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Case Study: Tullow Oil Resolves Drilling Uncertainty in Compartmentalized North Sea Reservoir
"Petrel RE increased our confidence that we would drill a successful well in a questionable sector. It was really fantastic having a user-friendly tool with which to forecast and play different development scenarios."
Alex Kirsch
Reservoir Engineer
Tullow Oil Company
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3D modeling and reservoir simulation enable reservoir engineers to refine understanding of depositional environment and evaluate drilling options
Challenge
Determine the flow potential of a gas reservoir compartment with anomalous pressure rate as a drilling target, considering the possibility of an isolated fault block.
Solution
Use Petrel Reservoir Engineering (RE) and ECLIPSE reservoir simulation software to better understand sand-body architecture and fault transmissibility, and to evaluate drilling scenarios.
Results
Identified three viable scenarios from 100 geologic models used to test the sensitivity of reservoir properties; evaluated the effectiveness of development scenarios; and received approval for the drilling proposal.
Evaluate drilling locations
While evaluating drilling locations in the Southern North Sea, Tullow Oil PLC discovered a reservoir sector in which the pressure differed noticeably from the pressure in adjacent sectors. Tullow reservoir engineers needed to understand whether this sector had become compartmentalized by faulting.
To ascertain whether the sector was completely isolated, the Tullow team decided to study fault transmissibility and the sand-body architecture. An in-depth analysis was undertaken—including a sensitivity study on channel orientation and the time frame of deposition—to decide whether they needed to drill an additional well to reach this compartment.
Assess the geological conditions
To better understand the uncertainty in the reservoir description, especially fault transmissibility, Schlumberger Information Solutions (SIS) recommended Petrel seismic to simulation and ECLIPSE reservoir simulation software for optimum modeling, analysis, and forecasting.
One hundred sector model scenarios were generated that varied channel orientation, boundary conditions around the faults, porosity, permeability, and water saturation, and which were efficiently tested via the flexible, easy-to-use subsurface workflows.
The comprehensive Petrel modeling workflow (Tullow opted for nested workflows within one main workflow) facilitated collaboration among reservoir engineers, geologists, and geophysicists by allowing them to easily interact with static and dynamic data, integrate their domain-specific knowledge, and draw final conclusions to expedite decision making.
Zero in on the best possibilities
The rapid history-matching features of Petrel RE and ECLIPSE software dramatically reduced the number of possibilities, providing three viable models that would form the basis of Tullow’s development plans.
The ability to reduce uncertainty and make accurate predictions based on the three viable geological realizations increased Tullow reservoir engineers’ confidence that they could drill a successful well in this compartment. The next step was to evaluate development plans, including options to drill horizontal or straight holes. Using the Petrel Reservoir Engineering/ECLIPSE workflow, they were able to evaluate a number of development scenarios, visualize well locations, evaluate projected production results, reposition the wells, and retest.
As a result, the team confidently submitted a well proposal and obtained the necessary approvals to move forward with a development plan designed to effectively drain the isolated compartment.
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