Reservoir Characterization of Carbonate in Low Resistivity Pays Zones in the Buwaib Formation, Persian Gulf

Abstract

Carbonate reservoir characterization and estimation of fluid saturation seem more challenging in the low resistivity pay zone (LRPZ). The Lower Cretaceous Buwaib Formation is important reservoir in the Persian Gulf. The formation in the Salman Field is divided into three reservoir zones and four barriers and tight zones. These reservoir zones show low resistivity characteristics, high fluid saturation, but good oil production. In some intervals resistivity responses reach less than 1 ohm•m. Petrophysical properties measured from laboratory and logging tools have been combined with thin section X-ray diffraction (XRD) and PNN (Pulse Neutron Neutron). Geological studies define presence of 8 facies from wackeston to packstone. In general, reservoir potential of the Buwaib Formation is under influenced by the development of lithocodium mound facies that along with moderate to high porosity intervals. Micritization and pyritization of digenetic process along with clay-coated grains, carbonate with interstitial dispersed clay have conspicuous impact on LRPZ. Based on XRD analysis, Montmorillonite and Kaolinite of main clays types have high CEC and greater impact on lowering resistivity. To describe pore systems of rocks, the Lønøy method applied to address pore throat sizes which contain mudstone micro porosity related to lithocodium mound facies and uniform interparticle at class 3 Lucia as pore size varies from 0.2 to 10 micron. Some constraints were defined to estimate reliable water saturation that checked by sigma logs. Water saturation is 42%, 34% and 40% respectively in BL1, BL2 and BL3 zones.

Reservoir characteristics and control mechanism of resistivity low-contrast oil pays in Chang 8 tight sandstone of Longdong West area, Ordos Basin

“…Kusuma et al (2016) proposed an effective method to identify resistivity low-contrast oil pay zones during the re-evaluation of old wells in the "S" field by integrated analysis of the main factors causing the low resistivity zones. Arbab et al (2017) established a reliable water saturation model based on the pore structure characteristics of resistivity low-contrast oil pay in carbonate reservoir of Buwaib Formation in the Persian Gulf. Bai et al (2019) proposed a comprehensive fluid identification method for fluid typing in the Huanxian area of the Ordos Basin in China by analyzing the regional distribution characteristics of resistivity low-contrast oil pay reservoir.…”