热采水平井近井地应力分布及影响因素分析

Analysis on In-situ Stress Distribution and Influencing Factors Near the Thermal Recovery Wellbores of Horizontal Well

水平井近井地应力分布规律是疏松砂岩热采水平井井壁稳定性分析、出砂预测的基本条件。综合考虑原始地层主应力、注汽温度效应、井壁渗透性及注入压力、井下管柱外挤等多种因素,建立了热采水平井近井地应力预测的基本模型。模拟计算表明,井周角和井底流压变化对近井地层轴向应力的影响较小。随着水平井井眼与原始最大水平主应力方向的夹角增大,轴向应力减小。在r<10rw范围内,井底流压对地层周向应力和径向应力的影响较大,随着井底流压的上升,径向应力增大,周向应力减小;r<5rw范围内温度对地层应力的影响剧烈,超过该半径范围后温度对水平井近井地应力的敏感性减弱。模型预测结果大于常规模型的预测结果,能从应力角度说明热采水平井井壁稳定性变差、出砂加剧的根本原因,研究成果对指导热采水平井井壁稳定性分析、制定合理的工作制度有重要意义。

The rule of in-situ stress distribution nearby the wellbore is essential for wellbore of horizontal well was the basic condition for stability analysis and prediction of sand production in the wellbore of thermal recovery horizontal well.A numerical model was established for predicting the in-situ stress in the nearby wellbore of thermal recovery horizontal well based on the parameters of main stress in formation,gas injection temperature effect,wellbore permeability,gas injection pressure and squeezing outside casing strings.It was proved by numerical simulation that calculating angel around the wellbore and changes of bottom hole flowing pressure had less influence on axial stress of formation near the wellbore,while with the increase of azimuthal angle of the horizontal well and the original maximum horizontal stress,the axial stress decreased.The effect of bottom-hole flowing pressure on the circumferential stress and radial stress in the formation was serious within the r<10rwscope,and radial stress increased and the circumferential stress decreased with the increase of bottom-hole flowing pressure.The effect of temperature on in-situ stress was severe within the r<5rw scope.The sensitivity of temperature to stress in the near wellbore was weakened over the scope.The prediction result of the model is larger than that of conventional model,and it is possible to interpret the reason of wellbore stability declined and severe sand production in thermal recovery wells.It is of great significance for guiding wellbore stability analysis and setting up a reasonable operation system for thermal recovery horizontal wells.