A Case Study on Integrated Petrophysical Characterization of a Carbonate Reservoir Pore System in the Offshore Red River Basin of Vietnam

Characterization of a carbonate reservoir is often difficult due to the complexity of its pore system. This study presents an integrated approach using well-log and microgeological data to characterize rock fabrics and their pore system for a carbonate reservoir in the Ham Rong (HR) structure, offshore the Red River basin, Northern Vietnam. Based on such well-log data as gamma ray (GR), photoelectric factor (PEF), neutron porosity (PHIN), and bulk density (RHOB), two major rock types of dolostone and limestone were identified. A further combination using the results of thin-section and scanning electron microscope (SEM) analysis indicated four types of carbonate rock fabric, and namely, limestone with grain-dominated grainstone, limestone with grain-dominated packstone, dolostone with grain-dominated grainstone and dolostone with grain-dominated packstone. For each identified carbonate fabric, two types of pores were found, including interparticle and vuggy pores. The latter can be further subdivided into separate-vug pores and touching-vug pores. For the HR structure, the touchingvug porosity and the interparticle porosity were estimated to be in the range of 1 to 3% and 1 to 8%, respectively. The intercrystalline porosity, which might be considered as a subset of the interparticle porosity and could be estimated by SEM analysis, was found in the range of 1.5 to 3%. It is expected that the integrated analysis approach using well-log and microgeological data employed in this study can be applied to evaluate the characteristics of carbonate reservoirs at other wellsites in the Red River basin. It worth noting that the fracture porosity calculated based on thin-section analysis matched quite well with the porosity calculated by resistivity log data and using 2D and 3D fracture models.