Numerical Studies on the Geomechanical Stability of Hydrate-Bearing Sediments

Abstract

The thermal and mechanical loading of oceanic hydrate-bearing sediments (HBS) can result in hydrate dissociation and a significant pressure increase with potentially adverse consequences on the integrity and stability of the wellbore assembly, the HBS, and the bounding formations. The perception of HBS instability, coupled with insufficient knowledge of their geomechanical behavior and the absence of predictive capabilities, has resulted in a strategy of avoidance of HBS when locating offshore production platforms and can impede the development of hydrate deposits as gas resources.In this study, we investigate coupled (interacting) hydraulic, thermodynamic, and geomechanical behavior of oceanic HBS in three cases. The first involves hydrate heating as warm fluids from deeper conventional reservoirs ascend to the ocean floor through uninsulated pipes intersecting the HBS. The second case describes system response during gas production from a hydrate deposit, and the third involves mechanical loading caused by the weight of structures placed on the ocean floor overlying the HBS.For the analysis of the geomechanical stability of HBS, we developed and used a numerical simulator that integrates a commercial geomechanical simulator and a simulator describing the coupled processes of fluid flow, heat transport, and thermodynamic behavior in the HBS. Our simulation results indicate that the stability of HBS in the vicinity of warm pipes may be affected significantly. Gas production from oceanic deposits may also affect the geomechanical stability of HBS under the conditions that are deemed desirable for production. Conversely, the increased pressure caused by the weight of structures on the ocean floor increases the stability of underlying hydrates.Geomechanical Properties of the HBS To simulate the mechanical behavior of the HBS, we apply an elastoplastic mechanical constitutive law with a modified Mohr-Coulomb failure criterion. The elastoplastic properties of the HBS

Evaluation of the Gas Production Potential of Some Particularly Challenging Types of Oceanic Hydrate Deposits

“…Earlier studies (Rutqvist and Moridis 2009) have shown that gas production from such deposits is often accompanied by significant subsidence, with potentially important consequences for well and reservoir stability, as well as for the evolution of the sediment permeability. Because this study indicated the generally low production potential of CH (a determination that does not encourage their further evaluation when more promising hydrate deposits are available), the issue of geomechanical response of CHs was not pursued in this study.…”

Gas production from a silty hydrate reservoir in the South China Sea using hydraulic fracturing: A numerical simulation

“…In this work, TOUGH + HYDRATE 62 software was employed to address this issue because the software was generally used to simulate gas recovery from hydrate reservoirs in marine and permafrost regions, 27,28,30,[63][64][65] The geomechanical response was not considered because the influence of effective stress variation on the sediment and fracture properties in GHBS at this site during depressurization is currently unclear, even though the coupled thermo-hydro-mechanical model was proposed and used to perform the coupling processes during drilling and gas recovery. 25,29,[66][67][68][69][70][71][72] However, the assigned permeability of fractures takes the influence of the effective stress into account. The latter means that the value adopted is the experimental measurement in other sediments after which the bottom hole pressure remains constant after initially decreasing (i.e., the assigned fracture permeability is measured at the corresponding effective confining pressure condition).…”

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

“…This class of deformation, which is caused by changes in stress states, whether volume contraction or expansion, can be assessed based on the material stiffness. Many of reservoir-scale geomechanics simulators, including those presented by the Lawrence Berkeley National Laboratory (LBNL) group [40][41][42], by the Korea Advanced Institute of Science and Technology (KAIST) group [39,43], and by the Cambridge University group [44][45][46], adopt elastoplasticity to model sediment deformation behaviors. Thereby, one of the elastic moduli (typically Young's modulus or bulk Energies 2016, 9, 775 15 of 23 modulus), Poisson's ratio ν, and strength parameters (cohesion and friction angle, if Mohr-Coulomb yield criterion used) for material yielding are typically used as input parameters for describing elasto-plastic behavior.…”

“…Accordingly, Young's modulus of hydrate-bearing sediments is assumed based on linear interpolation between the values at two different hydrate saturations-typically, one for hydrate-free sediment and the other for a certain hydrate saturation (e.g., [40][41][42][43][44][45][46]62]). On the other hand, a logarithmic increase of the secant Young's modulus of hydrate-bearing sediments has been also observed with increasing hydrate saturation by Yoneda et al [25].…”