Pirauna is a mature field which has produced almost all of its predicted total recoverable oil. The expected field life after 2002 was about 3 years, when the economic constraint would be achieved. Faced with the decision of abandonment, a revitalization program of this mature field was started. The existing simulation model did not reflect the present geological interpretation and dynamic behavior of the field, and hence, was not reliable for planning new well locations. In order to characterize adequately the oil zone and model the reservoir dynamics accurately, a close integrated teamwork was formed and developed a full subsurface work program. Three-dimensional seismic data was reprocessed to increase resolution and reinterpreted, allowing a better identification of the surfaces. Once the seismic interpretation of the field was completed, the geological model was constructed. The 15 years history-matched simulation model was suitable for modeling the remaining reserves and to identify possible new wells location. The sweep patterns showed in the simulator model highlighted opportunities on the North flank of the main block and on the central part of the secondary block. Horizontal wells close to the top of the sand bodies were designed to maximize the drainage area and the productivity index. The first well was completed in July 2004 and the first oil came in October 2004. The initial well rate was about 9,000 bopd, increasing the field production rate to almost 15,000 bopd. The second well is supposed to be drilled in February 2005 and start to produce in April 2005, increasing the field production rate to 18,500 bopd. With this revitalization program the abandonment date of the field will be postponed to 2010.

Field Overview

Pirauna field is located at Campos Basin in southeastern Brazil continental shelf. It is a field placed at water depths ranging from 200 to 300 meters (Figure 1). The field was discovered in November/1981 and has an amount of 175 millions of oil barrels originally in place. The reservoirs are composed of turbidite sandstones aged of Cretaceous and Tertiary. There are three producing blocks in the field. Two of them were subject of this study, the Cretaceous and the Tertiary A blocks (Figure 1). The other block (Tertiary B) was not included in the study because a new seismic processing is expected for this area. These reservoirs have an excellent permeability (1.5 Darcy) and porosity (28%). The oil has 28o API and a viscosity of 2 cp at reservoir conditions. These conditions, associated with the strong performance of the existing aquifers, allowed the high value of 44% to be achieved for the actual recovery factor. Nowadays, the cumulative oil production is about 77 millions of barrels. The three blocks are hydraulically connected through the aquifers. The measured static pressure data shows a complete communication among them. The initial reservoir pressure was 258 kgf/cm2 and the bubble point pressure is 144 kgf/cm2. The present reservoir pressure is around 185 kgf/cm2. Ten wells, deviated and vertical ones, were drilled to be producers.

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