The field in which took place the remedial intervention discussed in this article is located offshore West-Africa, in the gulf of Guinea. Oil is produced from unconsolidated sandstone formations of Miocene/Pliocene reservoirs. Currently, out of 360 wells drilled in the field, about 140 wells are still in production and nearly all of them are equipped with sand-control. Historically, the wells were completed as vertical or slightly deviated Internal Gravel-Packs (IGP), Open-Hole Gravel Pack (OHGP) with milled-windows or with Pre-Pack screens, then since 2001 as Frac-Pack and High Rate Water-Pack (HRWP).
With the first development dating back from 1978 (over 30 years of production) and 50% of the producing wells older than 20 years, this asset is clearly a mature field. Therefore, the durability of sand control systems has been dearly challenged and on some wells, failure of the sand-control has occurred before the production had been exhausted.
This paper will present several rig-less operations that have been performed for sand-control remediation in this mature offshore field environment and the results obtained.
We will first discuss possible scenarios of failure of the existing sand-control completions and then present the choices that have been made for the sand-control remediation, in particular the use of premium through-tubing sand screens with no gravel placement and the use of swell packers for the screen anchoring rather than mechanical devices.
We will then present the productivity and longevity achieved with such equipment and will demonstrate that even in some unorthodox cases, as can be often found in mature fields, remedial sand-control operations can still prove successful. Practical aspects that are important when considering such operations will also be covered.
Finally, recommendations and lessons-learnt derived from successes and failures will be presented.