Gravel packing very unconsolidated, high permeabllity 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. 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. pack assembly. Previous laboratory work and field experience has shown 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 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. 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.
As part of the appraisal of the Forth Field in the UK northern North Sea, BP Exploration has conducted a number of cased hole gravel pack DSTs where losses of hundreds of barrels an hour have been experienced during well completion operations. Coping with these high losses presents problems of minimising formation damage and maximising well productivity while maintaining well control.
In an attempt to minimise the adverse effects of loss control material (LCM) on well productivity, a perforation tunnel prepacking technique has been used.
The prepack technique has developed greatly during the field appraisal with a resultant improvement in well completion efficiency.
The overall gravel pack design and operations programme are discussed in this paper with the prepack programme are discussed in this paper with the prepack technique covered in detail. The successes and failures of this gravel pack campaign are presented and the results to date are discussed.
Illustrated in Figure 1, the Forth Field is located in the northern North Sea on UKCS Block 9/23b. Discovered in early 1986, over the last five years a large number of wells have been drilled to appraise the area with several being tested.
These Eocene reservoirs are typically located in massive, clean sands. Key formation parameters are listed below.