Production Improvement from Increased Permeability Using Engineered Biochemical Secondary Recovery Methodology in Marginal Wells of the East Texas Field

DE-FG26-03NT15440

Program
This project was selected in response to DOE's Oil Exploration and Production solicitation DE-PS26-02NT15377 (March 15, 2002). The objectives of this solicitation were to allow small, independent companies to test high-risk technologies that can lower operating costs and extend the life of aging and declining U.S. oilfields.

Project Goal
Project objectives include 1) the testing and evaluation of a method for increasing oil production by implementing innovative technology using a multidimensional biochemical secondary recovery treatment engineered to remove permeability impediments, e.g., paraffin, asphaltene, inorganic scale, and iron corrosion and to mobilize residual frac gels, etc., accumulated over the 70-year production history of East Texas field; and 2) devising a protocol that has the significant environmental advancement that no petroleum-based solvents or additives are required-consequently, permits, remediation, and spill clean-up are avoided.

Performers
TENECO Energy, LLC
Wheat Ridge, CO

MICRO-TES, Inc.
San Antonio, TX

Project Results
A combination of a regenerating biochemical mixture and an organic surfactant was applied to wells in East Texas field with the goal of restoring permeability, reversing formation damage, mobilizing hydrocarbons, and ultimately increasing production. Initial work was designed to open the perforations and remove blockages of scale, asphaltene, and other corrosion debris. This was accomplished on three wells that produce from the Woodbine formation and was necessary to prepare the wells for more-substantial future treatments.

Two wells were treated with much larger quantities-25 gallons-of the biochemical mixture with a 2% KCl carrier solution that carried the active biochemical solution into the near-wellbore area adjacent the producing reservoir. After a 7-10 day acclimation and reaction period, the wells were put back on production. The biochemical solution successfully broke down the scale, paraffin, and other binders blocking permeability and released significant debris, which was immediately produced into the flow lines and separators. Oil production was clearly improved, and the removed debris was a maintenance issue until the surface equipment could be modified.

The permeability restrictions in a cylindrical area of 10-20 feet from the wellbore within the reservoir were treated with the biochemical solution. Fluid was forced into the producing horizon using the hydraulic head of the well filled with 2% KCl solution, allowed to acclimate, and then withdrawn by pumping. The chloride content of the produced water was measured, and production of oil and water was monitored. The most significant effect in improving permeability and removing scale and high molecular weight hydrocarbons was accomplished in the wellbore perforations and near-wellbore treatments performed earlier in the project. Deeper insertion of the solution had a minimal impact on production. .

Benefits
The methods developed and used in this project can be used to:

• Increase oil production.
• Reduce operating expenses.
• Eliminate dangers associated with manufacture, transportation and handling of and worker exposure to hazardous chemicals.

Background
East Texas field is a "giant" oilfield discovered in the 1930s, with about 35,000 wells drilled to date. The field, comprising over 140,000 acres, is a classic stratigraphic trap with active water and solution gas drive. Production is primarily oil, with over 5 billion barrels produced to date. Overproduction and overdrilling (units of less than 4 acres) have plagued this field from its inception. Because of this overproduction and overdrilling, the reservoir pressure and temperature have dropped abnormally fast, resulting in precipitation of paraffin and asphaltene in the pore throats of the producing formation. This precipitation has resulted in reservoir plugging and greatly decreased total recovery for the reservoir. In addition, this overproduction caused water coning, resulting in emulsion blocks and inorganic solids being pulled into the oil leg of the formation. Frac gels and formation damage from numerous types of stimulation treatments also have damaged reservoir permeability. By using regenerating biochemicals and organic surfactants, it was deemed possible to restore permeability, resolubilize the paraffin and asphaltenes, break the emulsions, and dissolve the inorganic solids into the water phase. Additionally, the surface tension of the oil to the rock grain could be reduced, allowing more oil to be mobilized. Biochemical alteration of the oil lowers the cloud point of the oil and raises its gravity. This type of treatment should prove very cost-effective and environmentally friendly for the small, independent operators that dominate East Texas field. They can introduce the biochemical product into the reservoir through squeezes and soaks in the producing wells and by direct injection with saltwater as the carrier. The overall result of these processes and treatments should yield much greater recoverable reserves.

Project Summary

For Task 1, researchers:

• Added the engineered biochemical solution to the well by gravity feed down the annulus. For the initial well clean-up phase, the solution was mixed at the wellsite. The biochemical solution was allowed to acclimate and react for 24-72 hours, and then the well was placed on production.
• Treated three wells with known wellbore characteristics and perforation depths, and all three wells evidenced an improvement by either increased production volume or the pumping of sand, scale, and other debris with the produced water.
• Found that operations are affected at least two ways by the mobilized debris: 1) interference with pump action that requires pump removal and redressing, or 2) the removal of scale and paraffin exposes corrosion holes that were protected by the coatings of scale and paraffin.
• Learned that the use of cup-type tubing pumps significantly improves the capability of the pump to lift and discharge the mobilized debris with the produced fluid. The identification of weak or damaged tubing simply allows for proactive maintenance of tubing.

For Task 2, project performers:

• Selected two wells for the more-substantial biochemical treatment.. The treatment consists of at least 25 gallons of the biochemical solution, 25 gallons of nutrient solution, and about 140 barrels of carrier 2% KCl water.
• Transported the biochemical solution in drums and added it directly to the annulus of the well; and the 2% KCl solution was brought in by truck to the wellsite. Addition of the solution is rapid, and the only time constraint is the delivery time for trucking. Wells were left shut-in for 7-10 days for the microbes to acclimate and react. Wells were then placed back on production.
• Discovered that Well No. 9 was improved, with oil production increased from about 0.3 barrels of oil per day (BOPD) to 1.5-2.5 BOPD. Water production increased only slightly, indicating that the treatment could be improving the oil-wet permeability more than the water-wet permeability.
• Also successfully treated Well No. 8, as evidenced by the increase in gas pressure and the increase in oil percent. This well did not produce a total fluid volume that was sufficient to remove the mobilized material.
• Learned significant lessons that will benefit other operators in the future. The quantity of material that was mobilized is significant. Flow lines, separators, and valves all became clogged with debris, and pressure-actuated valves failed. A three-phase separator is not recommended; rather, a large gunbarrel works far more effectively in separation of oil and water in the presence of the mobilized sediment and debris. By using a cup-type tubing pump and gunbarrel, the movement of debris ceases to be a problem.

Researchers in Task 3:

• Selected the No. 1 well for the insertion of the biochemical treatment as much as 20 feet into the producing reservoir to treat the high molecular weight hydrocarbons. Fluids were not pressure-injected because of the age of these wells and uncertainty of well integrity when pressurized. The wellbore first was spotted with 25 gallons of the biochemical solution and 25 gallons of nutrient solution, and then the well was filled with a 2% KCl water carrier solution. The fluid level of this well was low, and thus the hydraulic head was able to force the reacting solution at least 20 feet into the selected portions of the reservoir.
• Shut in the well for 7 days, allowing the solution to react and acclimate. Production then was initiated at 150 barrels of fluids per day, and chloride, oil, and water were monitored for two weeks. The biochemical solution was withdrawn within 48 hours, and the production was restored to essentially the same pretreatment levels. It is concluded that the permeability-blocking material within the reservoir either is not easily accessed or not significantly affecting production.
• Observed that the most significant production improvements occurred when the immediate wellbore area is treated. The effects of deeper reservoir treatment are not significant, based on this limited testing.
• Reported that this procedure is now being used by other operators on nearby leases with notable success and with wells that are less deviated and have fewer mechanical complications. The long-term success should be significant.

Current Status (October 2005)
This research project has been completed. The procedures are currently being used successfully by other operators on nearby leases in cooperation with Micro-Tes, Inc.

Finney No. 9 location in East Texas Field, Rusk County, TX.

Publications
Semi-annual and final reports to DOE.

Project Start: June 1, 2002
Project End: September 30, 2006

DOE Contribution: $900,000
Performer Contribution: $1,011,710 (53% of total)

Contact Information
NETL - Dan Ferguson (daniel.ferguson@netl.doe.gov or 918-699-2047)
TENECO - R.L. Bassett (gtc@att.net or 303-423-8187)
MICRO-TES - William Botto (t5469@cs.com or 210-558-4757)