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

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 the gas permeability and hence 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. None of the state of the art is a panacea for the problem since each method has its own pros and cons.

In the current study, a novel chemical treatment formulation based on surface modified fluorinated silica nanoparticles (NP) was developed to mitigate the problem of condensate and water banking. The newly developed formulation is able to effectively alter the wettability of the rock surface from oil and/or water wetting to neutral wettability for both phases or to intermediate gas wet. The size distributions of the fluorinated silica nanoparticles were characterized by dynamic light scattering (DLS). The contact angle of water and decane on the new formulation-treated rock surfaces was measured to characterize wettability alteration of the treatment. Coreflood experiments were performed using outcrop samples and field gas condensate fluid composition under reservoir conditions (temperature is 300°F and pressure is 4000 psi).

To investigate the nanoparticle size effects, two batches of the fluorinated silica nanoparticles with average sizes of 135, 180 and 400 nm were synthesized. The contact angle measured of water and decane on the treated sandstone surface was found to be 120 and 51 degrees, respectively; indicating 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 the solvent package. It was revealed that only three pore volumes (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 reported herein was able to change the rock surface wettability to be non-wetting with liquids (both water and decane) or intermediate gas wetting effectively. More importantly, the treated surface was relatively long-lasting since the pressure drop after treatment was shown to be fluctuating around 33 to 36 psi (the same level after pumping 250 pore volumes of gas condensate mixture from our lab experiments under reservoir conditions.