Judy/Joanne Field Development

Abstract This paper describes the development history of the complex J-Block area fields, in the UK sector of the North Sea, along with an integrated reservoir modeling study. A general-purpose simulator, run in the compositional mode, has been used in this study. The Judy/Joanne fields consist of three main producing horizons. The shallowest reservoir is the Palaeocene formation, which is a relatively thin sandstone covering approximately 16,000 productive acres which essentially covers the entire Judy/Joanne reservoir area. The reservoir is faulted and the reservoir fluid is a rich gas condensate. The field has been developed with horizontal wells and a gas cycling program is in progress. The next reservoir is the naturally fractured chalk reservoirs in the Ekofisk and Tor formations. Volatile oil is contained in the thick chalk sequence and has been developed by four horizontal wells which are currently on production. The deepest reservoir is the Pre-Cretaceous with intervals that consist of a series of non-communicating fault blocks with complex sand geometries. Four separate PVT regions have been identified based on production results, consisting of three volatile oils and one gas condensate. A combination of vertical and horizontal wells are currently producing from these reservoirs. The field has been developed with a single platform and one subsea manifold. As all reservoirs are producing into a single platform, it was desirable to combine all the reservoirs into a single simulation to capture the interplay of the reservoirs with respect to platform operating constraints, well deliverabilities, gas contract deliveries, and gas availability for reinjection. The generalized model used in this study allowed development of a state of the art reservoir management tool, which is computation ally robust and efficient, while providing both flexibility and ease of use for the field engineers. Introduction The Judy/Joanne Fields are located in Blocks 30/7a, 30/6a and 30/12a in Quadrant 30 of the UK North Sea, 175 miles eastsoutheast of Aberbeen (Fig 1).Forty miles to the southeast lies the Phillips operated Ekofisk Chalk field I. Hydrocarbons were first discovered in the Joanne Field in 1981 by the 30/7a- Iwell, which tested high rates of oil and gas from the Upper Palaeocene Andrew, Lower Palaeocene Ekofisk and Upper Cretaceous Tor formations. Three additional appraisal wells were drilled on the structure that confirmed a significant Chalk reservoir and an extensive but thin Andrew sandstone reservoir. In 1985 hydrocarbons were discovered by the 30/7a-4a well on the Judy Field. Excellent flow rates were obtained from both the Pre-Cretaceous Jurassic and Triassic sands. These sands along with the Joanne formations were subsequently appraised by seven more wells drilled between 1985 and 1992, revealing the Judy Pre-Cretaceous reservoir as a complex fault compartmentalized structure. Along with the appraisal drilling program, a 3D seismic survey was carried out over the fields in 1986 with the primary objective of resolving the structural complexity in the Precretaceous. In 1992 Phillips Petroleum Co UK Ltd. with its co-venturers AGIP(UK) Ltd. and British Gas (E & P) Ltd made an application to the UK Government Department of Trade and Industry for the development of hydrocarbons from the Judy and Joanne fields. Approval was granted on January 28, 1993.