四川盆地龙女寺地区龙王庙组碳酸盐岩岩溶地层测井响应特征

Logging response characteristics of carbonate karst strata of Longwangmiao Formation in Longnvsi area,Sichuan Basin

以龙女寺构造龙王庙组碳酸盐岩岩溶地层为例,通过岩心标定成像测井,结合常规测井曲线识别岩溶地层,将龙女寺地区龙王庙组岩溶储层划分为裂缝-孔洞型、裂缝-孔隙型、孔隙型,并进一步研究了龙女寺地区龙王庙组碳酸盐岩岩溶地层的测井响应特征。结果表明:龙王庙组从风化壳顶部向下可划分为表层岩溶带、垂向渗流带和水平潜流带。表层岩溶带分布零星,厚度薄,溶洞全部被充填,测井显示为高伽马、低电阻率,电成像上见角砾状混杂堆积;垂向渗流带发育树枝状溶洞和溶缝,溶洞大部分被充填,测井显示为低伽马、较高电阻率,电成像见不规则分布的暗色斑点和正弦式的黑色条带;水平潜流带发育中—大型溶洞,溶蚀孔洞常见顺层状分布,测井显示为低伽马、低电阻率,电成像上见不规则的斑块或斑点和正弦式的黑色条带。

Anyue gas field of the Lower Cambrian Longwangmiao Formation in Sichuan Basin is the largest carbonate gas reservoir discovered so far in China.With the promotion of gas exploration,many gas wells with daily production capacity of million cubic meters have appeared in Moxi-Gaoshiti area in Central Sichuan.However,the reservoir development of Longwangmiao Formation in the adjacent Longnvsi structure is quite different from that in Moxi-Gaoshiti area,and the logging response characteristics of different karst facies zones in carbonate karst strata of Longwangmiao Formation in Longnvsi area are not clear.Taking the carbonate karst formation of Longwangmiao Formation in Longnvsi structure as an example,based on core calibration imaging logging and conventional logging curves,the identification mode of dissolution vugs and fractures is established to identify the karst formation.The karst reservoir of Longwangmiao Formation in Longnvsi area is divided into three types,including fracture-vug,fracture-pore and pore.The logging response characteristics of carbonate karst strata of Longwangmiao Formation in Longnvsi area are further studied.The results show that the carbonate karst facies zones of Longwangmiao Formation in Longnvsi area can be divided into superficial karst zone,vadose karst zone and underflow karst zone.The superficial karst zone is sporadically distributed with thin thickness,and all karst vugs are filled.The logging data show high gamma and low resistivity,and breccia mixed accumulation can be seen on the electrical imaging.Dendritic karst caves and fractures are developed in the vadose karst zone,most of the karst vugs are filled.The logging data show low gamma and high resistivity,and irregular dark spots and sinusoidal black bands are seen in electrical imaging.Medium-large karst vugs are developed in the underflow karst zone,and the dissolution vugs are commonly distributed along the layer.The logging data show low gamma and low resistivity,and irregular patches or spots and sinusoidal black strips are seen on the electrical imaging.