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Title: Modeling dolomitized carbonate-ramp reservoirs: A case study of the Seminole San Andres unit. Part 2 -- Seismic modeling, reservoir geostatistics, and reservoir simulation

Abstract

In part 1 of this paper, the authors discussed the rock-fabric/petrophysical classes for dolomitized carbonate-ramp rocks, the effects of rock fabric and pore type on petrophysical properties, petrophysical models for analyzing wireline logs, the critical scales for defining geologic framework, and 3-D geologic modeling. Part 2 focuses on geophysical and engineering characterizations, including seismic modeling, reservoir geostatistics, stochastic modeling, and reservoir simulation. Synthetic seismograms of 30 to 200 Hz were generated to study the level of seismic resolution required to capture the high-frequency geologic features in dolomitized carbonate-ramp reservoirs. Outcrop data were collected to investigate effects of sampling interval and scale-up of block size on geostatistical parameters. Semivariogram analysis of outcrop data showed that the sill of log permeability decreases and the correlation length increases with an increase of horizontal block size. Permeability models were generated using conventional linear interpolation, stochastic realizations without stratigraphic constraints, and stochastic realizations with stratigraphic constraints. Simulations of a fine-scale Lawyer Canyon outcrop model were used to study the factors affecting waterflooding performance. Simulation results show that waterflooding performance depends strongly on the geometry and stacking pattern of the rock-fabric units and on the location of production and injection wells.

Authors:
; ;  [1]
  1. Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
316257
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geophysics; Journal Volume: 63; Journal Issue: 6; Other Information: PBD: Nov-Dec 1998
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; TEXAS; PETROLEUM DEPOSITS; GEOLOGIC MODELS; RESERVOIR ENGINEERING; SEISMIC SURVEYS; SAMPLING; PERMEABILITY; COMPUTERIZED SIMULATION; WATERFLOODING

Citation Formats

Wang, F.P., Dai, J., and Kerans, C. Modeling dolomitized carbonate-ramp reservoirs: A case study of the Seminole San Andres unit. Part 2 -- Seismic modeling, reservoir geostatistics, and reservoir simulation. United States: N. p., 1998. Web. doi:10.1190/1.1444480.
Wang, F.P., Dai, J., & Kerans, C. Modeling dolomitized carbonate-ramp reservoirs: A case study of the Seminole San Andres unit. Part 2 -- Seismic modeling, reservoir geostatistics, and reservoir simulation. United States. doi:10.1190/1.1444480.
Wang, F.P., Dai, J., and Kerans, C. 1998. "Modeling dolomitized carbonate-ramp reservoirs: A case study of the Seminole San Andres unit. Part 2 -- Seismic modeling, reservoir geostatistics, and reservoir simulation". United States. doi:10.1190/1.1444480.
@article{osti_316257,
title = {Modeling dolomitized carbonate-ramp reservoirs: A case study of the Seminole San Andres unit. Part 2 -- Seismic modeling, reservoir geostatistics, and reservoir simulation},
author = {Wang, F.P. and Dai, J. and Kerans, C.},
abstractNote = {In part 1 of this paper, the authors discussed the rock-fabric/petrophysical classes for dolomitized carbonate-ramp rocks, the effects of rock fabric and pore type on petrophysical properties, petrophysical models for analyzing wireline logs, the critical scales for defining geologic framework, and 3-D geologic modeling. Part 2 focuses on geophysical and engineering characterizations, including seismic modeling, reservoir geostatistics, stochastic modeling, and reservoir simulation. Synthetic seismograms of 30 to 200 Hz were generated to study the level of seismic resolution required to capture the high-frequency geologic features in dolomitized carbonate-ramp reservoirs. Outcrop data were collected to investigate effects of sampling interval and scale-up of block size on geostatistical parameters. Semivariogram analysis of outcrop data showed that the sill of log permeability decreases and the correlation length increases with an increase of horizontal block size. Permeability models were generated using conventional linear interpolation, stochastic realizations without stratigraphic constraints, and stochastic realizations with stratigraphic constraints. Simulations of a fine-scale Lawyer Canyon outcrop model were used to study the factors affecting waterflooding performance. Simulation results show that waterflooding performance depends strongly on the geometry and stacking pattern of the rock-fabric units and on the location of production and injection wells.},
doi = {10.1190/1.1444480},
journal = {Geophysics},
number = 6,
volume = 63,
place = {United States},
year = 1998,
month =
}
  • Major issues in characterizing carbonate-ramp reservoirs include geologic framework, seismic stratigraphy, interwell heterogeneity including rock fabric facies and permeability structure, and factors affecting petrophysical properties and reservoir simulation. The Seminole San Andres unit, Gaines, County, West Texas, and the San Andres outcrop of Permian age in the Guadalupe Mountains, New Mexico, were selected for an integrated reservoir characterization to address these issues. The paper is divided into two parts. Part 1 covers petrophysical and geologic characterization, and part 2 describes seismic modeling, reservoir geostatistics, stochastic modeling, and reservoir simulation. Core data from Seminole showed that rock fabric and pore typemore » have strong positive correlations with absolute and relative permeabilities, residual oil saturation, waterflood recovery, acoustic velocity, and Archie cementation exponent. Petrophysical models were developed to estimate total porosity, separate-vug porosity, permeability, and Archie cementation exponent from wireline logs to account for effects of rock fabric and separate-vug porosity. A model for the style of high-frequency cyclicity and the distribution of rock-fabric facies within cycles was developed using continuous outcrop exposures at Lawyer Canyon. Petrophysical properties of total and separate-vug porosities, permeability, water saturation, and rock fabrics were calculated from wireline log data. The permeability-thickness ratios among these rock fabric units can be used to approximate fluid flow and recovery efficiency.« less
  • An integrated reservoir characterization of Seminole San Andres Unit was conducted using outcrop and subsurface data. The high frequency cycles and rock-fabric facies identified on outcrop and cores were used to correlate wireline logs. Reservoir and simulation models of the outcrop and a two-section area of the Seminole San Andres field were constructed using rock-fabric units within high-frequency cycles (HFC`s) as a geologic framework. Simulations were performed using these models to investigate critical factors affecting recovery. High-frequency cycles and rock-fabric units are the two critical scales for modeling shallow-water carbonate ramp reservoirs. Descriptions of rock-fabric facies stacked within high-frequency cyclesmore » provide the most accurate framework for constructing geologic and reservoir models because discrete petrophysical functions can be fit to rock fabrics and fluid flow can be approximated by the k{sub vh} ratios among rock-fabric flow units. Permeability is calculated using rock-fabric-specific transforms between interparticle porosity and permeability. Core analysis data showed that separate-vug porosity has a very strong effect on relative permeability and capillary pressure measurements. The stratigraphic features of carbonates can be observed in stochastic realizations only when they are constrained by rock-fabric flow units. Simulation results from these realizations are similar in recovery but different in production and injection rates. Scale-up of permeability in the vertical direction was investigated in terms of the ratio of vertical permeability to horizontal permeability (k{sub vh}). This ratio decreases exponentially with the vertical grid-block size up to the average cycle size of 20 ft (6.1 m) and remains at a value of 0.06 for a grid-block size of more than 20 ft (>6.1 m), which is the average thickness of high-frequency cycles.« less
  • Variably cyclic, fusulinid-rich, outer ramp facies of the Permian San Andres Formation are exposed along the Algerita escarpment, Guadalupe Mountains, New Mexico. We have used the outcrop exposures and cored wells drilled adjacent to the outcrop to assess reservoir- and interwell-scale variability of permeability as a potential analog for carbonate reservoirs in the Permian basin and elsewhere. Permeability distribution was evaluated using a field permeameter and conventional measurements on small core plugs taken along vertical and horizontal outcrop traverses and from the slim-hole cores. Geostatistical models of permeability variation, honoring the geologic and petrophysical data, were constructed and input intomore » a waterflood simulator to understand the interactions between heterogeneity and flow. Different vertical variogram characteristics are displayed by cyclic and less distinctly cyclic parts of the San Andres. Variograms constructed for horizontal transect data from three distinct stratigraphic units have nearly identical properties. Overall, the ranges of correlation are short (3-3.5 in; 10-12 ft) when compared to typical interwell distances, supporting a nearly uncorrelated and highly variable permeability model. Using observed short ranges of vertical and horizontal correlation and honoring the vertical transect data, cross sectional, conditionally simulated permeability fields were generated and used in simulated waterfloods to investigate the sensitivities to an oil recovery model and overall fluid injection rate for this style of stratigraphy and cyclicity. Cyclic parts of the section are characterized by a potential for early water breakthrough and relatively high vertical sweep efficiencies. Within the less distinctly cyclic section, waterflood fronts have a fingerlike profile and vertical sweep efficiency is generally poorer.« less
  • A synthetic section interpreted in lithofacies has been constructed from the study of a large outcrop in order to test on a {open_quotes}true{close_quotes} geological model different methods and tools in the field of the seismic processing and geostatistical reservoir modeling. The large outcrops of the Campanian deltaic series of Colorado were studied to build a 6 km long and 350 m thick 2D section. The section was interpreted in sedimentary facies then digitized in order to compile a high-resolution grid for both geophysical and geostatistical simulations. Eleven facies where then determined in offshore, shoreface, foreshore and coastal plain environments. Rockmore » properties such as P - wave, S - wave velocity and density were assigned to each cells of the model, and the target was buried. A fully elastic seismic modeling was then computed, and data post- processing included wavelet extraction, stratigraphic modeling and stratigraphic inversion. Pre - stack and post - stack inversions have also been performed. In the pre - stack inversion, the variation of the reflection coefficient amplitudes versus offset is taken into account, and, as consequence, resolution is very much improved. A geostatistical analysis as also performed on the same data - set, proportion curves of lithofacies and variograms were computed, and different stochastic approaches ere tested. The next step will be the computation of geostatistical parameters on seismic data in order to better constrain stochastic reservoir simulations with seismic data.« less
  • Vertical and horizontal transects were sampled from core and outcrop of the San Andres Formation at Lawyer Canyon, Guadalupe Mountains, New Mexico, to assess permeability variation in a geologic framework of upward-shallowing carbonate cycles and to show the potential effect these variations have on viscous-dominated flow behavior in analogous reservoirs. These cycles occur in a ramp-crest facies, tract, are 3-13 m (10-45 ft) thick, and contain both vertical and lateral variation of lithofacies. Thicker cycles consist of a basal dolomudstone, which is overlain by burrowed dolomudstone, and capped by bar-flank ooid-peloid dolograinstone and bar-crest ooid dolograinstones. In vertical transects, permeabilitymore » is extremely variable about the mean, yet upward-increasing trends coinciding with the succession of lithofacies typify a given cycle. Semi-variance analysis shows permeability to be uncorrelated vertically at distances greater than 5.5 m (18 ft), which is the average cycle thickness, suggesting that the cycles may equate to fluid-flow unit in a reservoir. Semi-variance analysis of measurements collected along a horizontal transect within bar-crest dolograinstones of a single cycle show permeability is uncorrelated at distances greater than 3.6 m (12 ft). This correlation distance appears to be controlled by alternating porous and tightly cemented zones that formed during dolomitization. Vertical and lateral variogram models were fit to the spatial parameters to generate a variety of conditionally simulated permeability fields. Fluid-flow simulations show viscous-dominated flow behavior is compartmentalized by both the individual cycles and groups of cycles. The basal dolomudstones are potential baffles to flow crossover between cycles, but poorly developed cycles (i.e., those that are mud rich and lack well-developed bar-flank and bar-crest facies) result in the greatest compartmentalization of fluid flow within a succession of cycles.« less