Planning and Operations of the Hydrate 01 Stratigraphic Test Well, Prudhoe Bay Unit, Alaska North Slope

Abstract

The National Energy Technology Laboratory, the Japan Oil, Gas and Metals National Corporation, and the U.S. Geological Survey are leading an effort to conduct an extended gas hydrate production test in northern Alaska. The proposed production test required the drilling of an initial stratigraphic test well (STW) to confirm the geologic conditions of the proposed test site. This well was completed in January 2019 in cooperation with the Prudhoe Bay Unit Working Interest Owners. The Prudhoe Bay Unit Hydrate-01 STW was spudded on 10-December-2018. Downhole data acquisition was completed on 25-December-2018, and the rig was released on 01-January-2019. The Hydrate-01 STW was drilled in two sections, including the surface hole that was drilled to a depth of 2248 ft measured depth (MD) (685 m MD) and cased, and the production hole section that was drilled to a depth of 3558 ft MD (1084 m MD) and also cased. A thermally chilled mineral-oil-based mud was used in the main (production) hole section of the well to maintain wellbore stability and quality of the wellbore acquired data. The primary wellbore data were acquired using logging-while-drilling tools. A sidewall pressure core system was also deployed to gather grain size and other data needed for the design of the future production test wells. In addition to confirming the geologic conditions at the test site, the Hydrate-01 STW was designed to serve as a monitoring well during future field operations. Therefore, two sets of fiber-optic cables, each including a bundled distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS), were clamped to the outside of the production casing and cemented in place. In March 2019, the project team acquired three-dimensional (3D) DAS vertical seismic profiling data in the Hydrate-01 STW. Temperature surveys were also acquired with the DTS as deployed in the Hydrate-01 STW during the completion of the well and nearly continuously since March-2019.

Gas Hydrate Saturation Estimates, Gas Hydrate Occurrence, and Reservoir Characteristics Based on Well Log Data from the Hydrate-01 Stratigraphic Test Well, Alaska North Slope

“…The group identified the Kuparuk State 7-11-12 well pad in the Prudhoe Bay Unit of the Alaska North Slope (USA) as an appropriate test site and drilled the Hydrate-01 Stratigraphic Test Well (STW) in December 2018 . The Hydrate-01 STW confirmed the presence of high gas hydrate saturations in the target reservoirs and provided a full suite of well log data with which to characterize these units, the adjacent seal layers, and the full stratigraphy at the site …”

“…Borehole LWD data acquired in the Hydrate-01 STW include a research-level log suite described in full detail by Collett et al Logging tools providing data used in this article include arcVISION (gamma ray and electrical resistivity logs), adnVISION (density and caliper), SonicScope (P- and S-wave slowness), and the proVISION (nuclear magnetic resonance, NMR). Caliper data (Figure a) show that borehole conditions were generally very good, with minimal washout in the zone of interest, and resistivity and sonic logs (Figure ) confirm the presence of gas hydrate in the B1 and D1 sands.…”

“…The sands are designated according to the informal unit within which they occur, and our two primary reservoirs of interest are the B1 and D1 sands at 2293 feet true vertical depth subsea (TVDss), and 2770 feet TVDss, respectively. These sands are well suited for gas hydrate reservoir response (production) testing due to lithology, gas hydrate saturation, and temperature, as reviewed by Boswell et al and Collett et al The base of gas hydrate stability (BGHS) was inferred based on regional data to occur below the B1 sand and confirmed, based on temperature data from the Hydrate-01 STW and assumptions of gas and water chemistry, to be 160 feet (49 m) below the base of the B1 sand …”

“…Planning for a gas hydrate production test and accurately interpreting the resulting data are dependent on thoroughly characterizing the reservoir itself as well as the nature of the gas hydrate within the reservoir. , More broadly, quantitatively characterizing natural gas hydrate deposits is essential for understanding the scale and occurrence patterns of gas hydrate deposits locally, regionally, and globally; such characterization informs studies of gas hydrate’s role in the carbon cycle, as a subsea hazard, and as an energy resource . Subsurface characterization to support the planned Alaska production test is provided by borehole log data , and sidewall core samples from the Hydrate-01 STW along with surface seismic and 3D distributed acoustic sensor (DAS) vertical seismic profile (VSP) data. ,, …”

Preface: Special Topics on Study Progress of Natural Gas Hydrate

“…tests in permafrost hydrate reservoirs in Mackenzie Delta and Alaskan North Slope (Boswell et al, 2017) in the Antarctic, and those in marine hydrate reservoirs in Nankai Trough, offshore Japan (Yamamoto et al, 2014(Yamamoto et al, , 2018, and South China Sea (SCS) (Li et al, 2018;Ye et al, 2020). As encouraged by the results obtained from the production tests, more tests are planned to develop technology for industrial exploitation of natural gas hydrate (Collett et al, 2022). Although production test can be conducted in permafrost hydrate reservoir for cost efficiency, generally it is thought industrial exploitation will be realized in marine hydrate reservoir because it is estimated with over 90% of hydrate resource.…”