Novel Surface Modified Nanoparticles for Long-Lasting Mitigation of Water and Condensate Blockage in Gas Reservoirs
Authors: Sayed Mohammed , Liang Feng , Ow Hooisweng 
Published: April 2018

Abstract
Appreciable liquid and gas reserves can be found in gas condensate reservoirs. During gas production from the gas condensate reservoirs, the bottom-hole pressure may drop below the dew point pressure. When this occurs, liquid condensate will start to drop out of gas phase and accumulate in the area close to the wellbore where the pressure drop will be maximum. The accumulation of condensate, and sometimes water, in the area around the wellbore will result in reduction in gas permeability resulting in the loss of production of gas and liquid condensate. Several techniques have been used to mitigate the problem of condensate and liquid blockage (banking) in gas reservoirs. These methods include injection of low flash point solvents, wettability alteration surfactants, gas cycling and hydraulic fracturing. However, none of these offer a comprehensive solution to the problem with each method having its own pros and cons.
In the current study, a novel chemical treatment formulation based on surface modified fluorinated silica nanoparticles (F-NPs) was developed to mitigate the problem of condensate and water banking. The performance of the developed F-NPs was compared to that of the commercial available fluorinated polymeric surfactant. The advantages of this approach over the commercial available treatment chemicals include a longer treatment lifetime with a lower concentration of effective nanoparticles. Both will be beneficial to the economics of the field operation. The newly developed formulation effectively alters the wettability of the rock surface from oil and/or water wetting to neutral wettability for both phases or to intermediate gas wet. This was achieved through creating an omniphobic and hierarchically roughened surface. The size distributions of the fluorinated silica nanoparticles were characterized by dynamic light scattering (DLS) technique. The contact angle of water and decane on the treated rock surfaces was measured to characterize wettability alteration. Coreflood experiments were performed using outcrop samples and real gas condensate fluid composition under reservoir conditions.
The fluorinated silica nanoparticles with average sizes of 100 nm and 400 nm have been synthesized. The contact angle measured of water and decane on the treated sandstone surface with the F-NPs was found to be 120° and 51°, respectively, compared to 90° and 50° when the surface was treated with formulations contain fluorinated surfactants. This indicates that the fluorinated nanoparticles were able to change the wettability of the rock surface to strongly non-water wetting and moderately decane wetting. Several coreflood experiments were performed to optimize the fluorinated nanoparticles concentration and solvent package. Fluorinated surfactants formulations were able to achieve 69% improvement after pumping 15 pore volumes (PV) of treatment. It was revealed that only 3 PV of a treatment formulation composed of 0.065 wt% concentration of fluorinated nanoparticles in butanol were able to achieve 37% improvement for gas and liquid relative permeability.
The new fluorinated nanoparticle-based treatment is able to change the rock surface wettability to be non-wetting with liquids or intermediate gas wetting effectively. More importantly, the treated surface is relatively long-lasting since the improvement was proved to be almost to the same level after pumping 250 PV of gas condensate mixture from our lab experiment under reservoir conditions. The novel surface modified nanoparticles show promise as an effective method for mitigating and water blockage in gas condensate reservoirs.