SINGLE WELL TO FIELD SCALE SECONDARY POROSITY CHARACTERIZATION IN CARBONATE RESERVOIR OF TUBAN FORMATION

摘要

Unlike sandstone with their well characterized correlation of porosity and other reservoir properties, the heterogeneous pore system of carbonate rocks disobeys routine petrophysical analysis. Secondary porosity has great impact on fluid flow and recovery efficiency in reservoir. The carbonates of Tuban formation in the Sukowati Field has produced oil and gas since 2004. There are 2 carbonates build up identified, the Northern Area build-up and Southern Carbonate build up, which shows small difference in total porosity. However, these 2 carbonates build up show different productivity rate, therefore it is important to understand porosity distribution and to characterize the porosity heterogeneity of the carbonate reservoir for better development plan. To overcome the great complexity in characterizing secondary porosity in carbonate formation, an integrated workflow was proposed. This approach composed of quantitative and textural analysis based on borehole image to define secondary porosity type and quantify full porosity distribution. This is, then, combined with seismic inversion result to control the lateral distribution of the secondary porosity. The single well analysis workflow provides high resolution of quantitative secondary porosity analysis based on its type. This analysis shows most of the productive wells which contained high amount of interconnected vugs and fracture porosity type. In contrast, most of the less productive wells have dominant isolated vugs and cemented intervals. Combination of seismic inversion result such as acoustic impedance with single well analysis result provides lateral distribution of secondary porosity based on its type in field scale. The secondary porosity distribution model shows that most of interconnected vugs and fracture porosities developed in the carbonate build up at northern part of the field and less developed at the southern part of the field. This is aligned with the productivity data of the wells in the field. This workflow greatly improved the porosity characterization and reduced uncertainty during production planning and well placement.