Annular Ledge Formation Method Allows Sidetracking in Multilateral Wells
Authors: Carpenter Chris 
Published: April 2020

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19350, “Effective Annular Ledge Formation Sidetracking in Multilateral Wells in the Vostochno-Messoyakhskoye Field,” by Andrey Voronin, Messoyakhaneftegaz, and Nikolay Abaltusov, SPE, and Anton Vershinin, Weatherford, et al., prepared for the 2019 International Petroleum Technology Conference, Beijing, 26–28 March. The paper has not been peer reviewed. Copyright 2019 International Petroleum Technology Conference. Reproduced by permission.
Multilateral drilling technology offers a highly effective method of enhanced oil recovery in fields characterized by complicated geological structures. This paper describes the analysis of sidetracks drilled in an open hole by an annular ledge formation method with a downhole motor in multilateral wells.
Introduction
Currently, industry growth requires development of fields with complicated geology. Drilling single-bore horizontal holes for these fields is insufficient, to say nothing of drilling vertical or directional wells. Multilateral wells with multiple horizontal sidetracks are drilled with increasing frequency. The competition between downhole motors and rotary steerable systems (RSS) in multilateral-well drilling is fierce.
In the complete paper, the authors describe deployment of a method previously only available with RSS that provides advantages to downhole-motor use: annular ledge formation, which involves sidetracking in an open hole. In the case study described, a conventional motor is used without additional electronics.
Conventional sidetracking methods in an open hole with the use of motors involve sliding. During sidetracking, the sliding is aggravated additionally by a low rate of drillstring movement. If side-tracking with the conventional method is impossible, then usually a special sidetracking bit is installed and the motor-bend angle is increased. Such measures result in additional time and financial expenditure.
The annular ledge formation method allows for sidetracking in an open hole with the use of a standard bottomhole assembly (BHA) with a motor, which also will be used for drilling a lateral. The key feature of this method lies in the fact that, during sidetracking, the drillstring is constantly rotating, which allows avoidance of the problems related to sliding. When sidetracking with the use of this method, the ledge is formed over the entire circumference of the borehole, not only on the bottom wall. But, when sidetracking deeper, a trough is formed on the low side of the hole and the upper side remains unaffected. Because of this, the annular ledge formation method is described by the authors as sidetrack with rotation. The authors discuss the deployment of this method in the Vostochno-Messoyakhskoye field when drilling multilateral fishbone wells. The complete paper presents a detailed discussion of the method and different situational approaches to its use.
Vostochno-Messoyakhskoye Field
The field is the northernmost developed onshore oil field in Russia in the Tazovsky region 250 km from the Arctic Circle in the Arctic climatic zone. The field is developed with horizontal production and injection wells along a horizontal section length of approximately 1000 m. The geology of the reservoirs is complicated with a large gas cap. In terms of geological conditions, the PK 1-3 pay zone is irregular within the field and is represented by loose sandstones both uniform and horizontally layered. The oil-bearing formations are isolated.