【摘要】 针对疏松砂岩储层高孔隙度、高渗透率、弱胶结和低强度的特点,在地应力作用下容易发生大变形,在钻井过程中经常发生缩径、卡钻以及下套管遇阻甚至挤毁套管等情况。根据地层实际状况和施工条件定量评价井眼的变形缩径规律,可以科学指导钻井设计或现场施工的思路。文章提出在疏松砂岩储层水平井井眼变形分析中应考虑疏松砂岩的粘弹塑性变形,综合考虑地应力和钻井液密度对井眼变形的影响。应用拉格朗日元法进行数值模拟计算,得出了疏松砂岩中水平井井眼缩径变形随时间变化的规律。研究认为①井眼变形中应考虑渗流以及因浸泡引起砂岩强度降低等因素的影响;②研究得到的井眼缩径率与时间的关系,对于进一步研究和预测疏松砂岩的储层安全钻井周期以及水平井水平段极限长度,具有理论上的指导意义。更多还原

【Abstract】 Due to the characteristics of high porosity, high permeability, weak cementation, and low strength of unconsolidated sandstone reservoirs, the wells drilled through are subject to undergauging deformation under the effects of earth stresses, pipe sticking and difficult casing running are often encountered during drilling. So the quantitative assessment of wellbore deformation behavior under actual formation and operation conditions can provide a scientific guidance on well design and field operation. In this article it is explained that when analyzing the deformation behavior of a horizontal well in the unconsolidated sandstones, the viscoelastic deformation of such formation should be considered as well as the combined effects of earth stresses and drilling fluid density. The Lagrange Element Method will be used to do the calculation, from which the undergauging deformation with time of a horizontal well will be concluded. It is thought after study here two main points which include: ①effects of seepage, and soaking induced sandstone strength reduction should be considered in wellbore deformation behavior; ②the relationship between undergauging rate and time, derived from the study, in theory will be a guide for studying and predicting safe drilling cycle of wells drilled in unconsolidated sandstone reservoirs and the horizontal length limit.更多还原