Ccpyr@f 1SS6 Sccmty of Patmfewn Err$nneers Tlus paper was prepared fw Wesentatw at the 1S9S SPE Euro~an Petroleum Conference held m Milan, Ilafy, 22-24 OdC&r 199S This paper was selected fw pfesentatwn by an SPE Prcgrwn CommMea folknwng rewmv of Imformabcm Ccntaiti In an abstract subrn tied by the 8wIKM(3) CcnrterW of the paper, as wosented, have not b6.8n revmwed by tha Sccmty of Petro!+um Engineers and are subject to cciredii by the aulh-ar(s) Tha materkd, as paenled does rmf rwcmaanly reflect any position of tfw Sacmty of Pdrdeum Engmeem, IIS otkers, or mwnhm Pepers presented al SPE meebngs are sub+ect to wbkAk3n revmw by Ed!twml CommW#s of the Scc@y of Pefro!eum Ergmeam Pernmsscm to rnpy 8s restmlad to nn abstrad of not mcxe than 303 words Iltudfat(ons may IW4 b+ ccpmd The sbstrad sfwukj -tam mspia$ ackncr.u~dgemo"t of vAwre ard by wtmm tf-m papsf was pmsemted Write Ltkwanan, SPE, P O eox S3338?6, RItiardscm, TX 7S0S3-3836 USA, fax 01-2 14-952-S4S'5Abstract Several wells in the Stattjord 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 atler gravel packing has been about 2-4000 std m]/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 frees/particles and poorly filled perforation tunnels.

To achieve the goals of maximum lifecycle value of wells in the Stafjord field, continuous improvements in well design, completion and well intervention techniques have been made over the past 10 years, A major challenge has been to simultaneously optimise reservoir penetration, drilling and completion operations and later well interventions, This paper will review the development in the well design and completion techniques from the low angle « 60°) wells with cemented liner and step down nipple profile completion to the horizontal and extended reach wells with monobore completions, This includes the lessons learned from the numerous workovers performed and how they lead to a change in completion design to ensure reliability, redundancy and optimised production. The impact of the well profile and how it should be optimised for future light interventions, i.e. coiled tubing, or wireline tractor will also be discussed.Finally, the advantages of working in multi-disciplinary teams from the early planning stage to completing the well will be addressed.

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