|Dick Ghiselin • Houston|
This month's column is all aboutproduction. While drilling is of critical importance, no operator makes any money until the well produces. As has been noted many times before, it is a shame that many producers are content to leave as much as 65% of crude oil in the ground. It is a shame because there is a proven solution.
About a year ago, I did research on enhanced oil recovery (EOR), the technique that purports to make a significant improvement in recovery factor—going after that 65% of residual oil. One question I asked the producers I interviewed had to do with the relative percentage of techniques employed to coax more crude out of the ground. The favored technique, by a long shot, was thermal, at almost 90%, followed by chemical at 9%. Lastly was biological, almost a nonentity.
It is a shame that my research was confined to North America. If I had looked overseas, I would have found a much more encouraging picture. The successful use of biological EOR has been experienced for the past 20 years by a leading national oil company, and several scientific institutes abroad. Spectacular results have been recorded by Statoil at itsNorne field in the Norwegian North Sea. Following 25 years of research and development (R&D) and deployment, the recovery factor at Norne is approaching 55%. More than 30 MMbbl of additional produced oil has been attributed to the applied microbial EOR (AMEOR) program there.
InRussia, the Winogradsky Institute of Biotechnology has done decades of work with the objective of harnessing the power of microbes to improve production. Biotopics in Argentina has had 20 years of experience in the area. And the Energy Resource Institute (TERI) in India is a derivative of the huge TATA Corp. All are energized by the aspect of recovering a significant fraction of crude oil left behind by initial production methods.
A North American company has benefited from all this R&D by mining the above sources for the most successful techniques and applying them to fields it has purchased. Glori Energy of Houston is a relative newcomer, but behaves like a seasoned veteran benefiting from 20 years of learning to avoid false starts.
The potential of AMEOR is huge, especially in this era of high crude oil prices. The good news is that offshore appears to be the biggest opportunity, because volumes are very high and initial recovery factors are low. In addition, many offshore fields are developed using a single centrally-located production facility to tap gathering lines. This layout typically favors EOR techniques, no matter which type is used. But the relatively small footprint of AMEOR production equipment poses an additional advantage for facilities where deck space is at a premium.
There is a major difference between AMEOR and thermal or chemical EOR—timing. The best time to deploy AMEOR is from the outset. Why wait until the field experiences problems such as loss of pressure, or severe water encroachment? The application of microbes can enhance production from the moment they are introduced. As a result, experience shows that the best time to deploy AMEOR is at the first detection of water in the flow stream. The treatment can slow the increase in water cut and ultimately enable more oil production. If an operator has produced 20% of the oil from the reservoir, 80% is still in place. If the producer can reduce the amount of water being produced, the fingering of water that is breaking through into production will stop and more oil will be produced. Glori Energy has experienced greatly-improved recovery factors on the fields it has treated.
In a water-wet reservoir, which most are, there is irreducible water that will never produce. It is held to the sand grains by surface tension. The greater the surface area of the sand grains, the more irreducible water will adhere. The trick is to shut off the mobile water by boosting the relative permeability to oil. You do not have to shut off all the water, just the mobile portion.
Timing is everything. Many operators wait too long to decide about using microbes. As a result, the challenges can be insurmountable. Many prefer to "trial" the technique on fields that are old and tired, justifying their decision under the philosophy of "do no harm," rather than investigating the real potential. Too little, too late, and the challenges of performing a well-configured and appropriate test can be significant. Results are sometimes difficult to quantify because there is limited or low quality non-granular baseline data.
Additionally, many engineers believe that bacteria are bad, that they contribute to corrosion or souring. Experience at Norne shows that souring is not an issue and the potential to corrode downhole tubulars can be eliminated by anti-corrosion coatings or the use of stainless metals. Actually the chemicals injected suppress souring. As far as corrosion is concerned, the only element involved is oxygen. In actual practice, only the injection zone is affected, the rest of the well tubulars are unaffected. None of the producing wells have been monitored producing any of the bacteria. It is consumed close to the injector. While inhibition steps cost money, the improvement in production completely justifies the techniques from a financial perspective. Glori Energy is a Clean-Tech 100 company, so there is no downside risk. The process does not increase souring potential.
Addressing the technique from the financial point of view, leads to another issue. Some operators who have trialed AMEOR have chosen very low quality project opportunities—those deemed of lowest risk. Even though experience shows that risks are insignificant, they are reluctant to commit a well making 1,000 b/d or more, even though a significant production uplift could be attained. If stripper wells are offered, even if production is doubled, they are still stripper wells.
How does it work?
There is no need to inject "cultured" bacteria into the wells. In fact, most bacteria that is grown under surface conditions cannot withstand bottomhole temperatures. Glori Energy takes advantage of bacteria that is already in the reservoir, so it fully acclimatized to the environment. The bacteria are activated by injection of nutrients and a few parts per million of oxygen. Within six months a change of productivity should be observed. Over longer periods production rate increases up to 30% have been experienced along with a decrease in decline rate.
The project is easily controlled. To stop it, stop feeding the bacteria called a "soft kill," or oxygenate the water by adding about 4 ppm O2. The idea that double-digit improvements in recovery factor are attainable from reservoirs that have already been discovered and developed should attract operators everywhere, but especially in North America offshore.