The magnetic ranging method is used in many oil-field drilling applications, especially in heavy oil production. One typical example is used in the steam-assisted gravity drainage (SAGD) technique to enhance oil recovery of heavy crude oil and bitumen. Such SAGD applications require drilling two horizontal twin wells that are parallel and separated by a few meters. As a result of accumulated survey errors, it is very challenging to achieve a controlled separation and good relative well placement among wells using conventional logging-while-drilling (LWD) survey data. Current practice mainly relies on wireline technology to access one of the twin wells to generate an active ranging signal; however, this is costly and time consuming.
This paper presents a true access-independent magnetic ranging solution, designed around SAGD applications, that eliminates the need to access a target wellbore below the surface. A surface excitation is attached to a wellhead of a target well to introduce a current signal traveling along the entire target well. Concurrently, LWD gradient array sensors in a drilling well measure the induced field to determine the relative distance and direction between the two wells. This method permits operators to efficiently acquire access-independent active ranging measurements, enabling faster well placement optimization.
This paper discusses the fundamentals of the new ranging technique, including both the surface excitation and the gradient array systems. The paper also analyzes modeled responses, experimental data, and field trial results from a gradient discovery tool (GDT) to validate the proposed concept. Comparing the novel tool to the current industry standard tool, a magnetic guidance tool (MGT), the paper demonstrates that the GDT is capable of achieving accurate and valid ranging performance in SAGD applications. Furthermore, the described LWD system presents an alternative ranging tool to current wireline techniques and provides several advantages for well intersection and positioning applications that can help reduce overall time and costs.