Abstract
AbstractCarbonate matrix acidizing creates wormholes in the damaged formation around the wellbore and is used extensively to enhance well productivity. There are many factors discussed in literature that can positively or negatively affect the efficiency of carbonate matrix acidizing, such as mineralogy, permeability, porosity, and factors associated with the rock matrix and the acidizing fluids. However, the influence of reservoir crude oil on the acidizing operation has not been addressed and is the subject of this study.Several limestone outcrop samples were selected and used in this study after evaluation of their petrophysical properties. The samples were fully saturated with deionized water; some samples were centrifuged and aged at high-pressure/high-temperature (HP/HT) conditions with different grades of crude oils. Linear acidizing experiments were executed; the preliminary acidizing tests showed optimal flow rate of 2 cm3/min. A baseline test was then conducted, using preflush fluid injection prior to acidizing to represent the real scenario of a stimulation job in the reservoir. The preflush helped to clean out the rock matrix, preparing the sample for acid injection. Lower pore volume before breakthrough (PVBT) was observed compared to the preliminary tests without the preflush. Then, linear acidizing tests were run on oil-saturated core samples. The results showed that the lower crude oil API is, the less acid volume needed to achieve acid breakthrough. This is mainly due to the viscous fingering that occurs because of the high viscosity contrast between the low-API crude oil and the 15% HCl acid used.These results show the impact of crude oils with different API on the acidizing efficiency, which is very important information for reservoir engineers and should help proper planning the potential volume of acid needed and in making the right operational decisions for better financial impact.