A pressure core based characterization of hydrate-bearing sediments in the Ulleung Basin, Sea of Japan (East Sea)

Abstract

[1] The physical characteristics of hydrate-bearing sediments sampled by pressure coring from the Ulleung Basin in the Sea of Japan (East Sea) were investigated using an instrumented chamber capable of testing recovered natural sediments that have never left the methane hydrate stability field. The heterogeneous distribution of segregated hydrate veins and lens structures in sediments results in highly variable geophysical and geomechanical properties. The scaled production test was conducted by controlled depressurization of pressure cores while dissociation and gas production were concurrently monitored using various sensors in the instrumented chamber. The hydrate saturation was estimated to be ∼19.5% in the pore space. Data show a sharp reduction in sediment shear and bulk stiffnesses during hydrate dissociation. Relatively fast gas migration was observed, probably along high-conduction planes left behind as hydrate veins dissociated. The spatial distribution of hydrates in sediment was analyzed based on 3-D image processing. The phenomena relevant to the production test and sampling effects during pressure coring are discussed.

Effect of methane hydrate morphology on compressional wave velocity of sandy sediments: Analysis of pressure cores obtained in the Eastern Nankai Trough

“…Pressure core analysis technologies now enable the study of relatively undisturbed samples recovered from hydrate-bearing natural sediments, and pressure core analyses of P-wave velocities have been conducted for hydrate-bearing natural sediments (Yun et al, 2006(Yun et al, , 2010(Yun et al, , 2011Schultheiss et al, 2011). successfully determined the relationship between P-wave velocity and hydrate saturation from pressure cores recovered from the Ulleung Basin.…”

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

“…The probe constant N k is a function of soil type. Yun et al (2011Yun et al ( , 2006 took N k to be~10 in previous IPTC deployments, where hydrate appeared as lenses or nodules within fine-grained, relatively soft sediment into which the probe could be inserted its full 18 mm travel.…”

Scientific Drilling

“…Figure 5. Monitored gas production tests using IPTC: [A] Evolution of pressure, temperature, electrical resistivity, and produced gas (Krishna-Godavari Basin; Yun et al, 2010); [B] Typical wave signatures during gas production: P-wave signatures eventually fade out after gas production; S-waves detect the evolution of the skeleton shear stiffness during hydrate dissociation and gas production (Ulleung Basin; Yun et al, 2011). In addition to pressure core testing, comprehensive characterization programs should include sediment index properties analyzed within the framework of available data for natural hydrate bearing sediments, and tests with remolded specimens with synthetic hydrate.…”