27. DATA REPORT: NUCLEAR MAGNETIC RESONANCE LOGGING WHILE DRILLING, ODP LEG 204

Most published gas hydrate volumetric estimates have of necessity been made by broad extrapolation based on only general knowledge of local geologic conditions. The amount of gas that might be stored in a gas hydrate accumulation is dependent on a number of reservoir parameters, including the areal extent and thickness of the gas hydrate occurrence, sediment porosities, and the degree of gas hydrate saturation. Downhole logs often serve as a source of critical gas hydrate reservoir data. Before Ocean Drilling Program (ODP) Leg 204, however, only about seven gas hydrate occurrences had been sampled and surveyed with open hole well logging devices. From 16 July through 25 July 2002, a complex logging-while-drilling (LWD) and measurement-whiledrilling program was conducted on Hydrate Ridge during ODP Leg 204. During the cruise, and for the first time during ODP, the LWD tool string included Schlumberger’s Nuclear Magnetic Resonance While Drilling tool (proVision). Postcruise research with the proVision data has consisted of estimating bound fluid volumes and total fluid porosities, along with comparing nuclear magnetic resonance (NMR)-derived porosities with those derived from downhole measured neutron and density logs and core measurements. These efforts have focused on calculating gas hydrate concentrations by indirect methods using NMR data. It has been shown that it is possible to obtain gas hydrate saturations (percent of pore space occupied by gas hydrate) from downhole logging–measured NMR porosities. In this study, porosities derived from the NMR proVision 1Collett, T.S., Lee, M.W., Goldberg, D.S., Rack, F.R., and Williams, T., 2006. Data report: nuclear magnetic resonance logging while drilling, ODP Leg 204. In Trehu, A.M., Bohrmann, G., Torres, M.E., and Colwell, F.S. (Eds.), Proc. ODP, Sci. Results, 204: College Station, TX (Ocean Drilling Program), 1–22. doi:10.2973/ odp.proc.sr.204.106.2006 2U.S. Geological Survey, Denver Federal Center, Denver CO 80225, USA. tcollett@usgs.gov 3Borehole Research Group, LamontDoherty Earth Observatory of Columbia University, Palisades NY 10964, USA. 4Joint Oceanographic Institutions, Inc., 1755 Massachusetts Avenue Northwest, Suite 700, Washington DC 20036, USA. Present address: ANDRILL Science Management Office, University of Nebraska-Lincoln, 126 Bessey Hall, Lincoln NE 68588-0341, USA. Initial receipt: 14 January 2005 Acceptance: 24 July 2005 Web publication: 17 October 2006 Ms 204SR-106 T.S. COLLETT ET AL. DATA REPORT: NMR LOGGING WHILE DRILLING 2 tool were used along with porosity data from the Azimuthal Vision Density Neutron tool to calculate gas hydrate saturations at all nine LWD logging sites on Hydrate Ridge. The NMR-density-porosity relation yielded gas hydrate saturations ranging from high values near the crest of the ridge of ~50% and higher in Hole 1249A to much lower values along the flanks of the ridge. INTRODUCTION Leg 204 Operations One of the primary goals of Ocean Drilling Program (ODP) Leg 204 was to determine the distribution and concentration of gas hydrates beneath Hydrate Ridge, which is located ~90 km off the coast of Oregon (USA). After coring the first site (Site 1244), logging-while-drilling (LWD) data were acquired from an additional 10 holes at 8 respective sites (Table T1). The LWD data confirmed the general position of key seismic stratigraphic horizons and yielded estimates of gas hydrate concentrations through various downhole logging proxies. These records proved to be of great value in planning subsequent coring. After completing the 10-day LWD program, the LWD tools were removed from the ship by an open-ocean small boat transfer. The remaining portion of the cruise dealt with coring more than 45 holes at 9 sites on Hydrate Ridge. Eight of these sites were the same sites that were already drilled and logged during the LWD program. The Hydrate Ridge coring program also included acquisition of conventional wireline logs from an additional six holes. LWD Program The downhole logging program during Leg 204 was specifically designed to obtain the data needed to assess the occurrence and concentration of gas hydrates on Hydrate Ridge. During Leg 204, four LWD and measurement-while-drilling (MWD) tools were deployed at eight sites on southern Hydrate Ridge (Table T1; Fig. F1). These tools were provided by Schlumberger Drilling Services of Youngsville, Louisiana (USA), under contract with the Lamont-Doherty Earth Observatory (LDEO) Borehole Research Group in Palisades, New York (USA). Leg 204 LWD operations began on 16 July 2002 with initial bottomhole assembly (BHA) makeup and spudding of Hole 1244D. Figure F2 shows the configuration of the LWD/MWD BHA used during Leg 204. The tools (63⁄4-in collars) deployed in nine of the ten LWD logged holes during Leg 204 included the GeoVision resistivity-at-the-bit or “RAB” tool with a 9 -in button sleeve, a Power-Pulse MWD tool, the Nuclear Magnetic Resonance While Drilling tool (proVision), and the Azimuthal Vision Density Neutron (VDN) tool. Table T1 contains a detailed listing of the LWD data acquired during Leg 204. This was the first time that any downhole magnetic resonance device (proVision) was used during ODP. As shown in Table T1, the proVision was deployed a total of nine times during Leg 204, and in all cases the quality of acquired data was very good. LWD measurements are made shortly after the hole is drilled and before extended pumping and coring operations adversely affect in situ hole condition and all subsequent downhole measurements. Fluid invasion into the borehole wall is also reduced relative to wireline logging T1. Leg 204 holes surveyed with LWD and MWD tools, p. 22. 0 0 2 1 0 0 1 1 0 0 0 1