Abstract

In volatile oil reservoirs, the presence of two fluid phases (gas and oil) near the wellbore is a common problem that affects well deliverability. As the pressure falls below the bubble point the presence of two immiscible phases reduces the oil relative permeability and leads to lower oil production rates. In this paper, we show that the application of fluorinated chemicals can mitigate this impairment associated with gas blocking of volatile oils. We show through laboratory experiments that the treatment not only removes the water from the treated zone, but also modifies the wettability of the rock surface to neutral wet, minimizes capillary trapping and enhances the mobility of oil and gas. The chemical treatment is effective in the presence of connate or flowing water over a range of temperatures. This technique may be used as a curative or preventive treatment in volatile oil reservoirs, potentially increasing oil production rates and recoverable reserves. High-pressure high-temperature (HPHT) coreflood tests were conducted that show that the treatment improved the relative permeability, by a factor of about 1.3 to 2.6 at a GOR of 6000 to 7000 scf/STB in sandstone and limestone cores at low capillary numbers (Nc). Wettability alteration was measured using contact angle and imbibition tests. These tests together with x-ray photoelectron spectroscopy (XPS) analysis were used to screen the selected surfactants. Since this durable enhancement is achieved by treating a small area around the wellbore, it may be applicable in a wide variety of wells.

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