Case Histories Of Loran C Radionavigation Usage For Oil Exploration Activities Offshore Newfoundland

Abstract

Abstract Offshore eastern Newfoundland has become an area of great interest to the oil industry ever since the Hibernia oil discovery by Chevron Standard Limited in 1979. The general area of current interest lies far offshore, as much as 200 miles (or more) east of St. John's, Newfoundland. The distance of this area from shore and the shoreline characteristics of Newfoundland severely restrict the number of navigation systems which can be used for seismic surveys, well site surveys, and drilling vessel navigation and positioning. Though Loran C coverage exists in the area, currently only it's use in the range-range mode (circular geometry) is practical for hydrocarbon exploration activities. This paper describes the Loran C systems and techniques used to position the drilling vessel for the Hibernia discovery well and for the navigation of the vessel for the well site surveys which preceeded the drilling operation. In addition, subsequent use of Loran C for a major seismic program in the area is described, including the implementation of a Loran C "monitor" station deployed on an offshore drilling vessel. Data are presented showing relative position results of real-time navigation for the seismic program and a comparison to results of sophisticated post-mission processing. The computer program and post-mission processing techniques are also described. Results of these case histories show the value of using Loran C in the range-range mode and the benefits derived from post-mission processing of the real-time (or "raw") navigation data. In addition, the results support further planned expansion of the the Loran C network in eastern Canada waters. Introduction In May, 1979, Chevron Standard Limited began drilling a wildcat well offshore Newfoundland. This operation resulted in one of the most significant oil discoveries ever made offshore North America. Subsequent drilling by Mobil Oil Canada of the structure known as Hibernia has confirmed that the oil field is indeed a major discovery. Partners in the Hibernia field are Mobil Oil Canada, Ltd., Gulf Canada Resources, Inc., Petro-Canada, Chevron Standard Limited and Columbia Gas Development of Canada, Ltd. This paper describes the Loran C and satellite systems selected for phases of Chevron operations leading up to, and following, the initial Hibernia discovery. The geographical area and the operations performed are briefly described and the physical limitations imposed on navigation system selection are mentioned. Very brief descriptions are given of the navigation equipment used for the well site survey, the rig positioning, and some subsequent seismic surveys in the general area. In addition, a description is given of a post-mission navigation computer processing program used to enhance results of the real time navigation provided for the seismic surveys. Results are given and discussed for each operation conducted, with particular attention paid to the improvement in positional information for seismic surveys when sophisticated post-mission navigation data processing is performed. Geographical Area And Coastal Geometry The Hibernia discovery well is on the Grand Banks approximately 310 Km (167 nautical miles) ESE of St. John's, Newfoundland.