Evaluation of glutenite reservoir using nuclear magnetic resonance T2 spectrum of oil-based drilling cuttings

Abstract

Cores and cuttings are the only materials that directly show characteristics of glutenite reservoirs, and most wells have few or no cores. This raises the question of whether cuttings can be used to evaluate glutenite reservoir. In this study, six key issues related to the application of cuttings in evaluating reservoir firstly were analyzed. Then glutenite reservoir of Baikouquan Formation in Jungar Basin was taken as the research object, and experiments of cuttings and cores were carried out. Repeated experiments confirmed the stability of cuttings performance. T2 spectrum of glutenite cuttings after treatment exhibits a single peak with a relatively short T2 time, which indicates pore structure and sorting of rock change due to mechanical effects and gravity. By comparing T2 spectra of cores and artificially crushed debris, it can be found that sandstone cuttings are less affected by mechanical effects, while for glutenite, macropores decrease a lot, mesopores increase, and micropores have few changes. Afterwards, a method of cuttings depth correction is proposed based on comparing the morphology of the spectra corresponding to micropores in T2 spectra of cuttings and nuclear magnetic resonance (NMR) logging. Finally, irreducible water saturation and porosity are calculated and corrected using T2 spectrum of cuttings, and results are in agreement with those obtained from logging data, which confirm the feasibility of evaluation method using cuttings.