Abstract
Dynamic flow modeling has been an essential part of the planning for the Gullfaks C-5A well. This paper discusses the use of such modeling and presents the main results related to:
Design of operational window
Transient scenarios
Development of detailed procedures.
Training
Flow test modeling
Design of under-balanced cementing
First, the operational window was defined by means of steady state modeling. Various combinations of influx rates and choke pressures were simulated to ensure that bottomhole pressure could be controlled. Also modeling was applied to ensure that proper hole cleaning was maintained during the operation. Modeling of the running of the 7" liner quantified the surge/swab pressures and laid the basis for the liner running procedure.
Next, a number of scenarios were developed by means of transient simulations. It was essential to evaluate the dynamics of the system if a fracture with high productivity was drilled through. This would assist the wellsite team detecting the situation and making the correct adjustments with the choke to maintain BHP. Also the effects of choke adjustments on the production rate as well as the transient conditions in the well were evaluated. Various procedures were simulated e.g. connection procedures in order to arrive at the optimal for this well.
Dynamic modeling was an important element in the well specific UBD training course which was held for all the personnel involved in the operation. This increased the understanding and preparedness of the crew prior to operation.
Modeling of the flow test prior to the drilling of the planned section was also performed.
The displacement of heavy kill mud out of the well under pressure was modeled prior to the operation.
Modeling of the underbalanced cementing operation was performed for the purpose of developing guidelines for controlling the choke while maintaining constant bottomhole pressure.
