Numerical Analysis of Dynamic Instability of Juncture in Multilateral Drilling Based on Chemo-Mechanical Coupling

Abstract

ABSTRACT During the drilling of multilateral wells in oil and gas fields, the juncture in multilateral drilling is a high risk area for collapse. Studying the factors affecting the stability of the multilateral well juncture is helpful to improve the success rate of sidetracking in branch wells. In this paper, based on the experiment, the variation law of shale rock mechanical parameters before and after drilling fluid immersion is obtained. The three-dimensional model of the juncture of multilateral drilling considering the decrease of rock strength under the action of hydration is established. The angle of the main branch well and the borehole azimuth angle of the main branch well on the stability of the multilateral well juncture is analyzed. The three-dimensional Coulomb failure criterion is introduced to characterize the dynamic failure of the rock, and the failure range and failure length of the multilateral well juncture under different conditions are obtained. The results show that the smaller the angle, the more obvious the stress concentration and the longer the failure length; the smaller the azimuth, the more stable the multilateral well juncture; with the increase of drilling time, the failure range of the multilateral well juncture is gradually expanding, and after 2d, the hydration effect gradually slows down. The model can simulate the influence of different conditions on the failure range and failure length of sidetrack multilateral well juncture, and has certain guiding significance for improving the success rate of sidetrack drilling and increasing production efficiency. INTRODUCTION After continuous production in oil and gas fields, production well output decreases and some production wells may even break down leading to scrapping or shutdown, and these conditions are a common problem in the middle and late stages of oil and gas field development. If new wells- are deployed, a significant increase in economic investment is required. However, if these low-producing wells, faulty wells, and shut-in wells are transformed into an optimized new well that can be reused in the original well network, the drilling cost will be greatly reduced and old wells will be revived, dead wells will be revived, and oil fields will gain increased production (Zhu et al, 2011). Lateral drilling branch well technology is to make full use of the old well network and the re-usable well section in the upper part of the old well to drill a new borehole that can reach the target layer and be used again. Lateral drilling branch wells are widely utilized because they have the characteristics of less time, low cost, increased oil absorption area and higher recovery rate (Sun et al, 2018 and Chen et al,2022). It provides economic development and relieves energy tension.