The success of a horizontal drilling campaign highly depends on the implementation of appropriate well placement procedures to manage the constraints, risks, and uncertainties that may have a negative impact on the overall economy of the project. The magnitude of the uncertainties associated with the horizontal well trajectory and the geology is usually higher than the magnitude of that particular target within the reservoir that would maximize the production. The risk and uncertainty factors can be handled with the use of particular well placement techniques during the planning and execution phases.
In the planning phase, these techniques include proper geological modeling methods and flexible well planning to allow room for changes if unexpected events arise while drilling. During the well execution, procedures should include the use of appropriate technologies to understand in real time the rock properties, the reservoir geometry, and horizontal well position, and, based on this information, to steer the well within the desired geological target.
Girasol field, located in the Middle Magdalena Valley basin in Colombia, is composed of a sequence of sandstone channels that contain heavy oil with gravity ranging from 11 to 13° API. The main targets are five stacked sandstone reservoirs, from 10 to 35 ft thick, located 1,100 to 1,500 ft true vertical depth below surface. The field development included cyclic steam injection applied in horizontal wells to improve the heavy oil mobility. To maximize oil production and improve the cumulative steam/oil ratio, the objective was to place horizontal wells of up to 2,500 ft lateral extension within 3 to10 ft distance from the bottom shale of each reservoir.
The horizontal well placement under this type of scenario required the use of precise horizontal well placement techniques and drilling practices to avoid exits from the predefined geological targets. These techniques relied on the use of deep directional electromagnetic measurements that enabled real-time bed boundary mapping.
This paper presents the main challenges and uncertainties faced for well placement in the Girasol field horizontal drilling campaign, the technical solutions implemented, and the lessons learned in more than 80 horizontal wells drilled.