The Scope 

Tullow wanted to acquire interference test data from two discovered fields in the area.  The reservoirs are complex multi-layer sand/shale systems. The Nautec brief was to design a well completion which allowed independent flow and data from individual layers to be acquired while also optimising the use of available drilling units.  The reservoirs are sub-hydrostatic in original pressure and the crude has 35 – 40% wax content.

Added Value

To satisfy the data acquisition and flow objectives the resulting completion incorporated artificial lift via hydraulic rod pump, multiple packers and remotely controlled inflow control valves (ICV), permanent downhole pressure/temperature gauges and distributed temperature sensing (DTS).
The use of intelligent completions in combination with rigless clean-up and testing for the EWT wells resulted in rig time savings of approximately 25 – 30 days per well compared to Tullow’s benchmark timing for completion and testing of previous appraisal wells in the Turkana Basin. This was equivalent to a cost saving of $7.5MM per well. The benefits of the approach are:

  • Rigless testing allows acceleration of the drilling programme in conjunction with the testing activity.
  • The data which have been, and continue to be, captured from the well clean-up flows and the EWT production phases are already having a significant effect on the formulation of field development plans, particularly with respect to well spacing and identification of the required number of development wells.
  • The approach can be applied to field appraisal data gathering in any discovered field, potentially enabling the acceleration of development planning and reduction of the time to first oil production.
  • Interference data acquired significantly derisks reservoir continuity and improves subsurface understanding to narrow the range of uncertainty around field recovery factors.
  • Capture of DTS data is enabling the evaluation of the downhole heater performance in real-time. It is expected that when wells are produced for longer periods the risk of wax deposition related flow assurance problems is reduced (as a result of more residual heat remaining in the wellbore). This could lead to modifications to downhole heating i.e. a reduction in the installed heater length, which could have a significant effect on development well costs.
  • The immediate availability of the five permanent completions enables consideration of early production to accelerate the revenue stream from the Amosing and Ngamia fields.

The project is the subject of SPE 178878 which was presented at the SPE/IADC Conference in Fort Worth, Texas in March 2016.