The conference was planned to coincide with the finalization and issue of the UKOOA mobile drilling rig site survey procedures. It was also intended to review the state of the an in shallow gas surveys and point up desirable and likely future trends in shallow gas surveys.
The conference was planned around opening introductory remarks from Dr H. Hughes of UKOOA> and a scene setting contribution from P Prince of BP Drilling Deparment.
Dr Hughes highlighted the importance of operators conducting their business safely and pointed out the essential requirement for an accurate prognosis of shallow gas conditions. A UKOOA study of the U K sector has indicated that some 1000 exploration wells and 2300 appraisal wells will be drilled in the next 25 years and that the development and refinement of a shallow gas prognosis capability is important and will continue to be a vital ingredient in offshore drilling.
P Prince of BP Drilling stated that one third of all blowouts are caused by shallow gas. The prevention of shallow kicks and blowouts must rely initially upon a quality shallow gas survey and report Relocation, directional drilling, careful selection and setting of casing depths, faster mud circulation and correct tripping techniques were all proposed as practical methods to reduce the chance of a shallow gas blowout The role of riserless drilling was discussed together with a plea to ensure that gas surveys are planned and completed well in advance of spud date to fully assist in the formulation of the drilling programme.
Dr A. Judd questioned the importance of gas seepages and pockmarks pointing out that. In the medium to longer term life of an oilfield, wells and piles may act as a focal point to gas migration and escape He suggested that operators should bear In mind the possible requirement for repeat surveys of gas prone areas to ensure that no migration and potential problems arise during the working life of an offshore installation.
R Prince amply summarised the requirement for correct and proper source specifications pointing oput that just providing criteria for source level and p/b ratio was insuffient. He highlighted the importance of providing a specification including definition of the pulse In the frequency domain as a necessity to accurate source specification.
P Newman (formerly of Horizon) discussed the application of the short offset 3D technique for high resolution site surveys. He questioned the need to shoot even low fold data as detail is lost in the spatial averaging of the stack process Time slices from a small 3D survey were shown from the Ekofisk area revealing detail that would never have been possible to interpret from a 2D data set The concept of low fold or even single fold data was proposed to optimize costs whilst producing a far superior dataset Newman foresees a situation where single fold data would provide sufficient S/N and penetration relying on velocities generated from migration testing and application to permit depth conversion
