应用数学和力学(英文版)
應用數學和力學(英文版)
응용수학화역학(영문판)
APPLIED MATHEMATICS AND MECHANICS(ENGLISH EDITION)
2013年
11期
1421-1432
,共12页
程远方%李令东%崔青%Qing CUI
程遠方%李令東%崔青%Qing CUI
정원방%리령동%최청%Qing CUI
gas hydrate bearing sediment%wellbore stability%fluid-solid coupling%mechanical property%drilling fluid
As the oil or gas exploration and development activities in deep and ultra-deep waters become more and more, encountering gas hydrate bearing sediments (HBS) is almost inevitable. The variation in temperature and pressure can destabilize gas hydrate in nearby formation around the borehole, which may reduce the strength of the formation and result in wellbore instability. A non-isothermal, transient, two-phase, and fluid-solid coupling mathematical model is proposed to simulate the complex stability performance of a wellbore drilled in HBS. In the model, the phase transition of hydrate dissociation, the heat exchange between drilling fluid and formation, the change of mechanical and petrophysical properties, the gas-water two-phase seepage, and its interaction with rock deformation are considered. A finite element simulator is developed, and the impact of drilling mud on wellbore instability in HBS is simulated. Results indicate that the re-duction in pressure and the increase in temperature of the drilling fluid can accelerate hydrate decomposition and lead to mechanical properties getting worse tremendously. The cohesion decreases by 25% when the hydrate totally dissociates in HBS. This easily causes the wellbore instability accordingly. In the first two hours after the formation is drilled, the regions of hydrate dissociation and wellbore instability extend quickly. Then, with the soaking time of drilling fluid increasing, the regions enlarge little. Choosing the low temperature drilling fluid and increasing the drilling mud pressure appropriately can benefit the wellbore stability of HBS. The established model turns out to be an e?cient tool in numerical studies of the hydrate dissociation behavior and wellbore stability of HBS.