Abstract

The primary goal of the Gulf of Mexico (Gulf of Mexico) Joint Industry Project (JIP) Leg II drilling program was to locate and record the occurrence of gas hydrate in high-quality deepwater sand reservoirs. In the first week of May, 2009, the JIP utilized the Helix Q-4000 semi-submersible to drill and log two wells in the Diana sub-basin in the northwestern Gulf of Mexico at the Alaminos Canyon (AC) 21 Site. The AC 21-A and AC 21-B wells confirmed the presence of an areally extensive, sand-rich deepwater fan system that was predicted from industry 3-D seismic data and existing industry well penetrations. The primary targets were encountered within 600 ft of the seafloor, well above the predicted base of gas hydrate stability depth of approximately 1,500 feet below sea floor (fbsf). The target sand reservoirs as seen in the A and B wells measured 62 ft and 125 ft, respectively, and contained elevated formation resistivity consistent with low to moderate saturations of gas hydrate (20% to 40%). The interface between the overlying shales and the hydrate-bearing sands is one of high acoustic impedance, thus providing an anomalous response on the 3-D seismic data with a strong peak-leading top.

Introduction

In April, 2009, the Gulf of Mexico (Gulf of Mexico) Gas Hydrate Joint Industry Project (the " JIP??) conducted its Leg II operations at three Sites in the northern Gulf of Mexico (Figure F1) using the semi-submersible Helix Q-4000 (see Boswell et al., 2009a). These locations were selected to test geological and geophysical analyses conducted with the intent of locating gas hydrate-bearing sand reservoirs (see Hutchinson et al., 2009a, 2009b; Shedd et al., 2009b) and conducting comprehensive logging while drilling (LWD) operations (see Collett et al., 2009b) in advance of planned Leg III coring and pressure coring. This report presents the geologic setting and initial scientific results of LWD operations conducted at the Alaminos Canyon block 21 site (Site AC21). Detailed descriptions of the LWD operations and data acquisition for this site are provided in Mrozewski et al. (2009) and Guerin et al. (2009).

The AC 21 site lies within the northwestern Gulf of Mexico along the boundary between the Alaminos Canyon and East Breaks (EB) protraction areas (Figure F2). It is one of two drill sites evaluated by the JIP for possible Leg II operations within the Diana intra-slope basin (Shedd et al., 2009b). Three well locations were permitted at Site AC 21 to test gas hydrate targets, including two wells in block AC 21 and a third in block AC 65. An additional drill site, including four permitted wells, was in EB block 992 (Site EB 992). Both sites featured very similar geologic targets. Site EB 992 is approximately nine miles to the east/northeast of Site AC 21 and located in the central part of the Diana basin (Figure F2). At all of the target locations, thick sandstone reservoirs (50 ft to 200 ft) were predicted based on the integration of existing industry well data and seismic attribute analysis from 3-D seismic data. Low to moderate saturations of gas hydrate were predicted in these reservoirs based on the slightly elevated formation resistivity measured in the EB 992 #001 industry well and the high impedance leading peak event associated with the seismically-defined top of the sandy facies. A primary scientific objective of the drilling was to collect high-quality LWD data through this sand facies to further refine estimates of gas hydrate saturations.

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