Design and Performance Analysis of Fishbone Wells in Solution Gas Drive Reservoirs for Drilling Decarbonization
Authors: Ouadi H. , Laalam A. , Bakelli O. , Chemmakh A. , Gyimah E. , Fadairo A. , Tomomewo O. , Biheri G. , Fadili M. E. , Mellal I. 
Published: September 2023

ABSTRACT
Multilateral wells have been proven to effectively produce hydrocarbons by increasing reservoir contact, decreasing the drilling footprint and process cost, and reaching target reservoirs in different formations. Fishbone drilling technology, a new multilateral design, has significantly improved productivity in oil and gas fields worldwide by drilling multiple branches from the lateral section of a wellbore using Coiled Tubing Drilling technology. Selecting the optimum fishbone well design depends on investigating several parameters, including the number and length of branches, distance between them, and angle between the branch and the main horizontal well. This study compared vertical wells to a fishbone well using numerical simulation of real field data in Algeria. The suggested fishbone well design (8 branches, 800m length, 200m distance between branches, and 65° angle) significantly improved reservoir recovery and reduced drilling cost compared to the existing setup. These findings provide new insights into oil and gas field development in Algeria.

INTRODUCTION
Algeria, one of the biggest oil and gas producers globally, showed an evolution in applying new technologies for oil and gas recovery enhancement (Djezzar et al. 2020a). To effectively produce hydrocarbons, multilateral wells have proven to be a perfect strategy to increase the reservoir contact, decrease the drilling footprint as well as the process cost, and reach the target reservoirs in the same or different formations with multiple branches from one vertical well. One of the newest multilateral designs that have been recently used in the industry is called fishbone drilling technology. This technology consists of drilling a number of branches from the lateral section of the wellbore, which has the shape of the skeleton of a fish drilled using the Coiled Tubing Drilling (CTD) technology (Ouadi et al., 2023a). The fishbone well significantly improved productivity in many oil and gas fields around the world. One of the most challenging applications of the fishbone drilling technology concerns green fields, where selecting the optimum design depends on investigating several parameters. The shape includes the number and the length of the branches, the distance between them and the angle between the branch and the main horizontal well, with the aim of reducing operational cost and increasing cumulative production (Ouadi et al., 2023b). Fishbone well design has never been used in any Algerian oil and gas field. The objective of this study is to compare well deliverability between vertical wells and a fishbone well. Our study is based on a numerical simulation of a solution gas drive reservoir in Algeria in a formation called Lower Argillaceous-Sandy Trias (TAGI). Sensitivity analysis was provided to get the optimum design of the fishbone well. The obtained production results from the fishbone well were compared with the existing vertical wells and concluded with an economic study. The discovery of these results will undoubtedly offer novel perspectives on the development of Algeria's oil and gas fields. This is especially crucial in the case of unconventional reservoirs, where various impediments are primarily linked to the use of hydraulic fracturing as stated by Chellal et al. (2022) and Laoufi et al. ()2022. However, with the introduction of fishbone drilling, a technologically advanced and environmentally conscious solution, hydraulic fracturing can be replaced, thus paving the way for a more sustainable and effective approach to reservoir enhancement Through a comparison with Merzoug et al. (2022a) study. Drawing inspiration from the results of a study conducted by Ouadi et al. (2023b) who extensively examines the fishbone design - a prevalent type of multilateral well - with the goal of enhancing its productivity through increased reservoir contact. Subsequently, a comparative analysis of optimizing multilateral wells under reservoir conditions and horizontal wells was conducted using reservoir simulation models for a specific target reservoir. The research employed an experimental design approach to investigate the impact of four essential factors on the ideal arrangement of the multilateral well. The numerical simulation section provided an in-depth analysis of these specific parameters (Merzoug et al., 2022b). The study took into account productivity, as well as drilling capital and operational expenses, as the target function. At the outset, the research displayed the effects of single parameters and interaction graphs to illustrate the connection between the chosen factors and their influence on the target function.