No abstract

Seismic inversion emerged as an important tool for reservoir characterization and quantifying reservoir properties. It combines geophysical, geological and petro physical data through a robust inversion scheme to extract more meaningful reservoir information. When compared to working with seismic amplitudes, inversion results show higher resolution with accurate interpretations, which in turn facilitates better estimates of reservoir properties such as porosity.In this study, Mauddud carbonate reservoirs of western flank of Sabriyah, saddle part between Raudhatain -Sabriyah and South of Sabriyah were considered for porosity studies. The two fields namely Raudhatain and Sabriyah are well developed. The Mauddud Limestone of Upper Cretaceous is one of the main producer in these fields. Around 600 wells drilled over the main structures of these fields show good porosity development in Mauddud reservoir ranging from 15-35%.This paper mainly deals to know the porosity development towards the Western flank of Sabriyah, saddle part between Raudhatain and Sabriyah and Southern part of Sabriyah through the post stack Constrained Sparse Spike Inversion (CSSI), which was successfully performed on a 3D seismic volume over a carbonate reservoir Mauddud. The Inversion results improved the structural model, closely represented the true sub-surface geology and predicted reservoir porosity. A relationship between acoustic impedance and porosity was established using well data and applied in transforming into porosity volume. This porosity volume was used to generate porosity maps for Mauddud reservoir interval to analyze the porosity distribution. The generated maps show moderate to good porosity development in the Western flank, moderate porosity developed in the saddle part, moderate to good porosity development in SE of Sabriyah field and some isolated porosity development in South West of Sabriyah field. This study has allowed understanding the internal reservoir heterogeneity, facies variation within the reservoir and has provided a strong base to refine the planning and placement of development and exploratory wells with higher confidence.

High permeable layers are one of the key factors of heterogeneity in the Mauddud carbonate reservoir. The objective of this study is to use a field scale definitive approach to characterize high permeable layers with limited data control and derisk their presence at pilot scale using multi-disciplinary data sets acquired from EOR pilot wells An appropriate definition is assigned to characterize high permeable layers based on core and log data. High permeability layers thus defined were indexed as facies logs at well locations. The indexed facies logs were correlated with different data sets in connection with from NMR, FMI, mud logs and tracers. Before incorporating surveillance data, a base case facies model was generated out of multiple distribution runs using facies index logs from pilot wells. The geological uncertainty associated with high permeable facies identified at pilot wells was decreased by incorporating previously acquired PNL logs, C/O logs, tracer, ILTs, PLTs and SNL-HPT data. It is found that there is no mud loss or any fractured core detected in pilot wells, thus indicating that there is no interference with faults or fracture networks. Tracer test data show short breakthrough times and are correlatable to identified high permeable intervals in the reservoir. The correlation of TDT log saturations, RFT fluid samples and cooling anomalies behind the casing based on SNL-HPT data matches with interpreted Hi Perm layers. This explains a preferential movement of water into the pilot area resulting from potential connection between Hi Perms and surrounding water injector wells outside the pilot area. Finally, the modelling of identified high permeable layers as imprinted facies established quantification of high permeable layers in terms of areal extension, thickness and connectivity between the pilot wells. This multi-disciplinary approach is useful to de-risk the geological uncertainty associated with high permeable intervals in carbonate reservoirs. Early detection and characterization of high permeable layers within a selected EOR pilot area is beneficial to mitigate preferential sweep and maximize the ultimate oil recovery as a result of chemical EOR depolyment.