来凤地区龙马溪组含气页岩测井识别——以WY1井为例
Log-based identification of gas-bearing shales in the Longmaxi Formation of the Laifeng area: A case study of well WY1
通讯作者: 张鹏(1986-),男,教授,从事矿山勘查与环境治理研究工作。Email:283176398@qq.com
责任编辑: 王萌
收稿日期: 2023-02-15 修回日期: 2023-05-11
基金资助: |
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Received: 2023-02-15 Revised: 2023-05-11
作者简介 About authors
裴圣良(1992-),男,高级工程师,长期从事矿山地质环境调查与生态修复工作。Email:
湖北龙马溪组海相页岩是除四川盆地外可能实现页岩气勘探突破点之一,测井技术是一种十分成熟的油气勘探开发研究手段,本文以来凤地区WY1井的测井为基础,对龙马溪组含气页岩层段测井响应特征进行系统研究。结果表明,WY1井龙马溪组含气页岩层段具有高自然伽马、高铀、高钍、高补偿中子、高声波时差及低密度的测井响应特征,深、浅侧向电阻率低于下伏宝塔组碳酸盐岩,高于砂质页岩,且正差异反映岩层中发育高角度裂缝的层段。通过测井曲线叠合以及交会图版分析发现,含气页岩层自然伽马—岩性密度测井叠合曲线及声波时差—岩性密度测井叠合曲线具有明显的正差异,而自然伽马—补偿中子和声波时差—补偿中子呈现明显的负差异,且声波时差—岩性密度叠合测井曲线对于含气层段的指示作用最为准确;声波时差—补偿中子测井交会图、补偿中子—自然伽马测井交会图以及深侧向电阻率—补偿中子测井交会图对于富有机质含气页岩的识别作用最明显。
关键词:
Except for the Sichuan Basin, the marine shales in the Longmaxi Formation in Hubei show great potential for shale gas exploration. Logging technology is highly mature in the exploration and development of hydrocarbons. This study systematically analyzed the log response characteristics of gas-bearing shales in the Longmaxi Formation based on logs obtained from well WY1 in the Laifeng area. As indicated by the analysis results, the gas-bearing shales of the Longmaxi Formation in well WY1 are characterized by high natural-gamma-ray values, high contents of uranium, thorium, and compensated neutrons, high interval transit time, and low density. Their deep and shallow lateral resistivity is lower than that of the underlying Baota Formation carbonate rocks but is higher than that of the sandy shales. Moreover, the positive differences indicate that high-angle fractures occur in the shales. The superimposition of log curves and the analysis of cross plots for gas-bearing shales reveal that ① the superimposed log curves of both natural gamma ray-lithologic density and interval transit time-lithologic density show significant positive differences, while those of both natural gamma ray-compensated neutrons and interval transit time-compensated neutrons show significant negative differences; ② the superimposed log curves of interval transit time-lithologic density indicate the gas-bearing intervals the most accurately; ③ the organic-rich gas-bearing shales can be identified the most effectively using the log cross plots of interval transit time-compensated neutrons, compensated neutrons-natural gamma ray, and deep lateral resistivity-compensated neutrons.
Keywords:
本文引用格式
裴圣良, 屈建新, 张鹏.
PEI Sheng-Liang, QU Jian-Xin, ZHANG Peng.
0 引言
页岩气资源作为重要的非常规天然气资源,其勘探开发始于北美地区[1⇓⇓⇓⇓-6]。我国页岩气资源的勘探开发已经取得阶段性成果,并在四川盆地实现商业化开采[7],但除四川盆地外的其他地区仍在寻求突破,湖北、湖南、贵州等南方地区发育的龙马溪组海相页岩是目前最有可能实现突破的层系[8⇓⇓-11]。前人对湘鄂西地区五峰—龙马溪组页岩的构造沉积特征、泥页岩展布特征、地球化学特征、岩石矿物特征和含气量特征进行了分析,五峰—龙马溪组整体上为一套深水陆棚—浅水陆棚沉积[12],页岩分布稳定[13],有机碳含量高,含气量为0.15~1.65 m3/t,具有良好的页岩气潜力[14]。五峰—龙马溪组页岩吸附储气能力虽然较好,但其孔隙结构复杂、连通性差,较四川盆地其遭受构造运动的破坏更加强烈,具有气藏破坏程度大、保存条件复杂的特点[15-16],至今尚未取得重大突破。因此本文以湖北来凤地区WY1井测井资料为基础,对钻遇的龙马溪组页岩储层测井响应特征进行系统研究,分析研究其测井响应特征,以期为该区页岩含气层段识别和页岩气资源勘探提供理论支撑。
1 地质概况
图1
图2
龙马溪组页岩有机质类型以Ⅱ1型为主,Ⅱ2型次之,显微组分主要表现为腐泥组和惰质组,缺乏镜质组和壳质组。总有机碳含量为0.33%~4.18%(其中龙一段16个样品TOC为0.48%~4.18%,平均2.05%;龙二段19个样品TOC为0.33%~1.44%,平均0.77%;龙三段9个样品TOC为0.42%~1.95%,平均1.2%),主体上大于1%,平均值为1.33%。镜质体反射率在2.79%~3.32%,平均3.11%,处于过成熟阶段。
2 富有机质页岩测井响应特征
2.1 自然伽马测井响应特征
2.2 自然伽马能谱测井响应特征
自然伽马能谱测井通过测定地层中铀、钍、钾含量确定岩石泥质含量和生烃条件等性质。龙一段、龙二段的能谱曲线钟型包络线形态明显,底部富有机质黑色页岩段均出现高值。龙三段钟型包络线形态特点不明显,这与龙三段岩性均为页岩有关,中下部黑色页岩能谱曲线中钍和铀含量偏高。自然伽马能谱测井与自然伽马测井曲线形态基本一致,未出现异常值,也反映WY1井整体保存条件较好,无热液侵入等现象。
2.3 密度测井响应特征
2.4 声波测井响应特征
声波测井通过利用声波在不同性质的介质中传播速度、振幅、频率等的变化来反映岩石的各项性质,有机质含量、含气量和孔隙度等的增加均能够使声波时差增加,裂缝较为发育时还可能产生周波跳跃现象。龙一段和龙三段下部的声波时差高值明显,反映这两段岩石的有机质丰度高、含气潜力较大,龙二段未出现明显高值,向下呈现逐渐增大的趋势,反映中下部也有一定的含气潜力。
2.5 补偿中子测井响应特征
2.6 电阻率测井响应特征
图3
图3
WY1井龙马溪组泥页岩高角度裂缝照片
a—913.31~913.97m岩心照片,高角度剪切裂缝,方解石充填;b—934.49~934.92m岩心照片,平行高角度剪切缝
Fig.3
High angle crack photo of shale in Longmaxi Formation of well WY1
a—core photo at the depth of 913.31~913.97 m,high angle shear crack filled with calcite; b—core photo at the depth of 934.49~934.92 m, parallel high angle shear cracks
3 富有机质页岩测井识别方法
3.1 测井曲线叠合法
通过WY1井测井曲线综合分析,选取自然伽马、去铀伽马、岩性密度、补偿中子、声波时差等测井曲线叠合分析。研究发现含气页岩层段具有明显的高自然伽马、高声波时差、高补偿中子,低岩性密度的特点,叠合图中自然伽马—岩性密度测井叠合曲线及声波时差—岩性密度测井叠合曲线具有明显的正差异,自然伽马—补偿中子和声波时差—补偿中子呈现明显的负差异,与实验测得的含气量大小均有较好的对应关系。综合对比发现声波时差—岩性密度叠合测井曲线对于页岩含气量大小的指示作用最为准确,龙一段下部含气量最高,龙三段含气量也较高,龙二段中下部泥页岩具有一定含气量,且上覆新滩组也具有一定含气量,这与岩心样品的含气量实验测试结果具有很好的对应关系,证明测井曲线叠合对识别含气页岩层系具有准确的指示作用(图4)。
图4
3.2 交会图法
根据岩性和含气特征,WY1井龙马溪组发育灰色含气泥页岩、黑色含气泥页岩、含气粉砂质泥岩及泥质粉砂岩4类岩石,选取自然伽马、深测向及浅侧向电阻率、岩性密度、补偿中子及声波时差测井数据进行分析整理,发现不同岩性、不同含气性特征的岩石的测井响应特征(表1)。
表1 WY1井龙马溪组泥页岩测井响应特征
Table 1
岩性 | 含气量 | 自然伽马/API | 深侧向电阻率 /(Ω·m) | 浅侧向电阻率 /(Ω·m) | 岩性密度/ (g·cm-3) | 补偿中子/% | 声波时差/(μs·m-1) |
---|---|---|---|---|---|---|---|
黑色泥页岩 | 高 | 180.0~495.0 | 48.5~876.5 | 16.0~717.5 | 2.63~2.71 | 4.0~18.5 | 195.0~269.0 |
灰色泥页岩 | 高 | 204.0~305.0 | 27.0~313.5 | 20.0~232.5 | 2.67~2.71 | 5.0~17.5 | 206.0~263.0 |
粉砂质泥岩 | 高 | 230.0~300.0 | 87.5~63.5 | 75.0~495.0 | 2.65~2.70 | 9.0~11.5 | 203.0~234.5 |
中 | 200.0~250.0 | 120.0~1000.0 | 80.0~770.0 | 2.64~2.72 | 6.0~10.0 | 192.0~211.0 | |
泥质粉砂岩 | 低 | 150.0~230.0 | 120.0~1300.0 | 100.0~1100.0 | 2.66~2.71 | 3.5~9.5 | 192.0~206.5 |
将龙马溪组岩层分别进行测井交会图版分析(图5),图版反映自然伽马、补偿中子测井对岩性的有较好的显示作用,对岩石中有机质含量也有较好的识别效果,声波时差、深侧向电阻率对岩石含气量的指示作用较好,综合分析认为声波时差—补偿中子测井交会图、补偿中子—自然伽马测井交会图以及深侧向电阻率—补偿中子测井交会图对于富有机质含气页岩的识别作用最好,可以作为后期单井解剖识别含气层的重要依据。
图5
图5
WY1井龙马溪组泥页岩测井识别交会图
Fig.5
Logging identification cross plot of shale in Longmaxi Formation in well WY1
4 结论
1)WY1井所揭示龙马溪组泥页岩具有高自然伽马、高铀、高钍、高补偿中子、高声波时差及低岩性密度的测井响应特征,深、浅侧向电阻率低于下伏宝塔组碳酸盐岩但高于一般砂泥岩地层,且在发育高角度裂缝的层段呈现深、浅侧向电阻率的正差异。通过对测井曲线响应特征的研究总结,可将WY1井钻遇的龙马溪组泥页岩自下而上分为3个层段,龙一段下部发育一段高含气层,龙二段下部发育一段中高含气量,龙三段中下部均为中高含气层。
2)将自然伽马、去铀伽马、岩性密度、补偿中子、声波时差等测井曲线进行测井叠合分析,含气泥页岩层系的自然伽马—岩性密度测井叠合曲线及声波时差—岩性密度测井叠合曲线具有明显的正差异,而自然伽马—补偿中子和声波时差—补偿中子呈现明显的负差异,其中声波时差—岩性密度叠合测井曲线对于泥页岩含气量大小的指示作用最为准确。
3)将龙马溪组岩层分为灰色含气泥页岩、黑色含气泥页岩、含气粉砂质泥岩及泥质粉砂岩4类进行测井识别交会图版分析绘制,自然伽马、补偿中子测井对岩性有较好的显示作用,对岩石中有机质含量也有较好的识别效果,声波时差、深侧向电阻率对岩石含气量的指示作用较好,综合分析认为声波时差—补偿中子测井交会图、补偿中子—自然伽马测井交会图以及深侧向电阻率—补偿中子测井交会图对于富有机质含气页岩的识别作用最好,可以作为后期单井解剖识别含气层的重要依据。
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页岩气成藏控制因素及中国南方页岩气发育有利区预测
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在系统研究美国页岩气成藏理论和成藏条件的基础上,分析了页岩气成藏的主要控制因素,分为内部因素和外部因素:前者指页岩本身的因素,包括有机质类型和含量、成熟度、裂缝、孔隙度和渗透率、矿物组成、厚度、湿度等;后者主要包括深度、温度和压力等。其中,有机质类型和含量、成熟度、裂缝及孔隙度和渗透率是控制页岩气成藏的主要因素。结合主要影响参数,建立了预测页岩含气的种类、比例和页岩气藏发育有利区的参数模型。运用此模型类比研究发现,中国南方古生界海相页岩层中,寒武系和志留系是页岩气发育的最有利层系。寒武系页岩气藏发育最有利区位于四川盆地和米仓山—大巴山前陆以及渝东、黔北、湘西—江南隆起北缘一线;志留系页岩气藏发育最有利区位于上扬子的四川盆地和米仓山—大巴山前陆和渝东—鄂西一带、中扬子鄂北以及下扬子苏南等地。并对各有利区的泥页岩指标进行分析,以期为中国页岩气早期评价提供参考。
Controlling factors for shale gas accumulation and prediction of potential development area in shale gas reservoir of South China
[J]. ,DOI:10.7623/syxb200904002 [本文引用: 1]
On the basis of the pool-forming theory and conditions for shale gas in the United States,the controlling factors for shale gas accumulation were analyzed and divided into internal and external factors.The internal control factors include the type,content and maturity of organic matters,and the fracture,porosity,permeability,mineral composition,thickness,humidity of shale.The external control factors include reservoir depth,temperature and pressure of formation.Among them,the type,content and maturity of organic matters,as well as the fracture,porosity and permeability of shale are the main factors for generating shale gas reservoir.The favorable areas for developing shale gas reservoirs were predicted by using parameter model.The analogical analysis based on the model suggests that the Cambrian system and the Silurian system are the most favorable strata for developing of shale gas reservoirs among the marine Paleozoic strata in South China.The most favorable areas of the Cambrian are located in Sichuan Basin,the Micangshan-Dabashan foreland,the northern Guizhou Province,West Hunan Province,East Chongqing and the north part of Jiangnan uplift.The most favorable areas of the Silurian are located in Sichuan Basin,the Micangshan-Dabashan foreland and East Chongqing,West Hubei Province of Upper-Yangtze River,North Hubei Province of Middle-Yangtze River and South Jiangsu Province of Lower-Yangtze River.The indexes of shale in the favorable areas were analyzed to provide reference for early evaluation of shale gas in China.
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A study on sequence stratigraphy and sedimentary microfacies of longmaxi formation of early Silurian in the Baojing area,Hunan Province
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Identification method and distribution characteristics of high quality source rocks in West Sichuan depression
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鄂西来凤—咸丰地区五峰组—龙马溪组岩石学特征及其成因
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Petrologic characteristics and genesis analysis of the Ordovician Wufeng Formation-Silurian Longmaxi Formation in Laifeng-Xianfeng area of western Hubei
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复杂构造区页岩气储层特征及含气性控制因素——以湖北来凤—咸丰区块来地1井龙马溪组为例
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Characteristics and gas-bearing controlling factors of shale gas reservoir in complex tectonic provinces:A case from the Lower Silurian Longmaxi Formation of Well Laidi 1 in Laifeng-Xianfeng block,Hubei Province
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The particle size characteristics of pyrite in western Hunan and Hubei areas’ Wufeng-longmaxi formation shale
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Conditions of shale gas accumulation and gas-bearing factors of lower Cambrian niutitang formation in western hu’nan and Hubei
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四川盆地及其周缘奥陶系五峰组-志留系龙马溪组页岩气富集主控因素分析
[J]. ,DOI:10.13745/j.esf.2016.02.002 [本文引用: 1]
四川盆地及周缘地区奥陶系五峰组志留系龙马溪组页岩气富集主控因素包括:(1)特殊的古环境所形成的优质页岩是富集的基础。四川盆地及其周缘在五峰组和龙马溪组沉积时期,在弱挤压背景下发生了陆内拗陷沉降,奥陶纪末期冰期后全球性海平面快速上升,形成了较大规模的深水陆棚环境,为低等生物的大规模繁殖提供了有利条件,闭塞的海湾背景,为有机质的保存提供了有利的地球化学环境,欠补偿状态导致了地层中的高有机质含量。特殊生物类型所形成的大量有机硅,使成岩早期就形成了具有较强抗压实能力的岩石骨架,为早期生成原油的滞留提供了良好的空间,也为后期油向气转化时形成并保持大量的有机质孔奠定了物质基础。(2)有机质孔和特殊裂缝是页岩气富集的重要保障。有机碳含量高的优质页岩,有机质孔也发育较多,页岩的含气量大,游离气所占的比例更高。特殊裂缝主要指页岩层理缝和小尺度裂缝。在层理面堆积的笔石和藻类等成烃生物促进了这类层理缝的发育。小尺度裂缝提高了页岩自身的储集空间和渗流能力,有利于页岩气的聚集和成藏。(3)适度抬升状态下的有效保存是富集的关键。构造变形和抬升剥蚀是一把双刃剑。如果变形与抬升剥蚀作用太强,地层的封闭保存系统会破坏,导致不论是常规还是非常规的油气系统完全或者部分失效。因抬升产生微裂缝但没有出现大的穿层裂缝或断裂,即表现为一种“裂而不破”的状态是最理想的。远离断裂尤其是通天断裂、具有一定埋深且地层平缓的地区页岩气保存条件良好。四川盆地内与周缘地区保存条件的差异,主要是由于燕山中期运动所控制的构造变形、沉降沉积与抬升剥蚀作用的差异性所决定的。四川盆地及周缘地区奥陶系五峰组志留系龙马溪组页岩气有利富集区是位于富有机质黑色页岩厚度较大的深水陆棚沉积中心区、有机孔和微裂缝或页理发育的层段以及燕山期抬升时间晚且喜山期抬升幅度小区带所叠合的区域。
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