Evaluation of reservoir environment by chemical properties of reservoir water‒A case study of Chang 6 reservoir in Ansai oilfield,Ordos Basin,China

The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.

Factors controlling the reservoir accumulation of Triassic Chang 6 Member in Jiyuan-Wuqi area,Ordos Basin,NW China

In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.

A quantitative evaluation for well pattern adaptability in ultra-low permeability oil reservoirs:A case study of Triassic Chang 6 and Chang 8 reservoirs in Ordos Basin

Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster analysis and gray correlation method, and it includes 10 evaluation parameters in the four aspects of optimal evaluation parameters, determination of weights for evaluation parameters, development stage division, and determination of classification coefficients. This evaluation method was used to evaluate the well pattern adaptability of 13 main ultra-low permeability reservoirs in Triassic Chang 6 and Chang 8 of Ordos Basin. Three basic understandings were obtained: Firstly, the well pattern for ultra-low permeability type-I reservoirs has generally good adaptability, with proper well pattern forms and well pattern parameters. Secondly, square inverted nine-spot well pattern is suitable for reservoirs with no fractures; rhombic inverted nine-spot injection pattern is suitable for reservoirs with some fractures; and rectangular well pattern is suitable for reservoirs with rich fractures. Thirdly, for the ultra-low permeability type-Ⅱ and type-Ⅲ reservoirs, with the principles of well pattern form determination, the row spacing needs to be optimized further to improve the level of development of such reservoirs.

Pore structure differences of the extra-low permeability sandstone reservoirs and the causes of low resistivity oil layers: A case study of Block Yanwumao in the middle of Ordos Basin, NW China

The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example. The relationship between the pore structure difference and the low resistivity oil layer was revealed and demonstrated through core observation, lab experiments, geological research, well log interpretation and trial production etc. The results show that there were two kinds of oil layers in Chang 6 oil layer set, normal oil layer and low resistivity oil layer in the region, corresponding to two types of pore structures, pore type mono-medium and micro-fracture-pore type double-medium; the development of micro-fracture changed greatly the micro-pore structure of the reservoir, and the pore structure difference had an important influence on the rock electrical characteristics of the extra-low permeability sandstone reservoir and oil reservoir; the normal oil layers had obvious characteristics of pore-type mono-medium, and were concentrated in Chang 61, Chang 6232 and Chang 62; the low resistivity oil layers had obvious characteristics of micro-fracture-pore type double-medium, which were mainly distributed in Chang 612 and Chang 63. The mud filtrate penetrated deep into the oil layers along the micro-cracks, leading to sharp reduction of resistivity, and thus low resistivity of the oil layer; the low resistivity oil layers had better storage capacity and higher productivity than the normal oil layers.

鄂尔多斯盆地蟠龙地区长6储层四性关系研究

针对蟠龙地区长6储层四性关系的研究与认识不足,利用蟠龙地区的测井数据、录完井数据、岩心分析和化验资料等资料进行整理与分析,对研究区储层岩性、物性、电性与含油性特征及其相互间的关系进行了研究。研究结果表明,①蟠龙地区长6油层组以长石砂岩为主;②储层平均孔隙度为8%,平均渗透率为0.79×10-3μm 2,属于低孔特低渗至低孔超低渗储层;③录井中岩心以油迹含油级别为主;④结合岩心测试资料建立了储层参数测井解释模型,并最终确定有效储层物性下限为:渗透率0.15×10^(-3)μm^(2),孔隙度5.5%,电阻率20Ω·m,声波时差215μs/m。研究了储层四性基本特征及其关系,并得出了蟠龙地区储层物性和含油性的电性解释图版,为后续蟠龙地区油层解释以及探明储量参数的确定提供了依据。

鄂尔多斯盆地南梁地区延长组长6沉积特征

为了研究南梁地区延长组重力流沉积特征,利用钻井岩芯、轻重矿物和测井解释等对鄂尔多斯盆地南梁地区三叠系延长组长6沉积体系特征与沉积模式进行分析。结果表明:鄂尔多斯盆地长6以K2、K3、K4这3套泥岩作为标志层,根据测井分析方法将延长组长6划分为3个小层;依据轻、重矿物数据资料分析,明确了南梁地区延长组长6发育有东北、西南2个物源,主要受东北物源的控制,东北部母源来自于大青山、阴山一带的太古界高级变质岩和火山岩;南梁地区延长组长6主要以陆源湖泊、三角洲沉积为主,不同的沉积相的类型控制着砂体的展布形状,长6期发育的砂体自北东向西南方向呈现出条带状展布;延长组在长6期湖盆面积逐渐减小盆地边缘的三角洲沉积范围向湖盆中心收缩。长6期自北东向西南发育了三角洲前缘亚相、深湖亚相、浅湖亚相,由于三角洲前缘斜坡地带沉积物发生了滑塌,在重力作用下形成了浊流沉积。

鄂尔多斯盆地延长油田双河西区块长6油藏开发参数

鄂尔多斯盆地延长油田双河西区块长6油藏为低渗透油藏,常规开发指标计算方法并不利于油田进行油藏地质研究、开发政策制定与成本控制。对延长油田双河西区块长6油藏产量递减规律、水驱储量动用程度、注采比、含水率、注水利用状况及采收率进行分析。结果表明:双河西区块长6油藏产量递减规律为双曲递减模式;区块注水开发潜力较大,目前该区块水驱储量控制程度为74.54%,水驱储量动用程度为36.94%,注采连通率为27.27%;合理注采比约为2.5,随着采出程度增加,含水率上升速度先增大,后有所减小;根据存水率、耗水指数及水驱指数可知,开发后期,区块注水开发效果逐渐变好,最终采收率增加,研究区在开发过程中含水上升率应尽量小于6.1%,地层合理压力应大于9.1 MPa,在该开发条件下,研究区最终采收率约为23%。

鄂尔多斯盆地双河地区延长组长6油层组地层水化学特征分布规律

致密油藏油水关系复杂,地层水化学组分及其分布规律对指导致密油勘探具有重要意义。基于此,对双河地区长6油层组地层水化学组成、矿化度、水化学特征参数与沉积微相、有效厚度及产能之间的关系进行了深入研究。研究表明,双河地区地层水类型主要为CaCl_(2)型,地层水的矿化度主要分布在2201.2~153670.9 mg/L,平均为53947.2 mg/L。矿化度在50000 mg/L之前,含油饱和度随着矿化度的增加而降低的,而在50000 mg/L之后,含油饱和度随着地层水矿化度的增加而增加。这是由于,较高的矿化度代表好的保存条件,利于油气长期大规模聚集,因而含油饱和度较高;而当目的层矿化度处于10000~20000 mg/L相对低的范围时,主要对应3~5 m薄层单砂体组成的复合砂体,因而含油饱和度也相对较高。分析认为,目的层矿化度、钠氯系数、镁钙系数特征均表明目的层处于相对封闭的沉积环境,有利于油气的保存,这些水化学参数均与致密油藏聚集及产能有较为显著的相关性。

鄂尔多斯盆地大路沟地区长6储层孔隙结构及物性特征研究

在油气勘探开发中,储层岩石孔隙结构对油气井采收量、产能以及油气储量均能产生影响,特别是孔隙结构参数可以用来表征储层孔隙质量,在油气勘探开发中具有重要意义。因此,本文以鄂尔多斯盆地大路沟地区长6储层为研究对象,对其孔隙结构及物性特征进行详细剖析,认为研究区长6储层岩性以长石砂岩和岩屑长石砂岩为主;孔隙度在9%~15%,渗透率在0.3~1.5 mD。同时,根据沉积旋回原理将研究区长6储层分为长6_(1)、长6_(2)、长6_(3)三个小层,各小层之间的物性差别较大,其中长61小层的储层物性最好,长63小层的储层物性较差。根据以上结论,得出长6储层属于低孔、低渗透储层。

鄂尔多斯盆地五蛟西地区长6段单砂体叠置特征研究

沉积微相控制下的单砂体发育类型、频率和叠置样式,控制了储层的连通性和井间剩余油的分布。本次研究综合利用丰富的岩心、测井和分析测试资料,在沉积微相精细刻画基础上,对鄂尔多斯盆地五蛟西地区三叠系延长组长6段单砂体发育特征和叠置样式进行精细研究。结果表明:五蛟西地区长6段岩性以粉砂岩、细砂岩、含泥砾或泥岩撕裂屑的细砂岩和泥岩为主,发育沉积微相类型主要为砂质碎屑流、浊流和半深湖泥3种。长6段垂向上可识别出5~8期单砂体,单砂体叠置类型包括孤立型、叠加型以及切叠型3种;平面上单层砂体多以枝状、网状、局部片状展布。湖平面升降导致的可容纳空间(A)变化及沉积物供给速度(S)匹配关系是控制单砂体空间发育特征的关键性因素。研究区长6段自下而上,随着A/S比值的变化,单砂体类型垂向上由叠加型、切叠型逐渐向孤立型、局部叠加型变化,平面上由网状、枝状向局部片状演化。

鄂尔多斯盆地陕北斜坡储层岩石学特征及油气勘探指示——以油房庄北部长6油层组为例

为明确鄂尔多斯盆地油房庄北部有利相带和优质储层发育区,推进鄂尔多斯盆地探明储量的进一步扩大,通过岩心薄片观察、岩石矿物成分分析测定等多种手段开展油房庄北部重点层段长6油层组储层的碎屑颗粒组成、填隙物组分等关键特征要素研究,并在此基础上分析长6油层组储层的重、轻矿物分布规律,进而探讨物源的指示意义以及油气耦合关系,以期补充该地区关于储层岩石学和物源分析的科研成果.经分析,长6砂岩储层主要为长石砂岩,并见少量岩屑长石砂岩;填隙物的类型多、含量变化大,主要包括黏土胶结物、碳酸盐类胶结物、硅质胶结物等;粒级分布以细砂为主,颗粒磨圆为次棱角状,颗粒分选中等以上占主体;胶结类型以薄膜-孔隙型和孔隙-薄膜型、孔隙型、薄膜型、加大-孔隙型胶结为主.长6砂岩储层标准偏差对粒度平均值图解和重矿物组合、轻矿物组分都揭示了长6油层组时期研究区主要受东北方向物源影响,发育了多期叠置的三角洲前缘水下分流河道砂体,并且由于长距离搬运效应,残余粒间孔、长石溶孔较为发育,长石、绿泥石和高岭石的矿物组合在一定程度上提升了研究区的储层物性,并增加了低阻油藏的渗透性.长61和长62的水下分流河道砂体为研究区的优质储层发育区.

鄂北S井区盒8上亚段砂体叠置类型及其对气藏分布的影响

为明确鄂北S井区盒8上亚段地层砂体叠置类型及其与气藏分布的关系,通过岩心观察、测井解释等方法对研究区盒8上亚段沉积微相类型、砂体的垂向叠置及侧向接触关系进行深入研究,再结合试气资料探讨不同砂体叠置类型的气藏分布特征。结果表明:鄂北S井区盒8上亚段为曲流河三角洲平原亚相,有利砂体对应的沉积微相类型为边滩与河道充填微相;砂体垂向叠置类型可划分为分离式、叠加式、切叠式、替代式,侧向接触关系可划分为间湾接触、堤岸接触、对接式、侧切式、替代式;鄂北S井区盒8上亚段砂体垂向叠置类型主要为侧向切叠式和替代式,增加了砂体在侧向上的连通性;盒8上亚段砂体侧向接触关系主要为侧切式,提升了砂体侧向上的连通程度,气藏储存关系较好;单一、孤立存在的砂体,其连通性较差,整体的含气性也较差。该研究对寻找低渗透背景下产能高、潜力大的砂体分布区具有重要指导意义。

鄂尔多斯盆地悦乐地区长6段储层特征及主控因素分析

为明确鄂尔多斯盆地悦乐地区三叠系延长组长6段储层发育特征及控制因素,以悦乐地区长6段砂岩储层为研究对象,结合岩心资料、薄片鉴定、扫描电镜、高压压汞与地球物理测井解释等技术方法,从岩石学特征、物性特征及孔隙结构特征多个方面,探讨了沉积作用和成岩作用在储层储集性能方面的重要意义。结果表明:悦乐地区长6段岩性以岩屑长石砂岩和长石岩屑砂岩为主,孔隙类型主要以粒间孔和长石溶孔为主。悦乐地区长6段孔隙度均值为9.27%;渗透率均值为0.142×10^(-3)μm^(2),以特低孔-超低渗储层为主;根据储层分类评价标准,长6段储层由好到差依次分为Ⅰ,Ⅱ,Ⅲ类。沉积环境为研究区长6储层提供物质基础,成岩作用是研究区目的层形成致密储层的关键因素。胶结作用一定程度上充填孔隙、堵塞孔喉,降低储层物性,而溶蚀作用对于改善储层物性具有积极的作用。该研究成果为研究区进一步勘探开发提供借鉴。

基于神经网络模型的致密砂岩储层流动单元分类与评价——以鄂尔多斯盆地WQ北部长6油层组为例

为了明确鄂尔多斯盆地WQ北部地区致密砂岩储层流动单元对剩余油分布的影响,通过岩心观察、铸体薄片鉴定、X衍射分析、高压压汞测试等方法分析了研究区长6储层的基本特征,并结合测井和神经网络模型分析,明确了区内长6储层流动单元类型、特征、分布规律,及其与储层的关系。结果表明:研究区长6油层组为典型的低孔-特低渗储层,主要发育长石砂岩和长石岩屑砂岩,孔隙类型以残余粒间孔和长石溶孔为主,储层孔隙结构以细喉大孔型和细喉小孔型为主。共发育4类储层流动单元。其中,长6^(2-1)小层以Ⅲ、Ⅳ类单元为主,长6^(1-2)小层主要发育Ⅰ、Ⅱ类流动单元,长6^(1-1)小层仅见零星分布的Ⅰ类流动单元,有利储层主要分布在长61-2小层。

张家滩地区长6油层组储层对致密油富集的控制作用

利用岩性、物性、高压压汞数据以及铸体薄片、扫描电镜资料并结合测井、试油和试采数据,分析张家滩地区长6油层组储层对致密油富集的控制作用。结果表明:长6储层含油岩性为细砂岩,粉砂岩不含油;油层厚度与砂体厚度呈现正相关关系,平面上集中分布于中西部和南部地区;孔隙结构主要分为两类:I类为细孔微细喉,以油浸、油斑级为主,Ⅱ类为细-微孔、微细喉-微喉,以油迹和荧光级别为主;各种成岩作用和沉积环境导致较强的储层非均质性,控制了石油的差异富集;层内非均质性形成相对高孔高渗砂体并控制致密油的聚集部位,平面非均质性导致油层厚度大的区域主要分布在砂体厚度大且稳定的区域。

鄂尔多斯盆地S区长6储层测井解释模型的建立及应用

鄂尔多斯盆地是我国典型的低渗透含油气盆地,受沉积、成岩以及构造作用的影响,具有孔隙结构复杂、非均质性严重和油、气、水分布规律不明显等特征,这导致了测井响应的复杂性,给测井参数的解释带来困难。以鄂尔多斯盆地S区长6储层为例,在大量文献调研基础上,基于搜集到的测井资料、岩心资料和地质资料等,首先开展了储层岩性特征、物性特征、电性特征和含油性特征的关系研究,得出储集层的岩性越好(泥质含量越低),则物性越好;其次对岩心数据进行了深度归位、插值滤波处理,在此基础上建立了相应的泥质含量、孔隙度、渗透率和含油饱和度等储层参数解释模型,并对所建模型进行精度检验;最后应用该模型对S区测井资料开展二次解释。研究表明,经过岩心深度归位及插值滤波处理后的岩心资料与测井资料相关性分析可靠,选用声波时差与岩心孔隙度回归建立的孔隙度模型、运用多元逐步回归法建立的渗透率模型精度较高。

致密砂岩储层“四性”关系及有效储层下限研究——以鄂尔多斯盆地东部王庄区长6油层组为例

鄂尔多斯盆地东部王庄区长6油层组为致密砂岩储层,储层物性差,非均质性强,明确其储层“四性”关系及有效储层参数下限对甜点预测具有重要意义。通过岩心、测录井以及物性分析资料,明确了王庄区长6储层“四性”关系。其中细砂岩物性整体相对较好,声波时差与储层物性具有较好的对应关系,深感应电阻率则对含油性具有较好的指示性,油水层的深感应电阻率平均值为20~40Ω·m,水层为12~16Ω·m。在此基础上综合岩心、测录井、试油试采及多种分析化验资料,采用多种方法,最终确定王庄区长6油层组有效储层各项参数下限,分别为:孔隙度为8.0%,渗透率为0.2 mD,岩性下限为细砂岩,含油级别下限为油迹,含油饱和度为38.0%,深感应电阻率为20.0Ω·m,声波时差为215μs/m。

黏土矿物对于储层敏感性的影响与控制作用——以庆阳合水地区长6超低渗砂岩储层为例

以鄂尔多斯盆地合水地区长6超低渗透砂岩储层为例,综合应用储层敏感性、扫描电镜、X射线衍射等实验技术方法,系统研究了储层敏感性类型及损害程度,并深入地探讨了黏土矿物对于长6储层敏感性的影响与控制作用。结果表明:(1)长6油层的储层敏感性整体表现为中等偏强水敏性和速敏性、弱酸敏性、强盐敏性以及中等偏弱碱敏性的五敏特征;(2)储层黏土矿物主要有高岭石、伊利石、绿泥石以及伊蒙混层等4种类型,且以伊利石含量最高;(3)储层敏感性及其程度明显受控于黏土矿物类型及其含量,并且具有黏土矿物含量越高、储层敏感性越强的特点。本研究成果将为合水地区长6油层注水开发过程中有效保护储层以及提高采收率提供重要的参考依据。

胡尖山油田延长组长6段三角洲前缘致密砂岩储层特征及其主控因素

采用粒度分析、真空浸渍铸体薄片分析、扫描电镜检测、压汞测试、黏土矿物X射线衍射和常规物性分析等方法探究胡尖山油田延长组长6段三角洲前缘致密砂岩储层特征及其主控因素。结果表明:长6段储层致密砂岩主要为岩屑长石砂岩和长石岩屑砂岩,岩石成分成熟度和结构成熟度均较低;主要孔喉组合为残余粒间孔+长石溶孔+晶间孔的小孔-微细喉道组合,孔隙度和渗透率均值分别为10.70%,0.69×10^(-3)μm^(2);孔渗相关性较好,为低孔特低孔-特低渗超低渗小孔微细喉道型储层,渗透率主要由数量较少的微孔、中孔贡献,孔隙度主要由数量较多的微米孔贡献;强烈的压实、泥质、碳酸盐胶结作用是长6段储层致密的主要原因;水下分流河道等优势沉积相带和溶蚀作用是储层形成的主控因素。

鄂尔多斯盆地七里村油田长6油层储层物性影响因素

为明确鄂尔多斯盆地七里村油田长6油层储层物性的影响因素,利用物性测试、岩性分析、高压压汞、核磁共振和电子显微镜以及扫描电镜等技术,分析了研究区长6油层的岩石类型、孔隙类型、孔喉结构特征等。结果表明:研究区长6储层岩石类型以细粒长石砂岩为主,孔隙类型以残余粒间孔和长石溶蚀孔为主,平均孔隙度为7.30%,平均渗透率为0.21 mD。通过储层微观结构特征将研究区孔喉分成Ⅲ类,Ⅰ类孔喉半径一般大于3μm,主要分布在中-细砂岩中,Ⅱ类孔喉半径一般处于0.1~3μm之间,主要分布在细砂岩中,Ⅲ类孔喉半径一般小于0.1μm,研究区以Ⅱ类孔喉代表的储层为主。石英含量与储层物性具有正相关趋势,长石和岩屑的含量与储层的物性有负相关趋势,孔喉大小和连通性与储层物性相关性较好,孔喉越大、连通性越好,储层物性越好,孔喉的分选性对储层物性具有两面性,较差的分选性有利于后期溶蚀作用的发生。