Correlating Wettability Alteration with Changes in Eelative Permeability of Gas Condensate Reservoirs

Abstract

In gas condensate reservoirs, considerable productivity loss occurs after the pressure near the production wells drops below the dew point of the hydrocarbon fluids. Over the years, several methods have been proposed to restore gas production rates after a decline in well productivity owing to condensate and/or water blocking. These methods such as gas recycling, hydraulic fracturing and solvent injection have shown to restore the production on a temporary basis only. Altering the wettability of reservoir rock using fluoro-chemical treatments has proved to be a viable and permanent solution to this problem. The selection of these treatments from a large pool of potentially effective chemicals requires extensive laboratory testing which requires time and money.In this paper, we present data that correlates changes in wettability with improvements in relative permeability. Imbibition, contact angle and X-ray photoelectron spectroscopy (XPS) tests along with coreflood results are used to characterize wettability changes. XPS tests, drop tests and core flood experiments were conducted and correlated with each other. It is shown that XPS analysis and imbibition tests provide a quantitative measure of chemical adsorption and surface modification, but only a qualitative measure of the possible change in relative permeability. As such these simple analytical tools may be used as a screening tool. A positive but imperfect empirical correlation was obtained with results from core flood experiments. The varying concentration of fluorine observed on the rock surface was found to be directly correlated to the wettability change in the rock, which in turn is responsible for improving the deliverability of wells in gas condensate/volatile oil reservoirs.The method discussed in this paper can be successfully used to identify chemical treatments that can change rock wettability and, therefore, relative permeability. This provides a simple and inexpensive way to screen chemicals as wettability altering agents and relative permeability modifiers. In this way the number of HTHP core floods needed is minimized which saves time, cost and effort. IntroductionGas condensate reservoirs are becoming more common as the petroleum industry goes to greater depths to explore for oil and gas. When we compare dry-gas reservoirs with gas-condensate reservoirs, there are many factors which affect the performance of gas-condensate reservoir during the exploitation process that need to be understood. As the reservoir pressure declines below the dew point of the fluid, a liquid rich phase starts to drop out of the gas phase. This liquid rich phase is termed "condensate" and the phenomenon is called "condensate banking". Since the largest pressure drop occurs near the producing wells, the formation of a condensate phase usually occurs as a near well bore phenomenon. As the pressure continues to drop, the liquid continues to accumulate occupying the rock pores leading to a decrease in the effective permeability to gas.Several cases have been reported i...

Wettability Alteration of Berea Sandstone for Gas Condensate Applications

“…Normal decane spontaneous imbibition before and after treating the core sample with 4% at high temperature, reprinted with permission from Alajmei, 2017. Copyright (2017, University of Oklahoma) …”

“…Relative permeability of the Berea sandstone before and after treatment with 4 and 8%, reprinted with permission from Alajmei, 2017. Copyright (2017, University of Oklahoma) …”

“…Core flooding apparatus, reprinted with permission from Alajmei, 2017. Copyright (2017, University of Oklahoma) …”

Pore-Scale Analysis of Condensate Blockage Mitigation by Wettability Alteration

“…Bang et al [1] evaluated the effect of wettability alteration in a sandstone core at higher interfacial tension conditions (≈12 mN/m) and reached IFs between 3 and 4. Other authors reported IF in the range 1-2, for both sandstone and carbonate cores [61][62][63], but no details of the fluid properties were discussed.…”

Development and Applications of a Compositional Pore-Network Model for Gas-Condensate Flow

“…Bang et al [86] evaluated the effect of wettability alteration in a sandstone core at higher interfacial tension conditions (≈ 12mN/m) and reached IFs between 3 and 4. Other authors reported IF in the range 1-2, for both sandstone and carbonate cores [99,100,101], but no details of the fluid properties were discussed.…”