Study on the Evolution Law of Wellbore Stability Interface during Drilling of Offshore Gas Hydrate Reservoirs

Abstract

The study of wellbore stability in offshore gas hydrate reservoirs is an important basis for the large-scale exploitation of natural gas hydrate resources. The wellbore stability analysis model in this study considers the evolution of the reservoir mechanical strength, wellbore temperature, and pressure parameters along the depth and uses plastic strain as a new criterion for wellbore instability. The wellbore stability model couples the hydrate phase transition near the wellbore area under the effect of the wellbore temperature and pressure field and the ‘heat–fluid–solid’ multifield evolution characteristics, and then simulates the stability evolution law of the wellbore area during the drilling process in the shallow seabed. The research results show that, owing to the low temperature of the seawater section and shallow formation, the temperature of the drilling fluid in the shallow layer of the wellbore can be maintained below the formation temperature, which effectively inhibits the decomposition of hydrates in the wellbore area. When the wellbore temperature increases or pressure decreases, the hydrate decomposition rate near the wellbore accelerates, and the unstable area of the wellbore will further expand. The research results can provide a reference for the design of drilling parameters for hydrate reservoirs.

Numerical Simulation of Hydrate Dissociation Behaviors in Hydrate Reservoir with Different Properties during Horizontal Well Drilling

“…The results revealed that the well permeability has the most significant impact on well temperature, while the hydrate saturation has little influence on the well temperature. Li et al [39] developed a wellbore stability analysis model, indicating that maintaining drilling fluid temperature below the formation temperature effectively inhibites hydrate dissociation in the wellbore area. When the wellbore temperature increases or the pressure decreases, the dissociation rate of the hydrate near the wellbore accelerates, and the wellbore instability area will further expand.…”

Risk Assessment Method for Analyzing Borehole Instability Considering Formation Heterogeneity

“…The uncertainties surrounding in situ stresses, along with those related to rock strength and deformation properties, significantly widen the range of outcomes in the probability distribution for both minimum and maximum mud weights required to prevent fracturing and cracking [38][39][40][41][42]. Given this complexity, when embarking on the development of new fields, it is advisable to adopt a deterministic approach that relies on the most reliable estimates of input parameters to ascertain borehole stability [43][44][45][46][47][48]. In this scholarly contribution, we established a risk assessment model specifically tailored to evaluate borehole stability.…”