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The AAPG/Datapages Combined Publications Database
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Abstract
Sigal, R. F., C. Rai, C. Sondergeld, B. Spears, W. J. Ebanks Jr., W. D. Zogg, N. Emery, G. McCardle, R. Schweizer, W. G. McLeod, and J. Van Eerde, potential
gas-hydrate-bearing reservoirs in the Sagavanirktok, Prince Creek, and Schrader Bluff formations of Alaska's North Slope: Part 3—Electrical resistivity core studies
, in
potential
and associated geologic hazards
DOI:10.1306/13201128M892598
2009 by The American Association of Petroleum Geologists.
Characterization of a Sediment Core from
Potential
Gas-hydrate-bearing Reservoirs in the Sagavanirktok, Prince Creek, and Schrader Bluff Formations of Alaska's North Slope: Part 3—Electrical Resistivity Core Studies![ast](IMAGES/AST_BOLD.JPG)
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R. F. Sigal,1 C. Rai,2 C. Sondergeld,3 B. Spears,4 W. J. Ebanks Jr.,5 W. D. Zogg,6 N. Emery,7 G. McCardle,8 R. Schweizer,9 W. G. McLeod,10 J. Van Eerde11
1Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma, Norman, Oklahoma, U.S.A.
2Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma, Norman, Oklahoma, U.S.A.
3Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma, Norman, Oklahoma, U.S.A.
4Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma, Norman, Oklahoma, U.S.A.
5Consultant, College Station, Texas, U.S.A.
6PTS Labs, Houston, Texas, U.S.A.; Present address: Marathon Oil Corp., Houston, Texas, U.S.A.
7PTS Labs, Houston, Texas, U.S.A.
8PTS Labs, Houston, Texas, U.S.A.
9PTS Labs, Houston, Texas, U.S.A.
10Lone Wolf Oilfield Consulting, Calgary, Alberta, Canada
11Consultant, Calgary, Alberta, CanadaEditor's note: This report is part of a five-report series on the geologic, petrophysical, and geophysical analysis of a sediment core recovered from the Hot Ice 1 gas-hydrate research well drilled in northern Alaska during 2003–2004. Each of these reports (Chapters 25–29 of this volume) deals with specific topical observations and/or core measurements, including (part 1) project summary and geological description of the core; (part 2) porosity, permeability, grain density, and bulk modulus core studies; (part 3) electrical resistivity core studies; (part 4) nuclear magnetic resonance core studies; and (part 5) acoustic velocity core studies.
ABSTRACT
The Anadarko Hot Ice 1 well was cored as part of a project to study the occurrence of gas hydrate on the North Slope of Alaska. The observations and measurements made at the drill site along with the subsequent core analysis are described in five individual reports published in this Memoir. This report deals with the electrical resistivity measurements made on the recovered core.
The measurement and analysis of core electrical resistivities followed different procedures depending on the sample type. The sandstone samples recovered in phase II were from unfrozen sediments. These samples were processed after cleaning and drying and resaturating with brine. Porosity and formation factor were measured as a function of confining pressure. Shale samples recovered from this section of the corehole were measured at their recovered states. The phase I recovered sandstone samples came from the permafrost zone. They were first measured at below-freezing-temperature conditions with the pore fluids contained on recovery.
The phase II recovered sandstones were saturated with a 3% KCl solution, and resistivity was measured at 20C (68
F) at confining stresses ranging from 600 to 2200 psi (4.1 to 15.2 MPa). The cementation factor extracted from the core resistivity measurements had a median value of 1.94 at 800 psi (5.5 MPa) and 1.87 at 1800 psi (12.4 MPa). Two sand-core samples were also measured as recovered to estimate the salinity of the pore water in the phase II recovered cores. These estimates were 5400 and 13000 ppm.
Two shale samples from the phase II recovered cores were measured in their recovered state. Within this study, both horizontal and vertical resistivities were measured. The horizontal sample measurements had resistivities of 3.26 and 3.25 ohm m, respectively. The corresponding vertical resistivity values done on companion plugs were 6.02 and 7.57 ohm m.
A resistivity analysis of the phase I recovered samples required assumptions and approximations because neither the percentage of unfrozen brine nor its salinity was known. The basic approximation made was that, for a plug containing both ice and unfrozen brine, the unfrozen brine has a salinity that is the lowest value needed to keep it from freezing at that temperature. We also assumed that the frozen samples satisfied Archie's Law with a cementation factor of 2. These assumptions, along with the resistivity measurements, were used
to estimate the unfrozen fluid porosity and the salinity before freezing of the pore fluid. With these assumptions, the estimated salinity of the brine in the pore space before the formation of permafrost had a median salinity of 7100 ppm. The percentage of the pore space filled with brine is a function of temperature. The measurements ranged from 5% of the pore space unfrozen at
7.5
C (18.5
F) to 55% unfrozen at
1.5
C (29.3
F).
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