Chasing the Rose Run play with 3D seismic in New York

Bruce Hart
New Mexico Bureau of Mines and Mineral Resources
Socorro

David Copley Stuart Loewenstein
Ardent Resources Inc.
Buffalo

The Rose Run play is fraught with the types of challenges that increasingly typify U.S. domestic production. Comprised of heterolithic dolostones and sandstones in a subcrop belt beneath a regional unconformity (Knox unconformity; Fig. 1a [24578 bytes]), reservoir heterogeneity is associated with truncation and topography beneath the unconformity, faults, fractures, and depositional features.

These complexities challenge the exploration and production capabilities of the independents who are the main players but who typically lack the resources needed to exploit new technologies such as 3D seismic.

Several technology transfer programs, including one based in New York and two based in New Mexico, target these problems. The New York State Energy Research and Development Authority (NYSERDA) funds projects that have the potential to help industry measurably increase New York state production by demonstrating or developing innovative exploration and production technology. In New Mexico, the Advanced Reservoir Management (ARM) Program of Los Alamos National Laboratory has joined with independent and major oil companies on a national level to promote the use of advanced reservoir management tools.

The New Mexico Bureau of Mines and Mineral Resources (NMBMMR) has a mandate to assist petroleum producers and, with the SeisX interpretation package operating on a workstation, has recently acquired capabilities in the field of 3D seismic interpretation.

Rose Run extension

Significant interest in the Rose Run play began in Ohio over 30 years ago, then spread to Pennsylvania. In recent years, the play has been one of the most active in the Appalachian basin. In Ohio, the Rose Run accounted for nearly 70% of the exploratory wells drilled in 1995 (OGJ, Apr. 15, 1996, p. 80). Although some wells drilled in the 1960s in New York penetrated to the Cambrian, no economic production was ever established (OGJ, Apr. 1, 1991, p. 74), and the subsurface geology remained unclear.

If the play were to be extended into New York, Ardent recognized the need to develop a better understanding of the geology of the Cambro-Ordovician. Furthermore, it needed to prove that suitable reservoirs existed, and that commercial hydrocarbons were present in the reservoirs.

Ardent's Northwoods Project seeks to bring the Rose Run play into New York (OGJ, Mar. 11, 1996, p. 43). The principal target is the Upper Cambrian Theresa formation (Fig. 1b [24796 bytes]), consisting of sandstones and dolostones, in the south-central part of the state. This area was believed to be an eastern extension of the Rose Run subcrop belt as mapped in Ohio and Pennsylvania (Fig. 1a). The Theresa is equivalent to part of the Knox Group (that includes the Rose Run sandstone) of Ohio and Gatesburg formation of western Pennsylvania.

Partnerships formed

Although 2D seismic profiles had been acquired in this area, the traditional "patchwork" method of acquiring and interpreting the data was not converging toward a final solution. The structural complexity and reservoir heterogeneity that typify the Rose Run in Ohio led Ardent to believe that 3D seismic would be needed to derive an accurate subsurface image.

Lacking the in-house resources to test the technology alone, Ardent forged partnerships with NYSERDA and the ARM Project, and in 1995 collected a 2.7 sq mile 3D seismic survey from Wyom- ing County, N.Y. (Fig. 2a [19960 bytes]). Data collection and processing were by Duncan Geophysical, Newark, Ohio, and Lauren Geophysical, Denver, Colo., respectively. Technical support for the seismic interpretation came from the NMBMMR, working under the auspices of the ARM Project.

Buried structure

As hoped, 3D seismic demonstrated its strength in removing ambiguity in zones of complex structure. Previous structure maps, based on well control and some 2D seismic lines, from Upper Ordovician to Devonian horizons present a northeast-southwest trend within and adjacent to the study area (Fig. 2a). Prior to the collection of the 3D data, and in the absence of much well control, the 2D seismic data were contoured to extend this structural fabric to the Cambrian (Fig. 2b [21614 bytes]). Although some nosing was noted in structure and isopach maps from shallow horizons, the origin of these features remained problematic.

The new 3D data quickly provided a major surprise: a hitherto unsuspected northwest-southeast structural grain, running at a high angle to the northeast-southwest trend, dominates at the level of the Knox (Fig. 2c [29480 bytes]). Although Middle and Upper Ordovician rocks tend to drape the unconformity and preserve the northwest-southeast structure, thick shales of the latest Ordovician Queenston formation all but buried the underlying structure, so that it is not readily apparent at the top of the Queenston or above. Trend surface analyses of strata above the Queenston are needed to detect the structural fabric that dominates at the level of the Knox.

The structural trend at the Knox level is locally associated with faults that affect the section below the unconformity (Fig. 3 [131437 bytes]). These faults are believed to be associated with northwest-southeast trending Proterozoic wrench faults that were reactivated during the Middle Ordovician tectonic activity that generated the Knox unconformity.

Only one well, the 1 Matusik, penetrates below the Knox unconformity within the limits of the 3D seismic data. This well, drilled in 1994, targeted the sub-Knox Theresa formation high on a structure identified from 2D seismic mapping (Fig. 2c). The 3D data show that, in fact, the well narrowly missed penetrating a small graben (Fig. 3). The 1 Matusik (Fig. 4 [23029 bytes]) penetrated a thick (over 50 ft) Theresa section with porosity of 10-12% with gas shows. Original production (gas) from the Theresa was near 1 MMcfd, but water production became too high and the interval was plugged off. The well was recompleted in a naturally fractured Middle or Upper Ordovician interval about 100 ft above the unconformity, and production (gas) is currently 75-95 Mcfd.

A location for a new well, the 1 Stahl, high on the ridge in the northwest corner of the 3D survey (Fig. 2c), has been chosen based on the structure mapping. The Theresa is approximately 240 ft higher here than at the 1 Matusik well, and it is thought that the formation will be well above the gas/water contact at this site. Although there is no closure on this structure within the 3D survey area, existing 2D seismic data can be used to infer closure to the north.

With only one well, and given the complex lithologic nature of the sub-Knox interval, it was not possible to establish correlations between seismic attributes and reservoir physical properties. We note however that two factors, tuning effects and fractures, seem to be affecting seismic amplitudes in addition to porosity. Tuning effects on amplitudes are sometimes used in Rose Run studies in Ohio to determine the presence or absence of reservoirs. As additional data are acquired through drilling, it should be possible to help resolve the relative contribution of the factors that affect seismic amplitudes and other attributes.

Project success

Although production has not yet been established from the Theresa, the Northwoods Project can already be deemed a success. Together, the seismic and well data have demonstrated that the structural and stratigraphic complexity that characterizes the Rose Run play in Ohio are present in New York. Furthermore, the 1 Matusik well demonstrated that significant porosity is present below the Knox unconformity. Some wells that tested gas, but were not completed, in the Cambrian are potential recompletion targets.

Given the structural complexity associated with the Rose Run play, strategically chosen 3D seismic surveys can be a cost-effective technology for confidently identifying drilling targets. Acquisition and processing for the small survey used in this study cost less than $80,000. This price compares quite favorably with the approximately $150,000 cost of a dry hole that might be drilled based on incorrect structure maps derived from 2D seismic lines. Furthermore, as new well and seismic data are acquired, links between seismic attributes and reservoir properties will be recognized, allowing accurate prediction of reservoir properties in inter-well areas. Aeromagnetic surveys (e.g., OGJ, Mar. 11, 1996, p. 43) and trend surface analyses of structure maps of shallow horizons both can be used to help "high-grade" the search for buried Cambrian structures, thus increasing the success potential of a 3D survey.

In line with the NYSERDA, ARM, and NMBMMR objectives of technology transfer, the results of this study are being presented to independent petroleum producers across the country. A meeting in western New York in June drew over 100 attendees, from Appalachian and Midcontinent regions, to listen to the results of the Northwoods Project study. Some of those attendees participated in a short course on 3D seismic interpretation for independents that was held following the meeting. Information on the ARM Project can be obtained through:

http://ees-www.lanl.gov/EES5/arm/ index.html

Information about the New Mexico Bureau of Mines can be reached at:

http://geoinfo.nmt.edu/

A full report on the 3D seismic interpretation will soon be available on-line through those sources.

The Authors

Bruce S. Hart has been a petroleum geologist with the New Mexico Bureau of Mines since 1995. He previously held research positions with Geological Survey of Canada and the Penn State Department of Geosciences. His principal research interests lie in understanding how sedimentary strata are deposited and how seismic can be used to study those rocks. Current responsibilities include technology transfer, and he has given talks and short courses on 3D seismic interpretation. He has an Honours BA from McMaster University, an MSc from the Université du Québec ô Rimouski, and a PhD from the University of Western Ontario.

David L. Copley is a petroleum geologist and president of Ardent Resources Inc., Buffalo, N.Y. He has been a practicing petroleum geologist in the Appalachian basin for over 25 years. He holds a BA in geology from Alfred University and an MS in geology from the University of Toledo. Ardent Resources drills and operates in the northeastern U.S. and Canada.

Stuart Loewenstein is a geophysicist and exploration manager for Ardent Resources. Previously he held geological and geophysical positions at Copley Exploration Group, Inc., and Berea Oil and Gas Corp. He holds a BA in geology from SUNY at Buffalo, where he has also completed the course work for an MA in geology with a concentration in geophysics.

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