NMR is widely used in the petroleum industry to analyze fluids within reservoir rocks, both under laboratory and profiling conditions. In the second case, the analyzes can be carried out under relatively smooth conditions, where the measurements are performed with the logging tool standing still or in slow motion (wireline logging), or under conditions where the tool is moving relative to the rock during drilling (LWD – logging-while-drilling). In order to improve the interpretation of these NMR measurements, we have developed part of our equipment (NMR probes) and signal processing software. In the case of LWD, we developed an experimental simulator, controlling the operational parameters, necessary for a correct interpretation of the observed data. (1)
In the specific case of interpretation of relaxation data, based on Brownstein and Tarr model (2), used to determine the pore size, it is necessary to know the surface relaxivity. For this purpose, we used 3D X-ray Microtomography (microCT), which gives us the pore size. Consequently, we can determine the surface relaxivity. (3)
The need to use a reliable microCT brought us closer to the fourth generation Brazilian Synchrotron Light Laboratory (LNLS), called Sirius. With this infrastructure, we can obtain both 3D images of rocks with high resolution (~100 nm) and detailed physicochemical information on pore surfaces, a fact that considerably increases the quality of interpretation of NMR data, allowing more accurate information to be provided on the quality and productivity of an oil well.
Based on the partnership with Sirius and CENPES/Petrobras collaborators, we decided, due to the quality of the data to be obtained, to also take the opposite route. By knowing the characteristics of the pore surfaces, instead of just analyzing the quality of a reservoir for oil exploration, we decided to also analyze its capacity to store CO2 (geological sequestration of CO2).
This opportunity allowed us to continue contributing to the oil industry, now at the interface between Oil exploration and Geological CO2 storage, something necessary for the sustainability of this industrial sector.
In the presentation of this work, we will partially discuss the constructed NMR instrumentation, as well as the data obtained with this technique and microCT, highlighting their correlations.
References:
(1) E. Lucas-Oliveira, A.G. Marassi, A.G. Araujo-Ferreira, E.L.G. Vidoto, A.D.F. Amorim, W.A. Trevizan, T.J. Bonagamba, Mechanically oscillating sample under magnetic field gradients: MOS-NMR, Journal of Magnetic Resonance Open 12-13 (2022) 100084
(2) K.R. Brownstein, C.E. Tarr, Importance of classical diffusion in NMR studies of water in biological cells, Phys. Rev., 19 (1979), pp. 2446-2453
(3) E. Lucas-Oliveira, A.G. Araujo-Ferreira, W.A. Trevizan, B.C.C. Santos, T.J. Bonagamba, Sandstone surface relaxivity determined by NMR T2 distribution and digital rock simulation for permeability evaluation, Journal of Petroleum Science and Engineering 193 (2020) 107400