Modeling Study of Natural Fracture Activation and Wormhole Creation During Acid Fracturing Operations in Oil and Gas Reservoirs

Large reserves of oil and gas in Saudi Arabia exist in carbonate formations. To increase well production, acid fracturing is a potential stimulation method especial in tight heterogeneous formations. Better design of acid fracturing operations requires a sophisticated model that can reproduce actual field results. Acid fracturing modeling did not receive a lot of attention from researchers as the physics of reactive fluids is complex and hard to predict. To correctly model acid fracture, fluid transport and reaction should be integrated to fracture propagation, heat transfer, and productivity models. This work was the focus of my research during my Ph.D. study where a fully integrated acid fracture model is developed. However, the model developed still cannot predict all the phenomena that occur during operations. One challenging Issue during acid fracturing is the fracture closure during acid pumping. This is usually not an issue when a non-reactive fluid is pumped. There are several explanations to clarify this phenomenon such as extensive wormhole creation, acidizing vuggy formation, or natural fracture network activation. Nevertheless, there are no experimental or numerical studies to validate the explanations. The model developed from my Ph.D. work will be modified to explain the premature fracture closer because of acidizing. Wormholes creation and natural fracture network activation have always been perceived as an undesired process during acid fracturing. The reason is the fact that it limits the acid penetration distance. Creating good conductivity is favored over long acid penetration distance in high permeability reservoirs. The model can be modified to test when wormhole creation and fracture network activation can enhance fractured well productivity. Even though the created model has been validated theoretically, it was not tested over real filed data or experimental results. A possible outcome of this research is also to validate the model and use it in the actual design of acid fracturing operations.