This paper presents two case histories that demonstrate the effectiveness of an active geosteering approach using computer networking between rig site and operator office. A satellite link was used to update well trajectory and LWD data in StrataSteer™ geosteering software located within the operator’s asset group. This link provided the key advantage of allowing subsurface staff to become an integral part of the geosteering process.
The geosteering software enables a geological / petrophysical model to be created based on offset well log data and seismic profiles. The LWD log responses are modeled along the planned well trajectory and then compared to the actual LWD log responses (gamma, multi-depth resistivity, neutron, and density). The responses are then used to adjust the geological model and take geosteering decisions.
The amended geological situation enabled immediate and enhanced decision-making regarding adjustments to the well path in order to remain within the optimum reservoir zone. Good communication between all parties involved, both onshore and offshore, undoubtedly contributed to the success of both operations.
The two example wells, "A" and "B", present different challenges. In both cases, it was clear prior to drilling that active geosteering would be necessary. Well A was planned as a horizontal oil producer. The vertical thickness of the pay section was estimated at 13 ft, and the bed dip was expected to vary between 0 and 2 degrees in the direction of drilling. Following successful landing of the well, a total of 1300 ft of target reservoir was drilled using the geosteering software to actively guide the well path. Production rates from this well were significantly above pre-drill expectations.
The objective in Well B, a deviated sidetrack, was to drill through four reservoir zones, two on either side of a major fault. Recognition of the fault in real-time was critical due to different reservoir thickness and bed dips across the fault and significant uncertainty regarding the position of the fault. The use of geosteering software enabled the fault to be quickly recognized when it appeared — some 450 ft along hole earlier than expected. The geological model was quickly revised and the well path adjusted to optimize placement in the final two targets.