Aqueous fluids are shown to interact strongly with sandstones at elevated temperatures and have been reported to produce formation damage related to dissolution and precipitation of minerals. But the presence of crude oil, along with the crude-oil type, may affect the rate and amount of this chemical interaction. Additionally, if the crude oil has small but important amounts of organics acids (> 2 mg KOH/g oil), these can react with the alkaline solutions to produce "in-situ" surface active compounds. These surfactants can be adsorbed on rock surfaces and alter the wettability of reservoirs rocks.

An experimental study was conducted to examine and predict the effect of crude oil composition on in-situ surfactant production and to evaluate the potential formation damage on friable sandstones of heavy crude oil reservoir — Western Venezuela. The tests were carried out at relatively high temperatures (200° C) of system mineral/crude oil/aqueous fluids and the system crude oil/aqueous fluids. Minerals, crude oils and solutions were analyzed by different analytical techniques before and after reaction took place.

The results from this investigation showed that pH and presence and type of crude oil affect the dissolution of minerals. Experimental evidence suggested a strong reduction of the interfacial tension after the reaction of acidic crude oils with alkaline solutions. NMR, IR and GC/MS analysis indicate the presence of organic compounds in the aqueous phase.

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