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WTGS October 8, 2019 Luncheon Meeting

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Date(s) - 10/08/2019
11:30 am - 1:00 pm

Midland Country Club Upstairs Ballroom


Determining Water Saturation in Permian Basin Intercalated Reservoirs using NMR Log Data

Pedro Romero Rojas

Weatherford Intl





Alternating conventional and unconventional reservoir layers in the Permian Basin challenge the acquisition, processing, and interpretation of water saturation (Sw) using nuclear magnetic resonance (NMR) log data. A new-generation NMR wireline tool addresses these challenges using a specially designed conventional-unconventional activation sequence to enable construction of optimized maps of Longitudinal–Transversal Relaxation times (T1-T2 maps) at regular depth intervals.

T1-T2 maps are used to compute level-by-level Sw based on a multicomponent fluid model with appropriate statistical properties.  Each spot in the T1-T2 space represents a fluid component from which a volume fraction is calculated. Integrating the volume  fractions gives the total porosity.  Because of the diverse relaxation mechanisms in the conventional and unconventional layers, oil  spot positions with T1/T2 values greater than two reflect either viscosity (for bulk relaxation) or pore-size distribution (for surface/volume relaxation). Water tends to be close to the 1:1 T1/T2 diagonal line with T1/T2 values less than two. Low permeability means that mud-filtrate invasion does not appear on the T1-T2 maps.

NMR porosity matched expected values based on core and density-neutron log analysis.  NMR  fluid-typing-derived Sw―including  clay bound water (CBW), capillary bound water (BVI), and free water―matched values from tested intervals. Results are in good agreement with reference values from production and core data within an uncertainty of one standard deviation. The resolution of    fluid components in intervals where the components overlap can be enhanced by changes in the inversion parameters and map-grid dimensions.

This methodology for conventional-unconventional data acquisition followed by a multimodel approach for fluid typing will be applied   to other wells. It enables a more accurate assessment of water saturation, especially when intercalated layers of conventional and unconventional reservoirs are present.


  •      The Challenge
  •      Proposed Solution
  • Applied NMR Logging Technology
  • NMR Data Preparation
  • Methodology for Calculating Water Saturation (SW)
  • Results
  • Summary
  • Discussion

Pedro A. Romero Rojas is a Principal Research Geoscientist for NMR and Data Science at Weatherford International since early 2017. His prior professional experience had been as Engineering and Petrophysics Chief at Halliburton Technology Center in Rio de Janeiro Brazil and Deep-Water Reservoir Group. He also worked several years as Research Scientist and Manager at Baker Hughes Inc. in Houston, Buenos Aires and Rio de Janeiro and at Petróleos de Venezuela (PDVSA-Intevep), where he started his R&D career in NMR-Petrophysics in 1996. He received his Doctor of Engineering in Electrical Engineering (1994) and Diploma in Experimental Physics (1986) from the University of Siegen, Germany.

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