Horizontal well success spurs more Devonian work in Michigan

Oct. 28, 1996
James R. Wood, J. R. Allan, Jacqueline E. Huntoon, Wayne D. Pennington Michigan Technological University Houghton, Mich. William B. Harrison III Western Michigan University Kalamazoo, Mich. Eric Taylor, Craig J. Tester Cronus Development Corp. Traverse City, Mich. The principal objective of this DOE-sponsored project was to drill a horizontal demonstration well in order to test the viability of using horizontal wells to recover bypassed oil from the Dundee reservoir in Crystal field.
James R. Wood, J. R. Allan, Jacqueline E. Huntoon, Wayne D. Pennington
Michigan Technological University
Houghton, Mich.

William B. Harrison III
Western Michigan University
Kalamazoo, Mich.

Eric Taylor, Craig J. Tester
Cronus Development Corp.
Traverse City, Mich.

The principal objective of this DOE-sponsored project was to drill a horizontal demonstration well in order to test the viability of using horizontal wells to recover bypassed oil from the Dundee reservoir in Crystal field.

In addition, a modern log suite through the entire Dundee formation and a conventional core through the productive interval, the oil/water contact, and the upper part of the water leg were to be obtained.

During the early years of Dundee development in central Michigan, it was common practice to drill only a short distance below the cap limestone into the top of the Dundee porosity zone before completing a well in order to prevent lost circulation and blowouts in vuggy and fractured dolomites and to avoid penetration of the oil/water contact and minimize water coning.

As a result, the characteristics of the Dundee reservoir in central Michigan are poorly known and the decision to attempt an improved recovery program in Crystal field had to be based on field volumetrics, individual well productivities, and well development/abandonment histories. The new core and log data from the demonstration well will provide an important anchor point for regional Dundee reservoir characterization studies.

The TOW No. 1-3 HD-1 demonstration well was spudded on Sept. 20, 1995. It was sited near the crest of the structure (Fig. 4) in an area where most wells had high IPs (Fig. 6). The well was located near the eastern edge of an 80 acre drilling unit containing eight original wells that had been plugged and abandoned for 20 years or longer. As originally planned, the horizontal leg was to follow a trajectory between four well pairs (Fig. 4).

Because the field has a strong water drive and flow rates for these eight wells were so high (average IP 2,000 b/d of oil), it was theorized that the wells had coned water, leaving a large volume of bypassed oil between wells (Fig. 7 [14650 bytes]). Our plan was to drill a horizontal well along the top of the Dundee porosity zone between these abandoned wells to recover this bypassed reserve. Because existing wells are less than 400 ft away from the trajectory of the horizontal well, geologic control was excellent.

The drilling program was as follows. A vertical well was drilled to the base of the Bell shale (Fig. 2). A conventional core was taken through the cap limestone, the oil leg, and upper part of the water leg in the Dundee reservoir; 59.3 ft of core were recovered from the top of the Dundee, and the well was then drilled 150 ft below the base of the core to TD at the base of the Dundee formation (top of the uppermost Lucas formation anhydrite). The vertical well was then logged from TD (3,334 ft) to the base of casing (683 ft).

The following logs were obtained: a gamma ray, dual laterolog with microresistivity, a lithodensity log (compensated formation density plus photoelectric factor), and a compensated neutron-porosity log (Fig. 8 [49416 bytes]).

The top portion of the Dundee displayed good oil staining in the core, confirming that the log suite has good coverage of both the oil leg and the water leg in the reservoir. Later fluid saturation analyses of core samples showed 29 ft of higher residual oil saturations at the top of the Dundee (3,190-3,219 ft), indicating significant unrecovered oil, 7 ft of lower residual oil saturations beneath the oil leg (3,219-26 ft), indicating either a transition zone or a swept zone where the oil-water contact moved up as a result of primary oil production, and a water leg (below 3,226 ft) where residual oil saturations are 0% (Fig. 8).

After the vertical well was cored and logged, the borehole was plugged back above the Dundee and a medium-radius lateral was drilled. The lateral leg approached 90o at about 450 ft west of the vertical well, at which point the well was cased.

An 1,800 ft horizontal leg was planned (Fig. 9 [26729 bytes]), but when drilling reached 95 ft beyond casing, the well lost circulation and began flowing oil to the surface. A decision was made to discontinue drilling, and the well was completed as a producer, flowing 50 b/d of oil with no water cut.

In January 1996, new surface facilities were completed and production was raised to 100 b/d. The water cut remained at 0%, and bottom hole pressure was maintained at 1,445 psi by an active water drive. Restricted production rates are maintained by a 6/64 in. choke at the well head.

Although higher production rates are feasible, the well has been allowed to flow at rates of 80-200 b/d to prevent water coning (Fig. 10 [48276 bytes]). Estimated reserves for the well are 200,000 bbl of oil. Plans have been made to drill six additional horizontal wells in Crystal field in the coming year. Cronus Development believes that use of underbalanced drilling techniques could prevent the lost circulation experienced in the first well and allow completion of successful laterals of 1,500-2000 ft in future wells.

Reservoir character

Preliminary examination of the core from the TOW No. 1-3 HD-1 well indicates that along with dolomitization and fracturing, depositional facies may exert control on the location of productive zones, as in Dundee limestone fields in eastern Michigan.

Several parasequences are observed in the core. Two of them are topped by thin (1-2 ft) grainstone beds with good porosities and permeabilities. However, the most important porosity types in the Crystal field Dundee reservoir appear to be fractures and vugs.

The upper 15 ft of the Dundee is heavily fractured in core and contains centimeter-sized vugs. Most fractures are subvertical with highly variable azimuths, but some fractures are developed at lower angles. Most fractures and vugs are lined with white, sparry dolomite.

In the demonstration well, the top of the Dundee was encountered 8 ft lower than projected, the cap limestone was missing, and shale appeared to have infilled one major vug (Fig. 11 [49462 bytes]). Together, these observations suggest that a top-down solution process (karst?) may have led to fracturing and erosion of the uppermost Dundee.

Our reservoir characterization work has produced a Dundee reservoir model for the central Michigan area that includes the results of geological, geophysical, and reservoir engineering investigations.

Twenty-nine additional central Michigan Dundee fields with similar reservoir lithologies are being characterized so that operators can easily apply the results of our Crystal field demonstration project to other "lookalike" fields (Fig. 1). Well data, including drillers' logs and wireline logs for the 8,526 wells in a seven county study area, which includes 4,785 wells that penetrate the Dundee, are in our oil and gas well data set.

About 50 cores of the Dundee formation from throughout Michigan have been identified and are currently available in public repositories. Cores from the central Michigan area are being examined and compared to the Crystal field core.

A 51,359-well drillers'-log data set obtained from Angstrom Precision Inc. has enabled us to undertake a basinwide sequence stratigraphy study of the Paleozoic section at a higher resolution than previously attempted.

Structure contour maps of the top Dundee, the top of the Dundee porosity zone, and the tops of several other formations, as well as contour maps of IP and simple cross sections have been completed for Crystal field and for all 29 other Dundee fields in the study area. Maps and cross sections are being compiled into notebooks for each field, along with field and reservoir data, field production histories and decline curves, type logs, and core data.

We plan to incorporate these field summaries into an "Atlas of Michigan Dundee Reservoirs." As presently envisioned, this atlas will include discussions of Dundee stratigraphy, reservoir variability, development history of the trend, comparisons between different fields, production history (including a discussion of engineering and completion techniques) and tables of important reservoir parameters for use in characterizing the Dundee reservoir.

The Michigan Basin Geological Society has expressed interest in publishing the atlas, which will be made available to the public as a Geological Society special publication.

Conclusions

The play concept tested in this DOE Class 2 Reservoir Demonstration Project, that bypassed oil remained in the Dundee reservoir between wells that had been produced at excessively high flow rates and had coned water during primary production, appears to be correct.

As of July, 1996, the TOW No. 1-3 HD-1 well in Crystal field had produced over 25,000 bbl of oil with a 0% water cut. As a result of this success, six to nine additional horizontal wells are planned for Crystal field, and horizontal wells which target the Dundee and Traverse lime in other fields have been announced.10

Data have been compiled for Crystal field and 29 additional Dundee fields in central Michigan. These data include formation tops, production histories, well logs, drillers logs, and core samples. These materials are available to the public through Michigan Technological University and Western Michigan University.

A regional characterization of the Michigan basin is also under way. When completed, the results will be published as an "Atlas of Michigan Dundee Reservoirs" and will include reports on each of the 30 fields in our study area. This atlas should enhance the ability of operators in the state to explore and develop this valuable hydrocarbon resource.

Acknowledgments

This project was supported by the U.S. Department of Energy's Class 2 Reservoir Program, Cooperative Agreement No. DE-FC22-94BC14983, and by cost-share contributions from Terra Energy Ltd. (now Cronus Development Corp.), Michigan Technological University, and Western Michigan University.

References

1. Champion, B.L., Oil and gas producing zones in Michigan, in Oil and gas fields symposium, Vol. 1, Michigan Basin Geol. Soc., 1969, pp. 17-36.

2. Catacosinos, P.A., Daniels, P.A., Harrison, W.B., III, Structure, stratigraphy and petroleum geology of the Michigan Basin, in Interior Cratonic Basins, AAPG Memoir 51, 1991, pp. 561-601.

3. Harrison, W.B., III, Devonian introduction, in Wollensak, M.S., ed., Oil and gas field manual of the Michigan basin, Vol. 2, Michigan Basin Geol. Soc., 1992, pp. 29-30.

4. Gardner, W.C., Middle Devonian stratigraphy and depositional environments in the Michigan basin, Michigan Basin Geol. Soc. Spec. Paper No. 1, 1974, 138 p.

5. Upp, J.E., Jr., Reed City field, in Oil and gas fields symposium, Vol. 1, Michigan Basin Geol. Soc., 1969, pp. 149-160.

6. Curran, B.C., and Hurley, N.F., Geology of the Devonian Dundee reservoir, West Branch field, Mich., AAPG Bull., Vol. 76, 1992, pp. 1,363-83.

7. Harrison, W.B., III, South Buckeye field, in Wollensak, M.S., ed., Oil and gas field manual of the Michigan basin, Vol. 2, Michigan Basin Geol. Soc., 1992, pp. 85-93.

8. Chittick, S.D., Characterization of the Dundee formation, Winterfield field, Clare County, Mich., unpubl. MS thesis, Michigan Technological University, 1995, 150 p.

9. Eddy, G.E., Geology of the Crystal oil field, Montcalm County, Mich., State of Michigan, Department of Conservation, Geological Survey Division, Progress Report No. 1, 1936, 8 p.

10. Petzet, G.A., Horizontal Devonian well spurs Michigan work, OGJ, July 29, 1996, p. 114.

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