A Novel Method for the Estimation of the Recoverable Reserves in oil Reservoirs Using Nuclear Magnetic Resonance Relaxometry
Mirotchnik, K., Kantzas, A., Allsopp, K., Berman, L., Aikman, M. and Waymouth R.
CIM Paper 98-40, presented at 49th Annual Meeting of The Petroleum Society, held in Calgary, Alberta, June 8-10, 1998.
Evaluation of hydrocarbon reserves and the design of the optimal recovery process are usually based on the assumption that the physico-chemical properties of the hydrocarbons (including viscosity) are practically constant within the limits of the reservoir or that they monotonically change with depth. Examples include the composition of the oil deposits and the in-situ viscosity variability. Sometimes it is also assumed that viscosity can vary laterally, predominantly within the limits of deposits with tectonic dislocation.
The properties of hydrocarbons, as determined by a laboratory study of the reservoir fluid, may not be representative of in-situ oil properties. Such discrepancies may be due to fluid segregation, or chromatographic separation of hydrocarbon components in-situ. This distinction usually is not taken into account during the evaluation of the reserve base or the optimal recovery process.
A method for the direct determination of the physico-chemical properties of hydrocarbons in porous media using Nuclear Magnetic Resonance (NMR) was developed. This method provides the possibility of estimating the variability of hydrocarbon properties at the pore level (i.e., in pores with different sizes). Our research has shown that within the reservoir, residual oil is characterized by a wide range of physico-chemical properties which are dependent on the properties of rocks and the properties of hydrocarbons.
Using the above approach, a study of the fluids produced from a core containing oil that is rich in polar components was performed. It was found that aliquots of the oil, sampled at different times during the production period had markedly different NMR properties.
The developed method can enable a more accurate evaluation of the recoverable hydrocarbon reserves and a correction of the existing methods of the recovery efficiency of oil and productivity of oil-bearing formations (taking into account the properties of the residual fluids and the surface wettability in the different pores within the specific reservoir). It is anticipated that this method can be extended to generate predictive methods for well stimulation programs.