Large potential reserves remain for secondary recovery in Ohio

Thomas E. Tomastik
Ohio Division of Oil and Gas
Columbus

As part of the U.S. Department of Energy's (DOE) Tertiary Oil Recovery Information System (TORIS) project, the Ohio Department of Natural Resources, Division of Geological Survey and the Division of Oil and Gas conducted an evaluation in 1995 of the oil remaining in about 80% of the reservoirs in the Appalachian basin portion of Ohio.

This study indicated that these reservoirs contained approximately 5.7 billion bbl of original oil in place (OOIP) and that only about 369 million bbl of oil or 6.5% had been recovered. This is a very low recovery and essentially only primary production.¹

Since 1903, when the first known attempt at increasing oil production by secondary recovery was initiated in Ohio, at least 340 secondary and enhanced oil recovery projects have been documented. All of the early projects involved either air injection or natural gas repressurization.

Ohio legalized waterflooding in 1939, and secondary recovery operations increased dramatically. By 1942, secondary recovery operations reached their peak and accounted for 15.9% of Ohio's daily oil production. However, since 1942, secondary recovery of oil in Ohio has continued to decline. By 1996, secondary recovery operations accounted for only 1.2% of Ohio's annual crude oil production. This is appalling when compared to the surrounding Appalachian states, where secondary recovery accounts for 25-50% of their oil production.

Problem and solutions

What seems to be the problem in Ohio?

First of all, many of the secondary recovery projects were poorly documented. Records were unavailable or just didn't exist. More importantly, however, was how many of these projects were constructed, completed, and operated.

Historically, most of Ohio's operators relied upon the secondary recovery technology developed in the early 1900s in the Bradford, Pa., oil fields. In fact, some of these same techniques are still being used in Ohio today.

What can be done to increase awareness of the potential for secondary recovery of oil in Ohio?

We must educate and demonstrate to operators that secondary recovery was and will continue to be a successful method of additional oil recovery in Ohio. This can be achieved by:

Evaluating successful projects and applying this information to other fields and reservoirs;
Conducting complete geologic, engineering, and reservoir characterization studies of various fields and reservoirs; and
Abandoning the old "Bradford" methods and start using modern secondary recovery techniques.

Case studies

In order to evaluate the potential for future secondary recovery projects in Ohio, the author selected several historical case studies to demonstrate the levels of success (Fig. 1 [115,425 bytes]).

Evaluating these studies will show how modern secondary recovery methods can be applied to Ohio's reservoirs to achieve greater success.

Chatham field, Medina County

The first case study involves one of the most successful waterflood projects in Chatham oil field. The Daniel S. Ross lease was situated in Tract 13, Lot 7 of Chatham Township, Medina County, and comprised 63 acres.

The reservoir is the Berea sandstone of Mississippian age. Depth to the Berea ranged from 242 to 494 ft. Pay thickness ranged from 2 to 182 ft and averaged 69 ft. Average core analysis indicated 40.1% oil saturation, 18.3% porosity, and 113.08 md permeability. Initial individual well production ranged from 25 to 275 b/d of oil.

The first wells on this lease were drilled in 1919. By 1940, 31 wells had been drilled and total primary production was 258,671 bbl.² In February 1940, the first injection wells were drilled and waterflooding was initiated using a five-spot pattern. A total of 125 wells were drilled on this lease by 1970. Cumulative secondary oil production from 1940 to August 1961 was 483,009 bbl. Waterflooding had a dramatic effect on this lease (Fig. 2 [69,394 bytes]).

Although this project was highly successful, it also demonstrates some of the problems associated with poorly completed and poorly operated secondary recovery projects in Ohio. Typical well completions on this lease, and in the field in general, are shown in Fig. 3 [44,823 bytes]. All wells were shot with nitroglycerin and commonly used 1 qt of nitroglycerin for every foot of sandstone. Little or no sealant was used behind the casing strings to isolate the aquifers or other formations. Additionally, many of the injection wells were operated at pressures that exceeded formation-parting pressure.

Gratiot-Newcastle field

The second case study is located in Sec. 16 of Perry Township, Coshocton County. The project involved 384 acres.

The reservoir was the Silurian "Clinton" sandstone, which was encountered at depths ranging from 2,998 to 3,250 ft. The first well was drilled in 1930, and by 1971 there were 14 producing wells, 10 injectors, and 2 water supply wells on the leases.

Reservoir thickness ranged from 20 to 61 ft. Initial oil production, after the wells were shot with nitroglycerin or hydraulically fractured, was 30 to 180 b/d/well. Primary production recovered 555,199 bbl.

Waterflood operations commenced in December 1965 using a five-spot pattern. Cumulative secondary recovery through 1971 was 106,161 bbl. Fig. 4 [64,631 bytes] shows the success of this project.

Union Furnace field

This project was located in Secs. 12 and 18 of Starr Township, Hocking County, and involved 667 acres.

The "Clinton" sandstone was the reservoir and occurred at depths ranging from 2,910 to 3,170 ft. A total of 28 producers, 5 injectors, and 1 dry hole were drilled on this project between 1915 and 1944. Sand thickness ranged from 22 to 32 ft. Initial well production ranged from 1 to 295 b/d after being shot with nitroglycerin.

Immediately prior to natural gas injection, this project had produced 659,540 bbl of oil. All wells were completed open hole, and the injection wells were completed without a packer.

Repressuring was initiated in October 1935 and used a random pattern. No cores were taken in this project. Maximum gas injection volumes reached 100 Mcfd, and it took approximately 2 years to attain peak production.³ Cumulative secondary recovery through 1966 was 95,132 bbl. Fig. 5 [60,718 bytes] demonstrates the effect of gas repressurization on this project.

Greasy Ridge field

Greasy Ridge oil field is located in Secs. 16, 17, and 20 of Mason Township, Lawrence County. The producing reservoir is probably a Pottsville Group sandstone of Pennsylvanian age.

This shallow oil field was discovered while drilling a deeper "Clinton" sandstone prospect in August 1985. The discovery well was completed at a depth of 570 ft. Initial production after hydraulic fracturing was 15 b/d. By 1989, 46 wells had been drilled, of which 42 were producers. Production peaked in the field at about 250 b/d by mid-1988.

Core analysis indicated an average of 37.4% water saturation, 16.2% porosity, and 50 md permeability. Depth to the reservoir ranged from 564 to 875 ft, and sand thickness averaged 16 ft. Initial well production was from 0.5 to 15 b/d after frac. The OOIP was calculated to be 3,040,000 stk-tk bbl of oil, and primary recovery was estimated to be 10% of OOIP, or about 300,000 bbl.⁴

A single five-spot pilot waterflood was initiated in early 1991 in which four wells were converted to injection. Within the first month, production began to stabilize, and injection rates were better than predicted.4 By late 1992, the entire field was under waterflood, and it now includes 30 producers, 22 injectors, and 1 water supply well. Production after all conversions were completed was about 40 b/d of oil, and by June 1993 the oil rate reached an average 170 b/d for the entire field.⁴

With injection rates running between 350 to 400 b/d of water, the ratio of oil production to water injected is about 0.5, which indicates this is a very efficient waterflood.4 Water-to-oil ratio is around 0.3, which is very low and shows that there have not been any water breakthrough problems. Fig. 6 [66,960 bytes] illustrates the success of this waterflood project.

Successful waterfloods typically have a secondary to primary production ratio of 1.0. Greasy Ridge field, with its low volume of gas dissolved in solution, can easily surpass this ratio. Estimates of the ultimate secondary to primary ratio could reach 2.0 or better. Cumulative production as of May 1998 was 544,056 bbl.

Conclusions

The TORIS study showed that a large volume of unrecovered oil remains in many of Ohio's reservoirs. Some of this oil should be recoverable through modern secondary or enhanced recovery techniques.

A preliminary evaluation of the potential reservoirs suitable for secondary recovery in Ohio indicates that the Berea sandstone, the "Clinton" sandstone, and the Rose Run sandstone are the most likely candidates. Areas of the state where these reservoirs have relatively low gas-oil ratios would be the sites of interest.

The Greasy Ridge waterflood project in Lawrence County is an example of how a modern, properly designed, secondary recovery operation can be highly successful in Ohio. By using this project and the other successful case studies, it should be possible to develop other successful secondary recovery operations in Ohio.

Acknowledgments

Thanks to Mark Fraser, senior engineering technician, Mitchell Energy Corp., and Paul Hyde, director of reservoir engineering, Columbia Natural Resources, for their contribution of data for this study. Thanks to Lisa Van Doren and Merrianne Hackathorn for drafting figures and editing.

References

Blomberg, J., Where might enhanced oil recovery (EOR) methods be successful in Ohio in the future?, in Riley, R., and others, eds., Ohio Geological Society 4th Annual Technical Symposium, 1996, pp. 10-24.
Tomastik, T.E., History and reservoir analysis of the Berea sandstone in the Chatham oil field, Medina County, Ohio, in Wickstrom, L., and Berg, T.M., eds., Ohio Geological Society 3rd Annual Technical Symposium, 1995, pp. 62-86.
Cashell, J., Reactions of Clinton sand to gas repressuring, The Oil Weekly, Sept. 13, 1943, pp. 34-36.
Fraser, M., written communication, 1998.

The Author

Tom Tomastik has been involved with the Ohio oil and gas industry for 16 years. Since 1988, he has been a geologist with the Ohio Division of Oil and Gas, Underground Injection Control Section. He is responsible for performing independent reviews of applications for Class II saltwater injection wells, secondary and enhanced recovery projects, and Class III salt-solution mining wells. He was involved in completion of the U.S. DOE-funded Atlas of Major Appalachian Gas Plays and the Ohio portion of the TORIS project. E-mail: [email protected]