Effect of eccentricity with different shape wellbores on the flushing efficiency of drilling fluid filter cake

• Published in: Journal of petroleum science & engineering 2023-01, Vol.220, p.111112, Article 111112
• Main Authors: Zhang, XiaYu, Bai, Yang, Du, Jiang, Lu, Chuan, Fan, LiKun, Song, Jian, Li, Zhen, Zhang, ShiHao, Zhang, XingGuo
• Format: Article
• Language: English
• Subjects: Casing eccentricity; Cementing; Flushing efficiency; Flushing law of elliptical wellbore; Wall shear stress
• ISSN: 0920-4105; 1873-4715
• DOI: 10.1016/j.petrol.2022.111112

The effective flushing of a drilling fluid filter cake is crucial for improving the zone isolation of cement sheaths during cementing operations, some studies have researched the flushing law of filter cake in circular wellbore, however, only a few have studied the flushing law and mechanism of elliptical wellbore and the irregularity of elliptical wellbore may lead to the increase of the non-uniformity of filter cake that may result in different flushing results than the circular wellbore. In this study, a filter cake formation and flushing experimental system is developed for circular and elliptical wellbore, and the formation and flushing experiments of drilling fluid filter cake in circular and elliptical wellbore are conducted, the flushing law and mechanism of drilling fluid filter cake in circular and elliptical wellbore are obtained by combining the computational fluid dynamics (CFD) simulation calculation results with the experimental results. The results revealed that the filter cake flushing efficiency of the same drilling fluid and displacement were primarily affected by the thickness of the initial drilling fluid filter cake, shear strength, wellbore shape, wall shear stress and eccentricity, the initial thickness and shear strength were higher, the filter cake flushing efficiency was lower, the wall shear stress of the flushing fluid was higher, the flushing efficiency of the filter cake was higher, and the change in wellbore shape and eccentricity led to an uneven distribution of annular velocity and reduced the flushing efficiency of the filter cake. The method and conclusion enable to gain an understanding for improving the flushing efficiency of the drilling fluid filter cake and forms a basis for the design of flushing fluids in cementing operations. •Established a more suitable for downhole of drilling fluid filter cake preparation and flushing system.•The filter cake flushing law of circular and elliptical wellbores were studied that combined with the wall shear stress and filter cake flushing efficiency calculated by CFD (computational fluid dynamics) simulation.•The flushing efficiency of filter cake in circular and elliptical wellbores was different, because the different annulus section and the different initial filter cake thickness and shear strength during the preparation of filter cake.