There has been a string of exploration discoveries in Cambrian Ara Group intra-salt carbonate reservoirs in the South Oman. Some of the reservoirs failed to produce at expected rates due to halite presence in the pore space, which is one of the highest risks for hydrocarbon exploration in this area. The objective of this study was to define novel quantitative algorithm to estimate halite volumes in the pore space. Although halite cementation is known as a major risk for hydrocarbon production, a limited number of studies have focused on the impact of halite cementation on productivity, well integrity and ultimate recovery. The quantitative halite volume evaluation based on the logging data required an integrated approach to open hole and cased hole data collection and analysis. The open hole data included: thin section and XRD core analysis, density, neutron, sonic, resistivity, formation pressure and sigma capture-cross section. Net pay cut-off based on calculated halite volume was defined. Cased hole production logging was used to confirm net cut-off definition. The integrated logging data analysis and the developed quantitative halite volume evaluation algorithm mainly based on sigma log was successfully implemented in a few ongoing development projects. The evaluation results were successfully used for hydrocarbon volume calculations, well placement and perforation interval selection to improve production performance and reduce field development uncertainty in recoverable volumes. Understanding of consistent pattern for halite distribution allow improve exploration success. Avoiding perforation of intervals with high halite content in the pore space reduced production deferment due to surface equipment and tubing plugging by salt. Appreciation for the role of halite plugging in the reservoirs properties distribution and deterioration significantly improve history match for hydrodynamic models. The evaluation algorithm for quantitative halite volume estimation in the pore space have been developed and introduced for the first time and benefits from its implementation are expected for the upcoming exploration and development projects for the salt encased carbonate reservoirs.

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.