The Marlim Field: Incorporating 4D Seismic in Reservoir-Management Decisions

Abstract

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract Many brownfields have had 4D-seismic technology applied successfully to optimize reservoir production and recovery. This paper describes how 4D-seismic results were incorporated into the geological model and illustrates applications in reservoir- management decisions, thereby mitigating drilling risks in Marlim deepwater turbidite heavy-oil field. It highlights the repositioning of many planned wells and the improvement in the history match by use of the updated geological model. The Marlim field is off the eastern Brazilian coast in water depths varying from 2,000 to 3,600 ft (Fig. 1). The field is the largest producing oil field in Brazil. Three seismic surveys cover the Marlim field. The first was acquired in 1986 and the others in 1997 and 2005. The most recent survey was acquired specifically for reservoir-characterization and -monitoring purposes. Introduction The Marlim field was discovered in 1985. The reservoir is an Oligocene/Miocene turbidite with excellent rock characteristics. Relative permeabilities are favorable to water injection, and well productivities are very high (Pinto et al. 2001). The field area is 56 sq miles. The oil gravity ranges from 18 to 24°API, the reservoir-oil viscosity is between 4 and 8 cp, the original pressure was 4,082 psi, and the saturation pressure was 3,769 psi. Initial oil production from the Marlim field was in March 1991. Water injection started in 1994. Currently, oil production is approximately 390,000 B/D, water injection is 705,000 B/D, and the actual recovery factor is 25%. The water production is 252,000 B/D (bottom sludge and water=39%). A total of 205 wells were drilled in the Marlim field, of which 125 wells are operating—81 producers and 44 injectors. The production peak (615,000 B/D) in Marlim field was achieved in early 2002. Three seismic surveys cover the field. The appraisal survey was acquired in 1986. A reservoir-characterization survey was acquired in 1997. The most recent survey, in 2005, was acquired specifically for reservoir-monitoring and -characterization purposes (Johann et al. 2006). The initial development phase ended in 2002, and a new phase of complementary development is under way. This new phase is characterized by projects of border wells and infill-drilling wells. The 4D seismic was identified as the best technology to minimize risk and optimize the new projects, mainly the infill-drilling projects. A new seismic acquisition, for monitoring purposes, is planned for 2009.