UK REPORT Advanced processing techniques net further finds for Amerada Hess

High exploration success rate derives from confident analysis of 3D seismic

Neil Potter
Contributing Editor

In the first two months of this year, Amerada Hess completed three wells, two in the UKCS and one in Danish waters. It was no surprise, given the company's track record, that all three were discoveries.

The first well was in the golden block 15/21 which contains the Scott, Ivanhoe/Rob Roy/Hamish producing fields and Perth, yet to be developed. Some 23 exploration and appraisal wells have been drilled here to date, of which ten have been oil discoveries or extensions to existing fields, six were successful appraisal wells, and only five did not discover oil or gas.

Last year, Amerada Hess drilled 11 exploration and appraisal wells on the UKCS, second only to BP, who drilled three more. But whereas BP announced only one discovery, Amerada had four major finds.

Two were on the western edge of the central graben. Well 21/16-2 tested 4,300 b/d of 34.2 API oil. Together with well 21/16-1, drilled in 1993, reserves are put at 30-40 MM bbl. Then in December, well 21/11-4 tested 6,077b/d of 32 API oil, and was named the Dauntless Field, where reserves have been estimated at around 50 MM bbl.

SE Fife was discovered with well 39/2-2 and will be tied back to the Fife development. And West of Shetland, well 204/25a-2 proved the southernly extension of BP's Schiehallion Field into the AH block.

Confidence

Amerada is, without doubt, regarded as not only one of the most successful field developers, but also as one of the best explorers.

There are a number of reasons, both human and technical. The main drive comes from the top, from a management prepared to have confidence in the teams which have been built up and to back their judgement not only in recommending acreage to apply for in licensing rounds, but also to support drilling programmes.

"We are," says Ian Norbury, who is in charge of drilling operations, "a company willing to take risks and drill in some places where others might not drill. But these are calculated risks and we respond to opportunities."

The calculated risks are based not only on 3D seismic, but on the ability to interpret the data quickly. It is here that Amerada believes on-board processing is playing a key role.

The discovery of Dauntless, utilising 3D seismic processed on board the vessel, was fast-track, made just three months after the award in the 15th round.

Some wells had been planned on previously shot 2D seismic. One of the main attributes of on-board processing of 3D seismic lies in the fact that it enables the rig to be sited on a more suitable location, and, if necessary, more quickly. Indeed, for one well, Amerada was able to mobilise a rig two weeks after on-board processing of data.

Shorter lead times

Robert Hardy, special projects geophysicist, says: "The last five years have seen a revolution in the acquisition and processing of 3D seismic data, in that both navigation and seismic information can now be processed onboard the acquisition vessel itself.

"The availability of instant 3D migrated volumes from the vessel has dramatically shortened the lead time between seismic acquisition and interpretation from nine months to nine days. This gives us the ability to move quickly, if necessary.

"Horizon Exploration, Simon Petroleum Technology, and Amerada Hess have been at the forefront in the development and utilisation of onboard seismic processing technology since the early 1990s. The first onboard migrated 3D survey was produced in 1991 and used by Amerada to plan the fast-track development of the Fife Field.

"Mapping based on onboard processed data was used to secure acreage in surrounding blocks that were awarded as part of an out-of-round agreement. The recently announced Dauntless, Durward, and Fergus discoveries were also drilled following 3D surveys which were processed entirely onboard the vessel. Similarly, onboard processing is planned for 3D surveys to be acquired during this year."

Jon Ashdown, manager, technical support and development, Geophysical Services at SPT, says: "We have now developed our own real-time interface in collaboration with Horizon Exploration, which removes the limitations with the Sterling and allows us to pass as many channels as we like to the processing system. Since we took the transition to UNIX workstations in 1992 we have progressed rapidly, culminating last year in the processing of two full-fold 3D surveys on-board for Amerada which were major successes."

Migration analysis

Amerada invested £1 million in the development of Project Hedera, together with the OSO, with the work being carried out at the Petroleum Science and Technology Institute. This is a geological basin modelling software package designed to improve understanding of how hydrocarbons form and migrate into reservoirs.

By simulating the processes of hydrocarbon generation, migration and entrapment, the presence or otherwise of oil and gas can be more precisely predicted reducing the costly incidence of dry holes. The package is already being used by the explorers, and is now being marketed to the industry.

But Amerada is not simply resting on the laurels of its recent success. The search for even better ways of obtaining and interpreting seismic continues. Andy Tilbrook, the company's new technology co-ordinator, has £1.2 million available for this process this year. "The New Technology area exists to help exploration, development, and production departments to meet their business needs through the application of technical innovation," he says.

The best ideas tend to come from within the company. One prime example of innovation within Amerada came about when a solution was needed to improve the rate of drilling through a formation in the Scott Field. It led to the development of a new form of drill bit with optimised hydraulics. The improved rate of progress resulted in significant cost benefit. Clearly this type of bit can be used in exploration drilling if similar formations are encountered.

"We want to improve even further the business of seismic acquisition," Tilbrook says, "particularly the sound sources and interpretation. There is the possibility of learning from other industries.

"There is a great deal of signal processing expertise in radioastronomy, defense and medical work which could equally well be applied to seismic acquisition. For example, we realised that oil wells are the same shape as torpedoes. So we are having discussions with contractors and the Ministry of Defence."

Drilling schedule

This year Amerada has an extensive operated drilling programme, with 12-15 wells planned. Three semi-submersibles are on contract - Glomar Arctic 1, High Seas Driller, and Dyvi Stena. These join the John Shaw and the Ross Isle which are drilling development wells on Fife, and Santa Fe Rig 140, now operating on production wells on Hudson. West of Shetlands there will be a minimum of three wells, with Amerada further appraising its portion of the Schiehallion Field and the Strathmore Field.

Last year Amerada and Texaco agreed to co-operate in the further exploration and appraisal of blocks 14/20b and 15/16b in the Outer Moray Firth. In return for carrying out an extensive work programme over the next three years, Amerada will earn a 50% interest in the blocks, excluding the existing producing fields.

Late in January, Amerada spudded exploration well 15/16b-21 with the semi-submersible John Shaw. Another well will be drilled in the acreage later this year. In the golden block 15/21, a further four wells will be drilled.

In the Central Graben an appraisal well will be drilled on Dauntless and one on Fergus in block 39/2. A new prospect on block 210/24a, adjacent to Hudson, will also be drilled, which, if successful, will be tied back. It will be surprising if there are not a goodly number of discoveries.

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