Gravel Packed Wells in the Statfjord Field: Completion, Workover and Production History
Authors: Nedregaard Rune , Lejon Kjell 
Published: December 2007

Several wells in the Statfjord field are restricted from producing at their maximum production potential due to sand production. To optimise production and reservoir drainage, different sand control techniques have been used ranging from conventional cased hole gravel packs to through tubing gravel packs on live wells using coiled tubing.

The gravel packed wells have made significant contribution to maintaining process capacity with the field moving into decline phase. Typical production increase after gravel packing has been about 2 – 4000 std m3/d. However, rapid plugging problems have been experienced after water breakthrough. Extensive scale dissolver and scale inhibitor treatments have been performed with varying success. Downhole video surveys have also been conducted to improve understanding of downhole well behaviour and well problems.

The plugging problems experienced in the gravel packed wells have been difficult to predict and overcome. It is currently believed that the plugging is due to a combination of scale, migration of fines/particles and poorly filled perforation tunnels.

Introduction

The Statfjord Field is located in the North Sea on the Norway/UK boundary. The field is approximately 24 km long and 4 km wide and consists of the Upper and Lower Brent, Dunlin and Statfjord reservoirs. The Brent group is subdivided into five formations; Broom, Rannoch Etive Ness and Tarbert while the Statfjord formation is subdivided into three members, Raude, Eiriksson and Nansen (fig-1).

The field has been developed with three concrete gravity base structure platforms. Each platform is a combined drilling and production platform with 42 slots divided between two wellhead areas. To date a total of 124 wells have been drilled, 10 of which are sidetracks. The oil production from the field is currently at 75.000 std m3/d with estimated total recoverable oil reserves at 620 × 106 std m3.

Sand production has been a limiting factor preventing wells in both the Brent group and Statfjord formation from producing at maximum production potential. To minimise sand production, selective perforation of the strongest sandbeds, was therefore implemented as the production strategy. Until 1990 this strategy was considered sufficient to produce the platforms at process capacity. However, with rising water cut and the field moving into decline phase, it became increasingly important to produce wells at highest possible rates to fill process capacity and maximise profits. A sand control programme was therefore initiated in 1990.

Sand Control Strategy. The main goal of the sand control programme was to gravel pack wells with a high oil production potential (PI = 500 – 2000 std m3/d/b) and low maximum sand free rate to maintain process capacity when other wells were shut in due to well activity, high watercut or high GOR. The Tarbert formation was selected as the ideal candidate for sand control measures since:–Sand production was most evident from wells in Tarbert.–The formation consisted of several less consolidated sandbeds with high oil production potential–Remaining reserves in this formation was estimated at 100 × 106 std m3

In the period from 1990 to 1995 a total of 8 wells were subjected to gravel packing:–4 gravel packs during workover and initial completion–2 gravel packs through tubing with the drilling rig–2 gravel packs through tubing on live wells using coiled tubing

P. 653