The 4D seismic technology has been successfully applied on numerous brown fields in order to optimize reservoir production and recovery. This paper will describe how we incorporated the 4D seismic results in the geological model and illustrate some applications in reservoir management decisions, thereby mitigating drilling risks in Marlim deepwater turbidite heavy oil field. It will highlight the repositioning of numerous planned wells and the improvement in the history match using the updated geological model.
The Marlim giant field is located on the eastern Brazilian coast in water depths varying from 600 to 1200m (Figure 1). The reservoir is characterized by an unconsolidated sandstone turbidite related to the regressive mega sequence of the Brazilian eastern continental margin. It is the largest producing oilfield in Brazil (production peak: 615,000 bpd in 2002), with the original oil-in-place volume of 6.4 billion STB. Production started in 1991 and injection of water in 1994.
Three seismic surveys cover the Marlim Field. The first one acquired in 1986, the others in 1997 and 2005. The most recent survey was specifically acquired for reservoir characterization and monitoring purposes.
The Marlim Field was discovered in 1985 by an exploratory well drilled in 850 m water depth. The reservoir is an Oligocene/Miocene-turbidite age with excellent rock characteristics. Relative permeabilities are favorable to water injection and well productivities are very high.
The STOIIP is estimated at 1,011 million STD m3 (6,360 million STB). The field area is 145 km2 and the water depth range is 600 / 1100 m. The oil gravity changes from 18o to 24o API, the oil viscosity in the reservoir is between 4 and 8 cp, the original pressure is 287 kgf/cm2 and the saturation pressure is 265 kgf/cm2.
Figure 1 - Location map of Marlim Field in Campos Basin.
Marlim Field produced the first oil in March 1991, in the pre-pilot production system. Injection of water started in 1994. Currently, Marlim Field oil production is around 62,000 m3/d (390,000 bpd), the water injection is 112,000 m3/d (704,000 bpd) and the recovery factor is 25%. The water production is 40,000 m3/d (BSW = 39%). A total of 205 wells were drilled in Marlim Field, of which 125 wells are presently operating, being 81 producers and 44 injectors. The production peak (615,000 bpd) in Marlim Field was achieved in the beginning of 2002.
Three seismic surveys cover the Marlim Field. The first one was acquired in 1986 (appraisal context), the others, in 1997 (reservoir characterization context) and 2005 (reservoir characterization and monitoring context). The most recent survey was acquired using WesternGeco's Q-MarineTM acquisition system and was specifically acquired for reservoir monitoring and characterization purposes (Johann et al., 2006).
The initial development phase of the Marlim Field ended in 2002, after the production peak and now, 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 being the best technology to minimize risk and to optimize the new projects, mainly the infill drilling well projects.