Estimation of Variable Fluids-Mixture Density With 4D NMR Logging (2007)

Estimation of Variable Fluids-Mixture Density With 4D NMR Logging Chanh Cao Minh; Chanh Cao Minh Schlumberger Search for other works by this author on: This Site Google Scholar Emmanuel Caroli; Emmanuel Caroli Total Search for other works by this author on: This Site Google Scholar Padmanabhan Sundararaman Padmanabhan Sundararaman Chevron Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Anaheim, California, U.S.A., November 2007. Paper Number: SPE-109051-MS https://doi.org/10.2118/109051-MS Published: November 11 2007 Connected Content Related to: Estimation of Variable Fluid-Mixture Density With 4D-NMR Logging Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Minh, Chanh Cao, Caroli, Emmanuel, and Padmanabhan Sundararaman. "Estimation of Variable Fluids-Mixture Density With 4D NMR Logging." Paper presented at the SPE Annual Technical Conference and Exhibition, Anaheim, California, U.S.A., November 2007. doi: https://doi.org/10.2118/109051-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search Abstract Whereas matrix density is known from core analysis or spectroscopy logging, so far no technique is available to estimate the apparent fluid density that the density log measures. In wells drilled with OBM, the near-wellbore fluids composition and distribution can be very complex. Yet, the current practice to compute density porosity is to use an ad hoc constant fluid density. This could lead to erroneous estimation of porosity. For example, in a 30 pu sandstone drilled with OBM, every 0.1 g/cm3 error in fluid density leads to 1.5 pu error in porosity.Numerous studies of near-wellbore fluids with 3D NMR (T1, T2, D) maps from NMR logging tools have shown a very complex fluids mixture that can include water, oil, OBM, and condensate/gas. However, the map acquired at a single depth of investigation (DOI) might not represent the fluids mixture that the density tool measures.The advent of radial fluid profiling with advanced magnetic resonance tools provides the needed fourth dimension—radial information that can be inverted jointly with conventional 3D NMR to unravel both fluids mixture and radial distribution. Because the near-wellbore NMR region closely matches the density region in both radial and axial directions, the two sets of data form "perfect" consonant volumes. Continuous 4D NMR maps are thus ideal to estimate the variable mixed fluids density. This value can be expressed as the double integration of all individual fluids detected by NMR weighted by the geometrical radial response function of the density log. The inner integration estimates the mixed fluids density. The outer integration computes it at 95% radial response of the density log.Examples are shown in which variable fluid density confirms subtle fluid changes recorded by density-neutron logs in sandstone formations offshore West Africa. These sands have variations in grain size and shaliness that control permeability and therefore the OBM invasion. Another example shows large porosity deficits when the contrasting fluids density is large, such as gas invaded by OBM. In all cases, density porosity computed with the variable fluid density agrees with local field knowledge and other methods. A side benefit is the reconciliation of NMR and density porosity discrepancy, because density porosity is often the reference to which NMR logs are judged. Keywords: log analysis, fluid mixture density, black curve, Neutron log, estimation, Upstream Oil & Gas, input fluid density, Symposium Transaction, variable fluid density, well logging Subjects: Formation Evaluation & Management, Open hole/cased hole log analysis Copyright 2007, Society of Petroleum Engineers You can access this article if you purchase or spend a download.