双电法测井在低电阻率储层流体性质识别中的应用

　[作者简介]郑雷清(19752),男,1999年大学毕业,工程师,现从事测井及测井地质综合评价工作。

双电法测井在低电阻率储层流体性质

识别中的应用

　　郑雷清　(吐哈油田分公司勘探开发研究院,哈密839009)

[摘要]以吐哈油田HN 油田低电阻率油层为研究对象,利用双侧向和双感应测井原理的不同及其对流体

敏感性的差异,建立了以双电阻率比值为基础的储层流体识别方法。在实际应用中极大地提高了测井解

释符合率,地质意义显著。

[关键词]双侧向;双感应;低电阻率储层,流体识别

[中图分类号]P631184[文献标识码]A 　　[文章编号]100029752(2006)0320304203

吐哈盆地存在大量的低电阻率油层,这些低电阻率油层的存在,造成电法测井不能很好的反映储层流体性质,给测井解释带来了极大的难度。通过分析,认为这些储层主要存在如下特征:①孔隙结构复杂;②渗透率变化区间较大,基本以低渗透为主;③地层水纵横向变化大、油水系统紊乱等。而吐哈油田自勘探开发以来一直在该类储层中采用侧向和感应电阻率同时测量,为准确识别储层的流体性质创造了有利条件。笔者以吐哈油田HN 地区侏罗系喀拉扎组(J 3k )地层为研究对象,在研究储层“四性”关系的基础上,研究以双电法比值为基础的流体识别方法,在实际应用中取得了很好的应用效果。1　储层“四性”特征

1)岩性特征　红南喀拉扎组储层岩性以细、粉砂为主,岩石成分主要为石英、长石,其中火山岩岩屑占3019%。泥质中粘土矿物以伊/蒙混层为主占57138%,其次为伊利石占28126%,高岭石和绿泥石分别占5162%和8174%。这些粘土矿物含量导致储层束缚水含量高,易形成低电阻率油层,同时给利用自然伽马测井识别储层岩性带来了难度。

2)物性特征　利用取心分析资料对所有岩性,分岩性统计分析,该区储层孔隙度在314%～2913%之间,平均渗透率为2618×10-3μm 2,其中细、粉砂岩主要为中孔中渗,泥质粉砂岩为低孔低渗,并且在岩性相同、孔隙结构相近的情况下,孔隙度和渗透率具有良好的相关性,说明孔隙结构是影响渗透率的另一因素。

3)水性特征　地层水矿化度在纵横向上在(1～4)×104kg/L 之间变化,具有多套油水系统,且由于顶部存在天然淡水水淹,使得储层水性更加复杂。

4)含油性与电性特征　该区油气显示层表明储层含油性与电性特征关系混乱,显示了不同砂层组控油因素变化、水性变化对电性的影响较大,总体反映岩性变粗,储层含油性逐渐变好,在岩性基本相近时,物性越好,含油级别越高,粉砂岩、泥质粉砂岩级别较低,而且在同一砂体内,含油性也表现出很强的非均质性。

2　双电法比值法识别流体性质的解释标准

211　双电阻率解释基础

在吐哈油田,无论是探井还是开发井,全套常规测井都采用双侧向和双感应2套电阻率测井系列,近年来大部分探井采用深侧向与阵列感应测井共存的双电阻率系列,这些资料的采集为进行储层流体性质的判别提供了基础。通过大量的试油资料分析,认为储层流体性质与感应电阻率和侧向电阻率的比值存在一定的关系。这种规律主要与侧向电阻率和感应电阻率的测井机理不同存在差异造成。

・403・石油天然气学报(江汉石油学院学报)　

2006年6月　第28卷　第3期Journal of Oil and G as T echnology (J 1J PI )　

J un 12006　Vol 128　No 13

　　按照聚焦测井系列来说,侵入可能是求解原状地层电阻率R t 的主要影响,从感应测井和侧向测井的响应方式来看,侵入带对它们的影响方式各不相同[1,2]。

按照几何因子理论,双侧向测井聚焦电流成束装进入地层,使井眼、侵入带和原状地层形成串联电路;而感应测井则相反,其涡流电流是以井周为中心的同心环形式进入地层,使井眼、侵入带和原状地层形成电阻率的并联。这就说明,侧向电阻率的影响主要来自2个带的高电阻率部分,而感应测井主要受2个带中低电阻率部分。研究发现,该区双侧向测井受岩性的应向较大,对储层流体性质反映较差,而感应测井探测深度较测向深,除反映储层岩性的变化之外还对储层流体性质有较好的反映。212　双电阻率比值解释方法

1)常规解释图版的局限性分析　目前电法测井依然是发现与评价油气层最主要的方法[3],但是由于低电阻率油气层的存在,导致油水层电阻率分异不明显,因此,传统的标准水层对比法、交会图法识别油水层存在一定的困难。如图1为研究区块内电阻率与孔隙度交会图版,通过实际应用得出,该图版对于粗岩性储层的流体性质识别效果相对较好,但是对于细岩性储层的流体性质识别效率大打折扣,致使油层与油水同层取分不开,导致该图版有一定的局限性。

2)双电阻率比值识别流体性质的建立　依据目前研究区块内储层的特点,岩性对储层测井响应特征影响明显,即储层岩性变细,中子、密度测井响应值均有所增大,电阻率值降低;反之,岩性变粗则中子和密度测井相应值均变小,电阻率升高。因此,在解释中利用这几条曲线之间的关系构造了岩性系数B ,此系数无实际物理意义和量纲,主要反映储层岩性的相对变化,然后以试油资料为基础利用该参数与感应电阻率和侧向电阻率的比值I 作交会图(图2),可以有效地识别油水层

。

图1　电阻率孔隙度交会图版　　　　　　　　　　　　　图2　电阻率比值与岩性系数交会

　　B =CN L 3D EN /RL L D

(1)　　I =RIL D/RL L D

(2)式中,B 为岩性系数;CN L 为中子测井响应值,%;D EN 为密度测井响应值,g/cm 3;RL L D 为深侧向电阻率响应值,Ω・m ;RIL D 为深感应电阻率响应值,Ω・m 。

由图2可知,该图版的应用,可以有效地进行油水层识别。但是,对于含油水层和水层的识别,由于低电阻率固有的特性加上人为因素,区分不明显;同时,由于在致密层段侧向和感应的测井响应值相当,不能利用该图版进行识别。

3　应用实例分析

该方法的建立,在研究区块内得到了广泛的应用,取得了良好的应用效果,新钻井的测井解释符合率达到了90%以上,基本上满足油田勘探开发的需要。如图3为HN9井测井曲线组合图。该井为部署在该区的一口重点探井,完钻后对HN9井进行解释,利用常规解释1号层为油水同层,4号层为水层,

・503・第28卷第3期郑雷清:双电法测井在低电阻率储层流体性质识别中的应用　

图3　HN 9井测井曲线组合图

主要依据是两层储层物性相当,岩性一致,其反映在电阻率上差异性较大,其中1号层与底部3号层标准水层电阻率差异明显;4号层与临近水层电阻率差异不明显。而利用该方法并结合其他资料进行解释,认为1号层为水层,电阻率的高值主要是受岩性的影响,4号层为油水同层,后分别对这两层进行试油,其中4号层试油日产油9,产水5m 3,1号层日产水28m 3,不含油,与解释结论一致。4　结　　语

利用电阻率比值与其他参数结合可以有效地识别低电阻率储层流体性质,现阶段较好的解决了该类储层的解释难题。但随着岩性油气藏勘探开发程度的进一步加大,加上钻井过程中对储层具有不同的污染,因此为了提高图版的解释精度,应进一步加强测井资料的环境效正方法,以期满足油田勘探开发的需求。

[参考文献]

[1]曾文冲,欧阳健1测井地层分析与油气评价[M ]1北京:石油工业出版社,1981140～421

[2]雍世和,张超谟1测井资料综合处理解释[M ]1北京:石油工业出版社,19961117～1211

[3]中国石油天然气集团公司油气勘探部1渤海湾地区低电阻率油气层测井技术与解释方法[M ]1北京:石油工业出版社,

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[编辑]　弘　文

・603・　石油天然气学报(江汉石油学院学报)2006年6月

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———By T aking Shu anghe Oilf ield for Example

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SONG Heng　(China Oil and Gas Ex ploration and Development Co1,Bei j ing100083)

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