Geological and Petrophysical characterization of the Ferron Sandstone for 3-D simulation of a fluvial-deltaic reservoir

Objective

Summary of Technical Progress

For the second field season, detailed geological and petrophysical characterization of the primary reservoir lithofacies typically found in a fluvial-dominated deltaic reservoir, is continuing at selected case-study areas. Interpretations of lithofacies, bounding surfaces, and other geologic information are being combined with permeability measurements from closely spaced traverses and from drill-hole cores (existing and planned). Petrophysical analyses are being incorporated with the geological characterization to develop a three-dimensional model of the reservoirs through fluid-flow simulation. Technology transfer consisted of publication of seven abstracts presenting project results, public release of the subsurface drill-hole database, and a project overview presented to the staff of an industry research lab.

Regional Stratigraphy

Data were collected from wells that penetrate the Ferron Sandstone in the area from Last Chance Creek in the south to Ferron Creek in the north (Fig 1). Lithologic and other data from coal-company exploration wells; oil, gas, and stratigraphic test wells; and government test wells were entered into the UGS Ferron Sandstone database. Stratigraphic data were transferred from the database to software which drafted strip logs and lithologic descriptions (Fig. 3). These strip logs, a total of 489, are being used for regional correlation of parasequences and lithofacies mapping. The files which produced the strip logs have been archived for possible future use and manipulation.

Digitized 7.5 minute base map files were converted to latitude/longitude coordinates from the existing 7.5 minute digitizer-inch coordinates. Rose diagrams of paleocurrents and other data are being plotted on the base maps for use in regional paleogeographic interpretation.

Case Studies

Core-Hole Program Two new core-hole locations are being permitted in the Ivie Creek case-study area; the Ivie Creek Nos. 10 and 11 (Fig. 4). These locations are set far enough back from the outcrop to avoid the coal burn and fracture zones encountered during the 1994 drilling program. Cores and geophysical logs from these wells will provide data for three-dimensional morphologic interpretation of individual lithofacies. The total depths of the core holes will be 500 ft and the Nos. 1 and 2 parasequence sets will be cored (about 150 ft thick).

Staking and permitting procedures were initiated through the Utah Division of Oil, Gas and Mining (DOGM), the oil and gas regulatory agency for Utah, and the U.S. Bureau of Land Management (BLM). The UGS plans to drill and complete the core holes by the end of September, 1995. An on-site inspection was conducted by the BLM which is also evaluating a request for surface right-of-way. An "Application for Permit to Drill" (APD), for an eight-point drilling program, was filed with DOGM and an application to appropriate water was filed with the Utah Division of Water Rights.

Mini-Permeameter and Gamma-Ray Measurements A large quantity of new permeability data was collected from both the Nos. 1 and 2 parasequence sets along five vertical permeability transects in the Ivie Creek case-study area. Transect locations contained examples of the majority of the lithofacies present in the delta-front sequences. An electronic, miniprobe permeameter (mini-permeameter) supplied by the Mobil Exploration/Producing Technical Center was used to make laboratory permeability measurements on trimmed, whole core plugs taken from the outcrops. Measured stratigraphic sections were tied to the permeability transects.

The lab permeability results, when combined with field and lab measurements taken during the 1994 field season and detailed geologic mapping, will improve understanding of the lateral variability in permeability for specific bedform types. Vertical permeability transects provide a preliminary view of vertical permeability variations. Data from these transects will be used to determine the statistical structure of the spatially variable permeability field within the delta front and to investigate how geological processes control the spatial distribution of permeability.

Outcrop gamma-ray measurements were taken along permeability transects to: (1) determine variations in clay-mineral content (or sand/shale ratios), (2) permit detailed correlation among and between outcrop traverses and core-hole gamma-ray logs, and (3) detect possible diagenetic changes associated with precipitation of uranium. Field measurements were taken using a portable 256-channel gamma-ray spectrometer capable of determining total natural gamma counts as well as concentrations of potassium, thorium, and uranium. Each transect consisted of 200 to 400 measurements at 0.5 to 1.0 ft intervals. Gamma-ray spectrometer readings are related to clay content in shaly sandstones; clay content influences the compartmentalization of flow units.

Photomosaic Scaling In the Ivie Creek case-study area, a laser theodolite and a tape measure were used to position and scale information about lithofacies and polygons (modeling units based on lithology, permeability, grain size, and sedimentary structures) on photomosaics. In the area of the No. 1a parasequence, for which detailed reservoir models will be developed, dimensional data need to be determined at a high level of precision. To achieve this, a number of points were surveyed with a laser theodolite followed by reduction of the survey data to yield horizontal and vertical scales. These scales were plotted on the photomosaics and will be used to determine dimensions of lithofacies units and polygons. These survey data also are being reduced to develop x-y-z coordinates to be used in making the three-dimensional geologic model of the case-study area.

A less precise technique was developed to produce horizontal and vertical scales for photomosaics throughout the rest of the case-study area where reservoir modeling will be at a coarser scale. For this information, there is no need to precisely position lithofacies and polygons, and horizontal and vertical scales were produced using a 50-ft nylon measuring tape. A 35 to 50 ft interval (horizontal or vertical) was measured in the field and the endpoints were recorded on the photomosaics. Key features on the photomosaics were recorded on 7.5 minute topographic maps and will be used to generate x-y-z coordinates for the three-dimensional geologic model.

Most field-interpreted photomosaics in the Ivie Creek case-study area have been redrafted and acetate overlays added which show the interpretation of parasequences and deltaic subfacies. The photomosaics will be the base for construction of scaled cross sections. In turn, the cross sections, which are being digitized, will form the base for construction of the three-dimensional model of the reservoir architecture.

Petrophysical Analysis Petrophysical measurements were made on 180 Ferron core plugs processed through Amoco Production Research's Geoscience Evaluation Module (GEM). The measurements consisted of: (1) saturated, dry, and grain densities, (2) effective and Boyle's Law porosities, (3) compressional and shear wave velocities as a function of effective pressure, (4) magnetic susceptibility, (5) qualitative and quantitative mineralogy, (6) air permeability, and (7) thin section-image analysis. The specific details of the GEM procedures used are given by Sondergeld and Rai.1-3 Velocities were measured using the pulse transmission technique of Schreiber, et al.4 and mineralogy was determined using a transmission infrared technique described by Griffiths and de Haseth.5 The final results are being compiled into hard copy and digital reports.

Stochastic Modeling and Fluid-Flow Simulation The homogenization code for one-, two-, and three-dimensional problems has been completed and tested extensively. The tests involved approximately 100 individual cases in one, two, and three dimensions. The test cases involved data sets with well known solutions and random examples to test the codes on more realistic problems. In addition to the homogenization codes, algorithms for computing the arithmetic, harmonic, and geometric averages of the permeability data were implemented to aid in testing the homogenization codes. The homogenization results should always be between the arithmetic and harmonic averages. This method is useful for testing the random cases even though the exact answer is not known. The codes were written in a form that is easy to install and test. All the test data sets are available and are generated in a self-contained program. The subroutines that compute the homogenized permeabilities can be plugged in at any point to a code with at most a minor amount of translation between data structures. The two-dimensional code has been written to simulate Ferron lithofacies and will be used as a means of extrapolating the outcrop data to both two and three dimensions. The permeability data from the transects collected from the Ivie Creek case-study area has been obtained and is being analyzed. The analysis involves the use of spectral decompositions and possibly wavelet representation. This data is being used to build depositional models.

Technology Transfer

A presentation entitled "Geological and Petrophysical Characterization of the Ferron Sandstone (Utah), for 3-D Simulation of a Fluvial-Deltaic Reservoir" was given to the Geoscience Technology Division staff of Amoco Production Research Company, Tulsa, Oklahoma, June 23, 1995. The project objectives and description, status of deliverables and accomplishments, potential application of results, benefits, and value were discussed.

Seven abstracts for presentation at the 1995 American Association of Petroleum Geologists (AAPG) Rocky Mountain Section meeting were published this quarter.8-14

References

2.C. H. Sondergeld and C. S. Rai, A New Concept in Quantitative Core characterization, The Leading Edge: 774-779 (July 1993).

3.C. H. Sondergeld and C. S. Rai, A New Exploration Tool: Quantitative Core Characterization, PAGEOPH, 141 (2/3/4): 249-268 (1993).

4.E. Schreiber, O. L. Anderson and N. Soga, Elastic Constants and Their Measurement, McGraw-Hill, New York: 196 pp. (1973).

5.P. R. Griffiths and J. A. de Haseth, Fourier Transform Infrared Spectrometry, John Wiley, New York: (1986).

6.B. P. Hucka, S. N. Sommer, D. A. Sprinkel and D. E. Tabet, Ferron Sandstone Drill-Hole Database, Ferron Creek to Last Chance Creek, Emery and Sevier Counties, Utah, Utah Geological Survey Open-File Report 317: 1130 pp., 9 pl. (May 1995).

7.B. P. Hucka, S. N. Sommer, D. A. Sprinkel and D. E. Tabet, Ferron Sandstone Drill-Hole Database, Ferron Creek to Last Chance Creek, Emery and Sevier Counties, Utah, Utah Geological Survey Open-File Report 317DF: 5 pp. 2 diskettes (June 1995).

8.R. D. Adams, The Cretaceous Ferron Sandstone of East-Central Utah: A Tale of Three Different Morphologies for Deltaic Parasequences, Am. Assoc. of Petr. Geol. Bull. 79(6): 914 (June 1995).

9.R. D. Adams, S. H. Snelgrove and C. Forster, A Methodology for Obtaining Detailed Geologic Descriptions to Constrain 3-D Reservoir Fluid-Flow Simulation Models in Delta-Front Lithofacies, Am. Assoc. of Petr. Geol. Bull. 79(6): 914 (June 1995).

10.P. B. Anderson and T. A. Ryer, Proposed Revisions to Parasequence-Set Nomenclature of the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale, Am. Assoc. of Petr. Geol. Bull. 79(6): 914-915 (June 1995).

11.T. C. Chidsey, Jr., Geological and Petrophysical Characterization of the Ferron Sandstone in Utah, For 3-D Simulation of a Fluvial-Deltaic Reservoir, Am. Assoc. of Petr. Geol. Bull. 79(6): 916 (June 1995).

12.J. A. Dewey, Jr., T. H. Morris and T. A. Ryer, Constraining Reservoir Models of Fluvial- vs. Wave-Dominated Delta-Front Sandstones through High Resolution and High Density Sequence Stratigraphic Analysis, Ferron Sandstone, Utah, Am. Assoc. of Petr. Geol. Bull. 79(6): 917 (June 1995).

13.T. A. Ryer and P. B. Anderson, Parasequence Sets, Parasequences, Facies Distributions, and Depositional History of the Upper Cretaceous Ferron Deltaic Clastic Wedge, Utah, Am. Assoc. of Petr. Geol. Bull. 79(6): 924 (June 1995).

14.T. A. Ryer, J. A. Dewey, Jr. and T. H. Morris, Distinguishing Allocyclic and Autocyclic Causes of Parasequence-Level Cyclicity--Lessons from Deltaic Strata of the Upper Cretaceous Ferron Sandstone, Central Utah, Am. Assoc. of Petr. Geol. Bull. 79(6): 924 (June 1995).