A Double-Parameter Optimization Method Based on the Open-Hole Extension Capability of Extended Reach Horizontal Well
Authors: Jia Zongwen , Zhou Changsuo , He Qinyi , Chen Xuyue , Gu Liangju , Wang Gan 
Published: September 2022

ABSTRACT:
Previous studies have found that the horizontal extension capacity of extended reach wells is affected by drilling fluid density and displacement, and a single parameter is optimized by taking the extension limit as the objective function. In this paper, the maximum open hole extension capacity is taken as the objective function, and the drilling fluid density and displacement are taken as the constraint conditions, the nonlinear programming equations are established, and dual parameters (drilling fluid density and displacement) are optimized. The density window was determined on the premise of wellbore stability, and the displacement range was determined on the basis of hydraulic conditions. Due to density will affect the selection of optimal displacement, a set of cyclic algorithm is designed to modify density and displacement. According to the analysis and calculation of an extended reach horizontal well, when the density is 1.02 kg/cm3 and the displacement is 20 L/s, the maximum open-hole extension capacity is 7028 m.

1. INTRODUCTION
In order to reduce drilling costs and increase drainage area, extended reach horizontal wells have been widely used in offshore oil and gas exploitation and shale gas exploitation in remote mountainous areas. When the reservoir is long and rich in oil and gas resources and the cluster wells are producing distant oil and gas reservoirs, it is necessary to maximize the lateral extension capacity to reduce costs and achieve greater oil and gas revenue. Gao systematically proposed the concept of extension limit for the first time, taking into account wellbore stability, hydraulic factors, drilling equipment and other influences, dividing the extension limit into open hole extension limit, hydraulic extension limit and mechanical extension limit (Gao et al., 2009; Gao et al., 2018). Wang et al. established a hydraulic extension limit model, taking into account the limitations of hydraulic equipment on the extension limit (Wang et al., 2008). Subsequently, Chen and Li et al. improved the theoretical model of open hole extension limit (Chen et al., 2018; Chen et al., 2018; Li et al., 2018). In the extension limit theory, drilling fluid density and displacement are closely related to the extension limit and directly affect the extension limit of horizontal section of extended reach wells, so it is of great significance to the optimization of drilling fluid density and displacement. A large number of scholars have determined the application range of drilling fluid density and displacement respectively (Tan et al.,2012). Li et al firstly optimized drilling fluid displacement based on elongation limit (Li et al.,2017). This paper focuses on the maximum open hole elongation, that is, the maximum elongation of horizontal wells with extended reach under the condition of stable borehole wall. Drilling fluid density and displacement will affect borehole stability, thus affecting the open hole elongation capacity. However, the density and displacement are artificially controllable. Therefore, reasonable drilling fluid density and displacement can be selected to maximize the open hole elongation capacity.