Limits of 2D NMR Interpretation Techniques to Quantify Pore Size, Wettability, and Fluid Type: A Numerical Sensitivity Study

Abstract

Two-dimensional (2D) NMR techniques have been proposed as efficient methods to infer a variety of petrophysical parameters, including mixed fluid saturation, in-situ oil viscosity, wettability, and pore structure. However, no study has been presented to quantify the petrophysical limitations of such methods. We address this problem by introducing a pore-scale framework to accurately simulate suites of NMR measurements acquired in complex rock/ fluid models. The general pore-scale framework considered in this paper is based on NMR random walks for multiphase fluid diffusion and relaxations, combined with Kovscek's pore-scale model for two-phase fluid saturation and wettability alteration. We use standard 2D NMR methods to interpret synthetic data sets for diverse petrophysical configurations, including two-phase saturations with different oil grades, mixed wettability, or carbonate pore heterogeneity.Results from our study indicate that for both water-wet and mixed-wet rocks, T 2 (transverse relaxation)/D (diffusion) maps are reliable for fluid typing without the need for independently determined cutoffs. However, significant uncertainty exists in the estimation of fluid type, wettability, and pore structure with 2D NMR methods in cases of mixed-wettability states. Only light oil wettability can be reliably detected with 2D NMR interpretation methods. Diffusion coupling in carbonate rocks introduces additional problems that cannot be circumvented with current 2D NMR techniques.In this equation, ␥ is the proton gyromagnetic ratio, G is the average magnitude of the background magnetic field gradient over the spatial zone of investigation, and TE the interecho time or the interval between two radio-frequency pulses.Limits of the Relaxation Model. The model described previously assumes that the protons relax within one pore independently from the surrounding pores. When the bulk and diffusion terms in the

A rapid measurement of : The DECPMG sequence

“…Although some promising methods have been proposed recently to relate NMR relaxation parameters and wettability [43][44][45][46], mixed wettability surfaces are still difficult to characterise [47]. The T 1 =T 2 ratio can be used to estimate the average surface residency time of liquid molecules in a pore.…”

Random-walk technique for simulating NMR measurements and 2D NMR maps of porous media with relaxing and permeable boundaries

“…Fluid phases are distributed in the pore space of a disordered grain pack (Fig. 10) according to geometrical models in agreement with thermodynamic capillary equilibrium [32] or with more complex principles of drainage, imbibition, and electrical properties [33]. In these models, as exemplified in Fig.…”

“…For instance, Refs. [32,33] study the reliability of D/T 2 2D NMR interpretation to accurately assess hydrocarbon content and rock properties under the assumption of specific fluid displacement mechanisms within the pore space. Fig.…”

“…The diagonal line in the two panels represents the D/T 2 correlation characterizing hydrocarbons in the conditions assumed for the simulations (after Ref. [32]). …”

A Review on Nuclear Magnetic Resonance Logging: Simulation Schemes

“…(Hidajat et al, 2003;Ramakrishnan et al, 1999;Talabi, 2008;Vivek and Hirasaki, 2007). 그러나 최근 들어 외부 자기장구배뿐만 아니라 더불어 내부 자기장구배까 지 고려한 시뮬레이션 연구가 수행되되고 있다 (Arns et al, 2011;Mohnke et al, 2011;Toumelin, 2002;Toumelin et al, 2004aToumelin et al, , b, 2006Toumelin et al, , 2007 …”