ARISSTON: Development and validation of an integrated numerical tool for scaling control and squeeze treatment optimization
The main objective of ARISSTON project was to develop and validate an integrated numerical tool that should assist essentially in the design and optimisation of squeeze treatments for the prevention of scaling. The formation of mineral scales from produced water/brines in oil/gas wells and pipelines constitutes an old but persistent problem for the oil industry. The tool predicts the timing of scale deposition, the consequent formation damage distribution and the effects associated with the placement and flow of inhibitors in the near well formation. The validation of the tool and methodology involved both laboratory and field scale activities. Calcium carbonate is the most common scale during oil recovery. The sparingly soluble CaCO(3) may form when a solution is supersaturated (i.e. the product of the concentrations of the precipitating ions (Ca(2)(+), CO(32)(-)) exceeds the solubility product, Ksp). Supersaturated calcium carbonate can be meta-stable in a solution for some time before precipitating, so that a period of time usually elapses between the achievement of supersaturation and the appearance of formed crystals. This time lag, is known as the 'induction period', tind. Up to date, there has been no available method for the prediction of the time of onset for scale deposition and pore blocking in the near-well zone. During ARISSTON project, a new technique was developed using a gamma emitter tracer, which allows measuring on-line the induction time of mineral scale deposits (e.g. CaCO(3), BaSO(4)) under continuous flowing conditions. Only the use of a radiotracer technique can detect the presence and concentration of a specific element or compound at a certain position and time. This kind of information is not readily obtained by conventional methods used in standard scaling experiments. Based on this innovation, ARISSTON project aimed to develop and validate an integrated numerical tool that can be used to optimise the formation treatment (inhibitor placement), carried out to prevent calcite and barium sulphate precipitation around the production wells. Indeed, the ARISSTON tool combines all the necessary features, i.e. the black-oil module (main simulator), sorption as well as tracer data and geochemical model (chemical reaction), offering a fair estimation of the calcite precipitate mass within/throughout the near well zone that is of interest during the squeeze treatment. Presently there is no other similar tool available and this is why it comprises an important development and efficient tool for the well operators. The main individual results that were achieved at the end of the project can be summarized as follows: - Introduction of tracer technology in scaling experiments. Aiming to qualify the tracer technology as a reliable source of information in scaling experiments, a series of laboratory experiments were performed with and without tracers, in order to deduce the induction time of scaling, the calcite scale growth and the profile of calcite deposition along the deposition medium. The corresponding results showed that the introduction of the tracer technology for the first time in scaling experiments has been successful. The experimental investigation of scaling has attracted an increased interest from the part of the industrial participants as it proved capable of providing unique information on scaling onset and evolution. - Small scale modelling and simulations (pore and core). Porous media have been characterized and reconstructed by means of the reconstruction method. A code has been produced by combining several existing codes in order to simulate deposition of a single solute in multiphase flows at the pore scale. Relationships of the porosity and permeability evolution as function of precipitating scale have been generated that were further used in the integrated numerical tool. - Testing and evaluation of new, environmentally friendly inhibitors. Measurement of the adsorption isotherms and precipitation/dissolution coefficients for several, both standard and new inhibitors. In addition, the efficiency of the inhibitors in preventing scaling was evaluated with regard to both calcite and barium sulphate scales. - Development and validation of the integrated numerical tool. The single well black oil injection/production model has been completed and tested successfully using field data provided by the industrial partners. The module simulating the inhibitor flow has also been completed and tested against both laboratory and field data. The geochemical model simulating calcite scaling has been completed, tested against laboratory data and coupled to the main black oil simulator. All the above components were integrated to generate the ARISSTON tool, which has been tested successfully against the field data provided by the industrial partners BP (Miller field) and Amerada Hess (Ivanhoe field). To summarize, the project achieved the whole range of its original objectives and produced results, which are not only scientifically advanced but also carry high commercial value. Of special interest in that direction are the following ARISSTON features: - The successful introduction of the tracer technology into scaling studies and evaluation and optimisation of inhibitor performance. It has been demonstrated how the tracer technology can be used to study the effect of several parameters (temperature, saturation ratios, velocity, etc) on scaling and how the technology can be used to evaluate inhibitors and determine the Minimum Inhibitor Concentration. Further work is needed in order to streamline the experimental procedures, enhance the corresponding operative capabilities (High Pressure- High Temperature) and make the methodology cost effective so that to become commercially competitive and viable. - The development of the integrated tool with unique features, which brings together the geochemical and the inhibitor flow model into a single well simulator. Although each of these modules is valuable on its own merit, it is their integration that adds extra value to the overall product.