Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0906.5327

Effect of inhomogeneous surface relaxivity, pore geometry and internal field gradient on NMR logging:exact and perturbative theories and numerical investigations

Seungoh Ryu
View original source ↗Read source document ↗Export metadata ↓

Abstract

Nuclear magnetic resonance is widely used as a probe of pore geometry and fluid composition in well logging. One of the critical assumptions often made is that the diffusion of fluid molecules is sufficiently fast to warrant the condition for direct mapping between the surface-enhanced relaxation rate and the pore geometry. In pores satisfying such a condition, but having a significant spatial variation of surface relaxivity (rho), one can show that the one-to-one mapping may break down. The degree to which the NMR logging interpretation is affected has not been systematically studied until now. In this work, we theoretically investigate the interplay between the pore geometry, internal field and the inhomogeneous surface relaxivity. We develop a perturbative framework and compare its results with exact solutions obtained for a class of rho textures in a pore with simple geometry. Its effect is quantified for a wide range of diffusivity and/or rho strength. The result allows us to set the bounds for the change in the final slope of the relaxation curve and may serve as a useful guide for logging applications in real rocks with a wide range of pore sizes and fluid diffusivity. We further employ large scale numerical simulations to perform virtual experiments on more complex situations. Internal field and its gradient distributions were obtained and analyzed for up to 1.5^3 cm^3 based on tomograms of carbonate rocks. We find that the texture of rho based on the internal field gradient induces a small, but observable shift, compared to a random noise generated texture for which no shift is observed.

Explore related subjects

cond-mat.other

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Seungoh Ryu. 2009-06-29. Effect of inhomogeneous surface relaxivity, pore geometry and internal field gradient on NMR logging:exact and perturbative theories and numerical investigations. https://arxiv.org/abs/0906.5327

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Spin-Axis Dynamic Locking

The all-electrical realization of highly spin-polarized currents and their efficient conversion into pure spin currents remains a fundamental challenge in spintronics. Here, we report a spin-axis dynamic locking (SADL) effect in altermagnets that pins the high and dynamically robust spin polarization to the crystalline axes: an in-plane electric field along one principal axis drives a highly spin-up-polarized current, whereas along the orthogonal axis, it generates a symmetry-enforced, equal-magnitude spin-down current. Consequently, applying an electric field diagonally yields a transverse pure spin current, reaching 100% charge-to-spin conversion in the ideal limit. Mechanistically, SADL originates from a spin-split tent-state band structure whose Lifshitz transitions delimit an open-Fermi-line regime. The momentum-separated Fermi lines carry orthogonal nonzero winding vectors, producing a pronounced velocity contrast while suppressing ordinary backscattering to dynamically stabilize the axial spin selectivity. High-throughput first-principles screening confirms SADL in broad materials. Notably, monolayer Cr2WSe4 and synthesized bulk (BaF)2Mn2Se2O exhibit efficiencies close to the ideal limit, paving the way for ultra-low-power, reconfigurable spintronic devices where the spin states are governed solely by electric field orientation.

cond-mat.other↗
arXiv2026

Antisymmetric spontaneous resistivity anisotropy due to hard-axis collapse in polycrystalline Co thin films

We investigate magnetoresistance phenomena associated with the magnetization hard-axis collapse in polycrystalline Co thin films. Transport measurements reveal that, for specific orientations of the applied magnetic field, the system exhibits distinct remanent resistance levels in both the in-plane longitudinal and transverse voltage responses. In particular, the planar Hall resistance shows multiple stable and reproducible levels at room temperature, enabling the identification of at least three remanent states that can be distinguished and used for information storage. These resistance levels originate from non-uniform magnetic configurations stabilized after the application and removal of the external magnetic field in the hard-axis region. Since this phenomenon remains largely unexplored, we present an incipient study addressing its potential implications from an applied-physics perspective. The observation of such behavior in polycrystalline Co thin films grown on Si substrates suggests a simple and low-cost platform for spintronic memory and sensing devices based on the remanent planar Hall effect.

cond-mat.other↗
arXiv2026

Exact Phase-Space Rotation in the Trapped Quantum Calogero Model

We develop a microscopic phase-space description of the quantum Calogero model in the presence of an external harmonic confining potential. Building on the quantum Lax-pair structure, we construct a Hermitian Wigner operator whose expectation value obeys the exact phase-space evolution equation d_t rho + lambda d_x rho - Omega^2 x d_lambda rho = 0 for arbitrary initial states and to all orders in the interaction strength. The resulting dynamics is a rigid rotation in phase space with period 2 pi/Omega, providing a microscopic realization of the isochronous dynamics of the trapped Calogero model. We further show that the moments of the phase-space density form rotating multiplets rather than independent conserved quantities. In particular, within the quadratic sector, the unique conserved combination is proportional to the trapped Hamiltonian, providing a nontrivial consistency check of the construction. In the limit Omega -> 0, the equation reduces to the exact free-streaming equation of the untrapped model.

cond-mat.other↗