| dc.description.abstract | The two-scale continuum (TSC) model for simulating carbonate acidizing gained substantial attention recently. The previous studies mainly dealt with matching experimental homogenous limestone experiments. The previous work only considered the pore volume to breakthrough (PVBT) to match experimental results and assumed linear kinetics for HCl-carbonate. The objectives of the current study are to 1) build a robust model for dolomite matrix acidizing simulation, 2) account for the effect of rock types in the TSC model, 3) study acid performance under field scale, 4) modify the traditional upscaling schemes utilizing the TSC model, and 5) quantify the effect of wormhole growth in vuggy and naturally fractured using field scale radial model. Unlike previous studies, experiments were performed on 6 in. length and 1.5 in. diameter vuggy dolomite cores at two sets of temperatures (150 & 200⁰F) and acid concentrations (15 and 20 wt% HCl). Computer tomography (CT) was used to generate porosity distribution and non-linear reaction kinetics was applied. The acid reaction rate and diffusion coefficient were modified based on X-ray fluorescence (XRF) results and effluent chemical analysis. Wormhole 3D shape and experimental PVBT were used to assess the quality of model results. The tuned model was used to simulate a hypothetical 18 in. core as well as large scale radial experiments to assess its prediction capabilities, and then the model was utilized to predict the dolomite acidizing performance under field conditions. Simulation results were compared with traditional 1-D models. Finally, the radial model was used to simulate multiple cases including vugs and natural fractured to assess the effect on the acidizing process. The simulation runs emphasize that the exclusion of the wormhole shape and branching from the matching process results in an unrealistic match. It is important to simulate the cylindrical shape of the core using the actual porosity distribution to capture the wormhole growth, which is increasingly important when the wormhole propagates near the core perimeter. The radial field scale model results show that the optimum velocity can be higher or lower than those predicted from lab experiments. Accordingly, caution must be taken when linear core flood data is used to predict acid propagation in the field. The simulations showed that traditional upscaling models over predict acid volumes, as the predicted volumes are double at moderate to high injection rates. Models using statistically distributed porosity can provide accurate acid propagation predictions, with a relative percentage error less than 25% at extremely high injection rates. The simulation results of vuggy carbonates show that the presence of vugs results in faster and deeper acid propagation in the formation when compared with homogenous reservoirs at injection velocities lower than 8E-4 m/s. Results also revealed that the size and density of the vugs have a significant impact on acid consumption and the overall performance of the acid treatment. The output of the fractured model illustrates that under field conditions, fracture orientations do not affect the acid propagation velocity. The acid does not touch all the fractures around the well.
Current model was able to match multiple sets of experiments (Dolomite and Limestone) and follow the experimental trend of longer cores and large-scale radial experiments. It was used to predict acid performance under field conditions and to adjust the traditional upscaling models. The effect of vugs and natural fractures on carbonate acidizing was quantified utilizing the field scale model. A new workflow for carbonate matrix acidizing based on petrophysical, experimental, and simulation results is introduced. | en |
