How Much Tar is too Much? Novel Methods for Tar Identification and Quantification for Real-Time Reservoir Assessment
Peter J. Jones1*, Peter M. Neumann1, Henry I. Halpern1, Edward A. Clerke1, Michael C. Dix2, Rachad Zeriek2, Isidore J. Bellaci1, Nasser A. Al-Khaldi1, Ridvan Akkurt1, Mohammed N. Khamis1, Said S. Malki1, Salman M. Al-Qathami1, Mohammed A. Al-Amoudi1, and Khalid R. Al-Malki1
New techniques for assessing reservoir impairment by tar have progressed using analytical, computational and dynamic methods. A particular application of Saudi Aramco’s Pyrolytic Oil-Productivity Index (POPI) technology has been the determination of tar volumes for assessing permeability impairment and optimizing injection and production well placement. Through the integration of real-time POPI tar volumes with formation pressure while drilling (FPWD) and LWD data, unimpaired and tar-impaired reservoir can be clearly differentiated. Combined POPI, FPWD, and modeled results suggest that the critical range of tar saturation is from 10% to 25% of the available pore space. If pore space filled with tar is less than 10%, reservoir performance is not significantly impacted. These tar volumes are consistent with new permeability occlusion calculations for the Arab D pore systems performed by E. Clerke. Traditional well-log tar-detection techniques cannot resolve these low tar volumes. Pyrolytic characterization methods provide direct assessment of residual hydrocarbons present in core or cuttings samples. POPI instrumentation and methods can accurately quantify tar volumes over a wide range of concentrations to within 0.5% of whole rock volume and provide the data in real time. Once tar saturations reach approximately 15% of pore volume, significant signs of reservoir degradation are often seen in FPWD data. At 25% or greater tar saturation, reservoirs often show no fluid mobility. Thus, tar saturations reach critical levels while the non-tar component is 75% to 90% of the available pore space. Cuttings-based POPI tar volume measurements are an important new data stream for this problem.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain