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The presence of tar or heavy oil that does not flow using conventional production technologies brings numerous challenges during field developments. Tar, acting as a permeability barrier, would often break flow or pressure communication from the aquifer to the oil zone. This results in inadequate pressure support, which is necessary for sustaining production levels and maximizing oil recovery. One of the key issues in developing a field with known tar mat accumulation is to optimally place injectors away from the tar. The problem becomes more complicated when the exact location of a tar mat is uncertain either laterally or vertically. Tar mats usually are neither flat nor uniform in thickness across a field. These uncertainties pose a challenge in planning wells especially water injectors. Detection of tar is critical for reservoir characterization, reserves calculation and well placement. Direct and indirect techniques are employed to detect tar including core analysis, well testing, wireline logging and Pyrolitic Oil Productivity Index (POPI). These measurements are good indicators of tar; however, the challenge is to identify the tar while drilling the well. Early detection requires the deployment of logging while drilling (LWD) technologies for real-time interpretation of data. In order to accurately identify tar in reservoir sections in real-time, integrating conventional LWD measurements with new technologies such as the slim hole Nuclear Magnetic Resonance (NMR) and the formation pressure measurements while drilling (FPWD) is necessary. This will allow for timely adjustment to the well path and prevent costly remedial actions This paper discusses successful real-time application of slim-hole NMR and FPWD technologies to detect tar and optimally place water injectors. This is demonstrated with two case studies involving extended reach power water injectors. |
