The introduction of a large monobore well completion design concept in combination with the deployment of intervention matched rig equipment constitutes one of the corner stones of Brent's strategy in the maximisation of the field's remaining net present value. The new completion strategy has been applied since 1995 and plans for the "activity-matched" rig strategy are being reinforced with proving trials which have been in progress since December 1996, and will continue through 1997. The approach involves the application of various new technology developments allowing rapid and low cost installation of artificial lift, full inflow control, maximum access for surveillance and further Through Tubing Drilling (coiled tubing and jointed pipe).
Increased major well intervention in the medium term, much of it associated with field de-pressurisation, will include installation of gas lift (inverse, concentric) completions, installation of ESPs, both conventionally deployed and also coiled tubing deployed, and a number of through tubing sidetracks. At present, the combined number of candidates for these technologies is estimated to be in the order of some 70 wells.
Detailed analysis of the Brent Long Term Drilling Sequence indicates that, by utilising activity-matched technology on the Brent platforms, cumulative cost savings likely to be in excess of 50 million are envisaged for the years 1997–2005.
The application of activity-matched well intervention technology could also create significant flexibility on the main rig sequences and provide, together with concurrent operations, the opportunity to investigate new drilling scope, both Coiled Tubing and Hydraulic Workover, as well as conventional.
During the coming year, de-pressurisation of the Brent field will commence. The object of de-pressurisation is to recover gas held in solution in the remaining trapped oil, by progressively dropping the reservoir pressure. This will be achieved by initially switching off water injection and later, from about the year 2000, by back producing water from the old water injection wells with high volume ESPs.
In Brent's Redevelopment planning phase, during the early 1990s, production optimisation and successful realisation of an ambitious long term well engineering programme were identified as two key business drivers that strongly impacted on Brent's Net Present Value (Ref. 1). The first driver constituted the prime reason for a critical review of Brent's conventional completion strategy and led to the current large monobore completion design, incorporating the most recent technology developments to cater for artificial lift and selective inflow control. The second driver triggered an extensive well engineering performance improvement initiative that apart from efficiency enhancements also comprised the introduction of new technologies across various areas of the Well Engineering business. The combined effort largely contributed to the successful de-congestion of the long term drilling sequence, and thus the safeguarding of remaining reserves now underlying Brent's base-case development plan. However, as explained below, further optimisation efforts are planned.
With the onset of de-pressurisation, and with most drainage points in their final positions, the Brent Well Engineering Sequence will change progressively from being dominated by reserves development activity to well management and production safeguarding operations. The majority of these, mostly remedial, activities will have to be accommodated within tight operating budgets. Operating expenditure will inevitably rise at a time when there is increasing pressure to drive costs down. Critical analysis of the scope for remaining well engineering activities indicates ample opportunity for further optimisation, principally through deployment of activity-matched intervention equipment. It is estimated that selective idling of main rigs, coupled with the utilisation of more appropriate well intervention technology, for example hydraulic workover limits (HWO) and coiled tubing (CT) units, will yield substantial savings as this approach enables economic access to reserves not commercially viable using conventional technology.
