Background Paraffinic Oil is a mixture of hydrocarbon that has dominant fraction of paraffinic isomers of hydrocarbon. These isomers have high viscosity, and tend to form solidified deposits if left unchecked. This make parraffinic oil tend to clog oil oil production lines and even make a oil-bearing underground earth layers lose their productivities.
Paraffinic oil in shallow oil wells (more or less 1000 ft deep) also tends to make emulsions of water and oil. These emulsions cannot be classified as either water or oil. If straightly produced and stored inside oil storage tank, the will make its own phase layers apart from oil. They are also considered worthless production. Throwing them straight into open water system (rivers, seas) also considered as polluting. Emulsions also contributing to sedimentations inside oil-bearing earth layers because of their interactions with both water and oil phases.
This guide will give an experience-based guide on how to increase oil well productivity using emulsion breaker solution. The usage of emulsion breaker solutions will break off the paraffinic deposits in well bore and in pores of oil bearing layers thus increasing productivity index of the well. Emulsion breaker also reduced the production of emulsions, thus increasing the production of oil and make produced water able to be dumped to seas safely.
This guide uses an actual well that was stimulated using the techniques mentioned below. The well is a single production layer oil well with high watercut (50%) and with paraffinic oil that must be separated from water-oil emulsions. The layer is perforated with 5 feet perforation intervals. The formation pressure is below 400 psig and the temperature is below 180oF
Data Collecting
The first step is to identify the characteristic of the wells. We must collect data that consist of:
1. The viscosities of produced oils
2. The watercut of produced liquids
3. The depths of oil-producing layers
4. The perforation intervals of the layers
5. The porosity of the layers.
6. The water saturation and oil saturation index of the layers (or can also be called formations)
7. The type of emulsion breaker that can turn emulsions into separate phases of water (polar) and oil (nonpolar)
8. The temperatures of formation layers.
9. The pressure gradient of produced oil.
10. The pressure gradient of produced water.
Laboratory Experiments
Next step is to perform small scale laboratory experiments by mixing emulsion breaker with diesel and oil samples from target oil wells.
Mix emulsion breaker with diesel fuel to produce 2%, 5%, and 10% emulsion breaker in diesel solutions. Call them A-n solutions, in which n is the code number of the concentrations. Make 200 mililiter each.
Mix the A-n solutions and sample oils with different ratios of mixture, i.e you can have 1 part 2% EB solution mixed with 2 parts sample oils. In the end you will have several mixtures, like these:
2% EB :
1:1 EB - oil
1:2 EB - oil
1:5 EB -oil
1:10 EB - oil
3 % EB:
1:1 EB - oil
1:2 EB - oil
1:5 EB -oil
1:10 EB - oil
and so on with 5% and 10% solutions.
After mixing them thoroughly, you need to heat them up to formation temperatures inside waterbath or oven.
When sufficiently heated, separate the polar and non polar phases of each Solution A-n + oil mixture with separating flask.
Measure the oil in water content of the polar phases of solution A-n + oil mixture.
Measure the pour points and water-in-oil contents of the non-polar phases solution A-n + oil mixture.
After u have series of data of oil-in-water contents and water-in-oil contents of each respected phases.
Find the suitably best combinations of emulsion breaker concentration and solution A-n + oil mixture. This combination will be used as guidance to calculate the amount of diesel fuel and emulsion breaker needed to perform the stimulations.
Calculating the Stimulation Requirements
When calculating liquid volumes for the well, remember that we are dealing with these conduits:
1. Wellbore
2. Stimulation strings: tubings and packers connected together to form conduit for the stimulation liquids to flow into the targeted formations
3. The targeted oil bearing layers
The wellbore is a cylindric form, the tubing needed for the stimulation string is a cylinder, and the reservoir targeted will be considered as solid cylinder with pores connected to each others.
This is where the data of the wellbore and the formation layers come in handy.
Target stimulation penetration depth must be decided: 5 feet, 7 feet, 10 feet or more. The well sampled for this guide had its producing formation penetrated with stimulation solution 10 feet deep.
There are at least three stages of stimulation injections:
1. Pre-flush liquid: to push the liquid contained in the string so that the main stimulation solutions will not be contaminated or contaminated minimally. Usually the liquid that is used as solvent in the main solutions
2. The main stimulation solutions
3. Post-flush liquid: to push the entire volume of the main stimulation solutions into the targeted formations and to prevent blowout.
The calculations are as the following:
1. Convert the formation pressure into wellbore liquid height by dividing pressure of formation with (X x water gradient + (1-X oil gradient) or you can divide pressure of formation with water pressure-gradient to give highest height.
2. Calculate cylindric volume using stimulation string inside diameter and the wellbore liquid height. This will be used as Pre-flush and Post-Flush volume.
3. Calculate the stimulation solution volume using target penetrated depth as its diameter and perforation interval as its height. Reduce the volume by multiplying it by the pore volume percentage (Porosity) gathered from the data. This will yield the required stimulation volume.
4. Calculate the diesel fuel (as solvent) and emulsion breaker volume needed as guided by the laboratory experiments results. Round up the emulsion breaker volume to the next higher number of drum unit (i.e 55 gallon per drum).
Job Executions
After all calculations are done, it is time for the stimulation job itself. This needs a workover rig pull out the well completion and install the stimulation string. Triplex-positive-displacement pump is also needed, preferrable two on each job site. The job steps are as the following:
1. Shut down the well if it is still producing
2. POOH any plugs installed using slickline unit.
3. Uninstall its well head (X-mas tree, PCP head, or HPU head)
4. Rig Up the workover rig
5. Pull out of hole (POOH) the installed production string.
6. Run In Hole (RIH) and install the designated stimulation string
7. Set isolating packer in desired depth (preferrable 5-10 feet above the perforation interval)
8. Connect the pumping equipment with the stimulation string and annulus valve.
9. Prepare the required solutions: Separate the Pre-flush volume and Post-flush volume into one container. Mix required diesel flush with the required number emulsion breaker drums. Put in a different container with Pre-and Post
10. Pump the Pre-flush diesel volume.
11. Pump main stimulation volume
12. Pump the Post-flush diesel volume.
13. Soak the well for 24 hours
14. Uninstall stimulation string.
15. Install the production string.
16. Rig down the workover rig.
17. Start up the well.
18. Monitor post-stimulation production.
Results
The well used as reference for this guide has its watercut level reduced from 50% to 10-30%. This result shows the success of breaking out paraffinic crystals clogging oil production of the well thus liberating the mobility of oil phase.
