Methods of decoupling diffusion effects from relaxation times to determine properties of porous media containing fluids

Abstract

Novel pulse sequences are used to probe the properties of porous media, such as are found in subterranean formations and core samples. This use allows diffusion effects to be uncoupled from the overall T relaxation time of the sample. Properties such as internal field gradient and distribution of diffusion coefficients may be determined. A series of pulse sequences are applied to the media to be evaluated. The series of pulse sequences include first and second windows. The first windows include pulse sequences have varying characteristics, such as increasing echo spacing, while the second windows preferably utilize similar pulse sequences which have very small echo spacing. Apparent internal field gradient distribution and apparent diffusion coefficient may be determined as a function of T relaxation time. These properties are readily visualized in a two-dimensional map with a first axis being the apparent internal field gradient or alternatively the diffusion coefficient of pore fluids, a second axis being the T relaxation times, and the vertical amplitudes being proportional to the proton population. Other properties which may be determined from use of this method include porosity, pore size distribution, oil and water saturation, oil viscosity, oil wettability, and permeability. Also, a method for determining and plotting a T -MAS D spectrum is provided where T relaxation time and chemical shift are plotted on x,y axes while intensity of proton population is displayed along a third axis.