本文针对鄂尔多斯盆地合水地区长8油藏北部富集好而南部富集差,油藏向南扩展困难的问题,运用大量的现场岩心资料、测井解释成果、薄片镜下鉴定和储层物性测试数据,对合水南北长8段储层的岩石学特征、孔喉结构特征、物性特征和成岩作用等进行了对比分析,明确了合水南北长8段储层含油性差异的控制因素。结果表明,研究区长8段储集层整体物性偏差,属于特低孔–超低渗储层,主要发育粒间孔和长石溶孔,见少量晶间孔和微裂缝;由北向南石英、岩屑含量逐渐增大,而长石含量逐渐减少;较合水南部,合水北部的孔喉结构和储层物性更好。在此基础上,总结和分析了研究区成藏控制因素,显示油藏在平面上的分布与优质储层和长石溶蚀相在平面上的分布具有密切联系,合水南部不具有连片开发的潜力,但小规模的甜点区任可作为下一步的开发目标。 The exploration of Chang 8 member of Yanchang formation in the north of Heshui area has made a great breakthrough, forming a contiguous oil-bearing area. But the exploration in the south of Heshui area is poor, and the reservoir is difficult to expand to southward. For this problem, this paper compares and analyzes the petrological characteristics, pore throat structure characteristics, physical characteristics and diagenesis of the Chang 8 reservoir in north and south of Heshui area, and identifies the accumulation controlling factors, basing on a large number of core observation, well logging interpretation, microscopic identification of thin sections and reservoir physical property. The results show that the overall physical properties of the Chang 8 reservoir in the study area are deviated, which belongs to an ultra-low porosity and ultra-low permeability reservoir. There are mainly intergranular and feldspar dissolution pores, and a few intercrystalline pores and microcracks. From north to south, the content of quartz and cuttings increased, while the content of feldspar decreased gradually. Comparing to north of Heshui area, the pore-throat structure and reservoir physical properties are better than those in the south of Heshui area. On this basis, the control factors of reservoir formation in the study area are summarized and analyzed, showing that the distribution of oil is closely related to the high-quality reservoir and diagenetic facies. There is no potential for continuous development in the south of Heshui area, but part of the dessert area can still be used as the next development target.
本文针对鄂尔多斯盆地合水地区长8油藏北部富集好而南部富集差,油藏向南扩展困难的问题,运用大量的现场岩心资料、测井解释成果、薄片镜下鉴定和储层物性测试数据,对合水南北长8段储层的岩石学特征、孔喉结构特征、物性特征和成岩作用等进行了对比分析,明确了合水南北长8段储层含油性差异的控制因素。结果表明,研究区长8段储集层整体物性偏差,属于特低孔–超低渗储层,主要发育粒间孔和长石溶孔,见少量晶间孔和微裂缝;由北向南石英、岩屑含量逐渐增大,而长石含量逐渐减少;较合水南部,合水北部的孔喉结构和储层物性更好。在此基础上,总结和分析了研究区成藏控制因素,显示油藏在平面上的分布与优质储层和长石溶蚀相在平面上的分布具有密切联系,合水南部不具有连片开发的潜力,但小规模的甜点区任可作为下一步的开发目标。
合水地区,长8段,储层特征,控制因素,开发潜力
Yingying Chen1, Shijia Chen2, Zhenglu Xiao1, Jingli Yao3, Guanglin Liu3, Pan Wang1
1School of Geoscience and Technology, Southwest Petroleum University, Chengdu Sichuan
2State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, School of Geoscience and Technology, Southwest Petroleum University, Chengdu Sichuan
3National Engineering Laboratory for Exploration and Development of Low Permeability Oil and Gas Fields, Research Institute of Petroleum Exploration & Development, PetroChina Changqing Oilfield Company, Xi’an Shaanxi
Received: Sep. 25th, 2020; accepted: Oct. 8th, 2020; published: Oct. 15th, 2020
The exploration of Chang 8 member of Yanchang formation in the north of Heshui area has made a great breakthrough, forming a contiguous oil-bearing area. But the exploration in the south of Heshui area is poor, and the reservoir is difficult to expand to southward. For this problem, this paper compares and analyzes the petrological characteristics, pore throat structure characteristics, physical characteristics and diagenesis of the Chang 8 reservoir in north and south of Heshui area, and identifies the accumulation controlling factors, basing on a large number of core observation, well logging interpretation, microscopic identification of thin sections and reservoir physical property. The results show that the overall physical properties of the Chang 8 reservoir in the study area are deviated, which belongs to an ultra-low porosity and ultra-low permeability reservoir. There are mainly intergranular and feldspar dissolution pores, and a few intercrystalline pores and microcracks. From north to south, the content of quartz and cuttings increased, while the content of feldspar decreased gradually. Comparing to north of Heshui area, the pore-throat structure and reservoir physical properties are better than those in the south of Heshui area. On this basis, the control factors of reservoir formation in the study area are summarized and analyzed, showing that the distribution of oil is closely related to the high-quality reservoir and diagenetic facies. There is no potential for continuous development in the south of Heshui area, but part of the dessert area can still be used as the next development target.
Keywords:Heshui Area, Chang 8 Member, Reservoir Characteristics, Controlling Factors, Developing Potential
Copyright © 2020 by author(s) and Hans Publishers Inc.
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鄂尔多斯盆地陇东地区延长组油气藏为典型的低孔低渗岩性油气藏,其长8油藏储层致密,非均质性强,成岩作用强烈且类型多样,在多个区块出现油水差异聚集的现象 [
鄂尔多斯盆地为我国第二大内陆盆地,蕴藏的石油天然气资源量十分丰富。延长组作为鄂尔多斯盆地最重要的含油层系组,一直以来是各方学者和石油企业的研究热点和开发重点 [
研究区紧邻西峰油田,按照西峰油田的油气规模,研究区不缺油源。合水地区属于西南物源和南部物源的混源区,油藏沿南北向的水下分流河道呈条带状展布,在南部分叉为宁县和正宁等多个分支(图1)。目前的勘探结果显示,以盘客为界,合水北部的油井沿河道砂体集中分布,而合水南部的勘探效果较差,即便是沿着河道砂体也少见出油井,油藏向南扩展困难。
图1. 研究区位置与油藏分布图
储层的岩矿特征是决定储层成岩作用、孔隙类型和储层物性的基础。岩石薄片镜下鉴定结果表明(表1和表2):合水地区长8储集层岩性以岩屑长石砂岩为主,其次为长石岩屑砂岩;填隙物成分中水云母、绿泥石、铁方解石和硅质的占比较大,占到填隙物总量的87.68%;碎屑颗粒多为细粒–中细粒结构,粉砂质结构次之,分选性以中、好为主,磨圆度中等。分别统计合水南北区块样品的岩石学特征发现,合水南北长8储集层的砂岩碎屑成分相差不大,但储层填隙物含量有明显的差异。合水北部相比合水南部来说绿泥石含量较高而铁方解石含量较低,反映出合水南北为同一物源,但后期受成岩作用的影响不同。
地区 | 石英/% | 长石/% | 岩屑/% | 样品数(块) | |||
---|---|---|---|---|---|---|---|
火成岩 | 变质岩 | 沉积岩 | 总量 | ||||
合水北 | 30.13 | 31.36 | 8.29 | 12.13 | 0.1 | 25.26 | 124 |
合水南 | 30.37 | 29.57 | 9.21 | 11.5 | 0.14 | 24.78 | 59 |
合水 | 30.19 | 30.86 | 8.58 | 11.58 | 0.1 | 25.02 | 183 |
表1. 合水地区长8段砂岩碎屑成分统计表
地区 | 填隙物含量/% | 样品数(块) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
高岭石 | 水云母 | 网状 粘土 | 绿泥 石膜 | 方解石 | 铁方 解石 | 白云石 | 铁白 云石 | 硅质 | 长石质 | ||
合水北 | 0.47 | 3.05 | 0.08 | 3.21 | 0.41 | 4.58 | 0.01 | 0.09 | 1.33 | 0.12 | 124 |
合水南 | 0.83 | 4.05 | 0.03 | 2.25 | 0.58 | 5.56 | 0.07 | 0.21 | 1.28 | 0.13 | 59 |
合水 | 0.59 | 3.39 | 0.07 | 2.96 | 0.48 | 4.87 | 0.03 | 0.12 | 1.31 | 0.12 | 183 |
表2. 合水地区长8段储层填隙物含量统计表
前人研究认为,沉积岩岩屑一般表现为塑性,含量越高储层物性越差,而长石含量较高的储层物性相对较好 [
储集空间的发育程度及配置关系决定了储层的储集性能及渗流能力。通过扫描电镜和铸体薄片镜下鉴定表明(表3),研究区长8储层砂岩孔隙类型主要为粒间孔和长石溶孔,见少量晶间孔和微裂缝,面孔率达到3.08%。由于储层成岩作用较强,孔隙往往受到成岩作用的改造,大多为原生残余粒间孔。镜下观察显示,长石常沿解理缝选择性溶蚀呈现不规则形态,部分长石溶孔与粒间孔连通,从而形成较大的孔隙。合水南北储层孔隙类型相同,但所占比例有所差别:合水南部粒间孔和长石溶孔共占比2.41%,面孔率为2.65%;而合水北部粒间孔和长石溶孔共占比3.0%,面孔率为3.21%。总体而言,合水北的储集空间发育程度较合水南部更好。
地区 | 粒间孔/% | 长石溶孔/% | 岩屑溶孔/% | 晶间孔/% | 微裂隙/% | 面孔率/% | 样品数(块) |
---|---|---|---|---|---|---|---|
合水北 | 2 | 1 | 0.16 | 0.02 | 0.02 | 3.21 | 88 |
合水南 | 1.52 | 0.89 | 0.18 | 0.02 | 0.01 | 2.65 | 32 |
合水 | 1.9 | 0.97 | 0.16 | 0.02 | 0.02 | 3.08 | 120 |
表3. 合水地区长8段储层孔隙类型表
岩石压汞测定是目前用来描述与揭示储层微观孔隙结构特征的主要技术手段 [
图2. 合水南(蓝)与合水北(红)长8储层压汞曲线对比图
储层物性是表征储层储集、渗透性能的指标,直接反映储层的好坏。对合水地区总共526块(北部306块,南部220块)样品的物性数据统计发现,合水地区长8段储集层孔隙度为0.18%~13.6%,平均为7.14%,渗透率为0.016~1.21 mD,平均为0.23 mD,依据鄂尔多斯盆地延长组物性分级标准 [
图3. 合水南北孔渗分布直方图
搞清楚储层各种成岩作用,对揭示研究区油气富集机理及预测有利油气富集场所有着重要的意义。通过岩心观察与铸体薄片、扫描电镜分析,合水地区长8段储集层发育有多种成岩作用类型:压实作用(图4(a))导致部分塑性颗粒发生变形,呈线形或凹凸形接触,刚性颗粒发生破裂,产生微裂隙;石英和长石自生加大以及泥质和碳酸岩胶结常见,绿泥石呈薄膜状围绕矿物颗粒环边生长(图4(c)~(f));偏光镜下通常会看到有碳酸盐和粘土矿物交代碎屑颗粒,使颗粒边缘变为凹凸状,也可以见到颗粒内部有方解石呈零星点状分布(图4(b),图4(e));长石和岩屑等碎屑遭受到不同程度的溶解改造形成多种类型的次生孔隙(图4(a),图4(b))。
图4. 合水地区长8储层成岩作用
合水地区长8储层普遍发育绿泥石环边,从成岩作用之间的接触和截断关系来看,绿泥石环边形成于溶蚀作用和石英加大边之前,既能抑制压实作用和其他胶结物的形成,还能在保存原生孔隙和形成较好的孔喉结构,为优质储层形成的重要因素。铸体薄片显示长8储层中的长石溶孔极为发育,部分视域范围内的长石溶孔占到长石颗粒总面积的40%~85%,可作为原油的主要储集空间。
根据以上储层特征的研究成果,并参考长庆油田分公司勘探开发研究院对鄂尔多斯盆地延长组长4+5–长8油层组的储层综合评价标准 [
图5. 合水地区长8段储层综合评价图
成岩相指的是成岩环境下岩石学、地球化学以及岩石物理学特征的总和,成岩相研究可以在沉积相研究之上更进一步地明确和储集能力有关的有利储集体,并以此来指导油气的勘探工作 [
上述研究结果表明,合水油田盘客以北地区储层大面积发育长石溶蚀相,其储集性较好,I、II类优质储层的分布面积大、连通性较好,容易形成大规模的油气富集区,在庄40和庄41井片区长石溶蚀相大片发育,储集性能较好,仍然具有精细化布井的价值。而盘客以南地区储层只有小面积发育长石溶蚀相,其优质储层分布较为分散,I、II类储层面积较小,不具有可连片开发的潜力。但合水南部依然有呈点状分布的储层甜点区,如宁12井、庄200井、宁99井等井区长石溶蚀相发育,属于II类储层区,因此可以作为下一步小规模油藏的开发目标。
图6. 合水地区长8段储层成岩相图
(1) 合水地区长8段储层岩性以岩屑长石砂岩为主;填隙物成分中水云母、绿泥石、铁方解石和硅质的占比较大;碎屑颗粒多为细粒–中细粒结构,分选性以中、好为主,磨圆度中等;主要发育粒间孔和长石溶孔,见少量晶间孔和微裂缝;储层普遍表现为排驱压力较低的特征,整体属于特低孔–超低渗储层。
(2) 合水南北的储层特征差异明显。相比合水北部,合水南部的绿泥石含量较低、铁方解石含量较高、面孔率较小、孔喉结构和物性较差,主要为III类和IV类储层。而合水北部主要为I类和II类储层,储层相对较好。绿泥石相和长石溶蚀相为研究区的有利成岩相,优质储层和成岩相的分布对油藏具有明显的控制作用。
(3) 合水北部优质储层的分布面积大、连通性较好,在庄40和庄41井片区仍然具有精细化布井的价值;合水南部的优质储层和成岩相分布较为分散、面积较小,不具有可连片开发的潜力,但宁12井、庄200井、宁99井等井区发育的小规模甜点依然可以作为下一步的开发目标。
感谢国家自然科学基金(编号41502146,41872165)和国家重大科技攻关项目(编号2017ZX05001002-003)联合资助。
陈莹莹,陈世加,肖正录,姚泾利,刘广林,王 攀. 我国鄂尔多斯盆地合水长8油藏储层特征及开发潜力Reservoir Property and Exploration Potential Analysis of Chang 8 Member in the Heshui Area, Ordos Basin, China[J]. 地球科学前沿, 2020, 10(10): 887-896. https://doi.org/10.12677/AG.2020.1010087