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PSSeismic and Structural Analysis of a Trenton-Black River Hydrothermal Dolomite Reservoir
By
Justine Sagan1 and Bruce Hart2
Search and Discovery Article #40129 (2004)
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1Earth and Planetary Sciences, McGill University, Montreal, Canada; currently Calgary, Alberta.
2Earth and Planetary Sciences, McGill University, Montreal, Canada ([email protected])
Trenton-Black River reservoirs in the Appalachian Basin are typically associated with fault-related hydrothermal dolomites that are sealed by unaltered host rocks; however, the details of how faulting and fluid flow have interacted remain poorly documented. Integration of 3-D seismic, wireline and production data from Saybrook Field in northeastern Ohio has shown that the productive trend is controlled by a 5-km long, NW-SE oriented basement fault that was probably reactivated during the Taconic Orogeny in Mid- to Late Ordovician. The far-field stresses of this compressional activity caused strike-slip movement of the pre-existing fault to create complex flower structures that branch 1350ft upward into the Trenton-Black River interval. Circular collapse structures within splays of the flower structure are the primary drilling targets. Faults were mapped using amplitude and coherency versions of the seismic data. Curvature analysis of horizons mapped in the seismic data allowed us to constrain further the location and orientation of subtle structures. Fault morphology provides insights into the path of the dolomitizing fluids, whereas the distribution of porosity, and thus the location of the reservoir, has been mapped in 3-D using a seismic attribute study. We integrated wireline log-based measurements of porosity with seismic attributes to predict the distribution of porosity throughout the 3-D volume. Advanced visualization technologies allowed us to integrate faults and porosity predictions, thereby gaining fundamental insights into the relationships between faulting, fluid flow, and reservoir development. Our results and the methodology that we employ have application in analog settings elsewhere.
uAttributes in porosity prediction
uAttributes in porosity prediction
uAttributes in porosity prediction
uAttributes in porosity prediction
uAttributes in porosity prediction
uAttributes in porosity prediction
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Figure Captions (1-5)
MethodologyThe following steps were taken in the completion of this study: First, the horizons were picked in the well logs; then synthetic seismograms were created to tie the wells to the seismic data. The horizons were then picked in the seismic data, and faults were mapped using a combination of coherency and conventional amplitude seismic displays; the resulting structural features were analyzed. We sought to create a porosity volume for the Trenton-Black River interval using the total average porosity (PHIA), which was generated from the average of the density-porosity and neutron-porosity logs. We used the methodology of Hampson et al. (2001) to identify the best combination of attributes for predicting PHIA. We then trained a neural network to convert the seismic amplitude data to a porosity volume. The porosity volume was combined with the fault mapping in order to examine relationships between porosity and structural features.
Attributes in Porosity PredictionThe attributes used in the porosity prediction were: RMS amplitude Perigram Reflection Strength Derivative of Instantaneous Amplitude Integrated Trace Cosine of Instantaneous Phase
ConclusionsThe Saybrook fault system is consistent with a left lateral strike-slip model, with the main fault movement accommodated by synthetic Riedel shears. Fluid migration may have been aided by the development of antithetic Riedel shears that formed between the overlapping synthetic Riedel shears (flower structures). This hypothesis is supported by the porosity prediction using seismic attributes that illustrated a clear relationship between high porosity values and areas where there are flower structures in the fault zone. Through the combined use of seismic attributes and fault mapping in 3-D, it is apparent that faulting is one of the key controls on dolomitization, and hence porosity development at the Saybrook Field. For plays similar to Saybrook in which the reservoir development is related to a strike-slip fault environment, detailed fault mapping should help to illuminate the impact these structures have had on reservoir development.
ReferencesAhlgren, S.G., 2001, The nucleation and evolution of Riedel shear zones as deformation bands in porous sandstone: Journal of Structural Geology, v. 23, p. 1203-1214. Ettensohn, F.R., J.C. Hohman, M.A. Kulp, and N. Rast, 2002, Evidence and implications of possible far-field responses to Taconian Orogeny: Middle-Late Ordovician Lexington Platform and Sebree Trough, east-central United States: Southeastern Geology, v. 41, p. 1- 36. Hampson, D.P., J.S. Schuelke, and J.A. Quirein, 2001, Use of multi- attribute transforms to predict log properties from seismic data: Geophysics, v. 66, p. 220-236. Larsen, G.E., 2000 (Hull, D.N., 1990, chief compiler), Generalized column of bedrock units in Ohio: http://www.ohiodnr.com/geosurvey/pdf/stratcol.pdf. Mandl, G., 1988, Mechanics of tectonic faulting: Models and basic concepts: Elsevier: Amsterdam, Netherlands, 407p. Middleton, K., M. Coniglio, R. Sherlock, and S. Frape, 1993, Dolomitization of Middle Ordovician carbonate reservoirs, southwestern Ontario: Bulletin of Canadian Petroleum Geology, v. 41, p. 150-163. Pearson, R.A., and B.S. Hart, 2004 (in press), 3-D seismic attributes help define controls on reservoir development: Case study from the Red River Formation, Williston Basin, in G.P. Eberli, J.L. Masaferro, and J.F. Sarg, eds., Seismic imaging of carbonate reservoirs and systems: American Association of Petroleum Geologists Memoir 81.
AcknowledgmentsWe thank Pete MacKenzie, formerly with CGAS Inc. for supplying the data used in this project. Funding was provided by an NSERC Discovery Grant to Hart. Software was furnished by Landmark Graphics Corp. and Hampson-Russell Software Services. |