天然气水合物降压开采过程中储层应力规律分析

Geomechanical stress law analysis of hydrate reservoir for gas hydrate production by depressurization

为了研究天然气水合物降压开采过程的储层应力及其稳定性,运用线性多孔弹性力学和岩石力学知识,考虑水合物储层原始应力、孔隙压力、渗流附加应力及降压开采水合物过程中水合物饱和度的变化,建立了降压开采天然气水合物储层的力学模型,结合墨西哥湾某处水合物藏的基本参数,对降压开采水合物储层应力变化和开采过程的储层稳定性进行研究。结果表明:井底压力是影响水合物储层应力变化的关键因素之一;渗流附加应力在一定程度上减小了储层的应力;水合物分解储层应力发生变化,储层应力在井壁处的波动最大,井壁处是整个储层所受轴向偏应力最大的位置,因此井壁处是优先发生剪切破坏的位置;为了储层的稳定性,降压开采水合物生产压差应小于2.19 MPa。

A model combining linear porous elasticity and rock mechanics knowledge is developed to analyze the geomechanical stress of the hydrate reservoir and assess the wellbore stability during depressurization.The proposed model considers the original reservoir stress,pore pressure,seepage additional stress,and depressurization of hydrate mining during the process of hydrate saturation change.This model is applied to the case of the Gulf of Mexico,where the hydrate reservoir basic parameters have been publicly published and depressurization of the hydrate mining reservoir has been simulated and analyzed.Results show that the effect of bottom hole pressure is the dominant factor affecting the formation of reservoir stress.Moreover,reservoir stress significantly affects the wall.Therefore,the wall is the location that is most prone to shear failure.To assess the wellbore stability during the process of depressurization,the production pressure difference of the hydrate reservoir must be<2.19 MPa.