Integration of Core, Log and Well Test Permeabilities in Deepwater Laminated Sand-Shale Reservoir
Atul Jamkhindikar, Bhawesh C. Jha, Samir Dhar, and Satyajit Taware
Reliance Industries Ltd., Navi Mumbai, India
Reservoir characterization requires accurate estimates of permeability at reservoir scale. Permeability data can be obtained from three sources- core measurements, log-derived permeability and well test data. However, the volume scales for these measurements are different by several orders of magnitude. In a heterogeneous, laminated sand-shale sequence, core measurements represent sandstone permeability, log measurements are influenced by average response to the sand-shale laminae, while well test permeability is influenced by rock fabric and reservoir connectivity. This paper describes the methodology to calibrate permeability measurements across the above scales and derive reservoir scale permeability as a continuous log in the well.
The workflow consists of estimation of laminated sand fraction, sand effective porosity and water saturation using Thomas-Stieber model incorporating resistivity anisotropy concept, and calibration of the estimated sand layer permeability to core measurements. Log-scale permeability is calculated using the layered sand-shale model and calibrated to well test permeability using pressure transient analysis.
This method was applied to a deep-water gas-bearing sandstone reservoir where laminated sand-shale sequences constitute a significant volume of the reservoir. The log-scale permeability was calibrated to well tests, one representing thick sands and another laminated sands. Good match was observed between log-scale permeability and well test permeability for thick sands whereas for laminated sands a significant difference was observed which was attributed to connectivity of sand laminae at reservoir scale. A non-linear correction factor, dependent on laminated shale fraction was derived to calibrate the log-scale permeability to the reservoir scale.
The methodology leads to upscaling of permeability from core to log to reservoir scale in a systematic manner which helps to achieve realistic permeability distribution for reservoir simulation studies.
Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery