Improved characterization of transition zones in carbonate reservoir by modern digital imaging technique

Transition zone (TZ) containing a large amount of oil plays a key role in a carbonate reservoir. Its characterization is challenging because it is difficult to define top and thickness of the transition zone and it may contain many kinds of rock types differently affecting the fluid flow behavior. Routine core analysis (RCA) and special core analysis (SCAL) can be used to study for characterizaiton and modeling of TZs, but these data can rarely be used to obtain the details of the pore structure governing the rock properties. In recent years, the digital imaging technique has made great progress, because the rock microstructures can be directly imaged by using modern digital imaging technique such as thin sections (TS), scanning electron microscope (SEM) images and X-Ray computed tomography (XCT) scans. This paper focuses on the application of digital imaging technique for characterization of TZs in carbonate reservoirs located within the Middle East region. The experimental data and digital imaging data are used to study the rock samples of TZ. The results show that: 1) the rock properties of TZ samples can be accurately predicted by using digital imaging technique; 2) the petrography and diagenesis of TZ are well studied; 3) the carbonate rocks are qualitatively and quantitatively classified into three types: matrix, fractured and vuggy; 4) digital imaging technique, generally, proves to be a powerful tool for characterization of TZs in carbonate reservoirs.