定向井井径扩大率计算模型及影响因素分析

Borehole diameter enlargement ratio calculation model of directional wells and influence factors analysis

井眼适度坍塌是缓解井壁稳定和储层保护矛盾的关键技术之一。根据弹性力学理论,建立了定向井井径扩大率计算模型,并分析了钻井液密度、井斜角和方位角对井径扩大率的影响规律。结果表明:对于任意井斜角、方位角的定向井而言,允许井壁适度坍塌,均可降低所需的钻井液密度;允许井径扩大一定程度的条件下,所需钻井液密度随井斜角增大呈增大趋势,但是随着钻井方位靠近水平最小地应力方位,此趋势逐渐改变为先减小后增大。通过该方法可得到任意井斜角、方位角井眼钻井液密度与井径扩大率的对应关系,根据钻井安全和储层保护的要求指导现场合理设计钻井液密度。

Moderate borehole collapse is one of the key technologies to solve the contradictions between wellbore stability and reservoir protection. According to the elastic mechanics theory, borehole diameter enlargement ratio calculation model of directional wells was established and the influence laws of drilling fluids density, hole deviation and azimuth angle were analyzed. The research shows that the drilling fluid density can be decreased when hole enlargement is allowed for any well; when the allowed borehole diameter enlargement ratio is fixed, the drilling fluid density increases with hole deviation angle increase, but the trend is transformed into decrease-first-then-increase when hole azimuth is gradually close to the minimum in-situ stress orientation. The corresponding relation between drilling fluids density and borehole diameter enlargement ratio is available for any well with this method, and the drilling fluids density can be rationally designed according to the requirements of drilling safety and reservoir protection.