Formation Water Processing
Formation Water Processing
(OP)
Hey there!
I have to design a formation water process, in which the oil content should be reduced from 1000ppm to below 200. Since it seems to be impossible to measure the droplet size, the residence time is based on experimental results (additional question: is it possible or reasonable to calculate the residence time without knowing the exact droplet size distribution?!?).
A pre-requirement is the use of tanks for the separation process. My problem now is, that I don't really know how to design the tank in order to guarantee the residence time not only theoretical but also in practice. Is there a correlation factor between theoretical residence time and the time I can achieve in such a tank in practise?!? How exactly do I design such a tank, how about fixtures and fittings?!?
I'd appreciate any helpful tip.
Thanks in advance.
I have to design a formation water process, in which the oil content should be reduced from 1000ppm to below 200. Since it seems to be impossible to measure the droplet size, the residence time is based on experimental results (additional question: is it possible or reasonable to calculate the residence time without knowing the exact droplet size distribution?!?).
A pre-requirement is the use of tanks for the separation process. My problem now is, that I don't really know how to design the tank in order to guarantee the residence time not only theoretical but also in practice. Is there a correlation factor between theoretical residence time and the time I can achieve in such a tank in practise?!? How exactly do I design such a tank, how about fixtures and fittings?!?
I'd appreciate any helpful tip.
Thanks in advance.





RE: Formation Water Processing
The device most often used for oil/water separation at the ppm level is called a "gun barrel" for reasons that seem to be lost in the mists of time. A properly designed gun barrel remains full to the oil and water overflow lines at all times. If a liter of fluid comes into the process than a liter of fluid must immediately leave the process. This implies that the inflow should be continuous and relatively slow (I like to keep it to about 1 gun barrel volume inflow in 24 hours).
If you are trucking to a gun barrel then you hit it with 80 bbl of cold fluid in a 10-15 minute period and blast a mixture of oil and water out of both the oil side and the gas side. I never design truck-unloading capability directly into a gun barrel. If I'm trucking water I put a HEATED pre-treat tank that is about twice the size of the gun barrel in front of it. Incoming fluid is discharged into the bottom of the tank and warm fluid leaves out the top through a choke set to my desired gun barrel flow rate. The big trick is to design the pre-treat tank with enough room above the overflow to accommodate anticipated truck arrival rated (i.e., if you expect one 80 bbl truck per hour and you are doing 400 bbl/day then you need to use a 1000 bbl pre-treat tank with the overfow set with about 200 bbl above the outflow, more trucks/hour requires a bigger pre-treat tank or multiple pre-treat tanks).
It is very important to set the pre-treat tank on a pedestal that puts the outflow line above the top of the gun barrel so that you don't have to pump the fluid (pumping creates a lot of shear forces that make the separation significantly more difficult).
I've designed systems that were anticipated to be 50% trucked and 50% piped and ran the piped water into the pre-treat tank along with the trucked water. The result was outstanding as long as I kept heat on the pre-treat tank and the gun barrel.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Formation Water Processing
It's a continuous process... The main part of oil and gas are sepparated in a first step already. There are approx. 1000m³/h od produced water left for which I have to reduce the oil content from 1000ppm to below 200ppm. Regarding the separation behavior the oil seems to be not to bad. (Static) Experiments showed that phase separation takes around 3 hours to yield the necessary oil content in the water phase.
Since I'd like to use a continuous process the question for me now is how to correlate the separation time of the static experiments (3 hours) to the tank volume in continuous operation. I guess it's not going to be 1000m³/h, 3 hours --> resulting tank (or filling) volume 3000m³ in order to reach an effective residence time of 3 hours?!? Or is it possible... due to using a gun barrel or any other flow-optimizing installations?!?
Thanks again for any advices...
RE: Formation Water Processing
30 years ago you would have dumped all this water into a pond and skimmed the oil off periodically. In North America the Migratory Bird Act put an end to that [pretty sloppy] activity. Other parts of the world have similar restrictions to open bodies of water with oil slicks.
I don't think you are going to be successful with tanks with this volume so I'd be looking really hard at throwing energy at it.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Formation Water Processing
If oil content is less than 200 mg/L, gravity separator doesn't work. The available options, depends on the flowrate, are: IGF, Oil Removal filter, or adsorption by clay.
If you choose to use a non-baffled skim tank(conventional tank) the real oil separation residence time is less than one fifth of the tank residence time.
Regarding droplet size distribution, actually it is very rare that we can have access to droplet size distribution. So, you are not alone.
Hope this help
RE: Formation Water Processing
The emission requirements in the north sea is less than 40 ppm and lower values will soon be introduced. Hydro cyclones eg can lower the oil content to 40 ppm. But on the top of my head i cant remember what the expected inlet oil contamination is for a oily water hydro cyclone. a 1000 ppm dose not sound totally off.
Best regards
Morten
RE: Formation Water Processing
RE: Formation Water Processing
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Formation Water Processing
I know that tanks are - from the engineers point of view - not compulsory the method of choice in this case. Unforunately the operators insist on using just separation tanks, if it works somehow. Trying hard to bring them around...
I've one more question regarding the oil/water separation resp. produced water treatment... is there any literature on this topic - going beyond basic principles?!? (maybe going more into details regarding design and newest separation technologies)
RE: Formation Water Processing
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Formation Water Processing
If you have sufficient pressure drop available then a hydrocyclone vessel (or two) would be ideal for your flowrates; and would exceed your 200ppm target with ease (as long as there's no odd chemistry).
For example: We have a 30" vessel with 60 hydrocyclones fitted (rental equipment) which can treat up to 300m3/hr of water. Depending on oil & water chemistry, in an ideal case it could treat water with 3% oil down to sub-30ppm discharge.
We also have equipment suitable for sizing oil droplets; which is usually used alongside a test hydrocyclone to prove the technology with the installation's fluids.
If you're looking for some basics on current technology the search phrase "PWSM SLB" will help. You may also find contact details that way. If you've any specific questions I can do my best to answer here also.
The major installed base in the North Sea is hydrocyclones, CFU and IGFU. There are other technologies in development but I don't believe they are public as yet.