Acid treatment in carbonate reservoirs targets to restore or to stimulate the near-well area. Emulsified acid can be used in matrix acidizing and acid fracturing treatments. The delayed nature of emulsified acid is useful in creating deep wormhole and etched fracture surfaces. Almost all coreflood work done before was performed on cores fully saturated with water. Therefore, the main objective of the present work is to study the effect of presence of crude oil in the formation on the performance of emulsified acid in stimulating carbonate formation.

A coreflood study was conducted using high permeability Indiana limestone cores which have dimensions of 1.5" diameter and 6" long. The effect of the presence of crude oil inside the core on the volume of acid to achieve acid breakthrough was studied. Also, the size, numbers and distribution of the resulted wormholes as a function of the core fluid content was studied through the analysis of the CT images on the core after injection of emulsified acid. Also, the effect of the acid injection rate on these parameters was studied. Cores that are fully saturated with water and cores saturated with crude oil and water were used to study the performance of emulsified acids.

From the coreflood study, there was no optimum injection rate for an emulsified acid system when it was tested against high permeability Indiana limestone cores fully saturated with water. For high permeability Indiana limestone cores, emulsified acid enhanced the rock permeability when the acid injected at high rates. For cores saturated with crude oil and water, there was no clear relationship between volumes of emulsified acid required to achieve breakthrough and emulsified acid injection rate. Also, volumes to emulsified acid to achieve breakthrough in cores saturated with crude oil and water are greater, compared to acid volumes required to achieve breakthrough in cores fully saturated with water. Emulsified acid system is effective in stimulating limestone cores, at different acid injection rates and at high temperatures, even the cores were saturated with water or saturated with crude oil and water.

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