The oil reservoirs of R. Trebs field are predominately heterogeneous carbonates with a well developed network of natural fractures, high formation temperature and high concentration of resins and asphaltenes in the produced crude.

Such complicated reservoir conditions entail integrated acid treatment engineering and design to include physical and chemical analysis of acid compositions, formation fluids and reservoir rock; physical simulation of acidizing on core from target intervals and numerical modeling of the optimum acid job design.

The conducted research supported the selection of the optimum acids for the geological and engineering conditions of R.Trebs oil field to secure better compatibility with the formation fluids from the target intervals, lower corrosion activity and retarded reaction rate. The findings also identified the range of critical values for permeability and mineralogy of the rock whereby acid flows through a reservoir rock in a growing dominant wormhole.

Based on the literature survey a semi-empirical model was chosen which describes the growth of a wormhole. The model was calibrated against the actual reservoir conditions of R.Trebs field using flow test results and reaction kinetics studies on the rock samples from the given pay zones.

The integrated approach introduced for acid job design can be applied to achieve the following:

  • select application or usability criteria of an acid job for a given field;

  • select optimum acids to secure minimum risks of primary and secondary formation damage and optimum reaction rate;

  • implement engineering optimization of acid job design by the identification of its most efficient parameters;

  • forecast post-acid production and other field performance indicators.

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