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Anisotropic models to account for large borehole washouts to estimate gas hydrate saturations in the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II Alaminos 21 B well

Marine and Petroleum Geology

By:
, , and
DOI: 10.1016/j.marpetgeo.2011.06.010

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Abstract

Through the use of 3-D seismic amplitude mapping, several gashydrate prospects were identified in the Alaminos Canyon (AC) area of the Gulf of Mexico. Two locations were drilled as part of the Gulf of MexicoGasHydrate Joint Industry Project Leg II (JIP Leg II) in May of 2009 and a comprehensive set of logging-while-drilling (LWD) logs were acquired at each well site. LWD logs indicated that resistivity in the range of ~2 ohm-m and P-wave velocity in the range of ~1.9 km/s were measured in the target sand interval between 515 and 645 feet below sea floor. These values were slightly elevated relative to those measured in the sediment above and below the target sand. However, the initial well log analysis was inconclusive regarding the presence of gashydrate in the logged sand interval, mainly because largewashouts caused by drilling in the target interval degraded confidence in the well log measurements. To assess gashydratesaturations in the sedimentary section drilled in the Alaminos Canyon 21B (AC21-B) well, a method of compensating for the effect of washouts on the resistivity and acoustic velocities was developed. The proposed method models the washed-out portion of the borehole as a vertical layer filled with sea water (drilling fluid) and the apparent anisotropic resistivity and velocities caused by a vertical layer are used to correct the measured log values. By incorporating the conventional marine seismic data into the well log analysis, the average gashydratesaturation in the target sand section in the AC21-Bwell can be constrained to the range of 8–28%, with 20% being our best estimate.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Anisotropic models to account for large borehole washouts to estimate gas hydrate saturations in the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II Alaminos 21 B well
Series title:
Marine and Petroleum Geology
DOI:
10.1016/j.marpetgeo.2011.06.010
Volume
34
Issue:
1
Year Published:
2012
Language:
English
Publisher:
Elsevier
Publisher location:
Amsterdam, Netherlands
Contributing office(s):
Central Energy Resources Science Center
Description:
11 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Marine and Petroleum Geology
First page:
85
Last page:
95
Country:
United States
Other Geospatial:
Gulf Of Mexico;Alaminos Canyon