WS07 C03 Summary Effect of Wettability Alteration on

WS07 C03 Effect of Wettability Alteration on Production Improvement in Gas Condensate Reservoirs: a Review Paper M. Sheydaeemehr* (Petroleum University of Technology), I. Shafiei Sarvestani (PARS Oil & Gas), M. Pasdar (RIPI)

Summary Wettability alteration is a novel approach in gas condensate reservoirs by altering the wettability of the reservoir rocks from strongly liquid wetness to preferential gas wetness or intermediate‐wetting by treating them with chemicals that it's effects has been proved in lab scale. Both gas and condensate cumulative productions are improved significantly after the wettability alteration. The effect of wettability alteration on gas‐condensate production improvement is more pronounced in the intermediate‐wetting state. Wettability alteration could significantly increase well productivity at relatively low cost because only the near well region needs to be treated. In this paper, a review of recent studies on effects of wettability alteration on gas and condensate production improvement in gas condensate reservoirs has been presented.

79th EAGE Conference & Exhibition 2017 – Workshop Programme Paris, France, 12-15 June 2017

Introduction

The ability of one fluid in the presence of another to spread on the surface of the rock is known as wettability of a reservoir-rock fluid system. Wettability plays an important role in the oil and gas production process. It determines the initial fluid distributions in reservoir conditions and also it is a main factor in the flow processes in the reservoir rock. The contact angle measurement is a typical method to determine the degree of wetting of solids by liquids (Heinemann, 2005).

Figure1: Wetting (water) and non-wetting (mercury) fluid shape on the surface. Theory

In gas condensate reservoirs, when the reservoir pressure falls below the dew point, a condensate phase will form and accumulate around wells. This liquid accumulation which is known as condensate blockage, results in well productivity reduction. As a consequence of this problem, gas and condensate production rates decrease dramatically (Fevang, 1995). Many investigators have proposed several methods such as gas recycling, hydraulic fracturing and solvent injection to restore gas and condensate production rates when condensate blockage has been occurred. These methods have not enough positive effects on this problem (Fernandez, 2011). In recent years, wettability alteration, as a new method, has become more attractive for researchers in industry. Most of the gas-condensate reservoirs rocks are naturally liquidwetting. Altering the wettability of the reservoir rock from strongly liquid wetness to preferential gas wetness or intermediate-wetting can increase the mobility of condensate and the relative permeability to gas. Li and Firoozabadi (2000) modeled the wettability alteration in hydrocarbon systems of gascondensate-rock. Using experimental methods, it was shown that the wettability of porous media in gas–liquid–rock systems could be changed from strongly liquid-wetness to preferential gas-wetness (Li and Firoozabadi, 2000). The wettability of the rock was altered by treating it with the chemical solutions FC759 and FC722 at laboratory conditions. Tang and Firoozabadi (2002, 2003) performed wettability alteration at high temperatures up to 90°C and measured the effect of wettability alteration on liquid mobility. This work has continued by Fahes and Firoozabadi (2005) for higher temperatures up to 140°C. The results showed that at high reservoir temperatures, wettability could be permanently altered from liquid-wetting to intermediate gas-wetting and wettability alteration significantly increased liquid mobility at reservoir conditions. Kumar et al. (2006) studied improvement of the gas and condensate relative permeabilities using chemical treatments under reservoir conditions. The experimental results showed that when Novec FC 4430 polymeric surfactant was used in the methanol-water mixture as the


solvent, the productivity index was improved by a factor of 2 to 3 for sandstone cores over the temperature range of 145 to 275 °F. Figure 2 shows the result of change in contact angle for Berea cores in Fahes and Firoozabadi's (2007) study on wettability alteration to intermediate gas-wetting in gascondensate reservoirs at high temperatures

Figure 2: Contact angle for untreated and treated Berea (Fahes and Firoozabadi's ,2007)

Noh and Firoozabadi (2008) investigated the effect of wettability on the high-velocity coefficient in two-phase flow. The measurements showed that when the core is strongly water-wetting, the high-velocity coefficient increases (about 270-fold) in two-phase flow of water and gas. It has been concluded that altering the wettability by treatment of the wellbore region can greatly improve the well deliverability. Zoghbi et al. (2010) studied an optimum wettability condition to maximize production enhancement. The simulation results indicated that when intermediate gas-wetting state was applied in the near-wellbore region, the gas-condensate well productivity increased significantly. Wu and Firoozabadi (2011) showed that the change in the mobility of gas-phase is a function of the minimum liquid saturation. It has been confirmed that the wettability alteration may result in a substantial decrease in the two-phase high-velocity coefficient (𝛽). The increase in the relative permeabilities and a decrease in the high-velocity coefficient of the two-phase flow from the wettability alteration will improve gas well productivity. Li et al. (2011) conducted a series of experiments in the rock sampled from Dongpu gas condensate field located in Henan, China and developed a new and cheaper chemical to alter the rock wettability to gas-wetness effectively. The results indicated that after wettability alteration from preferential water to preferential gas-wetness, the relative permeabilities of both the gas and the water phases were increased remarkably. Also the residual water saturation was decreased and the gas production was enhanced significantly.

Examples (Optional)

As it has been reviewed above, most studies have focused on finding chemicals to perform permanent wettability alteration experiments in lab scale, but the effect of wettability alteration on production improvement in field scale has not been studied well enough.


Sheydaeemehr et al, 2014 investigated gas-condensate production improvement using wettability alteration in a giant gas condensate field using simulation. The results showed that after the wettability alteration of porous media from liquid-wetting to intermediate- or gaswetting by changing relative permeabilities for a treatment radius of 5 m around the wellbore, the gas-condensate cumulative production was improved significantly (see figure 3&4).

Cumulative gas production, MMMSm3

Intermediate wet.

Gas wet.

Liquid wet. (reservoir)

3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

10

20

30

40

Time, years

Figure 3: Comparison of the cumulative gas production in the three different wettability states (Sheydaeemehr et al, 2014)

Cumulative condensate production, MMSm3

Intermediate wet. Liquid wet. (reservoir)

Gas wet.

2.0

1.5

1.0

0.5

0.0 0

10

20

30

40

Time, years

Figure 4: Comparison of the cumulative condensate production in the three different wettability state (Sheydaeemehr et al, 2014).

Conclusions

The main conclusions of this study are: 

Wettability alteration is a novel approach in gas condensate reservoirs by altering the wettability of the reservoir rocks from strongly liquid wetness to preferential gas wetness


  

or intermediate-wetting by treating them with chemicals that it's effects has been proved in lab scale. Both gas and condensate cumulative productions are improved significantly after the wettability alteration. The effect of wettability alteration on gas-condensate production improvement is more pronounced in the intermediate-wetting state. Wettability alteration could significantly increase well productivity at relatively low cost because only the near well region needs to be treated.

Acknowledgements (Optional) The author would like to thank Pars Oil and Gas Company (POGC) for financial support throughout this paper. References Heinemann, Z. E., 2005: Fluid Flow in Porous Media, University of Leoben., Leoben, Austria. Brooks, R. H. and Corey, A. T., Hydraulic Properties of Porous Media, Hydrology papers, No. 3, Colorado State University, Ft. Collins, Colo., 1964. Fahes, M. and Firoozabadi, A., Wettability Alteration to Intermediate GasWetting in Gas/Condensate Reservoirs at High Temperatures. SPE 96184, 2005. Fernandez, R. G., (2011)., Altering wettability in gas condensate sandstone reservoirs for gas mobility improvement, MSc. Thesis, Texas A&M University. Fevang, O. (1995). Gas Condensate Flow Behavior and Sampling. Ph.D. thesis, University of Trondheim. Henderson, G.D. et al., The Relative Significance of Positive Coupling and Inertial Effects on Gas Condensate Relative Permeabilities at High Velocity. paper SPE, 62293 presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 1-4 2000. Henderson G.D., Danesh A., Tehrani D.H. and Al-Shaidi S., June 1996: Measurement and Correlation of Gas Condensate Relative Permeability by the Steady State Method, Paper 31065, SPE Journal, 191-201. Kumar, V., Pope, G.A., and Sharma, M.M., Improving the Gas and Condensate Relative Permeability Using Chemical Treatments. SPE 100529, 2006 . Li, K. and Firoozabadi, A., Experimental Study of Wettability Alteration to Preferential GasWetness in Porous Media and its Effect. SPE 62515, 2000. Li, K., Liu, Y., Zheng, H., Huang, G., Li, G.,. 2011. Enhanced gas-condensate production by wettability alteration to gas wetness. Journal of Petroleum Science and Engineering 78 (2011) 505–509. Noh, M. and Firoozabadi, A. 2008. Effect of Wettability on High-Velocity Coefficient in Two-Phase Gas/Liquid Flow. SPE J. 13 (3): 298–304. SPE-102773-PA Tang, G. and Firoozabadi, A. 2003. Wettability Alteration to Intermediate Gas-Wetting in Porous Media at Elevated Temperatures.Transport in Porous Media 52:185–211. Tang, G.-Q. and Firoozabadi, A. 2002. Relative Permeability Modification in Gas/Liquid Systems Through Wettability Alteration to Intermediate Gas Wetting. SPEREE5(6): 427–436. SPE-81195-PA. Wu, S., Firoozabadi, A., Simultaneous Increase in Gas and Liquid Relative Permeabilities and Reduction of High-Velocity Coefficient From Wettability Alteration. SPE-144637-PA-P, 2011. Zoghbi, B., Fahes, M.M., Nasrabadi ,H., "Identifying the Optimum Wettability Conditions for the NearWellbore Region in Gas-Condensate Reservoirs,. SPE 134966 ,Texas, USA, 2–3 November 2010. M. Sheydaeemehr, B. Sedaeesola, A. Vatani,"Gas-condensate production improvement using wettability alteration: a giant gas condensate field case study", Journal of Natural Gas Science and Engineering, Volume 21, November 2014, Pages 201–208, DOI: 10.1016/j.jngse.2014.07.011.
