A New Solution to Restore Productivity of Gas Wells With Condensate and Water Blocks

Abstract

During production from gas condensate reservoirs, significant productivity loss occurs after the pressure near the production wells drops below the dew point of the hydrocarbon fluid. Many of these gas reservoirs also have some water accumulation near the wells. This adds significantly to the total liquid blocking. Experiments were conducted using both outcrop sandstone and reservoir cores to measure the effect of liquid blocking on gas relative permeability. A chemical treatment was developed to reduce the damage caused by condensate and water blocking. The treatment is composed of a fluorinated material delivered in a unique and optimized glycol-alcohol solvent mixture. The chemical treatment alters the wettability of water-wet sandstone to neutral wet and increases the gas relative permeability. The increase in gas relative permeability was quantified by comparing the gas relative permeabilities before and after treatment. Improvements in the gas relative permeability by a factor of about 2 were observed. The alteration of wettability after the chemical treatment was evaluated by measuring the USBM wettability index of treated reservoir cores. Measurements show a significant amount of the surfactant is adsorbed on the rock surface, which is important for the durability of the treatment. Many attempts have been made to develop effective chemical treatments to mitigate the damage caused by condensate and/or water blocking with little success until now under realistic reservoir conditions. Using inexpensive, safe and effective solvents was one of the keys to the success of our new approach. Others have mostly tried reactive materials that are subject to complications in downhole applications. We use a non-reactive, nonionic polymeric surfactant that does not have any of these problems and is robust over a wide range of temperature, pressure, permeability and brine salinity. We have developed a chemical treatment for liquid blocking that shows great potential to increase production from gas condensate wells. Compositional simulations indicate the economics of this treatment process are likely to be very favorable. Introduction In gas condensate reservoirs a significant loss in the well productivity is observed when the bottomhole pressure in flowing wells falls below the dew point pressure of the fluid (Afidick et al., 1994; Barnum et al., 1995; Engineer, 1985; Ayyalasomayajula et al., 2005). The reduction in well productivity is caused by the buildup of a condensate bank around the well, which impeded the flow of gas to the well and thus reduces its productivity. Since the reduction in well productivity is primarily associated with the reduction in gas relative permeability, a great deal of effort has gone into measuring and modeling the relative permeability of gas-condensate fluids. Initially, the studies were done at low pressure and temperature (Ham and Eilerts, 1967). Later studies were done at reservoir conditions with synthetic fluids (Henderson et al., 2000; Kumar et al., 2006; Kumar, 2006; Ayyalasomayajula et al., 2003; Bang et al., 2006) as well as with reservoir fluids (Nagarajan et al., 2004; Mott et al., 2000). Various parameters such as interfacial tension (Henderson et al., 2000), high flow rates (Kumar et al., 2006; Kumar, 2006; Ayyalasomayajula et al., 2003; Bang et al., 2006; Nagarajan et al., 2004; Mott et al., 2000), non-Darcy effects (Kumar et al., 2006; Nagarajan et al., 2004), fluid composition (Mott et al., 2000) and rock (Mott et al., 2000) have been investigated.

A Combined Experimental and Theoretical Investigation on Application of Wettability Modifiers in Gas-Condensate Reservoirs

“…The idea of wettability alteration for gas-oil systems was first proposed by Li and Firoozabadi (2000). Since then, extensive experimental studies have been dedicated to this subject with the main concentration on finding appropriate wettability modifiers for sandstone substrates (Kumar et al, 2006;Panga et al, 2006;Fahes and Firoozabadi, 2007;Bang et al, 2008). There are limited number of CT field trials in sandstone gas-condensate reservoirs reported with promising (i.e.…”

Wettability Alteration at Optimum Fluorinated Polymer Concentration for Improvement in Gas Mobility

“…The mobility zone near the wellbore is the region of interest in this study. In order to overcome this problem, procedures like hydraulic fracturing or solvent injection can be considered with the objective to decrease interfacial tension and increase liquid vaporization rate (Bang et al 2008). Another approach has been proposed, altering wettability of the system to intermediate gas-wetting.…”

“…These tests were also performed at reservoir conditions. Bang et al (2008) conducted experiments at reservoir temperature and pressure with a different set of mixtures. L19945 was mixed with 2-butoxyethanol (EGMBE) and ethanol, which showed an increase in oil and gas relative permeability of a factor of more than 2.…”

Identifying the Optimum Wettability Conditions for the Near-Wellbore Region in Gas-Condensate Reservoirs

“…This method is based on reducing the liquid-wetting of the rock surface to enhance liquid mobility and reduce the accumulation of liquid condensate. A few other research groups at universities and companies have also been investigating this method (Bang et al, 2010;Ahmadi et al, 2010;Al-Anazi et al, 2007;Zheng and Rao, 2010). Pilot tests were also conducted in recent years (Butler et al, 2009;Liu et al, 2008).…”

“…The authors believe that the low permeability of the reservoir could be one of the main reasons for the failure. In another field application in 2009, a team from Trueblood Resources Inc., The University of Texas at Austin and 3M Company conducted a chemical treatment for a gas-condensate reservoir (Bang et al, 2010). The average permeability was 20 md and the reservoir pressure was 2971 psi.…”