Application of Nanotechnology in EOR, Polymer-Nano Polymer-Nano flooding (the nearest future of chemical EOR methods) By/ Mohammed Elkady, B.Sc. Petroleum department, Engineering faculty, Al-Azhar University, 1st place award at the SPE Middle East Regional Student Paper Contest(ATSE 2016) and SPE research & development committee member. Oil reserve is the commercial oil which can be produced with current technology. In this article we will try to show the effect of nanotechnology nanotechnology on EOR methods specially polymer flooding, which will make the range of the oil recovery technology wider than before. Also this new technique (Polymer-Nano flooding) will be cheaper than polymer flooding and other expensive EOR methods. Oil recovery is classified into three recovery types: primary recovery, secondary recovery and tertiary recovery or enhanced oil recovery (EOR). EOR refers to processes in porous medium that recover oil which is not recovered by the conventional methods (primary and secondary recovery) by reducing the remaining oil saturation (residual oil or by-passed oil or both).EOR is categorized into three major recovery methods: chemical recovery methods, thermal recovery methods and miscible recovery methods. Our focus will be on chemical recovery methods. Chemical recovery methods refer to adding chemical components such as polymer, Surfactant or alkaline to the
injection fluid to improve mobility ratio through increasing the displacing fluid viscosity, reduce IFT and alter the wettability. But the problem these chemicals are liable to degradation due to intense reservoir condition (high salinity and high temperature), but the actual problem lies in the fact that these chemicals are very expensive. And after the sharp decline in oil price since the mid of 2014 up till now; it i t has become economically economically difficult to use these expensive chemicals in flooding projects. So, thinking about a new technique for saving the amount of these chemicals used at the same level of efficiency. Therefore, thinking has been directed to Nanotechnology. Nanotechnology describes the usage of particles which have a size less than 100 nm (nanoparticles) to gain more
benefits through their unique properties due to their small size and their type, such as very high mechanical strength, catalytic properties, super conductivity and penetrability through very small medium. Nowadays nanotechnology has proved its efficiency in most oil and gas fields especially EOR through many previous experimental works, so the author has attempted to investigate the effect of nanoparticles on chemical EOR methods through experimental work to solve this economical problem.
Experimental work (Polymer-Nano flooding) Polymer flooding was chosen rather than other chemical EOR methods, because it's more common and applicable in chemical flooding projects. And according to the knowledge of the author, there is no pervious experimental works related to the application of nanotechnology nanotechnology to polymer flooding. Polyacrylamide was used because it's most extensively used in polymer flooding projects due to its good effect on improving mobility ratio through increasing the injection fluid viscosity. Aluminum oxide NPs was chosen due to its good effect on R.F through IFT reduction, wettability alteration and its good stability at reservoir conditions (high salinity and high temperature) through many previous experimental works. Also it’s cheaper than most NPs which have also a good effect on R.F. The size of alumina NPs used in the experiments was approximately 50 nm according to Scanning & Transmission Electron Microscopy images (SEM &TEM). Figure (1)
Figure (1): size of alumina NPs used in the experiments.
Core preparation:
Samples were cleaned from any hydrocarbon or salts. Then diameters and lengths, basic parameters (porosity and permeability) were measured. After that, samples were saturated with brine (3 wt.% NaCl).Then samples were drained with mineral oil (21c.p) until reaching irreducible water saturation (Swi). Experimental procedures:
Water flooding was performed then normal polymer flooding (the concentration of polymer 2000 ppm) then polymer-Nano flooding (the concentration of the polymer was 1000 PPM -saving a half amount of it- and concentration of alumina NPs was 0.02 wt.%). After that polymer-Nano flooding was performed above polymer flooding to show the effect of Polymer-Nano flooding on R.F even after polymer flooding. Results and Discussion: Recovery factor 70
69.3
68
67.16
66 ) P I O64 O f o %62 ( , F . R60
66.29
60.65
58 56 Water flooding
polymer flooding then Polymer-Nano flooding
Polymer-Nano flooding
Figure (2): R.F values after various flooding
:
Water flooding
: Polymer flooding
: Polymer-Nano flooding
As we see in Figure (2), after water flooding the R.F was 60.65 % and after polymer flooding the R.F was 67.16 %. When Polymer-Nano flooding was performed directly above polymer flooding, the R.F increased by 2.14 % to be 69.3 %. When made Polymer-Nano flooding instead of polymer flooding, the value of R.F became very near the value of polymer flooding R.F (the difference is less than 0.9 %). So, how was the R.F value of Polymer-Nano flooding very near the R.F value of polymer flooding, although we used only half the amount of polymer with the mobility ratio becoming less? The answer is clear from the relative permeability curves through the intersection point's value as we
see in figure (3); the intersection point value after polymer-Nano flooding is higher than the intersection point value after polymer flooding. This means that the rock was more water wet after Polymer-Nano flooding rather than polymer flooding. And as we see in figure (4), the permeability of water at residual oil saturation after Polymer-Nano flooding is lower than the permeability of water at residual oil saturation after polymer flooding by approximately 20 md.
Intersection of Kro & Krw Water flooding
) e c 80 a p s 70 e r o p 60 % ( o r 50 K @ 40 w r K f 30 o n 20 o i t c e 10 s r e t n I 0
Polymer flooding
polymer-Nano flooding
68.8
70
Polymer flooding
polymer-Nano flooding
56.5
Water flooding
Figure (3): values of Kro & Krw intersection after various flooding
Kw @ Sor (md) 195 190 185
Polymer flooding
polymer-Nano flooding
189.03
r o 180 S @ 175 w r K
170
170.3
165 160 Polymer flooding
polymer-Nano flooding
Figure (4): values of Kw at Sor after polymer and Polymer-Nano flooding
So we can say that, at polymer flooding the main mechanism was mobility control, due to the presence of polyacrylamide which improved the mobility ratio through increasing the injection fluid viscosity. But When Polymer-Nano flooding was performed it was found that there was more than one mechanism affecting the R.F as wettability alteration due to the presence of Al2O3 NPs and mobility control due to the presence of polyacrylamide. What about the cost?
The average price of polyacrylamide was 34.4 $/1kg, and the average price of alumina NPs was 30 $/1kg (If we buy large amounts of them). And here is a comparison of the materials used in polymer and Polymer-Nano techniques at 1 litter. Normal polymer flooding
Polymer-Nano flooding
Materials used at 1 liter
2gm polymer
1gm polymer + 0.2gm NPs
Cost per USD
0.0688
0.0404
Percentage of cost reduction =
0.0688−0.0404 0.0688
*100 = 41.28 % cost reduction
Finally, an effective reduction of cost was found - more than 41 % cost reductions. This large cost reduction is due to saving a very large amount of polymer by adding a very small amount of NPs due to its low concentration. Summary:
Using Polymer-Nano flooding after polymer flooding can increase the R.F more than 2 % of OOIP.
Using Polymer-Nano flooding instead of polymer flooding almost gives the same R.F as polymer flooding.
Polymer-Nano flooding has proved its effect to overcome the financial obstacles of traditional polymer flooding.
Now we can save more money
Finally, Polymer-Nano flooding is a new technique in chemical EOR methods which has many advantages like polymer flooding technique and additional advantages due to presence of Alumina NPs as follows: higher R.F (having two main mechanisms: mobility control & wettability alteration), cheaper than polymer flooding method and other expensive EOR methods, not complex (easy to be applied in oil fields), environmental and no fire hazards. Currently more experimental work is conducted to understand the different factors affecting the new technique and to optimize all the parameter to show the highest R.F this technique can reach with large cost reduction. Conclusions
Nanotechnology can be used as one alternative method to unlock the remaining oil resources.
Polymer-Nano flooding can be used at the near future as an enhancement for chemical EOR methods.
Written by/ Mohammed Elkady
[email protected]
