Successful Interception of Uncased Boreholes Using Integrated Ranging Technology and Advanced Survey Management

Abstract As part of a major project, the operator was faced with the need to abandon an open borehole in the vicinity of a planned infrastructure. To complicate matters, the borehole contained a fish and, close by, was another fully cased borehole and a second, which had multiple side-tracks containing steel components, but which had the casing milled out and been fully abandoned with cement to surface. It was necessary to drill a new borehole to intercept the old borehole, which raised several challenges including ranging detection through salt, safe drilling among multiple boreholes, effective integration of three independent ranging technologies, and re-entry into and abandonment of the open borehole. The problem of intersecting and sealing an open borehole in the presence of offset cased boreholes and fish left in the ground was unique and required multiple ranging technologies to be employed. Adding to the complexity of this interception was the presence of up to six sidetracks from other (older) boreholes in the immediate (less than 5 meters) vicinity of the intercept and target boreholes. Initial forensic analysis of all the borehole data was made to see if a borehole intersection project was feasible. Following this, the planning and execution of the work followed the usual oil and gas industry practices for relief well interception, including the established locate, follow, and intercept process. The planning phase highlighted the need for combining advanced survey management with active acoustic, active magnetic and passive magnetic ranging methods. Project success hinged on the effective integration of these three technologies. By integrating all survey and ranging data, the lower section of the target borehole was located, re-entered and cemented on the first attempt without incident. Despite the combination of ranging technologies, it proved impossible to locate and re-enter the upper section of the borehole due to the propagation of survey uncertainties. The outcomes highlight the efficacy, and limitations of this integration for complex abandonment scenarios using: Active Magnetic Ranging (AMR) to track the nearby casing down to the abandoned fish,Passive Magnetic Ranging (PMR) to locate offset casing stubs and fishes especially through the salt layer, andActive Acoustic Ranging (AAR) to locate offset casing and open-hole intervals. Intercepting a 6½" open hole at 1,031m MD in the presence of two other boreholes within two meters within a specific interval is the first of its kind and would have been impossible with conventional magnetic ranging technologies. For the first time in a relief well setting, it required the integration of magnetic and acoustic systems, where a science-based engineering approach was applied to make use of proven passive and active magnetic ranging in combination with acoustic ranging. This case study demonstrates the benefit of combining different technologies to achieve a safe and effective abandonment in a congested subsurface situation. It offers insights for similar challenges which might be encountered in the O&G industry.