Reservoirs of Bentiu Formation and Abu Graba Formation in Jake South oilfield,Muglad basin,Sudan,are anticline reservoirs and layered reservoirs of typical complex fault blocks,in which exist a number of low resistivity oil layers,causing a challenge in oil and water layers identification.First,the reservoirs in the two formations are categorized according to grain size,petrophysical properties,pore type and tightness,and low resistivity layers are defined in each type of reservoirs.Then such data as core,thin section,physical property test,SEM and X-diffraction are comprehensively used to study the cause and identification methods of low resistivity oil layers.The results show that the main causes are high irreducible water saturation due to high shale content and small pore throats,conductive minerals and low oil saturation caused by insufficient hydrocarbon charge.The causes of low resistivity oil layers in different reservoirs of different complex fault blocks are different.In Abu Graba Formation,cross plot,interpretation model considering the effect of silt component and comprehensive method are used to identify low resistivity oil layers.In Bentiu Formation,comprehensive method is preferably used.Using the new method,77 unperforated low resistivity oil layers with a total thickness of 275.9 m are identified.%苏丹Muglad盆地Jake South油田白垩系Bentiu组和Abu Graba组油藏分别为复杂断块背景下的整装背斜油藏和层状油藏,均存在大量低阻油层,对油水层识别造成较大困难.首先根据粒度、储层物性、储集空间类型、致密度等分别对Bentiu组和Abu Graba组进行储层分类,并在每类储层内部定义低阻油层;然后综合利用岩心、薄片、物性测试、扫描电镜、X-衍射资料,明确各类储层内部低阻油层成因,并根据储层类型和低阻成因分别建立识别方法.结果表明:低阻成因主要为泥质含量高或孔隙结构细造成高束缚水饱和度、存在导电矿物和油气充注不足造成低含油饱和度,不同类型复杂断块油藏不同储层类型内低阻油层成因不同.Abu Graba组低阻油层识别难度较大,依次采用图版法、考虑粉砂组分的解释模型法、综合法进行识别;而Bentiu组低阻油层识别相对简单,主要采用综合法进行识别.综合各种方法,在研究区共识别未射孔低阻油层77层275.9 m.
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