Low-Field Nuclear Magnetic Resonance Methodology for Analysis of Drill Cuttings from Unconventional Tight Reservoirs

Abstract

A nuclear magnetic resonance (NMR)-based method was developed to quickly and accurately determine porosities and densities of tight reservoir rocks from drill cuttings. The method combines low-field NMR and two mass measurements, one in the air and one in a fluid, to determine rock porosity, grain density, and bulk density. The method provides an inexpensive approach to deliver continuous data for evaluation of a drilled well and is especially useful for unconventional reservoirs for evaluating both vertical and horizontal sections of a well.

Improved Methods for Determination of Petrophysical Properties of Unconventional Tight Rocks Using Particulate Samples

“…Figure 4 plots the comparison of bulk density results obtained from the workflow of the current study with vendor GRI bulk density results. As previously reported, 13 the bulk density results are underestimated when compared to GRI results for samples that were saturated with sonication only. However, the results show that the measured bulk density for samples saturated with pressure is in good agreement with vendor-reported GRI results.…”

“…In addition, we did not have to worry about deformation of the drill cuttings from the PDC drilling bit that generates additional porosity. 13 As a result, we can focus solely on the effect of the saturation mechanism on the measured results.…”

“…The samples were crushed and sieved to a size between 0.5 and 3 mm to mimic the size of drill cuttings. First, an approximately 20 g portion of each sample was dried at 110 °C for 96 h. The samples were then saturated with diesel using the sonication method, as described in Althaus et al 13 for 24 h. NMR was then acquired on the saturated samples, followed by mass measurement of the samples performed in air and submerged in diesel. Next, we saturated the samples with diesel using a pressure cell.…”

“…The results from NMR and mass measurement were then used to determine the bulk density, matrix density, and porosity. A detailed description of the method is in ref ( 13 ), specifically.…”

“…In a recent study, we used a combination of NMR measurement techniques and Archimedes principle to obtain petrophysical parameters, including porosity, bulk density, and matrix density, of irregularly shaped drill cuttings. In the same paper, we used sonication to remove the drilling mud and other contaminants from the drill cutting surface 13 and as a method for saturating the samples. Although this method for sample saturation gives reliable estimates of petrophysical properties for many samples, there was an underestimation of bulk density in some samples, potentially due to incomplete saturation of the drill cuttings.…”