Advanced Porosity and Permeability Analyses Based on BHI Approach

Abstract

Carbonate intrasalt stringers formation evaluation proved to be complex due to the nature of the rock lithology through syndolomitization and postdolomitization process. The need for the radioactive data is highly recommended, however different degrees of depletion along the reservoir units are posing clear threat to data acquisition. This study aims to establish an advanced model of calculating the porosity and permeability using non-radioactive BHI approach without compromising with the quality of the formation evaluation. This study was conducted while facing the challenge of limited data acquisition with the pressure behavior across the carbonates stringers and the need to understand the nature of the permeability disturbance. The pilot covers two wells, Well-A was most useful regarding the source of the data for the analyses. Missing information was obtained from Well-B, which consist of the same dataset. The resistivity image data quality throughout the interpreted BHI section was good. Several analyses were carried out to characterise BHI data including fractures interpretation, porosity prediction (microfractures, intragranular pores and fluid inclusions) and permeability distribution (fracture aperture analysis). Based on this study, the following observations are obtained, the predicted porosity and permeability are well correlated with the core and density – neutron data. The net pay identification and porosity calculation is consistent with those derived from density-neutron logs. Highly fracture zones were detected across the reservoir, which explain the permeability disturbance. Natural fracture tends to be found in clusters throughout the borehole. Conductive fracture, which has direct influence to the permeability were interpreted using the electrical borehole image to estimate the electrical apertures of open fractures around the wells. Pressure behavior across the reservoir might be linked to the natural fracture networks (conductive and non-conductive fractures). In the development side, this study helps to have better understanding of the rock typing and Lithotypes associated with different permeability clusters and reservoir quality integrated with production behavior. The developed methodology of BHI evaluation provides reliable results in Porosity and Permeability evaluation. The model integrates relevant disciplines to evaluate intrasalt stringers dolomite and limestone mixed environment through independent lithology approach to eliminate the effect of the matrix heterogeneity. In addition, BHI approach provides safer logging acquisition and better option for advanced natural fracture analysis.