INORGANIC SCALE FORMATION AND ITS INDUCED PERMEABILITY IMPAIRMENT DUE TO WATER INCOMPATIBILITY ISSUE DURING THE WATER INJECTION PROCESS

摘要

Due to the different natures of formation and injection waters, especially in seawater injection cases, incompatibility may happen within the reservoir and cause supersaturation and precipitation of some salts. This precipitation may reduce the permeability of reservoir rock from the injector vicinity to far deep in the reservoir. This paper investigates a seawater injection project. First, the scale types and amounts due to different mixing ratios are studied employing commercial software. Then, dynamic injection of seawater into carbonate samples saturated with formation water is performed and the induced damages are analyzed. Finally, the types of scales formed within the core samples are analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy imaging. Dynamic conditions may change the behavior of scale formation and precipitation. Therefore, summation of the experimentally-observed scales and the software-predicted ones can lead us to scales happening in reality. The water incompatibility induced permeability damage ratio is characterized by an initial constant permeability period where no damage is induced. After that, it experiences a decrease that stabilizes around 2 pore volumes. The higher the permeability, the longer is the initial constant permeability period and the lower is the final induced permeability damage due to larger pore throats. The final stabilization time points to the situation where all of the core sample lengths have experienced maximum scale formation and precipitation. Overall, the high contrast of seawater and formation water raises the probability of scale formation especially of the sulfate type. Moreover, the extent of damage is much more important than the types of scales which should be investigated in each project.