鄂尔多斯盆地镇泾地区长8段致密砂岩油藏成藏孔隙度下限研究

鄂尔多斯盆地镇泾地区长8段现今含油储层孔隙度和渗透率下限分别为4%和0.03×10-3μm2,属于特低孔低渗油藏。主成藏期、成岩作用、埋藏史及模拟实验研究结果表明,高致密油藏缘于成藏后储层致密化。传统方法是通过统计现今含油物性下限作为成藏物性下限,这种方法不适用于成藏后再致密油藏的研究。以现今储层含油物性下限为切入点,利用砂岩孔隙度演化规律,对现今储层含油物性下限进行成藏后孔隙度损失量补偿,从而求取油气成藏孔隙度下限,利用该方法得出镇泾地区长8段石油成藏孔隙度下限为10.5%。研究表明成藏物性下限是镇泾地区长8段成藏的主控因素之一,只有成藏期孔隙度大于成藏孔隙度下限时油气才可能进入圈闭成藏。     

鄂尔多斯盆地吴堡地区延长组长8致密砂岩油藏成藏主控因素

鄂尔多斯盆地三叠系延长组长8油层组为近年来发现的勘探开发新层系,勘探实践证实其成藏条件优越,勘探潜力大。本文以盆地中南部志丹县吴堡地区为例,对该区长8油藏成藏条件及分布规律进行了研究,结果表明:长8油藏油源主要来自于上覆长73烃源岩、长8内部烃源岩和长9顶部烃源岩,具有良好的生储层组合配置;主成藏期运移动力主要为生烃增压等形成的异常高压,油气充注到长8致密储层后主要以近距离垂向和侧向运移为主;成岩作用加剧了储层非均质性,形成成岩遮挡型准连续型油气聚集。长8油藏平面及层位分布主要受控于有效烃源岩展布、储层质量和有效盖层的控制,多种地质因素共同形成现今长8油藏分布格局。     

鄂尔多斯盆地高桥地区盒8段砂岩储层致密成因

运用常规薄片、铸体薄片、扫描电镜及恒速压汞等实验手段,对鄂尔多斯盆地高桥地区盒8段储层特征进行研究,并以孔隙演化过程为线索分析了储层致密成因。研究结果表明:盒8段储层主要为岩屑石英砂岩、石英砂岩与岩屑砂岩,成分成熟度和结构成熟度均较高,储层物性差;砂岩分选性好,初始孔隙度整体较高,平均可达34.7%;受岩石组分、埋深及煤系烃源岩酸性流体的影响,压实作用强烈,破坏了大约20.4%的原生孔隙度,胶结作用破坏了其余13.9%的原生孔隙度,原生孔隙几乎被破坏殆尽;早期溶蚀产生的孔隙被压实作用破坏,而晚期溶蚀作用较弱,仅增加了大约3.4%的次生孔隙度,难以大幅度改善储层物性。因此,成岩期原生孔隙被破坏殆尽及次生孔隙形成较少共同导致该区储层致密。     

鄂尔多斯盆地镇泾油田致密砂岩长8储层特征及沉积相研究

利用扫描电镜、铸体薄片等多种方法,对鄂尔多斯盆地镇泾油田长8油层组低孔低渗的致密砂岩储层的储层特征和沉积相进行综合分析研究,发现该地区砂岩类型主要有细粒岩屑长石砂岩和长石岩屑砂岩,孔隙度和渗透率分别为3.9%%~11%和(0.04~0.55)×10-3μm2。研究区主要成岩作用包括压实作用、压溶作用、胶结作用、溶蚀作用、交代作用。通过对镇泾区块沉积储层形成的沉积相的研究,查明该区广泛发育三角洲相,进一步可划分为水下分流河道、水下天然堤、水下决口扇、水下分流间湾、河口坝等5种微相。上述研究为镇径油田长8段储层的研究和预测提供了理论依据。     

鄂尔多斯盆地杭锦旗地区盒一段致密砂岩储层特征及其主控因素

鄂尔多斯盆地杭锦旗地区盒一段富含天然气,但储层致密、非均质性强,从而制约了该地区天然气的增储上产.利用岩心、铸体薄片和场发射扫描电镜观察、孔渗测试、X射线衍射分析、高压压汞及恒速压汞分析等,分析致密砂岩储层的特征及其主控因素.以此将储层划分为优势储层和差储层两类,优势储层主要以心滩和河道内的粗粒岩屑石英砂岩,岩屑砂岩为主,泥质含量低,溶蚀孔隙发育,差储层主要以河道间的细粒岩屑砂岩为主,泥质含量高,孔隙不发育.物源的差异导致了西部石英含量高于东部.水动力条件的强弱是决定储层优劣的初始条件,早期泥质充填导致差储层的原始孔隙度较低.优势储层中泥质含量较少,更能抵抗上覆压力,孔隙流体更活跃,能形成更多的溶蚀孔.      

鄂尔多斯盆地东部盒8致密砂岩沉积特征及沉积模式

野外露头剖面和井下岩心的岩石学与岩相组合、沉积特征与岩相标志、室内砂岩碎屑矿物组成及其平面分布规律的研究结果表明,鄂尔多斯盆地东部盒8致密砂岩以岩屑砂岩为主,其次为岩屑石英砂岩,主要为深灰色、灰色、灰白色中砂岩和粗砂岩。研究区从北到南依次为冲积扇、辫状河及辫状河三角洲沉积体系。冲积扇以扇中和扇端为主,主要由冲积水道块状构造含砾粗砂岩组成。往南演化为辫状河沉积,主要包括河道砂坝和泛滥平原微相,其中河道砂坝为其骨架相,由大型交错层理和平行层理发育的粗砂岩和含砾粗砂岩组成。南部发育辫状河三角洲平原和前缘沉积,进一步划分出分流河道、泛滥平原、水下分流河道和分流间湾微相,其中分流河道及水下分流河道为其骨架相,类似于河道砂坝沉积,主要由板状、槽状交错层理粗砂岩及中-细砂岩组成,纵向上多期砂体叠置,横向上叠合成片,成为盒8致密砂岩气藏的良好储集层。     

鄂尔多斯盆地延长组致密砂岩孔喉结构与油藏物性表征

基于高压压汞和核磁共振测试方法,结合分形理论对鄂尔多斯盆地延长组致密砂岩孔喉结构与油藏物性进行了表征。采用毛管束模型和润湿相模型计算了高压压汞孔喉分形维数,利用核磁共振测试T₂谱分别计算了大孔、中孔、小孔以及总孔隙的分形维数;对各分形维数与油藏物性之间的关系进行了对比分析。研究表明：基于高压压汞曲线计算岩心分形维数时,相比于润湿相模型,毛管束模型计算得到的分形维数与油藏物性之间具有更好的相关性,随着分形维数增加,平均半径减小,孔喉结构非均质性增强,油藏物性变差。核磁总孔隙分形维数与油藏物性相关性较差,大孔和中孔的分形维数与油藏物性具有较好的相关性,其中随着大孔和中孔分形维数增加,岩心渗透率降低,油藏物性变差;与小孔相比,大孔和中孔的分形维数与油藏物性的相关性更强,表明致密砂岩储层物性主要受大孔和中孔控制,分形维数可以有效表征致密砂岩小孔、中孔和大孔对油藏物性的影响。     

鄂尔多斯盆地彭阳地区侏罗系延安组地层水化学特征及成因类型分析

运用地层水物理化学分析方法对鄂尔多斯盆地彭阳地区侏罗系延安组地层水离子浓度、矿化度、离子组合等特征进行综合研究,从而揭示其类型、演化过程和成因。研究结果表明,研究区地层水以Cl–、（ Na++ K+）离子为主,SO42-及Ca2+离子次之,具较高矿化度;地层水为盐水和卤水,主要为CaCl2型和Na2SO4型;Piper三线图解表明,未发生淡水混入作用,整体为交替停滞的缺氧还原环境。研究区延安组地层水矿化度高、离子浓度组合特征反映地层具较强的还原环境,有利于油藏保存;为原生沉积水,在演化过程中受到了蒸发浓缩作用、水—岩作用及生物作用的共同影响;地层水分布受前侏罗纪古地貌的影响较强,不同古地貌单元地层水的化学性质明显不同。     

鄂尔多斯盆地西南部镇泾地区长8油层组致密储层评价

综合鄂尔多斯盆地西南部镇泾地区延长组长8油层组的岩心、薄片、孔渗及压汞测试等资料,在长8储层结构、储层质量发育控制因素研究基础上,对长8低渗致密砂岩储层进行了分类评价。结果表明,长8砂岩储层发育低孔-特低渗储集物性,储层孔隙结构具有细-微孔喉、排驱压力大、分选差的特征,主要可分为3种类型,其中发育Ⅰ型曲线储层孔渗性最好。沉积作用形成的物质基础决定了储层原始孔渗性能,其中分流河道及水下分流河道具最优孔渗性能;成岩作用中,压实作用是储层储集性能破坏的主要因素;溶蚀作用起建设性改善作用。选取孔隙度、渗透率、孔隙排驱压力、中值压力和中值孔喉半径等主要储层参数进行聚类分析,将长8储层划分为3种类型:Ⅰ类为最好储层,Ⅱ类为较好储层,Ⅲ类为相对最差储层。其中,Ⅰ类储层主要分布于分流河道分叉叠置及水下分流河道汇聚叠合部位,储层品质最好,为最有利勘探目标。     

鄂尔多斯盆地临兴区块盒8段致密砂岩物性影响因素

通过分析铸体薄片、物性、扫描电镜及压汞等资料,探讨了鄂尔多斯盆地东北缘临兴区块盒8段致密砂岩的储层特征及物性影响因素。结果表明：盒8段储层岩性以岩屑砂岩和长石岩屑砂岩为主,平均孔隙度为7.1%,平均渗透率为0.38 mD;主要孔隙类型为次生溶孔,孔喉半径的分布以双峰状为主,主峰值偏向于相对小的半径,砂岩以相对小孔隙为主;成岩作用主要包括压实作用、溶蚀作用、胶结作用及交代作用等,具有压实强而普遍、溶蚀普遍但不充分、胶结和交代作用强等特征;受贫石英、富岩屑和长石的碎屑组分特征影响,各组分含量对物性有影响但无明显控制作用;粒度是物性的主控因素,粒度越粗物性越好;此外,溶蚀作用对砂岩物性也有一定的积极作用,而封闭成岩体系下的强胶结作用是导致储层致密的主要因素。     

鄂尔多斯盆地陕北地区延长组致密砂岩储层敏感性评价

以鄂尔多斯盆地陕北地区延长组致密砂岩储层为研究对象,在岩石学、孔隙结构、储层物性特征研究的基础上,开展储层敏感性流动实验,以此评价该地区致密储层的敏感性及敏感机制。研究结果表明：陕北地区延长组致密砂岩储层敏感性主要表现为中等偏强速敏、中等偏弱水敏、无酸敏到弱酸敏、弱碱敏、强压敏;临界流速、临界矿化度、临界pH值3个特征临界值分别为1.0 mL/min、8 500 mg/L、8.5。敏感程度主要受矿物成分和孔隙结构的影响。研究区储层速敏的形成源于其孔隙填隙物——高岭石的存在;绿／蒙混层及伊/蒙混层矿物是引起水敏及盐敏的主要因素;铁白云石及含铁绿泥石等酸敏矿物的存在使部分岩样显弱酸敏;极其复杂的孔喉结构、极易受压变形的片状喉道以及岩样中云母、黏土等塑性矿物导致储层具强压敏性。     

鄂尔多斯盆地陇东地区二叠系盒8下段致密砂岩储层特征

陇东地区是鄂尔多斯盆地上古生界天然气勘探的新区带,二叠系下石盒子组盒8下段气层组是其主力产气层,该区沉积、储层和成藏等方面具有一定的复杂性,天然气勘探研究程度较低.结合测井资料、岩心观察、铸体薄片、物性等资料,对鄂尔多斯盆地西南地区二叠系下石盒子组盒8下段储层的岩石学特征、物性特征、孔隙结构特征进行研究,探讨了影响储层...     

Characteristics of Tight Sandstone Reservoirs and Controls of Reservoir Quality: A Case Study of He 8 Sandstones in the Linxing Area,Eastern Ordos Basin,China

Determining the process of densification and tectonic evolution of tight sandstone can help to understand the distribution of reservoirs and find relatively high-permeability areas. Based on integrated approaches of thin section,scanning electron microscopy(SEM), cathode luminescence(CL), nuclear magnetic resonance(NMR), X-ray diffraction(XRD), N_2 porosity and permeability, micro-resistivity imaging log(MIL) and three-dimensional seismic data analysis, this work discussed the reservoir characteristics of the member 8 of the Permian Xiashihezi Formation(He 8 sandstones) in the Linxing area of eastern Ordos Basin, determined the factors affecting reservoir quality, and revealed the formation mechanism of relatively high-permeability areas. The results show that the He 8 sandstones in the Linxing area are mainly composed of feldspathic litharenites, and are typical tight sandstones(with porosity 10% and permeability 1 mD accounting for 80.3% of the total samples). Rapid burial is the main reason for reservoir densification, which resulted in61% loss of the primary porosity. In this process, quartz protected the original porosity by resisting compaction. The cementation(including carbonate, clay mineral and siliceous cementation) further densified the sandstone reservoirs,reducing the primary porosity with an average value of 28%. The calcite formed in the eodiagenesis occupied intergranular pores and affected the formation of the secondary pores by preventing the later fluid intrusion, and the Fe-calcite formed in the mesodiagenetic stage densified the sandstones further by filling the residual intergranular pores. The clay minerals show negative effects on reservoir quality, however, the chlorite coatings protected the original porosity by preventing the overgrowth of quartz. The dissolution of feldspars provides extensive intergranular pores which constitute the main pore type, and improves the reservoir quality. The tectonic movements play an important role in improving the reservoir quality.The current tectonic traces of the study area are mainly controlled by the Himalayan movement, and the high-permeability reservoirs are mainly distributed in the anticline areas. Additionally, the improvement degree(by tectonic movements) of reservoir quality is partly controlled by the original composition of the sandstones. Thus, the selection of potential tight gas well locations in the study area should be focused on the anticline areas with relatively good original reservoir quality. And the phenomena can be referenced for other fluvial tight sandstone basins worldwide.     

Diagenesis of the Triassic Yanchang Formation Tight Sandstone Reservoir in the Xifeng–Ansai Area of Ordos Basin and its Porosity Evolution

This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.     

Pore Size Distribution of a Tight Sandstone Reservoir and its Effect on Micro Pore-throat Structure: A Case Study of the Chang 7 Member of the Xin’anbian Block,Ordos Basin,China

Pore distribution and micro pore-throat structure characteristics are significant for tight oil reservoir evaluation, but their relationship remains unclear. This paper selects the tight sandstone reservoir of the Chang 7 member of the Xin’anbian Block in the Ordos Basin as the research object and analyzes the pore size distribution and micro pore-throat structure using field emission scanning electron microscopy(FE-SEM), high-pressure mercury injection(HPMI), highpressure mercury injection, and nuclear magnetic resonance(NMR) analyses. The study finds that:(1) Based on the pore size distribution, the tight sandstone reservoir is characterized by three main patterns with different peak amplitudes. The former peak corresponds to the nanopore scale, and the latter peak corresponds to the micropore scale. Then, the tight sandstone reservoir is categorized into three types: type 1 reservoir contains more nanopores with a nanopore-to-micropore volume ratio of 82:18;type 2 reservoir has a nanopore-to-micropore volume ratio of 47:53;and type 3 reservoir contains more micropores with a nanopore-to-micropore volume ratio of 35:65.(2) Affected by the pore size distribution, the throat radius distributions of different reservoir types are notably offset. The type 1 reservoir throat radius distribution curve is weakly unimodal, with a relatively dispersed distribution and peak ranging from 0.01 μm to 0.025 μm. The type 2 reservoir’s throat radius distribution curve is single-peaked with a wide distribution range and peak from 0.1 μm to 0.25 μm. The type 3 reservoir’s throat radius distribution curve is single-peaked with a relatively narrow distribution and peak from 0.1 μm to 0.25 μm. With increasing micropore volume, pore-throat structure characteristics gradually improve.(3) The correlation between micropore permeability and porosity exceeds that of nanopores, indicating that the development of micropores notably influences the seepage capacity. In the type 1 reservoir, only the mean radius and effective porosity have suitable correlations with the nanopore and micropore porosities. The pore-throat structure parameters of the type 2 and 3 reservoirs have reasonable correlations with the nanopore and micropore porosities, indicating that the development of these types of reservoirs is affected by the pore size distribution. This study is of great significance for evaluating lacustrine tight sandstone reservoirs in China. The research results can provide guidance for evaluating tight sandstone reservoirs in other regions based on pore size distribution.     

Geological Controls on High Production of Tight Sandstone Gas in Linxing Block,Eastern Ordos Basin,China

Tight sandstone gas in the Linxing Block, eastern Ordos Basin, has been successfully exploited. The high performance is mainly a result of the special geological conditions. The key geological controls for high production have been discussed on the basis of seismic data, field observation, sample features, mercury porosimetry, mechanical properties, and basin modeling. Firstly, the coal measures have good gas generation potential, not only because of the existence of coalbeds and organic-rich shales, but also because coal laminae and microbial mats in the shales significantly increase their total organic carbon(TOC) contents. Secondly, except for the uplifted zone of the Zijinshan complex and the eastern fault zone, rare large faults develop in the Carboniferous–Permian sequence, ensuing the sealing capacity of cap rock. Small fractures generally concentrated in the sandstones rather than the mudstones. Thirdly, gas accumulation in the Linxing Block was controlled by the tectonic, burial and thermal histories. Gas accumulation in the Linxing Block started in the Late Triassic, followed by three short pauses of thermal maturation caused by relatively small uplifts;the maximum hydrocarbon generation period is the Early Cetaceous as a combined result of regional and magmatic thermal metamorphisms. Field profiles show abundant fractures in sandstone beds but rare fractures in mudstone beds. Mechanical properties, determined by lithostratigraphy, confine the fractures in the sandstones, increasing the permeability of sandstone reservoirs and retaining the sealing capacity of the mudstone cap rocks. The modern ground stress conditions favor the opening of predominant natural fractures in the NNW-SSE and N-S directions. These conclusions are useful for exploring the potential tight sandstone gas field.     

鄂尔多斯盆地延长组长9小层致密砂岩含油性控制因素

综合分析鄂尔多斯盆地延长组长9小层典型的致密砂岩储集层物性、岩心照片及荧光照片等资料,研究长9小层致密砂岩含油性控制因素。研究表明,鄂尔多斯盆地延长组长9小层致密砂岩含油性主要受物性、非均质性、岩性等因素的影响,具体表现为：(1)高塑性岩屑含量影响砂岩含油性,高塑性岩屑含量越高,砂岩物性越差,其含油性也越差;(2)碳酸盐胶结物含量越高,砂岩物性越差,其含油性也越差;(3)物性与其含油性正相关;(4)非均质性,其对含油性的影响巨大,容易造成纵横线油气运移的“隔断”,油气难以进入储集层成藏;(5)岩性,水下分流河道砂体岩性以灰白色含泥砾中砂岩或中-细砂岩为主,而水下分流河道间以深灰色泥岩、粉砂质泥岩或泥质粉砂岩为主,水下分流河道砂在该层段含油性好;(6)裂隙,其对储层的运聚具有极大的改善作用。结合安定组沉积末期长9输导层顶面石油优势运移路径的模拟结果,优选出杏河地区向镰刀湾东方向、西河口-安塞-下坪、沿河口-冯庄北有利勘探区带。     

鄂尔多斯盆地西峰地区长8砂岩微观非均质性的实验分析

通过真实砂岩微观模型实验,客观地分析了鄂尔多斯盆地西峰地区长8砂岩的微观非均质性特征,发现该区长8储层为致密型砂岩,直观地显示出长8砂岩储层具有很强的微观非均质性,砂岩的成岩作用和孔隙结构是影响鄂尔多斯盆地西峰地区长8砂岩储层微观非均质性的主要原因。在低渗透砂岩中,引起砂岩产生强烈的非均质性,而这些砂岩则形成长8砂岩储层的高渗带。     

鄂尔多斯盆地陇东地区三叠系延长组长3油层组石油运移与充注研究

鄂尔多斯盆地是我国第二大沉积盆地,中生界延长组富含丰富的油气资源。陇东地区位于鄂尔多斯盆地西南部,延长组长3段是该区重要的含油层系。在长3油层组原油特征和油源条件分析的基础上,对长3原油中含氮化合物组成和分布进行了探讨,结合成藏期分析,研究了鄂尔多斯盆地陇东地区长3油层组石油运移特征和注入方向。结果表明,长3油层组原油含氮化合物的分布与组成在纵向和横向上均存在明显的运移分馏效应,较好地指示了该区石油的运移。晚侏罗世至早白垩世,鄂尔多斯盆地延长组长7优质烃源岩进入生烃门限,并开始大量生烃,且以垂向、侧向、垂向-侧向交替式混合运移的方式,从盆地中心和生烃中心向西部和西南侧向运移和充注,油气充注点位于M18、Z71和Z49等井区周边区域。     

A Volumetric Model for Evaluating Tight Sandstone Gas Reserves in the Permian Sulige Gas Field,Ordos Basin,Central China

To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas-bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore-throat structure. The porosity and permeability cutoffs are determined by distribution function curve,empirical statistics and intersection plot. Net pay and gas-bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10~(–3) μm~2, respectively. The net pay and gas-bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H_8(P_2h_8) and S_1(P_1s_1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas.