Characteristics of Chaotic Weak Reflection in Carbonate Fracture-Cavity Reservoirs: A Case Study of Ordovician Reservoirs in Block 10 of the Tahe Oilfield, Tarim Basin, China

The identification of carbonate reservoirs is a criticaltask inoil and gas exploration. Chaotic weak reflection is an important typeof reflection characteristic in carbonate reservoirs. Widespread distributionof chaotic weak reflection has been observed in the Ordovician YijianfangFormation in the Tahe area. However, there is still a lack of systematicresearch on the distribution, characteristics, reservoir space, andreservoir types of chaotic weak reflection in the Tahe area. To addressthis issue, this study conducted a comprehensive analysis of multiscaledata and found that chaotic weak reflections are distributed within100 ms below the top interface of the Middle Ordovician. Seismic profilesexhibit a "string of pearls" with a "tail"or "pearl-like" widening feature. On well logs, allthree 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 showpositive amplitude differences. In the FMI, they are represented bydark sinusoidal curves and dark small patches. Based on these responsecharacteristics, two types of reservoir spaces are identified forchaotic weak reflections: high-angle vertical fractures and caveswith heights less than 7 m, which can form independent reservoirsor fracture-cavity complexes. Three types of reservoirs aredistinguished: fracture, cavity, and cavity-fracture types.