Quantitative Remaining Oil Interpretation Using Magnetic Resonance: From the Laboratory to the Pilot

Abstract

Laboratory and single well pilot nuclear magnetic resonance (NMR) logging results are obtained for an enhanced oil recovery (EOR) project using a common physics of measurement at both scales. Screening for chemical EOR efficacy usually begins in the laboratory before moving to single or multiple well field pilots. Laboratory experiments were conducted on a low-field bench-top NMR magnet with fluid injection protocols that matched the log-inject-log concept of the single-well in situ EOR evaluation (Arora et al. 2010). In situ measurements of the oil and brine saturations during the flood, by "diffusion-editing" protocols and by relaxation measurements alone, are shown to be in quantitative agreement with gravimetric assays of recovered oil. Spatially resolved T 2 analysis (the laboratory equivalent of a standard NMR well log) revealed non-uniform oil saturation during the EOR process in short core plugs. The final remaining oil distribution is confirmed by a reservoir simulation in a geometry identical to the NMR-compatible core holder. In a region of the core-plug not influenced by end effects, complete recovery of the oil was observed, consistent with the the single-well in situ EOR evaluation. The quantitative estimates of remaining oil, using a tool-equivalent NMR protocol, demonstrate the potential for NMR logging of remaining oil in monitoring wells completed with NMR-transparent casing.

Mobile and Compact NMR

“…The low fields of compact tomographs and dedicated rock core analyzers approximate the stray fields of mobile well-logging tools. NMR imaging is particularly valuable in visualizing the flooding of cores by displacing one fluid with another [180][181][182][183][184][185][186] and to quantify local fluid concentrations and matrix properties [187]. Dedicated overburden equipment has been developed to study samples under the elevated pressure and temperature conditions prevalent at the recovery depths of oil wells [138,188].…”

Application Limits and Influencing Factors in Characterization of Rock Cores Using the Phase-Encoded T2-y Method in Low-Field NMR

“…The application of the SE-SPI method in oil recovery has been reported in several publications. 28,29 Nonetheless, it is evident that the observed signals and their processed results are subject to various influencing factors, including machine performance, acquisition model, magnetic field properties, and the experimental environment. For instance, the homogeneity of the magnetic field is frequently compromised by several factors.…”

Visual Laminations Combined with Nuclear Magnetic Resonance to Study the Micro-Unrecovered Oil Distribution and Displacement Behavior of Chemical Flooding in a Complex Conglomerate

“…The fluid types in the rock are determined from NMR signals; and then the derived fluid volume is estimated from a triaxial induction tool including one dimensional (1D) profile, two dimensional (2D) slice, and three dimensional data. For this reason, NMR is considered as being one of the most accurate methods for determining the amount of unrecovered oil. ,, NMR can also distinguish between multiple fluid phases present in core plugs. However, the fluids may not be distinguished if the rock contains paramagnetic substances, which will interfere with the magnetic responses of the fluids.…”

“…Screening for chemical-EOR efficacy usually begins at the laboratory scale before moving to single or multiple well field pilots. 12 The quantitative characterization of the physical properties, pore structures, original oil saturation distribution, and unrecovered oil distribution inside a core is a significant precondition for the proper chemical-EOR design. At the laboratory scale, most previous works have used cylindrical cores to study the oil displacement process.…”

“…For this reason, NMR is considered as being one of the most accurate methods for determining the amount of unrecovered oil. 8,12,15 NMR can also distinguish between multiple fluid phases present in core plugs. However, the fluids may not be distinguished if the rock contains paramagnetic substances, which will interfere with the magnetic responses of the fluids.…”