John Curley, facilitator of the welltesting network, reports on the group's most recent meeting held in Ballater, near Aberdeen.

Extended welltesting in the North Sea was something of a novelty when it was discussed by the Welltesting Network in mid 1995. A year later, the network's follow-up workshop was packed with British and Norwegian EWT case histories on jobs already completed or planned for summer 1996. There were 26 presentations of case histories and related EWT topics and some lengthy group discussions. The EWT cases included Statoil's Åsgard, Conoco's Banff (Early Production Scheme), Norsk Hydro's Hermod, BP's Schiehallion, Mungo and Machar (EPS), Saga's H-Central and Ranger/BP's Pierce.

EWTs are indeed becoming more familiar in the North Sea. Tony Oldfield of Schlum-berger Integrated Project Management (IPM) talked about the industrialisation of the EWT. But they are still far from being commonplace. The workshop thus came at a good time: the experienced players were ready to present their achievements and those with imminent operations were eager to ask detailed ques-tions. Others from further afield wanted to know more about the emerging North Sea approach to EWTs.

The two-day event was structured around attendees' interests and concerns. Priority was given to those topics which commanded most interest among the participants.

The EWT design and planning session looked at EWT planning, assessing which objectives are practical, setting the criteria for an EWT, how to optimise the interpretation of EWT pressure transient data and how well past EWTs have satisfied their objectives. Key lessons observed by delegates included:

Managing the interface - Communication between the operator and all contractors during the planning stages was good. However, different people were brought in to carry out the operations which was not ideal - they should be directly involved from the beginning.

Pressure transient analysis - The early radial flow observed during the pressure buildups was used to estimate Kv/Kh (horizontal well). Initially a fault bounded model, guided by seismic data, was used in the interpretation. However, the actual reservoir had more energy than this and a better match to the drawdown data was obtained by using an infinite acting system.

Risk management - It is best to focus on the downside - look for the regret costs' - assess the risks and consequent maximum financial exposure that could arise and create the means to manage and reduce them. Committed to on this basis, an EWT should hold no nasty surprises.

EWT cost neutrality - The primary purpose of an EWT is data gathering and it should be accepted that this costs money. But cost neutrality should not be made an objective in its own right. In round figures, an EWT may cost about £10 million ñ roughly the same as drilling, testing and suspending an exploration well. But once the revenue from oil sales is taken into account, the net cost may only be a few million pounds. The major issue is assigning a value to the data.

Dynamic positioned (DP) vs non-DP tankers - Moored tankers can be used in the North Sea and can offer significant cost savings.

Eliminating the rig - Getting rid of the rig for EWTs would provide very large cost savings but would restrict well operations.

Benefit of EWTs - The key benefit is the narrowing of uncertainty. EWTs can help reduce or avoid the downside ñ the risk and consequence of expensive failures. They can also help raise the upside by enabling earlier fine-tuning of the development scheme.

BP's Henry Webb, Fraser Elliott, Pam Quigley and Dave Neely made a particularly valuable contribution by sharing the considerable depth and breadth of the company's EWT and EPS experience. Trygve Gilhuus showed how Saga factors the risk assessment into its economic analysis. Knut Kviljo of Statoil drew credit for his honest portrayal of the Statoil Åsgard EWT operations, talking about the problems as well as the successes.

The contracts, organisation and interfaces session looked at the delicate balance to be struck between operators and contractors in the EWT alliances which are becoming more widespread. Key presentations were made by Tony Oldfield of Schlumberger IPM and Michael Barraclough of Vanguard on project management, contracts and incentives. Much of the discussion revolved around the alignment of objectives and rewards. In the case of an EPS, the primary objective is revenue so it is relatively easy to align contractor rewards with performance. However, in the case of EWTs net revenue is not the key driver and contractor rewards need to be linked to the data acquired. A case was also made for a contractor being rewarded for areas under his control ñ oil price and reservoir risk should be borne by the operator.

The safety and cost session presentations addressed the use of production-type equipment versus DST equipment, EWT safety cases and use of large bore DST tools. It was agreed that safe operations should be encouraged by all means possible and be part of the project team's culture. This might take the shape of a ìno blameî philosophy but under no circumstances should safety be financially incentivised.

The equipment and hardware session included a review of EWT equipment, talks on rig selection, an update on the Crystal Sea testing vessel and Dave Neely led a discussion about the future of EWTs. The long lead time required to obtain subsea christmas trees is a problem for operators. BP and Shell are looking at standardising the basic tree design in the UK; Norway already has some standard specifications. This situation should lead to more speculative builds and advance orders.

A session on new technology considered the challenge of gas disposal during EWTs. There is a need to avoid excessive flaring for environmental and economic reasons.

Gas liquefaction has been undertaken on tankers with the gas liquids being returned to the oil, but although this works reasonably well with heavy gas from stabilised crude, the process would be much more difficult with the lighter gas produced in well tests

Offshore conversion of the gas to methanol is another option but the market for methanol is very limited at present. With current technology, both these options are too expensive and the gas issue certainly remains a thorny problem.

The well monitoring, surface processing and data acquisition session looked at pressure gauge reliability during EWTs and the perils of testing heavy crude. For long tests with bottom hole temperatures over 150°C, twice as many gauges are used as normal. It was suggested that gauges should be changed or rotated after each run even if they have worked satisfactorily.

Looking to the future, EWTs were considered as a stepping stone, in terms both of technology and technique to the economic development of smaller discoveries in the North Sea.

By stimulating ideas and contacts the workshop has made a contribution to this year's EWT and EPS operations in the UK and Norway. But many of the issues raised at the workshop are not about to go away. So it was no surprise that the attendees gave a clear message that the welltesting network should arrange a follow-up workshop in 1997.

Members will be considering the recommendation at the network's annual general meeting in October.

For more information on this meeting or about the network in general, please contact John Curley of Win Cubed, the facilitator of the group. He can be reached on:

Tel/fax: +44 (0)1494 673339, Email

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