Abstract
Abstract Defining the depth of gas-oil contact (GOC) is essential for the volumetric and detailed petrophysical calculations. Variations in the entropy of pore fluids can serve as a diagnostic criterion for determining the interface between oil and gas phases. Inherently endowed with a high resolution of pore fluids, nuclear magnetic resonance (NMR) data is a highly promising candidate for extracting the entropy of pore fluids. As a paramount technique in extracting the hidden and significant temporal features of the original data, wavelet analysis can viably reveal the information of pore fluids encoded in the NMR log data and express it in terms of entropy. In this research, the discrete wavelet transform (DWT) was first employed to derive hydrocarbon relaxation time ( T H ) from the NMR echo signals in the reservoirs under study. The variations of T H reflected on the various decomposition resolution levels were then used to calculate the entropy of hydrocarbon fluids ( E H ) at each depth. Finally, by scrutinizing the entropy variations, the gas-oil contact in each reservoir was accurately determined. The depth of the gas-oil contact ascertained from the wavelet-based approach corresponds precisely to that determined from the conventional method of the neutron-density cross-plot.
Published Version
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