Gravel packing very unconsolidated, high permeability formations, such as those found in the Forth Field in the UK northern North Sea presents a number of problems. The main challenge is to maintain well control whilst minimising formation damage, thereby maximising well productivity.
Working from semisubmersibles, BP Exploration has tested a number of these wells using a gravel prepack and sized salt LCM to cure losses. This allows retrieval of the TCP perforating string prior to running the gravel pack assembly.
Previous laboratory work and field experience has shown that filling perforation tunnels with gravel is fundamental to successful, high productivity gravel pack completions. Pumping a gravel prepack ensures that this criterion is met whilst still allowing LCM to be used for loss control.
The prepack also aids LCM removal which is essential, both to minimise formation damage and to ensure adequate leak-off to the formation for subsequent gravel pack placement.
Whilst the innovative use of the prepack technique has significantly improved completion efficiencies, all aspects of the gravel pack operation must be carefully planned and executed. This paper presents BP Exploration's design philosophy and operational practices in the North Sea and discusses results to date.