Modelling chemical displacement in corefloods and the near-well formation to optimise treatments and minimise environmental damage

As waterflooded reservoirs mature, hydrocarbon production will probably be accompanied by high watercuts. However, there are various environmental and formation damage problems associated with water production, additional to the obvious economic disadvantages. For example, various forms of mineral scale can be deposited in and around production well bores. These may both restrict the flow of hydrocarbons, and cause environmental damage at the surface due to their radioactive nature. The duration of oil or gas production can be extended by the appropriate application of chemicals that inhibit scale crystal nucleation or aggregation. However, these inhibitor chemicals themselves can have a serious environmental impact at the surface as soon as the well returns to production after a treatment. Chemical retention within the formation for as long as possible is thus desirable for both flow assurance and environmental reasons. A unique flow simulator has been developed to help in the selection of chemicals and design of treatments. First of all an adsorption isotherm can be calculated from coreflood chemical effluent data by accounting for the time taken for the concentration to fall during the postflush stage. Subsequent modelling of the coreflood experiment typically gives a very good match, demonstrating that the derived dynamic pseudo-isotherm accurately describes the chemical-rock interaction. Using this derived isotherm, placement of the chemical in a radial or fractured near-well system is modelled. These calculations, which include heat transfer and temperature dependent isotherms, have been performed to optimise treatments in vertical and deviated wells. Incorporating near-well flow rates from a full field simulation increases the accuracy of the prediction. One example is presented, in which sensitivity calculations were performed that lead to improved treatment lifetime and reduced oil pollution at the wellhead. During previous treatments high concentrations of inhibitor on flowback had caused an oil-water emulsion band to form in the separator, resulting in contaminated water being dumped overboard. Application of the model lead to a choice of more appropriate inhibitor and better placement of the chemical in the formation.