6. Experience with unmanned platforms

06.04.2016
This section gives an overview of the operation and maintenance experience gained primarily from the Danish part of the North Sea. More detailed information about the experience with unmanned platforms can be found in the sub-report, ref. /8/.

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6.1 Introduction

Generally, there are good experiences with the UWHPs. Types 2 and 3 have very a high availability (uptime) - in the range of 95% - 99.5% - and the number of hours spent by personnel carrying out operation and maintenance is very low. For the new Type 2 platforms with few wells, this was in the range of 567 to 713 man-hours per year.

In addition, the UWHPs have proven to be very safe, and in the Danish part of the North Sea, no Lost Time Injuries (LTIs) have been reported.

Please note that the maintenance activities mentioned in this section do not include any well service activities.

 

6.2 Documented experience

Documented experience from the past regarding maintenance is very limited in the literature. In the present study, only 3 references (/2/, /3/ and /4/) were identified. These are all from Denmark and are published in the 1990ties. The early data presented in Table 6-1 is based on data for three type 2 platforms over a three-year period. The data excludes well service activities and solely covers the topside.

 

Table 6-1: Early maintenance data

Table 6-1: Early maintenance data

 

The data in Table 6-1 is based on relatively new facilities with only 1-3 wells. For more mature installations with 10 wells, the estimated scheduled and unscheduled yearly maintenance hours on the installation are shown in Table 6-2. The data is based on own experience and recent interviews with owners.

 

Table 6-2: Maintenance hours (scheduled and unscheduled) – yearly (one installation)

Table 6-2: Maintenance hours (scheduled and unscheduled) – yearly (one installation)

 

6.3 General highlights of experiences

Highlights of experiences, as outlined in the following sections, are:

  • Uptime is reduced in the more complex types of UWHPs (Types 0 or 1) compared to Types 2, 3 and 4
  • Visit frequency and hours spent on the platforms are higher on Types 0 and 1 than on Types 2, 3 and 4.
  • It is beneficial to reduce the F&G and fire water systems to an absolute minimum
  • Generally, equipment is minimised (no redundancy), but focus is on procuring highly reliable equipment with high MTBF
  • Using noble materials and special surface treatment systems reduces the need for surface treatment to about zero during the lifetime
  • The automation level must be balanced. The number of instruments and signals shall be kept as low as possible. On the other hand, operations needing human intervention (example: drain tank with manually controlled drain pump) shall be limited to a minimum
  • The use of electro-hydraulic cranes is not recommended on installations with diesel generators, as the diesel engine will be sized for the major user: the crane. Therefore, for the majority of the time, the engine will run on a very low utilisation, which causes problems for diesel engines
  • Extended design control checks and verifications are required to avoid any design errors. It is extremely expensive to rectify such design errors on an unmanned installation
  • Extended commissioning checks are required
  • Diesel engines cause downtime, and therefore cable supply from the host platform is preferred
  • Hydraulic systems also cause downtime and regular maintenance. They cannot be avoided, but focus must be on improving them and also to improve the skills of personnel working with hydraulic systems and fittings
  • Operational faults count very high. It is extremely important that the visiting crew is familiar with the installation.

It is important to have teams or at least job leaders, who are well acquainted with the installation. Having an expert team onshore dedicated to the UWHPs could be one way of ensuring this. Such a team could be mobilised to carry out all operation and maintenance work - not just on one UWHP - but on all the similar UWHPs owned by the company.

All disciplines shall have full focus on the manning, operation and maintenance strategy throughout the development project of an UWHP. In many development projects, there is a tendency to add «nice-to-have» equipment and systems, because it is possible, or because this is done in conventional development projects. Some of these are HSE-initiated elements, which do not really add any value, but which require a higher manning frequency, since the safety equipment has to be checked regularly. This must be avoided.

 

6.4 Summary and recommendation

The overall experience shows that the amount of equipment and systems should be minimised and only highly reliable equipment and noble materials should be used, which will reduce Capital Expenditure (CAPEX) as well as Operational Expenditures (OPEX).

The above points towards the simple UWHP type 2, 3 or 4 being the preferred concepts, however, other important factors need to be considered, such as:

  • Distance to the host facility
  • Production rates and number of wells
  • Major rotating equipment on board, such as downhole pumps, booster compressors, transfer pumps
  • Reservoir complexity as well as types and frequency of well interventions
  • Need for operator interventions and maintenance requirements So for some fields, the more complex type 0 or 1 could be the optimum concept.

 

Figure 6-1: The right type of UWHP for the job is essential

Figure 6-1: The right type of UWHP for the job is essential