Most horizontal wells have been drilled geometrically with relatively large targets to help reduce the risk of missing the pay zone. The recent introduction of geosteering, with real-time measurements at the bit, has enabled the directional driller to stay within thin pay zones by making course corrections in the drainhole based on geology. Geosteering visualization in 3D and 2D offers better understanding of the formations and trajectories in real-time and lowers the risk in the decision making process at the wellsite. This allows accurate well steering to complex targets where errors in TVD as small as 5 feet can represent the difference between success and failure.
In this paper, we discuss three real-time graphical applications which simplify correlation with offset wells and provide 3D visualization of the formations being drilled. These tools combine to make a comprehensive geosteering package. The first application is most useful in the top section of the well. It allows the wellsite geologist to better locate bit position by correlating offset and current log information, thus identifying markers, target zones and potentially dangerous sections.
The second application is a powerful graphical tool that enables the directional driller and geologist to steer using real-time formation measurements, thus maximizing the amount of horizontal drainhole in the pay zone.
The third application provides interactive 3D and 2D visualization of the wellbore, well plan, project ahead and offset wells, along with the formations and targets. With real-time updates, this is a powerful tool for visual confirmation of the wellbore proximity to the formation boundaries.
We give examples that illustrate how these tools have been used to improve the decision making process in directional drilling and to increase well production.
Drilling of horizontal wells can improve operators' production and return on investment, as well as reducing the number of platforms or wells needed to develop a field. Geosteering has been proven to be the most efficient way of drilling horizontal wells. At Anadrill, we have developed the GeoSteering* System, as shown in Figure 1, to aid in the geosteering process. The GeoSteering System is composed of the GeoSteering coordinator; planning, interpretation and evaluation products such as Integrated Forward Modeling (INFORM*) and Power Plan* the Integrated Drilling Evaluation And Logging (IDEAL*) Wellsite Information System (WIS*); and down-hole tool string.
The GeoSteering coordinator is the liaison between the service company and the operator, and is responsible for the complete geosteering process. The coordinator maintains a database of horizontal well information which is critical to the success of future wells. The most visible function of the GeoSteering coordinator is to supervise the steering of the drill bit into the reservoir.
INFORM is used for pre-job planning and formation evaluation. During pre-job planning, geologic information, including cross-section data and marker positions, is used to assist in the construction of a petrophysical and geometrical model of the prospect. This model is integrated with the trajectory information provided by Power Plan to predict Measurement While Drilling (MWD) and Logging While Drilling (LWD) tool responses. The tool response is a function of tool inclination and formation dip. The GeoSteering coordinator interacts with INFORM to adjust formation descriptions, which are verified by comparing forward modeled logs with field data.