WAG injection is an EOR process that was developed to mitigate the technical and economic disadvantages of gas injection. It is the most widely applied and most successful traditional EOR process.
It involves the injection of slugs of water alternately with gas although sometimes the two fluids are injected simultaneously (termed SWAG= zero slug size).
My question is: when optimising the slug size to achieve high oil recovery, the optimisation directs me towards small slug sizes that the period of injection will be one month to inject gas and one month to inject water, is that still considered as SWAG or is it considered as WAG injection at small slug sizes behaving similar to SWAG?
Keep in mind that I dont have a real field, and I didnt consider the economic part.
The only thing I can consider in my work is how much gas available to inject, which leads me to my second question.
I could not find a source to tell me approximately how much gas available to use for injection, I appreciate any suggestions or links I can find the answer?
Thanks in advance
I have a conference paper that presents oil recovery vs. different injection modes. You may find answer in that paper.
Hello Zainab
first, the slug size during SWAG injection is Not zero but at infinitesimal slug size.
Secondly, the answer of your question.
we differentiate between SWAG and Slug Size WAG from the injection strategy. in SWAG injection water and gas are simulatneously injected into the porous media whereas during Slug Size WAG, short slugs of water and gas are injected alternatenly into the rock. however, when the slug size of water and gas injections is reduced to 3% PV or less the injection process is approaching SWAG and some authors (e.g. Minssieux, L. and Duquerroix, J-P., 1994) identified 3% PV of water and gas injections as SWAG injection.
I do know how much pore volume of gas and water you injected each month but to me, the injection process seems like it is still Short Slug WAG. Since your injection is switched from water to gas and vice versa you are still applying WAG injection, however you need to determine the PV injected each month.
According to our experimental study (SPE-187537-MS) of the effect of slug size on oil recovery and injectivity, oil recovery performance keeps changing corresponding to the size of the injected water and gas slugs which means even at very short slug size I would still define the injection process as 'Short Slug WAG' not SWAG.
if you are interested to know more about the effect of slug size on oil recovery and fluid injectivity please refere to our SPE-187537-MS paper.
Conference Paper An Experimental Investigation of the Effect of Gas and Water...
SWAG is usually surfactant water alternating gas, but I suppose it could also be simultaneous water and gas. Usually if the later, injection is down two different strings with gas on bottom and water up high so they cross by gravity segregation. What gas are you using? Do you think you are miscible at reservoir conditions?
With WAG, the slug size and speed with which one WAGs is driven by the permeability and connectivity between wells. High connectivity and high permeability tend to need fast WAGs (days), low permeability (
You are talking about WAG. We run WAG cycles on 34 CO2 floods, over 1600 patterns that vary from days to 1 year. Shorter cycles can be helpful for better sweep, and gas management, but injection rate loss on WAG switches can result in reservoir pressure and oil rate loss. This is driven by rock quality, heterogeneity and relative permeability curves, all dependent on your specific reservoir. David
From a reservoir / recovery perspective one can consider that infinitely small sized slugs tangent the behavior of simulatenous injection. But this is not true from an operations and design of facilities perspective. Equipments and procedures for true simultanenous operations will differ from those of alternating with short slugs (CAPEX /OPEX will be different, HSE aspects too).
For the second question, there are many possible answers. I would structure things considering different configurations. First configuration would be reinjection of associated gas (minus whatever was used for compression and other utilities) eventually focusing WAG on part of reservoir(s), second configuration would be maximum efficiency level of gas injection (no limit on gas availability).
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