and permeability are positively correlated with grain size in these samples.Initial (connate) water saturation increases with grain size because of the strong correlation between increasing grain size and polycrystalline grains which have intra-grain microporosity. Increasing heterogeneity with increasing grain size is thought to contribute to higher residual oil saturations in coarser-grained, more poorly sorted sandstones. A decrease in oil recovery efficiency with increasing grain size and permeability may be predicted for other sandstone reservoir rocks deposited in similar types of environments.     

鄂尔多斯盆地白豹—华池地区长6砂岩储层特征

根据铸体薄片、扫描电镜、碳氧同位素、物性、孔隙结构和声发射、岩心和测井分析和化验资料,对鄂尔多斯盆地白豹—华池地区长6砂岩储层特征进行的研究结果表明,该套储层储集空间以剩余原生粒间孔和次生粒间孔组合为主;储层物性较差,微裂缝对改善储层孔隙渗透性贡献不大;排驱压力和饱和度中值压力较高,孔喉半径小且分选性较差,歪度细,溶蚀作用对改善喉道连通性的效果不佳,孔隙结构参数总体较差。储层质量受沉积微相和成岩作用的综合影响,其中,由三角洲前缘滑塌形成的内-中扇较粗粒水道砂体为最有利储层发育的微相,成岩早期碳酸盐矿物和环边绿泥石胶结作用有利于部分原生孔隙和喉道的保存。利用储层物性和孔隙结构参数,将长6砂岩评价为4类储层,其中Ⅰ、Ⅱ类储层在目前的工艺技术条件下为可动用储层,是增储上产的首选储层。     

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根据X衍射、包裹体、胶结物氧、碳同位素分析及显微观察，影响鄂尔多斯盆地北部上古生界碎屑储集岩孔隙发育和演化的主要成岩作用有压实作用、碎屑矿物蚀变作用、胶结作用、交代作用、溶蚀作用和自生粘土矿物生长作用。成岩序列为机械压实作用→碎屑矿物蚀变→自生绿泥石粘土边→石英胶结作用→溶蚀作用→自生粘土矿物→碳酸盐胶结。不同地区经历的成岩作用不同，造就了孔隙度演化的差异，形成南差北好的储层物性，即：北部地区砂岩估算的初始孔隙度为37%，至晚成岩B期孔隙演化至10.33%；中部地区砂岩初始孔隙度为38%，至晚成岩B期为6.98%；南部地区砂岩初始孔隙度为39%，至晚成岩B期仅为6.1%。     

成藏动力对束缚水饱和度的影响

束缚水饱和度是评价油层含油性的重要参数之一。前入研究普遍认为，砂岩储层的束缚水饱和度与砂岩类型、孔隙度和孔隙结构有关，粒度中值和孔隙度的影响最大。笔者认为，束缚水饱和度不仅取决于储层本身，还取决于储层之外的其他因素，其中成藏动力是决定其大小的一个重要因素。砂岩储层为孔隙型储层，它由微孔隙与有效孔隙组成。微孔隙完全被束缚水占据，流体在微孔隙中不能渗流；有效孔隙中充满油、气和水，水又分为可动水与束缚水，束缚水为亲水岩石孔壁及孔角上的薄膜滞留水。当有适当的外力驱动时，这部分束缚水是可以流动的，其含量取决于成藏动力的大小。     

深层砂岩储层成岩作用差异性及与储层质量的关系——以准噶尔盆地中部征沙村地区侏罗系为例

为认识深层碎屑岩储层质量的控制因素及有效储层分布规律,以准噶尔盆地中部征沙村地区下侏罗统三工河组砂岩储层为例,利用岩心样品的铸体薄片、扫描电镜、碳氧同位素、X?射线衍射及常规物性测试手段,研究了储层岩石学和成岩作用特征,讨论了成岩作用对不同类型储集岩石相的影响,并建立了岩石相—沉积微相的联系。结果表明：研究区三工河组砂岩成分成熟度低,主要为长石岩屑砂岩,自生矿物包括碳酸盐、自生黏土、硬石膏及硅质等;总体为低—特低孔渗性储层,非均质性强。依据岩石学组构和成岩作用差异,可将储集砂岩主要划分为极细—细粒富塑性颗粒砂岩、方解石胶结砂岩和中—细粒贫塑性颗粒砂岩。不同岩石相经历了差异性成岩作用：其中富塑性颗粒砂岩表现为强压实、弱胶结和弱溶蚀特征;方解石胶结砂岩则表现为强胶结、弱压实和弱溶蚀特征,二者均在成岩阶段早期致密化;贫塑性颗粒砂岩表现为中等压实、弱—中等胶结、强溶蚀。成岩阶段早期压实作用和胶结作用程度低,不但能保留原生孔隙,亦能遭受后期深埋阶段的酸性流体改造,形成深层物性较好的有效储集岩。不同岩石相的分布总体受沉积微相控制,物性最佳的贫塑性颗粒砂岩主要分布在分流河道中下部或河口坝中上部,这种分布模式将为寻找深层有效储层提供指导。     

Pore microgeometry analysis in low-resistivity sandstone reservoirs

The objective of this work is to analyse the pore microgeometry and its effect on petrophysical properties in six low-resistivity sandstone reservoirs by combining a 2D quantitative petrographic image analysis (PIA) and 3D petrophysical tools. The classic petrophysical tools enable the measurement of different classic reservoir properties such as specific surface area, average pore diameter, pore size distribution, macroporosity and microporosity, capillary pressure versus saturation, pore chamber–pore throat diameter ratio, electrical properties and permeability. The petrographic image analysis quantifies pore microgeometry in more than four orders of magnitude, from submicron to millimeter scale. Chloritic low-resistivity sandstones show dual porosity structure defined as chloritic texture. The pore microgeometrical parameters measured by petrographic image analysis allow one to model different reservoir properties such as capillary pressure, permeability and electrical behaviour. The results obtained in these models show that pore microgeometry plays an important role in the physical properties of low-resistivity sandstone reservoirs.     

Mutual relations between petrographical and petrophysical properties of Cretaceous rock samples for some wells in the North Western Desert,Egypt

The petrographical and petrophysical analyses are very important to understand the factors controlling the reservoir quality. So, these techniques have been applied on rock samples collected from the Cretaceous section for four wells drilled in the North Western Desert, Egypt. The wells are Gibb Afia-1, Betty-1, Salam-1X and Mersa Matruh-1. Lithostratigraphically, the studied rock samples are grouped into Lower Cretaceous sandstones, Upper Cretaceous sandstones and Upper Cretaceous carbonates.Petrographically, the Cretaceous rock samples can be differentiated into 14 microfacies, namely, chloritic ferrigenous quartz wacke, ferrigenous calcareous quartz wacke, laminated quartz wacke, calcareous glauconitic quartz arenite, laminated gypsiferous quartz arenite, fossiliferous glauconitic calcareous quartz arenite, clayey ferrigenous calcareous quartz arenite, ferrigenous calcareous glauconitic lithic arenite, feldspathic ferrigenous quartz arenite, fossiliferous biomicrite, glauconitic oolitic sandy biosparite, calcareous gypsiferous ferrigenous dolostone, calcareous algal siltstone and laminated sandstone and siltstone.Lower Cretaceous rocks have been deposited in a fluviatile in shallow marine environments, while the Upper Cretaceous rocks have been deposited in a fluviatile in marine environments. Diagenetic history has been controlled by diagenetic processes enhancing the porosity (dissolution of framework silicates, leaching and dolomitization) and diagenetic processes reducing porosity (mechanical infiltration of clays, formation of authigenic minerals, compaction and pressure solution, cementation and recrystallization).Porosity types are mainly interparticles, vugs and molds, in addition to fractures and channel porosities. The average porosity of the Lower Cretaceous sandstones, Upper Cretaceous sandstones and Upper Cretaceous carbonates are 16.6%, 16.7% and 22.0%, respectively, as depends mainly on the bulk density with average values of 2.22, 2.26 and 2.14 g/cm³, respectively.The permeability of both the Lower and Upper Cretaceous sandstones with average values of 114.14 and 50.40 mD, respectively, depends mainly on porosity with some other parameters, like pore throat sizes and it could be also related to the electrical tortuosity with average values of 2.27 and 2.40, respectively. The Upper Cretaceous carbonate rocks are characterized by high porosity (22.0%) and low permeability (3.91 mD), this could be attributed to the isolated pore space, and decreasing in pore throat sizes due the presence of significant amounts of fine particles (clay minerals having microporosity and reduce the pore throat radius).The reservoir quality index with average values of 0.43, 0.29 and 0.08 μm, depends mainly on permeability with average values of 114.14, 50.40 and 3.91 mD, of the Lower Cretaceous sandstones, Upper Cretaceous sandstones and the Upper Cretaceous carbonates, respectively. This indicates that, the sandstones of the Lower and Upper Cretaceous rocks are characterized by high to moderate reservoir quality, respectively, while the Upper Cretaceous carbonate rocks are characterized by low reservoir quality. This may be due to the combined effect of the porosity and permeability rather than the total porosity.The formation resistivity factor was measured at three consequent saline concentrations of 6, 30 and 60 kppm, it is controlled by the porosity and electrical tortuosity.     

Variation and mechanisms of clastic reservoir quality in the Paleogene Shahejie Formation of the Dongying Sag, Bohai Bay Basin, China

Reservoir quality varies greatly in the Shahejie Formation in the Dongying Sag. It is essential to analyze the variation and mechanisms of reservoir quality for determining the controlling factors based on cores, porosity measurements and fluid inclusion techniques and so on. The sandstones in the fluvial, （fan） delta-front have the best reservoir quality due to the depositional conditions mechanically controlling the petrology configuration and the primary porosity, and chemically influencing the diagenesis and development of secondary pores. The activity of the boundary faults and the sedimentary facies dominate the variation of reservoir quality in different areas and intervals. The reservoir quality varies with the position of sandstone beds in different vertical models of sandstone and mudstone. This mainly arose from the strong cementation or strong dissolution in the sandstone caused by the diagenesis evolution of adjacent mudstone. With higher oil saturation reservoir quality is better because the hydrocarbon charge favors dissolution and restricts cementation. Diagenesis, depositional conditions and tectonic setting are the key controls of reservoir quality in the Shahejie Formation of the Dongying Sag.     

页岩气储层Ramirez体积物理模型的改进

通过分析Ramirez等提出的页岩气储层体积物理模型,针对该模型没有划分黏土矿物的缺点,建立了黄铁矿含量与有机碳含量（TOC）的关系,并把利用多元统计方法评价的TOC结果作为模型输入参数的方式,进一步将该模型的无机矿物直接划分为黏土矿物、黄铁矿和其他矿物,弥补了该模型在黏土矿物变化大的层段计算精度低的缺陷,并简化了通过对无机矿物骨架与无机矿物孔隙中流体测井响应同时进行迭代的复杂求解过程。利用改进的Ramirez体积模型对实际资料进行了处理,计算结果表明：改进的模型比原模型计算的有机碳含量、孔隙度及含水饱和度更接近相应的岩心分析数据;其评价的黏土含量同样与岩心分析数据吻合良好,从而验证了改进的Ramirez体积模型的准确性与可靠性,为页岩气勘探、开发和储量计算提供了可靠资料。     

内蒙乌兰格尔地区上古生界砂岩的成岩作用

内蒙乌兰格尔地区的上古生界厚逾400m,大部分砂岩属于致密型低孔渗性的岩体。本文主要论述这些砂岩的成岩作用及其对储层孔渗性的影响。记砂岩具有四个成岩阶段:1.机械压实作用和早期胶结作用;2.碳酸盆的胶结作用和交代作用;3.溶蚀作用;4.晚期自生粘土矿物的形成和早期粘土矿物的重结晶作用。其中强烈的机械压实作用减少砂岩的孔隙,碳酸盆矿物的胶结作用尤其显著地减少了孔隙度和渗透率。但是,胶结物和部分颗粒的后期溶蚀作用是改善某些层段储集性能的有利因素。      

Characteristics of the Permian coal-formed gas sandstone reservoirs in Bohai Bay Basin and the adjacent areas, North China

This paper focuses on the physical properties and spatial distributions of the Permian sandstone reservoirs in Bohai Bay Basin and the adjacent areas in the northeast China. The coal-formed gas sandstone reservoirs occur in the Permian Shihezi Formation and the maturity of the sandstone in the lower part is gradually higher than that in the upper part. The high-maturity sandstones are mainly the channel lag deposits and widely distributed in the study area. Due to the low porosity and permeability, however, the sandstones formed only the medium-poor reservoirs. The sandstones contain clay matrix and commonly a small portion of calcareous, siliceous, and authigenic clay cement. On the other hand, severe compaction and cementation caused nearly complete destruction of the primary porosity during diagenesis. Therefore, the main space of the sandstone reservoirs comes from the secondary pores. The distributions of reservoirs are affected by several periods of faulting and denudation. The sandstones of the Lower Shihezi Formation are thicker in the Jizhong and Bozhong depressions, and Luxi areas, and those of the Upper Shihezi Formation are thicker in Jizhong and Jiyang depressions and thinner in Luxi areas.     

SHW地区阜三段砂岩储层变参数岩电研究

根据SHW地区岩电实验数据,讨论Archie公式中m、n变化对含水饱和度的影响。结果显示,m变化对饱和度影响较大,特别对低孔储层影响更甚,而n变化对饱和度影响远小于m,因此m的选取对饱和度的解释至关重要。鉴于SHW地区受泥质、灰质影响,含油砂岩储层岩性多样、孔隙结构复杂,研究不同岩性砂岩储层的m分布特征,得出相同岩性储层m与孔隙度在双对数坐标下呈线性正相关,而不同岩性砂岩储层的m与孔隙度关系表现出趋势线斜率不同。基于以上认识,建立不同岩性砂岩储层的岩电参数解释模型,实现变参数解释油层含油饱和度,提高解释精度,在实际应用中取得显著效果。     

微孔隙对低孔低渗砂岩储集层测井评价的影响——以苏里格气田A区块盒8段储集层为例

在低孔低渗砂岩储集层中,微孔隙给岩石的导电性及物性参数的评价带来了一定的困难。以苏里格气田A区块盒8段储集层为例,将动力与阻力平衡时所得到的孔隙半径0.15 μm作为微孔隙的上限,通过数值模拟及数理统计等手段解释了研究区的“非阿尔奇”现象。研究表明,孔隙类型决定微孔隙发育比例,孔隙度越大,微孔隙比例越小;随着微孔隙比例增大,渗透率明显降低;微孔隙发育的低孔低渗砂岩储集层具有中子孔隙度明显增大、密度和声波时差变化较小的特点,且随着黏土含量增多,束缚水饱和度增高,导电网络发育,导电性增强,电阻率降低。所以,微孔隙发育是研究区低孔低渗砂岩储集层出现低阻的主要原因。     

油气储层砂岩样品制冷—加热循环解离技术实验研究

制冷—加热循环解离技术(简称冷冻技术)是自生伊利石分离提纯过程中制备黏土悬浮液的一项新技术。利用批量典型样品对该项技术的解离效果及其影响因素进行了详细研究,并与常规湿磨技术进行了系统对比。与湿磨技术相比,冷冻技术既有优越性,也有局限性。优越性主要表现在剔除碎屑钾长石效果略微偏好和实测年龄数值相对偏小方面;局限性主要表现在解离效果变化较大,部分砂岩样品相对较好,部分砂岩样品则相对较差,样品埋深是影响解离效果的最主要因素,炭屑(薄煤层)、泥质含量以及是否含油等对解离效果具有明显控制作用。冷冻技术对于坚硬程度中等的中浅层或中深层砂岩效果较好,具有较好的应用前景;而对于坚硬程度较高的深层或超深层砂岩则效果较差,甚至不宜采用。研究还表明,湿磨仍不失为制备黏土悬浮液的一种行之有效的实用技术,简便快捷并且效果较好,具有较好的应用前景。     

川东北地区须家河组砂岩储层特征

根据铸体薄片、扫描电镜、物性、孔隙结构和声发射等分析资料,对川东北地区须家河组储层特征进行了研究,结果表明:该套储层储集空间以次生孔隙为主;储层物性较差,微裂缝对改善储层孔渗性有一定贡献;排驱压力和饱和度中值压力不高,但孔喉半径小且分选性较差,孔隙结构参数总体较差。储层质量受沉积微相和成岩作用的综合影响,其中由河控三角洲和扇三角洲形成的中粒分流河道砂体为最有利储层发育的微相,成岩早期环边绿泥石胶结作用对于部分原生孔隙和吼道的保存起到一定作用,溶蚀作用对改善吼道连通性效果不佳。利用储层物性和孔隙结构参数,将须家河组砂岩评价为4类储层,其中I、II类储层在目前的工艺技术条件下为可动用储层,是增储上产的首选储层。     

DIAGENETIC CONTROLS ON THE RESERVOIR QUALITY OF TIGHT OIL-BEARING SANDSTONES IN THE UPPER TRIASSIC YANCHANG FORMATION,ORDOS BASIN,NORTH-CENTRAL CHINA

Tight oil-bearing sandstones in the Chang 4+5, 6 and 7 Members of the Upper Triassic Yanchang Formation in the Ordos Basin, north-central China, in general consist of fine-grained, moderately- to poorly-sorted lithic arkoses (average Q₅₃F₃₀R₁₇) deposited in a fluvial-dominated lacustrine-deltaic environment. Diagenetic modifications to the sandstones include compaction and cementation by calcite, dolomite, ankerite, quartz, chlorite, kaolinite and illite, as well as partial dissolution of feldspars and minor rock fragments. Porosity ranges up to ~7% of the rock volume and was reduced more by cementation than by compaction. Fractures (tectonic macrofractures and diagenetic microfractures) provide important oil migration pathways and enhance the sandstones' storage potential. The pore network is heterogeneous due to processes related to deposition and diagenesis, and there are considerable spatial variations in porosity and pore connectivity. The pore system includes both macropores and micropores, and pore network variations depend on the type and distribution of authigenic cements. An analysis of the diagenetic and porosity characteristics of core samples of the Yanchang Formation sandstones from wells in the Youfangzhuang oilfield resulted in the recognition of six petrofacies (A-F) whose characteristics allow reservoir quality to be predicted. Fluid performance analysis for selected sandstone samples using nuclear magnetic resonance combined with helium porosity and air permeability shows that high permeability and large pore throats together result in high movable fluid saturation potential, and that effective pore spaces and throats are beneficial for hydrocarbon storage and flow. Relatively higher porosity and permeability tend to occur in petrofacies B sandstones containing abundant pore-lining chlorite with lesser kaolinite and minor carbonate cements, and in petrofacies C sandstones with abundant pore-filling kaolinite cement but little chlorite and carbonate cements. These petrofacies represent the best reservoir-quality intervals. A reservoir quality prediction model is proposed combined with the petrofacies classification framework. This model will assist future development of tight sandstone reservoirs both in the Upper Triassic Yanchang Formation in the Ordos Basin and elsewhere.     

永安镇油田沙四段自生粘土矿物及其对储层特性的影响

通过对永安镇油田沙四段砂岩储层中6口井的薄片、电镜及X衍射分析,研究了该储层中自生粘土矿物的分布产状、构成因素和成岩特征。根据自生粘土矿物在孔隙壁和孔隙喉道中的位置及分布状态,可将其分为孔隙分散粘土、孔隙衬边粘土和孔隙桥接粘土3种。研究区内自生粘土矿物的成岩相可划分为早成岩A期、B期及晚成岩A期和B+C期。在4个不同的成岩时期,自生粘土矿物的组合形式也不同。其垂向演化可以划分为3个带,即浆脱石带、I/S混层带和伊利石带。不同的转化带,自生粘土矿物的分布产状也不同,其中孔隙桥接粘土对孔隙度和渗透率影响最大。自生粘土矿物的存在,既可导致微粒的迁移,吸收或释放某些阳离子形成不溶沉淀物,堵塞孔隙喉道,改变储层孔隙结构,又可影响测井结果。为了减少自生粘土矿物对储层特性和测井结果的影响,文中提出了一些保护油层的措施。