水平井偏心环空顶替流体密度差优化

顶替界面失稳指进造成的钻井液迟流是导致油气水窜槽的主要原因。水平井顶替界面受到套管偏心引起的宽窄间隙阻力效应和密度差引起的浮力效应共同影响,且两者对顶替界面的影响相反,因此有必要根据水平井套管偏心情况优化顶替流体密度差,从而提高顶替界面的稳定性。在总结三维数值模拟方法优缺点的基础上,采用该方法分析了水平井顶替界面长度随顶替时间的变化规律,以实现最小顶替界面长度为目标,得出了水平井套管偏心度与最优密度差之间的匹配关系。研究结果表明:水平井顶替界面长度随顶替时间增加增长幅度趋缓,但并不明显;在水平井套管偏心的情况下,密度差过大或过小都会降低顶替界面的稳定性,需要根据套管偏心度选取合理的密度差使得顶替界面长度最短。研究结果为水平井顶替参数和封固段长度设计提供了必要的理论依据。

Density difference optimization of displacing fluids in eccentric annulus of horizontal wells

Slow-flow drilling fluid caused by fingering instability of displacement interface is the main factor to result in oil/gas/water channeling. The displacement interface in horizontal wells is affected by resistance effect in narrow and wide clearances caused by casing eccentricity and buoyancy effect caused by density difference. Besides, impacts of the two factors on displacement interface are opposite. Therefore, displacement interface stability can be enhanced by optimizing the density difference of displacing fluids based on casing eccentricity in horizontal wells. The change law of the displacement interface length with time is analyzed based on the advantages and disadvantage of the method of three-dimensional numerical simulation to realize the target of minimum displacement interface length and have the matching relationship between the optimal density difference and casing eccentricity. The conclusions are as follows: the growth rate of displacement interface length slows down with time increasing, but it is not obvious; the too large or small density difference will reduce the displacement interface stability in the eccentric annulus of horizontal wells. In order to achieve the shortest displacement interface length in cementing, reasonable density difference shall be chosen on the basis of casing eccentricity. The study results provides theoretical basis for the design of displacement parameters and cementing length in horizontal wells.