Micromechanical Investigation of Stress Relaxation in Gas Hydrate-Bearing Sediments Due to Sand Production

Abstract

Past experience of gas production from methane-hydrate-bearing sediments indicates that sand migration is a major factor restricting the production of gas from methane-hydrate reservoirs. One important geotechnical aspect of sand migration is the influence of grain detachment on the existing stresses. This paper focuses on understanding and quantifying the nature of this aspect using different approaches, with a focus on discrete element method (DEM) simulations of sand detachment from hydrate-bearing sand samples. The investigation in the paper reveals that sand migration affects isotropic and deviatoric stresses differently. In addition, the existence of hydrate moderates the magnitude of stress relaxation. Both of these features are currently missing from continuum-based models, and therefore, a new constitutive model for stress relaxation is suggested, incorporating the research findings. Model parameters are suggested based on the DEM simulations. The model is suitable for continuum mechanics-based simulations of gas production from hydrate reservoirs.

Particulate Modeling of Sand Production Using Coupled DEM-LBM

“…However, the key features of different sanding stages, including the impact of stress level and the changing role of fluid flow in the sand production process, are captured. The observed stress reduction during rapid particle production was also reported in both previous experimental [2] and numerical [83] studies. The stress reduction is most notable when a sudden burst of sanding occurs or when particles are eroded rapidly, usually leading to catastrophic sand production.…”

“…Since the inner hole diameter is assumed to be constant, the borehole choking could not be modeled in the current study. Thus, rapid erosion of numerous particles and the subsequent severe reduction of internal stress, also known as stress relaxation [83] (the difference between applied and averaged assembly stress), indicate catastrophic sanding in the present model. By focusing on the sanding time histories of models, it is possible to follow the evolution of sanding process under varying applied confining stress.…”

Sand Production Management during Marine Natural Gas Hydrate Exploitation: Review and an Innovative Solution

“…Both the erosion-based models and FEM-based models analyze sand production in the framework of continuum mechanics. However, these models were unable to evaluate the influences of grain detachment and hydrate on the existing microstress relaxation since they misrepresent a real granular matter with random geometry . A discrete element method (DEM) formulation for the soil solid particles was developed and implemented within the numerical scheme of PFC3D by Cohen et al…”

“…However, these models were unable to evaluate the influences of grain detachment and hydrate on the existing microstress relaxation since they misrepresent a real granular matter with random geometry. 70 A discrete element method (DEM) formulation for the soil solid particles was developed and implemented within the numerical scheme of PFC3D by Cohen et al 72 A continuum-discrete coupled sanding prediction model was proposed by Qingdao Institute of Marine Geology and China University of Geosciences, 71 in which the numerical schemes of TOUGH+HYDRATE, Flac3D, and PFC3D were combined. In this model, the thermal-hydro-mechanical response of HBS during NGH development was simulated through the combination of TOUGH+HYDRATE and Flac3D, 72 and then, hydrate saturation, fluid flow velocity, and stress distribution values were used as the initial and boundary conditions while predicting sand detachment and migration behaviors with PFC3D.…”

State‐of‐the‐art brief review on sanding problem of offshore natural gas hydrates sediments

“…Second, the phase change influences the reservoir stability by reducing the formation strength, especially for the weak consolidation NGH sediments. [156][157][158] It raises the sand collapse and sand invasion risks after formation deformation. The main research interest of phase change is related to reservoir stability,however, the phase change in the sand control process has not attracted researchers yet.…”