Nuclear Magnetic Resonance Logs While Drilling (LWD NMR were recently acquired in the Eldfisk Field in the Norwegian North Sea sector. The quality of this data, especially of the T1 log recorded under drilling conditions, meets and even exceeds the level of wireline logs. In addition to the T1 log recorded while drilling the well, some stationary T2 data and a moving T2 logs while wiping, were recorded. The spectral and vertical resolution of the T1 distributions surpass the resolution of the wiped T2 distributions, and are on par with the best wireline T2 distributions recorded at nearby Ekofisk Field. The vertical 2/7 A-29B well cuts through the Ekofisk, Tor, and Hod formations. The T1 distributions exhibit clear and distinct trends in different reservoir sections. For example, the faster component in the bimodal T1 spectra in the Ekofisk formation represents the water volume, and the slower component the remaining hydrocarbon. The T1 distributions are uni-modal in the water-flooded Tor formation, in response to the lower hydrocarbon saturations. In addition to hydrocarbon typing, the NMR logs can greatly reduce the uncertainty in total porosity. Apparent density and NMR porosities differ by as much as 8 p.u. The need for hydrocarbon and invasion corrections is evident from the T1 distributions that indicate a relatively high proportion of water-filled pores; both in the initial state and water-flooded intervals. Resistivity MAD passes also suggest mud-filtrate invasion, resulting in high Sxo values. Accurate porosity readings are obtained with proper accounting for the fluid density and hydrogen index of the fluids in the flushed zone. The results from this well show that While-Drilling T1 logs are viable alternatives to wireline NMR logs, enabling the accurate assessment of porosity and fluid types. Information obtained from these logs improves the confidence in the evaluation of reservoir properties of a complex chalk reservoir.
Porosity and Water Saturation from LWD NMR in a North Sea Chalk Formation
Reppert, Matt, Akkurt, Ridvan, Howard, James, and Ron Bonnie. "Porosity and Water Saturation from LWD NMR in a North Sea Chalk Formation." Paper presented at the SPWLA 46th Annual Logging Symposium, New Orleans, Louisiana, June 2005.
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