| 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. |
