An Experimental Investigation into the Effect of Injection Pressure on Formation Damage due to Asphaltene Deposition in Natural Gas Injection Process

With respect to the fact that most of the Iran oil reservoirs have elapsed their period of natural depletion, the usage of gas injection techniques renders necessary for EOR purposes. The formation of organic precipitates such as asphaltene and its subsequent precipitation over reservoir rock during the gas injection process is considered a critical problem due to causing damage to the formation. Therefore, prior to conducting any industrial gas injection projects, it is necessary to perform experimental research with the same type of reservoir rock/fluid, and then a field-scale project can be implemented, once the analysis of the experimental results and the simulation of the reservoir are completed. In this research, the effect of pressure of injecting natural gas on asphaltene precipitation and alteration of core characteristics is analyzed. Live oil samples from one of the Iran offshore fields were used. The permeability reduction before and after gas injection were determined. In addition, the produced fluid was sampled at different time scales and its asphaltene content was determined using the IP143 standard. Using the mass balance equations, the reduction in core porosity and the power relation between permeability and porosity in the damaged core were established. The results suggest that the asphaltene coagulation and precipitation should increase along with gas injection, which causes permeability reduction. Such damages tend to decrease by lowering pressure, and the analysis indicates the mechanism of precipitation to be of mechanical blockage.