Laboratory NMR Relaxation Measurements for the Acquisition of Calibration Data for NMR Logging Tools

Abstract

Abstract This paper presents results of laboratory studies of nuclear magnetic resonance (NMR) relaxometry for NMR log calibration aimed at enhancing petrophysical measurements in oil wells. Relationships between NMR longitudinal relaxation parameters and the Hydraulic Units (HU) concept for predicting petrophysical properties from wireline logs have been established previously. However, modern NMR logging tools measure the transverse relaxation parameters. Hence in this paper, we show that measurements of the transverse component of the NMR signal can provide the same information as the longitudinal. Laboratory NMR transverse relaxation characteristics of water in rock samples were measured with CoreSpec-1000. The NMR data were used to validate models for predicting permeability and producible fluid in clastic rocks. The predictive model for permeability includes the rock surface area to grain volume (Sgv) the tortuosity of the flow paths (), the shape factor (Fs), the transverse relaxation time (T2), relaxivity (), and porosity (). The models were used to develop the required NMR log calibration. The transverse relaxation parameters were used with core analysis data of permeability, porosity, and mercury injection capillary pressures to sort the rock samples into hydraulic (flow) units. Protocol for the use of laboratory NMR core spectrometry and core analysis data for NMR log calibration is presented. Relationships between T1 and T2, and between flow zone indicators (FZI) and relaxivity () were established. It was observed that T2 cut-off (T2c) is related to T1 cut-off (T1c) in the same way that T2 is related to T1. Relaxation time cutoffs are used for determining producible fluid (free fluid porosity or free fluid index, FFI). The results show that reliable prediction of permeability and producible fluid from NMR logging tools requires calibration of the tools with laboratory NMR measurements on representative rock samples. We demonstrate the use of T2c for determining FFI from T2 distributions. The methodology for identification and characterization of HU within geological facies based on NMR T2 was validated. Introduction The (HU) concept has successfully been integrated with laboratory core NMR measurements for evaluating petrophysical properties from wireline logs (Ohen et al.). The HU and NMR techniques were linked through the FZI and NMR relaxation parameters, because both the FZI and the relaxation parameters are related to the rock surface phenomenon which controls the microscopic attributes of the rock. Ohen et al. measured the longitudinal (spin-lattice) relaxation time (T1) on a number of reservoir rock samples at a Larmor frequency of 1 MHz with the CoreSpec-1000. P. 329