The project goal is to develop innovative seismic-based methodologies and workflows to visualize and map reservoir compartments in order to better locate vertical and/or horizontal wells for improved recovery of oil and gas from complex karst-modified carbonate reservoirs within the onshore continental United States. The project objectives are to 1) calibrate new multi-trace seismic attributes for improved imaging of hydrocarbon reservoirs, 2) develop attribute-based, cost-effective workflows to better characterize karst-modified (compartmentalized) carbonate reservoirs and fracture systems, and 3) improve accuracy and predictiveness of geomodels by simulating history matches of well performances.

University of Kansas Center for Research, Lawrence, KS
Kansas Geological Survey, Lawrence, KS
Allied Geophysical Laboratories, University of Houston, Houston, TX 
University of Oklahoma, Norman, OK

Karst-modified carbonate reservoirs account for 30-50 percent of the hydrocarbon production in the U.S. Midcontinent. These reservoirs are often characterized by low matrix permeability, fluid control problems, and low hydrocarbon recoveries. Fractures are important controls on development of permeability and hydraulic flow units in karst reservoirs and can produce significant reservoir compartmentalization. New technology is critical to the optimization of production from karst-modified reservoirs, and the project’s new multi-trace, geometric seismic attributes have the potential to image karst sinkholes, field-scale fracture systems and reservoir compartments, and other usually elusive subseismic features using relatively low-cost, conventionally acquired 3-D seismic surveys. In order to advance this imaging technology for the development and management of karst-modified reservoirs, these attributes must be calibrated at the field scale, i.e, used to match recorded well production/pressure histories. In this project, researchers are calibrating attributes from Midcontinent karst-modified reservoirs in West Texas, Colorado, and Kansas, that represent a wide diversity of karst types and validating their results through reservoir simulation and targeted infill drilling in select compartments.

The major deliverables from this project include:

• Catalog of karst features that can be imaged with newly developed 3-D seismic attribute analysis. The features shown in this catalog can serve as analogs for other karst-modified reservoirs.
• Best practices workflow for incorporating new geometric seismic attributes into the characterization of karst-modified reservoirs. The major elements defining the workflow developed in this project include the following:
  • Indentify karst features and associated reservoir heterogeneity
  • Predict lithology, porosity, and permeability
  • Visualize and map reservoir compartments as a result of karst processes
  • History match production/pressure data by reservoir simulation to validate reservoir compartments
  • Identify undrained or partially drained reservoir compartments for target infill wells

Demonstration of the above workflow was carried out within the study areas where well-level data was available to a) characterize reservoir compartments, b) develop an integrated reservoir model, c) use reservoir simulation to validate the size and location of compartment boundaries, and d) identify undrained or partially drained reservoir compartments for targeted infill drilling. The demonstrations can used as a guide for implementing the workflow in other reservoirs.

Successful application of the results of this research will have the potential for incremental recovery of hydrocarbons from karst-modified reservoirs within the onshore continental United States by improving the imaging and understanding of complex and compartmentalized karst reservoirs.

• Catalog of karst features – This catalog displays results of the 3-D seismic attribute analysis for the study areas, augmented with examples from other areas. A variety of karst features are displayed, including collapse features, solution-enlarges fractures, and geomorphologies that appear to be related to mature, cockpit landscapes. The catalog illustrates the utility of volumetric curvature attributes to reveal previously unknown features in the seismic data or to provide enhanced visibility of karst and fracture features compared with other seismic analysis methods. In all study areas, seismic curvature attributes illuminate lineaments that appear to be related to joint and fracture systems controlled by regional structure.
• Best practices workflow for characterizing karst-modified reservoirs – As a part of best practices workflow, geologic data is integrated with information from seismic horizon structure and geometric attributes. Geometric attributes such as volumetric curvature are particularly useful for 1) outlining potential reservoir compartment boundaries, and 2) classification of the type of karst and/or fracture overprint in an area, which can help predict reservoir quality, seal integrity, and general production performance.
• Integrated reservoir characterization studies – These studies, making use of complementary seismic, geological, petrophysical, and engineering data, have been completed for the following study areas:
  • At the Smoky Creek field (Cheyenne County, Colorado), 3-D seismic curvature attributes were used to identify compartments and build a geomodel which served as a basis to history match production performance of wells located in these compartments. The 3-D seismic survey over Smoky Creek field extends over the adjunct Cheyenne Wells field to the south, where the 3-D seismic curvature attributes have been used to identify prospective reservoir compartments for infill drilling. Industry partner Mull Drilling Co. (MDC) plans to drill one of the identified infill locations in the Cheyenne Wells field in the fall of 2009. Match between observed production performance at this well and that predicted from simulation studies will help validate the location of the karst compartment boundaries.
  • A 3-D seismic curvature map developed for a sparsely drilled Gove County karsted reservoir in Kansas revealed the presence of many reservoir compartments, and one of larger compartments was selected for infill drilling by MDC in February 2009. A modern suite of logs including CMR, run at this well, showed the presence of about 8 feet of pay at irreducible water saturation and isolated from the oil-water contact by a tight zone. CMR and DST indicate the pay zone permeability to be around 10 md. Low reservoir permeability coupled with low gravity of the produced oil (35.5 API @ 106F and 31.1 API @ 49F) has constrained the flow rate which at IP (on February 19, 2009) started at 43 BOPD and has stabilized around 12 BOPD by end of March 2009. The cumulative oil production to date has been around 850 BO, and the well continues to produce water-free at present. This infill well confirmed the validity of employing new attribute analysis to identify sizeable undrained compartments in new and mature fields for targeting infill drilling.
  • At the Dickman field (Ness County, Kansas), the 3-D seismic curvature attributes were used to map compartments bounded by karst-enhanced fractures. Fluid production was correlated with distance (of the well) from oriented seismic curvature lineaments. Also, undrained reservoir compartments were identified for prospective infill drilling. The industry partner, Grand Mesa Operating Co. (GMOC) drilled an infill well in one of the identified compartments in 2008. Unfortunately, the top of the Mississippian was encountered below the oil-water contact in this well resulting in the operator not completing the well.
  • At the Waddell field (Crane County, TX), 3-D seismic curvature attributes were used to map potential reservoir compartments. Seismic curvature lineaments suggest reservoir compartmentalization at a single-well scale, an interpretation supported by bulk volume water (BVW) analysis of wells in the study area. Tracer data indicate that there is some fluid communication across the lineaments, suggesting that, in this reservoir, the lineaments may be baffles to fluid flow, rather than no-flow boundaries.

The project website (http://www.kgs.ku.edu/ SEISKARST) provides timely, wide-audience dissemination of information related to the project. Also, several abstracts have been submitted for presentations at regional and national conferences.

(July 2009) 
The project ended on March 31, 2009, and currently the researchers are in the process of compiling all relevant data and analyses into a final report for submission to DOE.

$799,833

$297,770 (27% of total)

NETL - Chandra Nautiyal (Chandra.Nautiyal@netl.doe.gov or 281-494-2488)
University of Kansas - Saibal Bhattacharya (saibal@ku.edu or 785-864-2058)

Publications 
Nissen, S. E., Carr, T. R., Marfurt, K. J., and Sullivan, E. C., in press, Using 3-D seismic volumetric curvature attributes to identify fracture trends in a depleted Mississippian carbonate reservoir: Implications for assessing candidates for CO2 sequestration, in M. Grobe, J. Pashin, and R. Dodge, eds., Carbon Dioxide Sequestration in Geological Media - State of the Art, AAPG Special Publication.

Nissen, S. E., Doveton, J. H., and Watney, W. L., 2008, Petrophysical and geophysical characterization of karst in a Permian San Andres reservoir, Waddell field, West Texas, abstract, AAPG Annual Convention.

Carr, T. R., and Nissen, S. E., 2007, Application of curvature attributes to Kansas subsurface data, abstract, AAPG Midcontinent Convention.

Nissen, S. E., Sullivan, E.C., Marfurt, K.J., and Carr, T.R., 2007, Improving reservoir characterization of karst-modified reservoirs with 3-D geometric seismic attributes,” abstract, AAPG Midcontinent Convention.

Nissen, S. E., Carr, T. R., and Marfurt, K. J., 2007, Using new 3-D seismic attributes to identify subtle fracture trends in Mid-Continent Mississippian carbonate reservoirs, RMAG-DGS 13th Annual 3-D Seismic Symposium expanded abstract (also published in Geophysical Society of Kansas May-June newsletter: http://gsks.seg.org/newsletter/MAY-JUN07.pdf).

Sullivan, C., Nissen, S., and Marfurt, K., 2006, Application of volumetric 3-D seismic attributes to reservoir characterization of karst-modified reservoirs, in Slatt, R. M. et al., Eds., Reservoir Characterization: Integrating technology and business practices, 26th Annual GCSSEPM Foundation Bob F. Perkins Research Conference Proceedings, p. 409-428.

Rocke, B. J., 2006, Paleokarst morphologies of the Arbuckle Group and karst reservoir implications on the Central Kansas uplift, Russell and Barton Counties, Kansas, Master’s Thesis, The University of Kansas, Lawrence, 210 p.

Givens, N. B., 2006, An integrated study delineating karst and fracture features affecting reservoir performance in a Mississippian reservoir, Cheyenne County, Colorado, Master’s Thesis, The University of Kansas, Lawrence, 570 p.

Givens, N. B., and Nissen, S. E., 2006, Fracture and karst features affecting reservoir performance in a Mississippian reservoir, Cheyenne County, Colorado, Kansas Geological Survey Open-file report, 2006-14. http://www.kgs.ku.edu/PRS/publication/2006/2006-14/index.html

Sullivan, E. C., Nissen, S., Marfurt, K. J., and Blumentritt, C. H., 2006, Application of new seismic attributes to identify karst and fracture related compartmentalization: Permian San Andres Formation, Central Basin Platform, West Texas (USA), abstract, AAPG Annual Convention

Nissen, S. E., Bhattacharya, S., Doveton, J., and Watney, W. L., Semi-Annual Scientific/Technical Report, December 2007.

Nissen, S. E., Bhattacharya, S., Doveton, J., and Watney, W. L., Semi-Annual Scientific/Technical Report, June 2007, http://www.kgs.ku.edu/SEISKARST/DE_FC26_04NT15504_Jun07_semiannual.pdf.

Nissen, S. E., Watney, W. L., Givens, N. B., and Rocke, B. J., Semi-Annual Scientific/Technical Report, November 2006.

Nissen, S.E., Givens, N.B., Doveton, J.H., Byrnes, A.P., Rocke, B.J., Bhattacharya, S., and Sullivan, E.C., Semi-Annual Scientific/Technical Report, May 2006, http://www.kgs.ku.edu/SEISKARST/reports/DE_FC26_04NT15504_May06_semiannual.pdf.

Nissen, S. E., Sullivan, E. C., and Givens, N. B., Semi-Annual Scientific/Technical Report, November 2005, http://www.kgs.ku.edu/SEISKARST/reports/DE_FC26_04NT15504_Oct05_semiannual.pdf.

Nissen, S. E., and Sullivan, E. C., Semi-Annual Scientific/Technical Report, April 2005, http://www.kgs.ku.edu/SEISKARST/DE_FC26_04NT15504_April05_semiannual.pdf.