A Model of Open-Hole Extension Limit of Horizontal Extended-Reach Wells in the Cold Sea Area of the Arctic
Authors: Li Gengchen , Chen Xuyue , Jin Ming , Cao Xiaohua , Zhu Mingchi , Wang Rong 
Published: August 2024

ABSTRACT:
An open-hole extension limit prediction model of extended-reach drilling (ERD) in the cold sea area of the Arctic is established, considering wellbore stability and temperature field. The widely used open-hole extension limit model primarily relies on the concept of wellbore stability, this paper considers the impact of the circulating temperature field on the density of drilling fluid and analyzes the predicted results for the horizontal section extension limit in ERD, tripping in, and tripping out conditions. The findings suggest that considering temperature leads to a longer horizontal section extension limit during drilling and tripping in conditions, while decreases during tripping out condition. Additionally, an optimal drilling fluid flow rate exists during ERD, with the horizontal section extension limit initially increasing and then decreasing. Slowing the tripping in and tripping out speed can enhance the horizontal section extension limit during ERD. Moreover, reducing the flow behavior index and consistency coefficient can increase the horizontal section extension limit in ERD, with the flow behavior index demonstrating greater sensitivity.

1. INTRODUCTION
The oil and gas resources in the Russian, Arctic continental shelf region are abundant, and the economic outlook is favorable, leading to rapid economic development. Within the broader context of energy development, the abundant oil and gas resources in cold sea regions have attracted strong attention from various petroleum companies (Bukhanov et al., 2023). Horizontal extended-reach wells (ERDs) have the potential to generate significant economic benefits. It plays a crucial role in resolving conflicts over marine use in oilfield development, expanding platform coverage areas, and reducing the costs of oil and gas field development (Gao et al., 2019).
For the first time, the theoretical basis extension limit of ERWs is proposed, including three extension limit theories, which are open-hole extension limit, hydraulic extension limit, and mechanical extension limit; and their constraints are wellbore stability, rated pumping pressure, rated pumping power, and the ultimate bearing capacity of mechanical equipment, respectively (Gao et al., 2009). The open-hole extension limit model considering two-phase flow of rock chips is proposed, and its model considers ERD, tripping in and tripping out, and the open-hole extension limit is the minimum value in these several working conditions (Li et al., 2017). A model for extracting hydrates from ERWs and a machine learning drilling parameter optimization model are presented (Chen et al., 2024; Chen et al., 2022; Chen et al., 2023). A numerical model of wellbore heat transfer was pioneered, the theoretical framework has won extensive attention from scholars around the world (Ramey Jr, 1962). (Willhite, 1967) proposed a method for determining the heat transfer coefficient based on time iteration theory. (Wang et al., 2017) proposed a computational model for the temperature field in polar permafrost wellbores. (Deng et al., 2019) developed a computational model for the migration of moisture in permafrost layers due to thawing during the drilling circulation process. (Li et al., 2020) computational models for the calculation of offshore safety density windows and temperature fields in hydrate reservoirs. Furthermore, most models are only applicable to vertical wells, while the calculation for the horizontal well is more complex. (Ataga & Ogbonna, 2012) proposed that neglecting the effect of temperature on equivalent circulating density (ECD) could lead to serious drilling accidents due to the narrow safety density window, resulting in prediction errors.