Abstract
This paper presents the methodology for characterisation (sampling and analysis) of formation water and scale prediction in the waterflooding project of a deep-water field, from Campos Basin, Brazil. A subsea well A, representative from an oil-producing sandstone reservoir of this field was selected for sampling. Bottom-hole sample was taken in the open hole well at the oil-water contact using a modular formation dynamics tester – MDT. After completion operations, both wellhead and bottom-hole samples (positive displacement sampling – PDS) were collected in the aquifer zone.
The gas from the bottom-hole samples was analysed using chromatography. Bicarbonate determination was performed at offshore laboratory using a controlled microprocessing titration.
As the water sample at the oil-water contact was similar to the composition of the aquifer, it was used to predict the scaling potential in the field. Two models were considered for prediction: the thermodynamic model OKSCALE and the geochemical code GWB. These models predict the precipitated mass and calculate the saturation index (SI) of the most common scales in an oilfield during waterflood operations (BaSO4, SrSO4, CaSO4 and CaCO3). The mass and SI of the insoluble compounds were calculated for the various injection and formation water mixture ratios, occurring over the field life. Precipitation of barium sulphate and strontium sulphate was found to be likely at produced wells (downhole and flow lines) and surface facilities.
