First Break - Volume 16, Issue 2, 1998

In May 1989 the EEC accepted the directive 89/336/EEC which relates to electromagnetic compatibility (EMC, amended by directives 91/263/EEC, 93/68/EEC and 93/97/EEC). The directive is applied to 'all electrical and electronic appliances together with equipment and installations containing electrical and/or electronic components ('apparatus' in short in the terminology of the directive) liable to cause electromagnetic disturbance or the performance of which is liable to be affected by such disturbance'. The main objective of the EMC directive is to guarantee the free movement of apparatus and to create an acceptable electromagnetic environment in the EEA (European Economic Area) territory. The EEA includes all 15 European Community states, as well as Iceland, Liechtenstein and Norway. In a geophysical context, the directive may or may not define limits to the allowable electromagnetic (EM) field strengths emitted from geophysical apparatus, and on the other hand defines also the limits of EM noise-levels which such apparatus must withstand and still operate properly.

David Morrison, chairman of Wood Mackenzie Consultants, tells First Break how the Edinburgh-based company was born in the North Sea oil and gas boom of the 1970s and has provided information and consultancy on oil and gas activity ever since with a continuously expanding global brief. Don't change a winning formula is the philosophy that has stood Wood Mackenzie in good stead. One of the most quoted energy industry consultancies, the company is this year celebrating a quarter century in the business. Chairman David Morrison insists that the style, format and approach of the company's trade mark reports have altered very little over the years. The coverage has expanded both geographically and in scope but the presentation remains much the same. Indicative of Wood Mackenzie's durability is that their combination of reports and consultancy services have survived a number of ownership changes, the latest being the company's imminent move from NatWest to Bankers Trust. The Wood Mackenzie reports began life in 1973, two years before Morrison joined the partnership of the Edinburghbased stockbroker (as it was then). He had left St Andrews University with a degree in applied maths and was set to become an airline pilot with British Airways. Ironically it was the oil crisis of the time that put paid to his flying career, not that he has ever regretted the change of direction.

First Break picks out some of the main points from the 1997 review of exploration drilling activity in Northwest Europe and predictions for 1998 by the energy analyst company Arthur Andersen Petroleum Services Group. Drilling activity in Northwest Europe based on the total number of offshore exploration and appraisal spuds has risen for the third year in succession and returned to pre-1993 levels, according to the annual review by Arthur Andersen Petroleum Services Group, based in London. Fewer wells are expected to be drilled this year, based on estimates from Arthur Andersen, which publishes what it claims to be the longest running weekly service surveying exploration and appraisal drilling, says that the UK has lost its margin over other countries which was marked by a surge in activity from Norwegian companies. Only half of the wells spudded in 1997 were drilled on the UK Continental Shelf (UKCS) with other strong activity recorded in Ireland and Denmark but not in The Netherlands which was particularly busy in 1996. In the previous year 61% of Northwest Europe offshore spuds were in the UK and in 1995 the figure was 64%.

Numerical analysis of seismic data requires information to be expressed in terms of frequency, amplitude, phase and velocity. Picking in seismic data usually gives timing information for velocity analysis of reflected and refracted waves, for amplitude vs. offset studies (AVO), and for geological interpretation. In a complex geological setting, in the presence of ground roll or other organized interference and in seismic data with low ratio between signal and noise caused by energy attenuation, recognizing and following the horizons can be particularly critical. Errors in the travel time table, often unavoidable, propagate like random errors in every subsequent study. For these reasons, it is necessary to introduce a method to minimize wrong interpretations when determining the picked travel times. The method that we propose does not need any seismic data processing and can be applied in many geophysical fields. The algorithm is founded on the hypothesis that the wavelet in the same reflector changes laterally and with offset, but the crosscorrelation factor is sufficiently close to one. In this way, it is possible to extract coherent events from noisy seismic data.