松南长岭断陷火山岩亚相约束下的气层测井识别评价

Log identification of volcanic gas zone under volcanic facies in Changling sag,south Songliao Basin

松辽盆地长岭断陷营城组火山岩包括4相12亚相;优质储层主要见于爆发相热碎屑流、喷溢相上部和下部、火山通道的火山颈等4亚相.火山岩气藏普遍含CO_2,部分为纯CO_2气藏.基于26口重点探井的自然伽马、电阻率、声波时差和中子等测井参数分析,建立了岩相亚相-测井识别模式;进而在亚相约束下,用声波-中子密度三种孔隙度叠置图进行气层的识别评价.声波孔隙度大于中子孔隙度判别为可能的气层,两种孔隙度叠合曲线存在三种类型:高孔双孔近似型、低孔双孔差异型和低孔双孔近似型.前者均为气层,后两者可能为气层、差气层或干层;需要进一步用亚相与叠合曲线对应关系加以区分.用三孔隙度重叠法还可识别烃类气层与非烃类气层,在烃类气层(CH_4)声波孔隙度与密度孔隙度基本重合,而在CO_2气层处其差别较大.本文提供了火山岩亚相一测井综合识别气层及其流体类型的方法.

The volcanic gas-reservoir of Changling sag is an important deep exploration and development goal in South Songliao Basin. The volcanic rock lithology and lithofacies of Yingcheng Formation in the research area are complicated and multiple, including four facies and twelve subfacies. Volcanic gas-reservoirs generally contain CO2 gas and the CO2 contents are high in part wells. All of these make some difficulties in gas zone accurate identification. Through the analysis of natural gamma ray, electrical resistivity, acoustic time, neutron porosity and other parameters of 26 wells, the logging identification models of hot debris flow subfacies, upper subfacies, lower subfacies and diatreme subfacies are made, which control high quality reservoirs development. The method of logging accurate identification of gas zone is discussed under therestriction in the subfacies. Based on logging data, the three porosity overlay figures of acoustic, neutrons and density are drawn, and the one with acoustic porosity greater than neutrons porosity indicates the possible gas zone. Three types of the two kinds of porosity overlay curves are recognized： high porosity-double porosity similar type, low porosity-double porosity dissimilar type and low porosity-double porosity similar type. The subfacies are identified in possible gas drilling sections. The possible gas drilling sections can be interpreted as gas zone, bad gas zone or dry zone by corresponding relationship between subfacies types and overlay curves types. Hydrocarbon gas zone（CH4）or non-hydrocarbon gas zone is identified by the method of three porosity overlaying. The difference between acoustic porosity and density porosity is small in hydrocarbon gas zone, but it is very different in CO2 gas zone. This method can improve the accuracy for identification of volcanic gas zone.