Design and optimisation of acid fracture treatment in low permeability carbonate gas reservoirs
This study presents an innovative modelling scheme that can effectively optimise acid fracturing treatment. The scheme consists of a fracture geometry model, a thermo-kinetic model, a production model, an economic model, and an optimisation algorithm. Acid penetration distance was found to increase with the increase in injection rate, decrease in leakoff rate, and decrease in formation temperature. Fracture width increases with the increase in injection time and acid concentration. Fracture
... uctivity and half-length are used in the production model to estimate cumulative gas production over a period. Then, the economic model estimates treatment cost and net present value (NPV). An optimisation algorithm, based on the combined features of Genetic Algorithm and Evolutionary Operation, is used to maximise an objective function by manipulating free design variables. The effects of three objective functions − maximum NPV, maximum cumulative production and maximum NPV with minimum treatment cost on optimum acid fracturing design were investigated. A design based on maximum NPV yields almost the same cumulative production as that for maximum cumulative production but less treatment cost. In addition, a design based on maximum NPV with minimum treatment cost results in up to 19% saving in treatment cost with less than 1% loss in NPV. The effects of reservoir permeability, formation temperature and rock embedment strength on optimum acid fracturing design study indicates: The increase in formation permeability results in an increase in both treatment cost and NPV. Increase in formation temperature results in decrease in both treatment cost and NPV. Net present value increases with the increase in rock embedment strength.