Design and optimisation of acid fracture treatment in low permeability carbonate gas reservoirs

摘要

This study presents an innovative modelling scheme that can effectivelyoptimise acid fracturing treatment. The scheme consists of a fracture geometrymodel, a thermo-kinetic model, a production model, an economic model, and anoptimisation algorithm. Acid penetration distance was found to increase with theincrease in injection rate, decrease in leakoff rate, and decrease in formationtemperature. Fracture width increases with the increase in injection time andacid concentration.Fracture conductivity and half-length are used in the production model toestimate cumulative gas production over a period. Then, the economic modelestimates treatment cost and net present value (NPV). An optimisationalgorithm, based on the combined features of Genetic Algorithm andEvolutionary Operation, is used to maximise an objective function bymanipulating free design variables.The effects of three objective functions − maximum NPV, maximum cumulativeproduction and maximum NPV with minimum treatment cost on optimum acidfracturing design were investigated. A design based on maximum NPV yieldsalmost the same cumulative production as that for maximum cumulativeproduction but less treatment cost. In addition, a design based on maximumNPV with minimum treatment cost results in up to 19% saving in treatment costwith less than 1% loss in NPV.The effects of reservoir permeability, formation temperature and rockembedment strength on optimum acid fracturing design study indicates: Theincrease in formation permeability results in an increase in both treatment costand NPV. Increase in formation temperature results in decrease in bothtreatment cost and NPV. Net present value increases with the increase in rockembedment strength.