Understanding the Heterogeneous Fractured Carbonate Reservoir by the Integration of Advanced Logging Techniques and Core Measurements, Case Study From Beibu Gulf Basin, China

The exploration and development of carbonate reserves have primarily taken place onshore, achieving significant success in recent decades (Wen et al., 2024; Zeng et al., 2025). CNOOC Ltd has made notable breakthroughs in carbonate reservoir exploration in the Pearl River Mouth Basin and Bohai Bay Basin (Xie et al.,2021; Huang et al., 2024), underscoring the vast exploration potential of carbonate reservoirs in China's offshore oilfields. Since 2022, CNOOC Zhanjiang has been leading multiple drilling campaigns to confirm the presence of gas and oil in the Weixinan Sag, Beibu Gulf Basin in the South China Sea. Due to the carbonate reservoir's strong heterogeneity and complexity, resulting from fracture development and secondary dissolution, accurately evaluating this type of reservoir using conventional open-hole logs is highly challenging. To perform a comprehensive evaluation of the carbonate reservoir, high-resolution wireline logging techniques and advanced core measurements were utilized to qualitatively and quantitatively characterize the fractured carbonate reservoir. This paper discusses the petrophysical and geological evaluation of the deep-buried carbonate reservoir using extensive logging data from the Weixinan Sag, Beibu Gulf Basin. This includes the use of high-definition gamma-ray spectroscopy logs to quantify the mineral assemblage and the application of the Heterogeneous Rock Analysis (HRA) method for improved lithology determination in heterogeneous strata. Additionally, the development and openness of fractures were identified using resistivity image and acoustic image logging data, which correspond well with core analysis from the deep- buried carbonate reservoir. Furthermore, advanced core measurements revealed the categories of dissolved pores, the pore-throat structure, and the oil accumulation spaces. Lastly, the geological model and geological evolution of this deep-buried carbonate reservoir were established for the first time.