GPS subsidence study of the Costa Bolivar Oil Fields, Venezuela

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The Costa Bolivar Oil Fields, located along the east coast of Lake Maracaibo, contain some of the richest oil deposits in South America. Exploitation of these reserves, located some 300m to 1000m below the lake surface, has led to some considerable subsidence along the east coast shore. The accumulated subsidence since 1932 has resulted in the land mass being some 4m below the lake surface. Consequently, a 46m dyke was constructed and maintained to protect the low lying inhabited area and production utilities. Up until 1986, monitoring of the dyke and surrounding area utilised conventional geodetic measurements. At this time, UNB proposed that the Global Positioning System (GPS) could provide some significant savings by replacing some of the lengthy and costly levelling surveys. Since 1987 both GPS and geodetic levelling data have been collected periodically to assess the performance of the GPS in this project. Prior to 1993, problems with the GPS data and its processing have limited the analysis. An incomplete satellite constellation, noisy single frequency data, and systematic biases in both the data and the processing software, have all contributed to a problematic study. This thesis has evaluated the GPS data to date and assessed its usefulness for subsidence studies in this area. It has revealed that the present methodology employed has produced very promising results in the last two years, but some additional strategies are still required to gain full confidence in the GPS results.