Abstract Open hole wellbores present cost efficient completion solution; however, instability of such boreholes in weak formations such as chalk in the course of production raises a concern. This paper presents a method for predicting the stability of the radial jet drilling laterals in the Danish Gorm chalk field. The method is based on four main parts: (1) rock mechanics testing in the triaxial cell; (2) the single lateral hole testing consisting of loading and fluid flow test; (3) utilizing CT imaging for identifying the damaged zone and its extension; and (4) numerical simulations, utilizing a chalk model that takes into account the post-peak softening and the rate dependency of the pore collapse stress. Simulation of bottom hole and reservoir pressure decline over a year by 17 MPa and 9 MPa, respectively, showed a small development of the plastic strain at the borehole wall. Further simulation up to four years with constant stress (creep) resulted in a change in the cross-sectional area of the borehole, where shear cracks developed at the wall and some distance away from the hole stress concentrations associated with pore collapse was observed. By the end of the simulation, the borehole was likely to change its geometry by removal of the plastified area. The single lateral hole test with flow carried out with differential pore pressure, drawdown, of about 2.5 MPa within 5 h and 1 h, respectively, provided insignificant permeability change during the flow test.

中文翻译：

---

Gorm白垩矿区侧向钻孔行为的评价

摘要 裸眼井筒提出了具有成本效益的完井解决方案；然而，在生产过程中在白垩等薄弱地层中钻孔的不稳定性引起了人们的关注。本文提出了一种预测丹麦 Gorm 白垩油田径向喷射钻井支管稳定性的方法。该方法基于四个主要部分：（1）三轴单元中的岩石力学测试；(2) 单侧孔试验，包括加载和流体流动试验；(3)利用CT影像识别损伤区及其扩展；(4) 数值模拟，利用考虑峰值后软化和孔隙坍塌应力速率相关性的白垩模型。一年内井底压力和储层压力分别下降 17 MPa 和 9 MPa 的模拟，显示了钻孔壁塑性应变的小幅发展。使用恒定应力（蠕变）进行长达四年的进一步模拟导致钻孔横截面面积发生变化，观察到在井壁处出现剪切裂纹，并且在距离与孔隙坍塌相关的孔应力集中有一段距离时观察到。在模拟结束时，钻孔可能会通过去除塑化区域来改变其几何形状。分别在 5 小时和 1 小时内以大约 2.5 MPa 的孔隙压差和压降进行的单侧井流动测试在流动测试期间提供了微不足道的渗透率变化。观察到剪切裂纹在壁处发展，并且在距离与孔隙坍塌相关的孔应力集中有一定距离的地方被观察到。在模拟结束时，钻孔可能会通过去除塑化区域来改变其几何形状。分别在 5 小时和 1 小时内以大约 2.5 MPa 的孔隙压差和压降进行的单侧井流动测试在流动测试期间提供了微不足道的渗透率变化。观察到剪切裂纹在壁处发展，并且在距离与孔隙坍塌相关的孔应力集中有一定距离的地方被观察到。在模拟结束时，钻孔可能会通过去除塑化区域来改变其几何形状。分别在 5 小时和 1 小时内以大约 2.5 MPa 的孔隙压差和压降进行的单侧井流动测试在流动测试期间提供了微不足道的渗透率变化。