Applications will broaden if prices drop
Diversa Corporation gathers enzymes from thermal vents on the sea floor for use in well clean-up treatments.
Halliburton and Schlumberger are poised to enter the enzyme-based fluids market previously dominated by BJ Services. Halliburton is involved in a deal with Diversa Corporation to purchase enzymes designed to increase well productivity in high-pressure, high-temperature, high-alkalinity applications. Schlumberger has its own line of enzyme-based fluids, but these are limited by temperature and pH. If the Diversa deal actually opens up the market, it is possible the price of enzyme-based fluids for high pressure, high temperature (HPHT) wells will drop, broadening their application.
Earlier this year, Halliburton purchased a sample of a product called Pyrolase-160 from Diversa Corporation. Diversa took this enzyme from a thermal vent in a dormant volcano offshore Italy. This enzyme was collected from a submicroscopic organism that produces the enzyme from one of its genes. Diversa isolated the single gene that produces the enzyme, which performs a chemical reaction that is thought to be useful as the active ingredient in a fracture fluid.
Diversa representatives said the company plans to send Halliburton as much as a ton of this enzyme either as a liquid or as a capsulized solid. The capsulized product is designed in a time-release format so that it will not be released until it reaches the bottom of the well. The time-release capsule dissolves at the bottom of the well to break down the fracturing fluid so that it can be easily removed from the hole without affecting the propant.
Origin of enzymesThis is a unique enzyme because of its tolerance for high temperatures, pressures, and alkalinity. Diversa said the enzyme exists in very small quantities in nature. The enzyme is produced in only one gene of a submicroscopic organism found in small quantities in these unusual thermal vents. The protein produced by Diversa is inert. It cannot reproduce as it would in nature, and denatures once its down-hole task is performed (about 24 hours). At that point, it is completely biodegradable.
Diversa did not happen on this protein at random. The company approached Halliburton and other oilfield service companies seeking input into what enzymes the industry would find useful. Diversa then provided these companies with small samples of these enzymes. Testing and improvements allowed the company to develop an enzyme that had a long enough shelf life to be used offshore and withstand the great temperature and pressure fluctuations.
Diversa said it is in the enzyme business, but is looking to Halliburton for ideas on where the best application of these enzymes would be. The current generation of enzymes the company has developed can work at a range of temperatures from 28.4° to 235.4°, with pH ranges of 0 to 11, and with organic solvent concentrations up to 95%. This versatility lends itself to a number of offshore applications.
In addition to being tolerant to environmental extremes, these fluids are very efficient. They continue to break down the starch and calcium carbonate of the mud skin for up to 24 hours. A company could service a deepwater well with as little as 20 gallons of the enzyme.
Halliburton is not yet willing to discuss it arrangement with Diversa, but Diversa expects the product roll-out to be mid-year. Diversa is also shipping another compound product, to Halliburton for laboratory testing. This new product would tolerate up to 300 atmospheres of pressure.
Enzyme advantageBJ Services markets a clean-up product called Mudzymes that are polymer-specific enzymes matched with specific drill-in fluids. These Mudzymes degrade only the polymers in the drill-in fluids without damaging the formation. These linkage specific enzymes align with a cleavage site to totally degrade a polymer strand. The Mudzymes continue to break down the polymers as long as they are in contact with them.
Other clean up fluids, specifically oxidizers, such as bleach, and acid treatments are used to remove the polymer "skin" left by drill-in fluids, but have several drawbacks. Sodium hypo chlorite, lithium hypochlorite, persulfates, and acids are not designed to react with specific polymers and attack the polymer chain at any available site. Bleach is a free radical that attacks anything downhole. Acids and other agents are spent rapidly.
Once the oxidizing agents are spent, the remaining fragments of polymers clog pore throats and slotted liners. Bleach type agents can eat the wellbore, while acids cut "worm holes" into the formation.
Other enzyme fluidsSchlumberger has developed a hemicellulase enzyme in HEC and borate-crosslinked guar-based carrier fluids that can operate in temperatures below 200°. The fluid is used for cleaning during gravel packing or in an open hole completion as a soak treatment with or without screens. Schlumberger's latest development is a fluid system which contains a chelating agent solution and an alpha amylase enzyme.
According to Mahmet Parlar with Dowell, this fluid system attacks both the calcium carbonate and starch components of the mudcake. This was previously a two-stage process.
In the past, Schlumberger would use its enzyme-based system to treat the polymeric component of the cake followed by an acid treatment to remove the calcium carbonate. This combination solution is much less corrosive than an acid job, allowing it to be used as a soaking treatment without damaging sand screens downhole. The fluid can be viscosified or converted to a viscoelastic surfactant to be used as a simultaneous gravel packing and cake clean up fluid, in conjunction with shut screens. Schlumberger plans to present a paper on this new fluid at the Spring SPE conference.
With both Schlumberger and Halliburton are making progress in the area of enzyme-based fluids, making enhanced recovery and higher early production rates economically feasible for a wider range of wells. Only time will tell of this Halliburton deal is the first of several alliances between service companies and independent enzyme producers.
By out-sourcing this technology, service companies can focus on their core business while expanding the line of fluids they offer customers, and lower the price of these premium treatments.
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