EXPLORATION Ohio 1995 oil and gas activity and exploration highlights

April 15, 1996
Michael P. McCormac Mark E. Wolfe Ohio Division of Oil & Gas Columbus The Ohio oil and gas industry continued its progression from a low-risk, mature play (Silurian Clinton sandstone) to a higher risk, high reward immature play (Cambrian Rose Run sandstone).
Michael P. McCormac
Mark E. Wolfe

Ohio Division of Oil & Gas
Columbus

The Ohio oil and gas industry continued its progression from a low-risk, mature play (Silurian Clinton sandstone) to a higher risk, high reward immature play (Cambrian Rose Run sandstone).

The number of exploratory discoveries since 1990 has helped energize operators and change their drilling focus. The use of seismic-including three dimensional techniques-directional drilling, and advanced down-hole logging has become much more common. The recent deeper formation reserve additions have helped stabilize production declines associated with the more mature plays.

Permitting and drilling

The Division of Oil & Gas issued 855 permits to drill for oil and gas in 1995, a 14.2% decrease from the 1994 level. Deep well permits decreased 10.9% (48 permits) but accounted for 51% of all drilling permits. The division considers deep well permits as those issued to drill formations below the Cambro-Ordovician Knox unconformity such as the Beekmantown dolomite, Rose Run sandstone, Trempealeau dolo- mite, and Mt. Simon sandstone.

About 659 oil and gas wells were drilled, a decrease of 115 wells (14.9%) from 1994. Wells were drilled in 48 of Ohio's 88 counties, an increase of four counties from 1994.

Ohio oil and gas owners/operators submitted 561 well completion reports, representing 85.1% of the wells drilled in 1995. These reports showed that 421 wells were productive and 140 were dry holes, for a 75% completion rate. Average well depth was 4,653 ft, a decrease of 22 ft/well from 1994 (Table 1 [9304 bytes]). Total depths ranged from 360 ft in the Berea sandstone (Medina County) to 9,002 ft in the Rose Run sandstone (Washington County).

Completion zones ranged from several shallow Pennsylvanian sandstones to the Precambrian basement rock.

Completions

Despite a decline of 43 wells, the Silurian Clinton sandstone remained the most actively drilled zone since 1965. Forty one percent of the total wells were completed in this zone, with a 97.4% completion rate, and averaged 4,809 ft in depth, an increase of 77 ft/well from 1994. Clinton sandstone wells were drilled in 23 counties. The most actively drilled Clinton sandstone counties were Washington (40) and Mahoning (37).

Drilling to the Cambrian Rose Run sandstone broke the 200 well mark for the third consecutive year with 207 wells drilled. The productive rate was 57%, the same as in 1994. Fifty operators drilled Rose Run sandstone wells in 18 counties. Overall, 12 townships had first-time producing Rose Run sandstone wells. The average depth per well was 5,240 ft, a decline of 135 ft/well. This decline resulted from a shift in drilling from the northern to central and southern Ohio counties where the Rose Run sandstone is not as deep.

Although 84% of Ohio's estimated 1,668 Rose Run sandstone wells have been drilled since 1985, the significant upturn in activity began nine years ago. Since 1987, 1,351 Rose Run sandstone wells have been drilled (Fig. 1 [46027 bytes]) in 28 counties. In 1995, only 6% of Rose Run sandstone dry holes were plugged back to the Clinton sandstone, indicating that most Rose Run prospects are being drilled without the Clinton sandstone as a backup.

Wells completed to the Cambrian Trempealeau dolo- mite increased by four to 75 in 1995. Wayne County (36 wells) remained the most active county followed by Wyandot County (10 wells). Trempealeau dolomite drill- ing occurred in 11 counties, a decrease of four from 1994. Fifty five percent of all Trempealeau dolomite wells were completed as productive. The average depth per well was 4,699 ft, a decrease of 22 ft/well from 1994.

An estimated 23 wells were drilled to the Ordovician Beekmantown dolomite, the same as in 1994. Tuscarawas County led with seven wells, followed by Muskingum (five). The productive rate was 83%. The average depth per well was 6,492 ft, an increase of 155 ft/well. It is expected the number of wells drilled to this zone will increase in 1996 as the seismic interpretation of the Beekmantown subcrop becomes more advanced.

Directional drilling

Directional drilling technology is allowing operators to drill wells in previously inaccessible areas such as acreage covered by water, densely populated urban areas, and wetlands. Typically a directional well is drilled vertically to a predesignated depth, then deviated at an angle designed to encounter the producing formation. Use of this technology has opened additional areas for exploration and development in the more mature reservoirs typical of Ohio.

Before 1989, the division issued fewer than three directional drilling permits per year. Issuance increased to seven in 1989, 14 in 1990, and 41 in 1991. In 1995, a record 46 directional drilling permits were issued to drill wells in 11 counties. The most active counties were Summit (14), Stark (eight), Trumbull (eight), and Mahoning (six). Directional drilling permits issued in these heavily populated northeastern Ohio counties targeted the Clinton sandstone (37), while directional drilling permits issued in central Ohio targeted the Rose Run sandstone (nine). Four of these permits were issued to plug back to directionally drill after the intended vertical target was dry and seismic reevaluation suggested a revised target.

Drilling of the first horizontal well in the Rose Run sandstone of Ohio was completed last month. Ohio Energy Assets is evaluating the Stevenson No. 3 (Permit No. 58) in Wayne Township, Pickaway County, after drilling about 200 ft horizontally. The well was originally completed in 1994 at a depth of 2,490 ft and had an initial potential of 85 b/d of oil. A second horizontal test has been permitted.

Exploration results

Wells are classified as "development wells" or "exploratory wells" based on American Association of Petroleum Geologists guidelines. A well completed in a known oil and gas bearing formation within one mile of any well completed in the same formation is classified as a "development well." A well is classified as an "exploratory well" if completed in a formation not usually known to be oil and gas bearing or located more than one mile from the nearest well completed in the same oil and gas bearing formation.

Approximately 22% (122) of all wells completed were classified as exploratory wells. Forty nine exploratory wells were completed and 73 were dry holes, representing a 40.2% success rate, a 2% decrease from 1994. Wells classified as wildcats have the highest associated risk factor and had the lowest productive rate (23%). Wells classified as "deeper pool wildcats" did not fare much better, with a productive rate of 31%. Exploratory drilling remained steady in every classification. Some of the more significant exploratory wells drilled are highlighted in Fig. 2 [90432 bytes] and Table 2 [103708 bytes].

Wells drilled below the Knox unconformity accounted for 95% (116) of all exploratory drilling; 45 of these wells (39%) were productive. The Cambro-Ordovician Rose Run sandstone accounted for 80 of these wells; 30 were productive. The Cambrian Trempealeau dolomite had 21 exploratory tests, of which nine were productive. Six of the nine exploratory wells drilled to the Ordovician Beekmantown dolomite were productive.

Since 1990, 87 townships representing an estimated 2 million acres have had new Knox discoveries. Seven new townships were added in 1990, increasing to a high of 27 in 1993. The Rose Run sandstone accounted for new production in 70 townships, followed by the Trempealeau (11) and the Beekmantown (six). Muskingum County was the most active (12) followed by Fairfield (10). These recent discoveries indicate many opportunities still exist for exploration in the Knox play.

Production overview

Ohio's total reported crude oil production was 8,257,621 bbl (Fig. 3 [24018 bytes]), a decrease of 500,251 bbl (5.7%) from 1994. In 1995, production averaged 22,624 b/d compared with 23,994 b/d in 1994.

Ohio wells produced 126,335,936 Mcf of natural gas, a decrease of 4,519,312 Mcf (3.4%) from 1994 (Fig. 3 [24018 bytes]). In 1995, daily production averaged 346,126 Mcf, compared with 358,508 Mcf in 1994.

Computerizing well data

During 1995, the division began converting oil and gas well permitting, completion, and production data from an antiquated VAX system to a modern, user-friendly, fully relational data base.

Partial records for over 99,000 wells permitted since 1980, and all wells with reported production data since 1984 are now available for the oil and gas industry in a Microsoft Access data base. In addition, since January 1996, the public has been able to access the division's weekly permit and plug list in an ASCII tab-delimited format on our FTP site (DNR.OHIO.GOV. in the directory pub oil_gas).

By July 1997, the division will convert to an NT Server. Subsequently, the public will be able to download weekly permitting and plug lists via e-mail. Additionally, all production records for 1984 through 1994 are available on diskette in an ASCII fixed-length field format.

Toris, gas atlas projects

In 1995, the Divisions of Oil & Gas and Geological Survey completed research for the Tertiary Oil Recovery Information System (Toris) and Gas Atlas projects. These projects, primarily funded by the U.S. Department of Energy, were done in conjunction with other oil and gas producing states in the Appalachian basin (Kentucky, New York, Pennsylvania, and West Virginia).

The purpose of the Ohio portion of the Toris project was to create an electronic data base of compiled information pertaining to 30 oil fields that account for approximately 80% of the original oil in place in the Appalachian basin area of Ohio. The data base is expected to be released by U.S. DOE in 1996. It will include determination and estimates of average field parameters such as original reservoir conditions (OOIP, area, thickness, porosity, permeability, initial saturations, pressures, and temperatures); fluid data (oil gravity and viscosity, water salinity); geologic information (lithology, depth, depositional environment); and production data (cumulative production, well spacing, number of producing and injection wells).

The purpose of the gas atlas project was to collect and transfer geologic, reservoir, and production data for major gas plays to assist independent producers in developing exploration and production strategies within each play. The completed atlas will contain geologic play descriptions, in-depth discussions of key fields, tables containing reservoir characteristics of major fields, and an extensive bibliography. As a result of this three year effort, data have been compiled for 57,246 wells representing 537 Ohio gas fields. Total original gas reserves for all plays is estimated at 7.5 tcf. Total cumulative production for all plays is estimated at 6.2 tcf.

The U.S. DOE will release a data base and gas atlas manuscript this year. The Divisions of Oil & Gas and Geological Survey expect that the findings of the Toris and Gas Atlas projects will be a valuable resource for explorationists to advance the discovery and development of Ohio's remaining reserves.

Acknowledgment

The full, 56-page 1995 Ohio annual oil and gas report is available for $3 from: ODNR, Division of Oil & Gas, 4383 Fountain Square Dr., Columbus, Ohio 43224.

Copyright 1996 Oil & Gas Journal. All Rights Reserved.