Using Seismic Attributes To Estimate Net Thickness in Pinchout Areas-MarlimDeepwater Turbidite Oilfield, Campos Basin

摘要

The Marlim Field was discovered in 1985, about 100 km offthe southeastern Brazilian coast, under water depths between600 and 1,100 m. It is the largest producing oilfield in Brazil(average 500,000 bdp), containing an original oil-in-placevolume of 6.4 billion STB and began to produce in 1991,through a pilot system. The field is exploited through 87producing wells and 45 injectors connected to 7 productionfloatation units.The Marlim reservoir is part of the lowstand systems tractof a third-order sratigraphic sequence, which is associated toan important eustatic, sea level fall of about 25 Mmy. Theturbidite lobes fill an intra-slope, wide depression developedby down slope gliding of underlying, Aptian evaporites.Reservoir facies comprise amalgamated graded beds of poorlyconsolidated, unstratified, medium to fine-grained sandstoneswith very low silt and clay contents. Porosities andpermeabilities are relatively homogeneous. The Marlimturbidite system was subdivided into nine production zones,mostly on the basis of stratigraphic discontinuities recognizedin well logs and cores.The eastern margin of the field is fault-bounded with therest of the field limits defined by sand pinch-out thatdetermines the 'zero line' of the reservoir. The pinch-outpattern of the sands depends on a series of geological factors,such as the topography of the substratum, the depositionalsystem characteristics, and the intensity of erosive processes,among others. The way of modelling the pinch-out has animportant influence in the oil volume since the pinch-outregions occur in a very extensive area of the Marlim Field.Also it has a significant impact in the success of location,navigation and productivity of horizontal wells positioned inthe borders.The Marlim Field was discovered in 1985, about 100 km offthe southeastern Brazilian coast, under water depths between600 and 1,100 m. It is the largest producing oilfield in Brazil(average 500,000 bdp), containing an original oil-in-placevolume of 6.4 billion STB and began to produce in 1991,through a pilot system. The field is exploited through 87producing wells and 45 injectors connected to 7 productionfloatation units.The Marlim reservoir is part of the lowstand systems tractof a third-order sratigraphic sequence, which is associated toan important eustatic, sea level fall of about 25 Mmy. Theturbidite lobes fill an intra-slope, wide depression developedby down slope gliding of underlying, Aptian evaporites.Reservoir facies comprise amalgamated graded beds of poorlyconsolidated, unstratified, medium to fine-grained sandstoneswith very low silt and clay contents. Porosities andpermeabilities are relatively homogeneous. The Marlimturbidite system was subdivided into nine production zones,mostly on the basis of stratigraphic discontinuities recognizedin well logs and cores.The eastern margin of the field is fault-bounded with therest of the field limits defined by sand pinch-out thatdetermines the 'zero line' of the reservoir. The pinch-outpattern of the sands depends on a series of geological factors,such as the topography of the substratum, the depositionalsystem characteristics, and the intensity of erosive processes,among others. The way of modelling the pinch-out has animportant influence in the oil volume since the pinch-outregions occur in a very extensive area of the Marlim Field.Also it has a significant impact in the success of location,navigation and productivity of horizontal wells positioned inthe borders. Considering that several projects of horizontal wells areexpected to be drilled in pinch-out areas, the objective of thispaper is to present the correlations between seismic attributesand reservoir properties used to improve the estimate of netthickness in pinch-out areas that are below the limit of seismicresolution.