North Slope Hydrate Fieldtrial: CO2/CH4 Exchange

Abstract

CO2/CH4 exchange in a sandstone-hosted methane hydratereservoir was executed in the field, following several years of laboratoryexperimentation. Reservoir simulation and laboratory data informedfieldtrial design, including use of a cell-to-cell model that included correctliquid/vapor/hydrate phase behavior of methane, carbon dioxide, nitrogen, andwater. Most concepts for producing methane from hydrate deposits rely ondepressurization, heating, or chemical melting. These techniques resultin dissociation of hydrate into its water and gas constituents. Effectiveexchange of CO2 for CH4 in the crystalline hydratelattice, without dissociation, was long deemed an improbable recovery strategybecause experimental results on bulk hydrate samples indicated very slowreaction kinetics. Recent laboratory tests documented enhanced exchangekinetics and efficiency, attributed to the increased surface area present inporous media. A series of laboratory tests ranging from simple gas-richsystems to more complex gas-deficient / water-rich systems guided the design ofa field test program. Ignik Sikumi #1 was drilled in 2011 on the AlaskaNorth Slope, designed specifically for testing CO2/CH4exchange in hydrate-bearing sandstones. Ignik Sikumi #1 was drilled vertically with chilled oil-based mud to a depthof 2600ft. Four hydrate-bearing sandstones were encountered, andpetrophysical evaluation indicated the Sagavanirktok " C Sand" hosted thehighest hydrate saturations. These sandstones occur in the subsurface atreservoir conditions similar to temperatures and pressure conditions of labtests. Reservoir modeling with conventional simulators and in-housecell-to-cell models guided both equipment design and test parameters. Anticipated low injection rates and cryogenic injectant required the design ofspecialized pumping equipment. Operations at Ignik Sikumi #1 re-commencedin December 2011. Following perforation, over 200,000 scf of mixedCO2/N2 gas was injected. A short unassisted flowperiod was followed by extended production testing via jet pumping. Results from the production test will be shown. CO2/CH4 exchange is a novel approach to recovermethane from sandstone-hosted hydrates. Field trial has validatedlaboratory results and reservoir simulations, and has proven thatCO2 can be injected into naturally occurring sandstone-hostedhydrates. Subsequent flowback/drawdown testing produced injectants(nitrogen, carbon dioxide, and tracer gases) methane, water, and very finesand.

Transport Mechanisms for CO2-CH4 Exchange and Safe CO2 Storage in Hydrate-Bearing Sandstone

“…A binary gas mixture (25/75 mol% CO2/N2) was used to avoid plugging the sample during injection. Co-injection of N2 and CO2 (77/23 mol%) was also used in the Ignik Sikumi trial, which continuously injected over a period of 14 days [38]. Similar effluent profile as the other experiments was observed for the first injected pore volume in w5, while a deviating trend was observed as injection continued.…”

Strain Rate‐Dependent Hardening‐Softening Characteristics of Gas Hydrate‐Bearing Sediments

“…The presence of GH changes the mechanical properties of these sediments or soils, with increased GH saturations (S h ) often being related to higher shear strength, increased stiffness, and stronger dilatancy (e.g., Waite et al, 2009;Yun et al, 2007). The mechanical and hydraulic properties of GH-bearing sediments (GHBS) are considered to influence the stability of marine sediments and slopes (Bugge et al, 1988;Elger et al, 2018;Kvalstad et al, 2005;Mountjoy et al, 2014), and they are crucial factors for drilling operations (McConnell et al, 2012) and natural gas production scenarios (Boswell et al, 2017;Collett, 2002;Konno et al, 2017;Schoderbek et al, 2012;Yamamoto et al, 2014). Thus, considerable effort is invested in geotechnical testing of GHBS to better understand geomechanical properties and stress-strain behavior in slope failure events or GH production scenarios.…”

Salinity Effects on Pore‐Scale Methane Gas Hydrate Dissociation

“…Proposed gas production schemes are commonly based on methane gas hydrate dissociation-by either depressurization, thermal stimulation, injection of chemical inhibitors, or a combination of these (Moridis et al, 2011). We have previously demonstrated an alternative strategy for replacement of methane molecules in hydrate with CO 2 (Graue et al, 2008;Kvamme et al, 2007), which later resulted in a field trial on the North Slope of Alaska where more than half of the injected CO 2 was sequestered in the reservoir (Schoderbek et al, 2012). Carbon dioxide is the thermodynamically preferred guest molecule and this production scheme enables an option for carbon capture, utilization and storage.…”