鄂尔多斯盆地定边油田主力油层有效储层厚度

Effective reservoir thickness of main oil layers in Dingbian Oilfield,Ordos Basin

鄂尔多斯盆地定边油田沙涧区的中生界具有储层非均质性强、多套油水系统相互叠置和低电阻率与常规电阻率油层并存的特点。为了识别有效储层,基于岩心、测井、录井、试油试采、高压物性和密闭取心等资料建立了主力油层延9、长6和长9储层参数测井解释模型,综合分析了各油层组的有效厚度下限,并探讨了储层物性和电性下限的差异性成因。结果表明:①定边油田沙涧区延9、长6和长9油层组有效厚度孔隙度下限分别为12.5%,9.0%,7.0%,渗透率下限分别为2.0 mD,0.2 mD,0.3 mD,声波时差下限分别为239μs/m,222μs/m,213μs/m,电阻率下限分别为6.0Ω·m,13.0Ω·m,17.5Ω·m,含油饱和度下限分别为47.5%,44.0%,41.5%。②差异化成岩作用造成了各油层组物性下限的不同,其中压实和碳酸盐岩胶结作用发育较弱的延9油层组物性条件相对长6、长9油层组好;长6油层组中绿泥石膜的发育使部分粒间孔得以保存,而自生黏土易堵塞孔喉,导致渗透率低;长9油层组因强压实和胶结作用而减少的孔隙度大于长6油层组,但后期溶蚀作用对储层渗透性的改善作用较长6油层组强。③钻井液的侵入、储层物性和黏土附加导电作用的影响是导致延9油层电阻率下限值低的主要原因。客观理解主力油层有效储层厚度下限的不同和差异的成因,有助于深入认识鄂尔多斯盆地中生界油藏的储层变化规律,提高储层有利区预测的精度。

The Mesozoic reservoirs in Shajian area of Dingbian Oilfield,Ordos Basin are characterized by strong reservoir heterogeneity,overlapping of multiple oil-water systems and coexistence of low resistivity and conventional resistivity reservoirs.In order to identify effective reservoirs,based on core,logging,formation test and production test,high-pressure physical properties and sealed coring data,the logging interpretation models of Yan 9,Chang 6 and Chang 9 reservoirs were established.Then,lower limits of effective thickness of each reservoir were comprehensively analyzed,and the origin of the difference of lower limits of physical and electrical properties were discussed.The results show that:①The lower limits of effective thickness porosity of Main oil reservoirs in Shajian area of Dingbian Oilfield are 12.5%,9.0%,7.0%respectively,the lower limits of permeability are 2.0 mD,0.2 mD,0.3 mD respectively,the lower limits of acoustic time difference are 239μs/m,222μs/m,213μs/m respectively,the lower limits of resistivity are 6.0Ω·m,13.0Ω·m,17.5Ω·m respectively,and the lower limits of oil saturation are 47.5%,44.0%,41.5%respectively.②Differential diagenesis results in the difference of the lower limits of physical property of each reservoir.The physical property conditions of Yan 9 reservoir with weak compaction and carbonate cementation are better than those of Chang 6 and Chang 9;The development of chlorite film in Chang 6 reservoir preserves some intergranular pores,while authigenic clay mineral is easy to block the pore throats,resulting in low permeability.The porosity of Chang 9 oil reservoir reduced by strong compaction and cementation is larger than that of Chang 6 oil reservoir,but the improvement of permeability by dissolution is stronger than that of Chang 6 oil-bearing formation.③The intrusion of drilling fluid,the influence of reservoir physical properties and additional conductivity of clay are the main reasons for the lower limits of resistivity of Yan 9 oil reservoir.Understanding the difference and the origin of the lower limits of effective thickness for the main oil-bearing formations will help to understand the variation of Mesozoic reservoirs in Ordos Basin and improve the prediction accuracy of favorable reservoir areas.