Geomechanical, Hydraulic and Thermal Characteristics of Deep Oceanic Sandy Sediments Recovered during the Second Ulleung Basin Gas Hydrate Expedition

Abstract

This study investigates the geomechanical, hydraulic and thermal characteristics of natural sandy sediments collected during the Ulleung Basin gas hydrate expedition 2, East Sea, offshore Korea. The studied sediment formation is considered as a potential target reservoir for natural gas production. The sediments contained silt, clay and sand fractions of 21%, 1.3% and 77.7%, respectively, as well as diatomaceous minerals with internal pores. The peak friction angle and critical state (or residual state) friction angle under drained conditions were~26 • and~22 • , respectively. There was minimal or no apparent cohesion intercept. Stress-and strain-dependent elastic moduli, such as tangential modulus and secant modulus, were identified. The sediment stiffness increased with increasing confining stress, but degraded with increasing strain regime. Variations in water permeability with water saturation were obtained by fitting experimental matric suction-water saturation data to the Maulem-van Genuchen model. A significant reduction in thermal conductivity (from~1.4-1.6 to~0.5-0.7 W·m −1 ·K −1 ) was observed when water saturation decreased from 100% to~10%-20%. In addition, the electrical resistance increased quasi-linearly with decreasing water saturation. The geomechanical, hydraulic and thermal properties of the hydrate-free sediments reported herein can be used as the baseline when predicting properties and behavior of the sediments containing hydrates, and when the hydrates dissociate during gas production. The variations in thermal and hydraulic properties with changing water and gas saturation can be used to assess gas production rates from hydrate-bearing deposits. In addition, while depressurization of hydrate-bearing sediments inevitably causes deformation of sediments under drained conditions, the obtained strength and stiffness properties and stress-strain responses of the sedimentary formation under drained loading conditions can be effectively used to assess sediment responses to depressurization to ensure safe gas production operations in this potential target reservoir.

Depressurization‐Induced Fines Migration in Sediments Containing Methane Hydrate: X‐Ray Computed Tomography Imaging Experiments

“…There are many natural sediments of concern: coarse‐grained sediments with S h > 30% cored in hydrate deposits show FC values ranging from ~5% to ~20% (e.g., 5–8% of FC in Mallik2L‐38 Core 18, Canada; ~30% of FC in D‐GH, Mt. Albert, Alaska; ~20% of FC in NGHP‐01‐10D, India; ~32% of FC in U1326D‐7X‐1, Cascadia margin; ~30–40% of FC in AT1‐C‐8P, the Nankai Trough; 22% of FC in UBGH2‐6B‐22R and 2.4% in UBGH2‐5B‐22H in Ulleung Basin; data gathered from Cha et al, ; Collett et al, ; Ito et al, ; Torres et al, ; Winters et al, ). For a sand layer with high S h > 60%, the FC change can be greater than the values observed in our study.…”

“…For comparison, we used two types of sands as host sediments: coarse sand (Ottawa 20–30, U.S. Silica, Frederick, MD, U.S.A.) with a mean grain size (D 50 ) of 722 μm and fine sand (F110, U.S. Silica, Frederick, U.S.A.) with D 50 of 142 μm. The fine sands were specifically chosen because their grain size distribution was close to that of sand‐dominant sediments recovered from hydrate deposits in the Ulleung Basin offshore Korea (e.g., UBGH2‐6B‐22R, Cha et al, ). Silica silt and kaolinite clay were chosen as the fine particles; the silt has D 50 of 20 μm with a specific surface area less than 5 m 2 /g and no plasticity, while the kaolinite has D 50 of 10 μm with a specific surface area of 41 m 2 /g and low plasticity.…”

“…Gabriel & Inamdar, 1983;Moghadasi et al, 2004;Muecke, 1979;Oyama et al, 2015;Pang & Sharma, 1997;Sharma et al, 1992;Valdes & Santamarina, 2006;Wan & Tokunaga, 2002) and by mathematical modeling (e.g. Bedrikovetsky, 2008;Bedrikovetsky et al, 2011;Bergendahl & Grasso, 2000;Cerda, 1987Cerda, , 1988Kampel et al, 2009;McDowell-Boyer et al, 1986;Shapiro et al, 2007;You et al, 2016). However, due to the complexities associated with hydrate dissociation, it is difficult to adopt these results directly into models to predict depressurization-induced fines migration.…”

Introduction to Special Issue on Gas Hydrate in Porous Media: Linking Laboratory and Field‐Scale Phenomena

“…The presence of fines affects permeability and thus methane flux, which in turn control how and where gas hydrate concentrates and the saturations achieved. Fines can also govern the physical properties of bulk HBS and the response of sediments during production of methane from dissociating gas hydrates (Bahk et al, ; Cha et al, ; Jung et al, ; Lee, Santamarina, et al, ). Mobilized fines can clog pathways for gas or fluid flow through the reservoir (reduced permeability) or foul the screened intervals in extraction wells, making it more difficult to drive additional hydrate dissociation in the reservoir or to recover fluids and gas (Han et al, ).…”

Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs

“…However, hydrate reservoirs in deep water are generally low-strength formations, which make the wellbore collapse to be a commonly occurred issue during hydrate production process [9][10][11][12]. In addition, hydrate dissociation during hydrate production operation is another contributor to both the complex accidents within the borehole (i.e., borehole instability and casing damage, etc.)…”