UKOQA recommended procedures for mobile drilling rig site surveys have been developed. The procedures are, at present, in a proof form but they have been reviewed by UKOQA members and other interested parties. The procedures provide information for a standard approach to rig site surveys with emphasis on good oilfield practice. To illustrate the approach taken by these UKOQA procedures, this paper highlights areas of the procedures of particular interest for shallow gas surveys. Standards to ensure acquisition, processing and interpretation of seismic data that is suitable for shallow gas detection throughout the UKCS are proposed. Data examples are provided to illustrate the sensitivity of seismic data quality to acquisition specifications and processing. One of the conclusions of the procedures is that the quality of the survey results cannot be taken for granted. Careful quality control by specialists is required throughout acquisition, processing and interpretation of the data. Even with data acquired to the limits of available technology, shallow gas surveys should be viewed as a preventive measure, minimising the possibility of encountering shallow gas, and therefore reducing the risk to acceptable levels for rig owners and their insurers.
overview- Procedures have been developed by UKOOA for the geophysical and hydrographic aspects of mobile drilling rig site surveys in the UKCS. The procedures are, at present, in a proof form but they have been reviewed by UKOOA members and other interested parties. Relevant comments are currently being incorporated. To illustrate the approach taken by these UKOOA procedures, the following text highlights areas of the procedures of particular interest for shallow gas surveys. Some examples are provided to illustrate the sensitivity of seismic data quality to acquisition specifications and processing. AS the UKOOA document has yet to be finalised, the following text may not represent faithfully the final content of the procedures.
Background to the Development of the Procedures- With the discovery of offshore oil and gas fields the site survey industry has grown considerably over the past two decades. The primary tools of site surveys are very resolute seismic survey techniques which have developed from relatively simple analogue single channel recordings to more complicated digital milti-channel recordings which require data processing ashore. As the usefulness of the survey data has increased, more reliance has been placed upon the results. Rig site survey data are acquired for several objectives including shallow gas detection and prediction of soil lithologies, identification of seabed hazards, and measurement of water depth. Of prime importance is the use of shallow gas surveys to predict potential shallow drilling hazards. Substandard data and inadequate or improper use of survey results may have considerable financial implications in addition to jeopardizing safety. Despite these serious implications, no detailed procedures presently exist in the UKCS for performance of these surveys. In November 1986, UKOOA members suggested to the UKOQA Surveying and Positioning Committee that procedures for the performance of rig site surveys would be desirable. In November 1987 The U K a Seabed Survey Technical Sub Committee was therefore requested to develop procedures for the geophysical and hydrographic aspects of surveys of mobile drilling rig sites in the UKCS.