Exploration and Production Technologies

Fluid-Rock Characterization for NMR Well Logging and Special Core Analysis

DE-FC26-04NT15515

Project Goal
The objective of this project is to develop the techniques and interpretation methods to determine the maximum information about fluid and rock properties and interactions from in-situ measurements by nuclear magnetic resonance (NMR) well logging and fluid sampling and from special core analysis of formation material. The approach to this objective is twofold: 1) development of NMR techniques and interpretations for in-situ measurement of these properties by NMR well logging and 2) quantification of pore structure and wettability at the microscopic level to develop forward models for interpretation of multiphase fluid flow and NMR response.

Performers
Rice University, Houston, TX
University of Houston, Houston, TX

Results
A method was developed to interpret the irreducible water saturation in systems with diffusional coupling between microporosity and macroporosity. This was presented at the SPWLA Annual Meeting in June 2005 and SCA 2006 annual meeting. This presentation was awarded the third best presentation at the SPWLA 2005 Annual Meeting. Graduate student Mark Flaum was awarded the SPE Cedric Ferguson Medal for his contribution to the SPE paper “Wettability, Saturation, and Viscosity from NMR Measurements” that he coauthored with R. Freedman, N. Heaton, C. Flaum, G. Hirasaki, and M. Hurlimann. “Effects of OBM Invasion on Irreducible Water Saturation: Mechanisms and Modifications of NMR Interpretation” was presented at the 2004 SPE annual technical conference and exhibition.

A method has been developed to collect high-resolution images of rock thin sections. Pore structure and transport properties are being calculated from these images and being measured experimentally. These results were presented at the 2006 Gordon Conference on Flow & Transport in Permeable Media. Measurement of bitumen relaxation time, hydrogen index, and saturation was presented at the Shell Science Symposium in 2006. The poster, “Paramagnetic Relaxation in Sandstones: Distinguishing T1 and T2 Dependence on Surface Relaxation, Internal Gradients and Dependence on Echo Spacing,” was presented at the 2007 SPWLA annual meeting.

Benefits
The introduction of commercial NMR well logging in the early 1990s was a great contribution to formation evaluation. Initially, it was thought that the interpretation of the NMR well logs required different parameters, depending only on whether the formation was sandstone or carbonate and the hydrocarbon was oil or gas. Since then, many improvements have been made to the logging tools and the interpretation methods. The project researchers have participated in several of the improvements. The proposed research seeks to identify reservoir conditions where exceptional interpretation is required and to develop the recommended interpretation method.

Low-field NMR spectroscopy has become a common instrument in core analysis by service companies and research laboratories. Initially, the laboratory measurements were in support of NMR well logging by providing a core-to-log calibration. Recent advances in NMR technology have offered the possibility of determining information about pore structure and wettability that cannot be achieved by other means.


Modern NMR logging tool.

Background
This research program was initially funded by DE-AC26-99BC15201 in 1999 as Fluid-Rock Characterization and Interactions in NMR Well Logging. The most significant finding of this project was the recognition of the gas/oil ratio as a parameter in live oil relaxation time. Also, significant contributions were made in the recognition of the role of wettability and internal field gradients on relaxation time and that natural gas components ethane and propane have much longer relaxation times compared with methane. A correlation was developed between single phase NMR response and permeability for carbonate cores.

Summary
Project researchers determined the:

  • Diffusional coupling of microporosity and macroporosity. The degree of independence or coupling of the relaxation time of micropores and macropores was correlated by a dimensionless coupling parameter. This parameter is the ratio of relaxation and diffusion rates in a two-dimensional system. A method to estimate the irreducible water saturation, or BVI, was presented. It is the fundamental mechanism behind T1/T2 and echo spacing dependence.
  • Effect of wettability alteration by oil-based muds on estimation of BVI. The surfactants in oil-based drilling fluids can alter wettability and thereby increase the relaxation time of bound water.
  • Method to collect high-resolution images of rock thin sections. Pore structure and transport properties are being calculated from these images and being measured experimentally.
  • Length scales responsible for NMR response to internal field gradients. The echo spacing dependence of measured T2 has been recognized due to diffusion in inhomogeneous magnetic field due to the tool gradient and internal field gradient. However, we show that the ratio of T2/T1 (in the absence of manganese) may be due to internal gradients with a length scale too short to be affected by the echo spacing. Nanometer-size paramagnetic particles contribute to T2/T1 but if they are random, they will not have an echo spacing dependence. However, if the particles coat a sand grain with dimensions on the order of microns, echo spacing dependence will be observed. These observations are explained by theoretical expressions and numerical simulations that divide the NMR response into free-diffusion, motional averaging, and localization.
  • Internal field gradient with pore-lining paramagnetic chlorite flakes. Numerical simulations are being conducted to investigate the response of chlorite-lined sandstones.
  • NMR response of bitumen. NMR well logging or bitumen deposits is problematic because a portion of the bitumen T2 distribution may be shorter than the echo spacing and thus not be measured. We show that interpretation of bitumen/brine systems is greatly improved if the CPMG data is supplemented by a FID measurement to estimate the initial magnetization.

Current Status (December 2008)
This project has been completed and the final report is listed below under "Additional Information".

Funding
This project was selected in response to DOE’s Oil Exploration and Production solicitation DE-PS26-04NT15450-2C, Reservoir Characterization and Management.

Project Start: October 1, 2004
Project End: December 31, 2007

Anticipated DOE Contribution: $591,133 (Third period was not funded.)
Performer Contribution: $254,025

Contact Information
NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021) 
Rice U. - George J. Hirasaki (gjh@rice.edu or 713-348-5416)

Additional Information

Final Project Report [PDF]

Publications
The first and second semi-annual and annual reports have been submitted to DOE. The third annual and final report was submitted in February 2008.

Hidajat, I., Mohanty, K.K., Flaum, M., and Hirasaki, G., “Study of Vuggy Carbonates Using NMR and X-Ray CT Scanning,” SPE RE&E, October 2004, 365-377.

Flaum, M., Chen, J., and Hirasaki, G.J., “NMR Diffusion Editing For D-T2 Maps: Application To Recognition of Wettability Change,” Petrophysics, March-April 2005.

Hirasaki,G., and Mohanty, K.K., “Fluid-Rock Characterization for NMR Well Logging and Special Core Analysis, first annual report to U.S. DOE,” May 2005.

V. Anand and G.J. Hirasaki, “Diffusional Coupling Between Micro and Macroporosity for NMR Relaxation In Sandstones and Grainstones,” SPWLA 46th Annual Logging Symposium, New Orleans, LA, June 26-29, 2005.

V. Anand, G.J. Hirasaki, M. Fleury, “NMR Diffusional Coupling: Effect of Temperature and Clay Distribution,” Society of Core Analysts Annual Meeting, Trondheim, Norway, September 11-14, 2006.

G. J. Hirasaki, “NMR Applications in Peteroleum Reservoir Studies,” in NMR Imaging in Chemical Engineering, S. Stapf and S.-I. Han, Wiley-VCH (2006), 321-340.

J. Chen, G.J. Hirasaki, M. Flaum, “NMR wettability indices: Effect of OBM on wettability and NMR responses,” J. Pet. Sci. & Eng., 52 (2006) 161-171.

V. Anand and G.J. Hirasaki, “Diffusional Coupling between Micro and Macroporosity for NMR Relaxation in Sandstones and Grainstones,” Petrophysics, 48.4 (2007) 289-307.

V. Anand, G. J. Hirasaki, “Paramagnetic relaxation in sandstones: Distinguishing T1and T2 dependence on surface relaxation, internal gradients and dependence on echo spacing,” Journal of Magnetic Resonance, Available online 4 October 2007.

C. P. Aichele, M. Flaum, T. Jiang, G. J. Hirasaki, W. G. Chapman, “Water in oil emulsion droplet size characterization using a pulsed field gradient with diffusion editing (PFG-DE) NMR technique,” JCIS 315 (2007) 607-619.

Distribution of diffusion coefficient and relaxation time of a rock sample saturated with both oil and water. The water distribution is identified as the peak with a diffusivity corresponding to that for bulk water. The oil distribution is identified as the peak that is on the correlation line for the diffusivity - T2 relaxation time for crude oil.

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