The identification of carbonate reservoirs is a critical
task in
oil and gas exploration. Chaotic weak reflection is an important type
of reflection characteristic in carbonate reservoirs. Widespread distribution
of chaotic weak reflection has been observed in the Ordovician Yijianfang
Formation in the Tahe area. However, there is still a lack of systematic
research on the distribution, characteristics, reservoir space, and
reservoir types of chaotic weak reflection in the Tahe area. To address
this issue, this study conducted a comprehensive analysis of multiscale
data and found that chaotic weak reflections are distributed within
100 ms below the top interface of the Middle Ordovician. Seismic profiles
exhibit a “string of pearls” with a “tail”
or “pearl-like” widening feature. On well logs, all
three porosity curves exhibit localized peaks, with increases in acoustic
(AC) and compensated neutron (CNL) and decreases in density (DEN),
while the deep and shallow lateral resistivity (RD, RS) curves show
positive amplitude differences. In the FMI, they are represented by
dark sinusoidal curves and dark small patches. Based on these response
characteristics, two types of reservoir spaces are identified for
chaotic weak reflections: high-angle vertical fractures and caves
with heights less than 7 m, which can form independent reservoirs
or fracture–cavity complexes. Three types of reservoirs are
distinguished: fracture, cavity, and cavity-fracture types.