Forecasts and Alternative Analysis for Sulphate Removal or Chemical Treatments for Barium and Strontium Scale Deposition – Offshore Brazil

摘要

Waterflood projects in oil fields cause important thermodynamic effects in the aqueous phase, resulting in precipitation of insoluble salts due to changes in physical parameters. Giant fields offshore Brazil are operated by waterflooding. For some of the fields, injection of seawater, rich in sulphates, is not compatible with formation water that contains barium or strontium. Adding seawater to connate or aquifer water leads, during the field production life cycle, to saturation of certain compounds and hence their consequent deposition. Decision about prevention or remediation of barium and strontium deposition must be attained during the conceptual phase of the field development plan. So, forecasting of the possibility of occurrence of this problem may have a strong impact in the water injection system design specifications and the well completion and interconnections to the floating production unit. The scope of this paper is to present the results of the analysis conducted to investigate the scale deposition potential in Marlim Leste field, Campos basin, offshore Brazil. Estimates of intensity of occurrence of precipitation and the critical locations have been conducted in order to obtain the fraction of seawater in the produced brine, which is an important information for evaluation of the problems associated to scale deposition in producing wells. Based on these simulations economic feasibility studies (CAPEX versus OPEX) compared the alternatives of sulphate removal plants or well treatments with chemicals in order to obtain the final decision of what to implement in this field.