CURLEW C FIELD : SHELL'S FIRST FORAY IN THE DEVELOPMENT OF THE UPPER CRETACEOUS CHALK PLAY OF THE CENTRAL NORTH SEA, BLOCK 29/7
Field Developments and Case Studies
Alan McQueen1, Samantha Large1
1Shell UK Limited
The Curlew C field development is an example of unlocking potential within the fractured Upper Cretaceous chalk through drilling the field’s single production well.
The chalk discovery is associated with a relatively small four-way dip closed anticline, which is bisected by a NE-SW trending fault system. Smaller radial faults trend NW-SE and are related to the inverted structure. Porosity preservation of up to 36% is related to overpressure rather than burial within allocthonous units. Well test results showed a Tor and Ekofisk combined 7000bbl/d with a fracture contribution, producing light oil (40o API) within the vertical discovery well. The field STOIIP range is 34-64 MMstb.
Chalk porosity was found to inversely correlate with acoustic impedance. Minimum impedance yields high porosity zones. After calibration to well 29/7-5 and 29/7-7 max porosity maps were generated. Areas of high porosity within the Tor were interpreted as debris flows (allocthonous bodies). These units are closely related to the radial faults cutting the inverted anticline and suggest active seafloor topography during deposition.
The current field development plan executed during late 2007 includes a sub-horizontal development well 5000ft long targeting the Ekofisk and Tor Formations, with a trajectory trending parallel to the main NE-SW trending fault system relying on ADN LWD image data to aid well placement.
High resolution FMI was logged on PCL to prove the production mechanism of the Ekofisk and Tor Formations and optimise the completion. However, the data it returned was different from the original prognosis and then became integral in effecting redesign of the completion and the stimulation strategy.
In a first for Shell U.K., the drilling of this reservoir allowed us the opportunity to run the high resolution GVR LWD image tool. While drilling the sidetrack, Curlew C-P1Z the tool was used to steer the well with increased confidence and match the detailed features logged by the FMI across the 5000ft reservoir section. The positive correlation to the FMI data meant that a second PCL FMI was unnecessary therefore saving rig time.