Abstract
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 conductivity 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.