Chemical Tracing Diagnostic Application for Monitoring Flow Contribution in Unstimulated Open Hole Multi-Lateral Wells Utilizing An Engineered Solid Carrier

Abstract

The oil and gas industry approaches field development in many ways. One approach is to drill and produce unstimulated open-hole horizontal multilateral (also referred to as multileg) wells. The Clearwater formation, among others in the Western Canadian Sedimentary Basin (WCSB) is an excellent example of this strategy. A method to positively determine flow contribution from each leg has been historically lacking. An innovative approach, using existing tracer technology is now available to provide these insights. As drilling is completed for each lateral leg, a unique oil soluble tracer, chemically bonded to a resin (sand-like) solid carrier is displaced out the drilling string while pulling out of hole. This tracer is normally spotted in the toe region to provide toe flow monitoring; Occasionally, a second unique tracer is spotted halfway through the same leg for mid leg flow monitoring. Volumetric calculations estimate required volumes for displacement. This process is repeated with unique tracers for each displacement. Hydrocarbon samples collected at surface upon initial production are analyzed for the presence of these tracers to assess contribution from each traced section. Over the last three (3) years, oil tracers have been utilized in approximately two hundred (200) multilateral wells to monitor hydrocarbon contribution of each drilled/traced leg. On average these wells have six (6) legs but can range from two (2) to more than ten (>10). Approximately one thousand two hundred (1,200) individual lateral legs have been traced and monitored. Oil sample analyses results have provided indication of which legs contribute initial flow, or present partial or total leg integrity concerns. While sampling schedules are typically designed for three (3) months of monitoring, oil soluble tracers are detectable in produced hydrocarbon for periods ranging from weeks to months, depending mainly on production rates. Tracer concentrations provide a relative productivity assessment of each leg over time. Overall, the deployment of oil tracers with a solid carrying mechanism in unstimulated open hole multilateral wells has provided operators with an efficient strategy to verify hydrocarbon contribution from each individual leg. Future work to increase value of this diagnostic application aims to integrate tracer characteristic performance of each multilateral well with its production, drilling, and subsurface datasets, to identify patterns and correlations between datasets to assist operators in their development plans. Additionally, future work aims to extend the tracer detection window to allow for monitoring multilateral wells that present elevated borehole collapse risk beyond the initial months of flow.