A Laboratory Study of Nuclear Magnetic Resonance Relaxation and its Relation to Depositional Texture and Petrophysical Properties — Carbonate Thamama Group, Mubarraz Field, Abu Dhabi

Abstract

We performed laboratory measurements to determine whether NMR logging would improve log evaluation of the Mubarraz Field. The Mubarraz Field is a carbonate field in offshore Abu Dhabi, that produces from the Cretaceous Thamama Group. Existing log evaluation using classical logs has some shortcomings. Some zones that are not highly resistive actually produce water-free oil. This is because Mubarraz samples often have a large amount of microporosity. The microporosity occurs because samples are highly micritized, and grain-sized particles are generally peloidal with internal microporosity. The microporosity holds a large volume of capillary-bound water, which results in low resistivities in zones that still have producible oil in large pores. An additional evaluation problem is that permeability varies widely while porosity remains almost constant. As a result, permeability vs. porosity correlations are less valuable than normal. In laboratory measurements on Mubarraz samples, we found that NMR relaxation measurements can provide:–good estimation of the capillary-bound water volume at an air/water capillary pressure of 25 psi, using a cutoff on NMR T2 relaxation time of 190 ms.–good identification of the grainstones as opposed to the lower-permeability textures (packstone… mudstone) with a T2 threshold of about 225 milliseconds.–estimates of permeability that are significantly better than can be obtained from porosity alone. NMR relaxation measurements contain information about the pore size distribution, and it is this information that permits estimation of production-governing parameters. The estimators are based on parameters that can be obtained from continuous NMR logging. P. 477

Use of NMR logging to obtain estimates of hydraulic conductivity in the High Plains aquifer, Nebraska, USA

“…For an m value of 4, the constant b has been empirically determined through laboratory studies on consolidated sandstone materials to range from 4 to 5 mD m s À2 [Kenyon, 1997;Straley et al, 1997]; in petroleum applications, the standard value is 4 mD m s À2 [Kenyon et al, 1995]. To predict permeability in units of m 2 from T 2ML given in units of seconds, the corresponding standard b value is 3.9 Â 10 À9 m 2 s À2 .…”

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“…Here χ is an empirical factor related to the rock type with typical values of χ = 1.6 mD/(ms) 2 for sandstone (Kenyon et al, ), and χ = 0.1 mD/(ms) 2 for limestone (Kenyon et al, ; Kenyon, ). ϕ i is the porosity for the i th slice, and is the logarithmic mean value of the T 1 distribution obtained from the i th slice.…”

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“…The absorption of shale oil confined in kerogen slit pores was investigated by Yang et al These authors emphasized the significance of acquiring a comprehensive understanding of the interaction mechanisms between multicomponent fluids and organic shales. NMR measurements have been extensively employed in petroleum engineering to characterize various petrophysical properties of organic-rich rocks, including porosity and pore-size distribution, wettability, , capillary pressure, and permeability . However, interpreting NMR measurements can be challenging in porous materials with both a heterogeneous pore structure and a complex combination of hydrocarbon compounds.…”