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Artigo - Prof Gera - Geofisica, Manuais, Projetos, Pesquisas de Engenharia de Petróleo

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Tipologia: Manuais, Projetos, Pesquisas

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Baixe Artigo - Prof Gera - Geofisica e outras Manuais, Projetos, Pesquisas em PDF para Engenharia de Petróleo, somente na Docsity! GEOPHYSICS, VOL. 66, NO. 1 (JANUARY-FEBRUARY 2001); P. 25–30 Reservoir geophysics Wayne D. Pennington∗ INTRODUCTION The concept of petroleum reservoir geophysics is relatively new. In the past, the role of geophysics was largely confined to exploration and, to a lesser degree, the development of discov- eries. As cost-efficiency has taken over as a driving force in the economics of the oil and gas industry and as major assets near abandonment, geophysics has increasingly been recognized as a tool for improving the bottom line closer to the wellhead. The reliability of geophysical surveys, particularly seismic, has greatly reduced the risk associated with drilling wells in existing fields, and the ability to add geophysical constraints to statis- tical models has provided a mechanism for directly delivering geophysical results to the reservoir engineer. Several good examples of reservoir geophysics studies can be found in Sheriff (1992) and in the Development and Production special sections of THE LEADING EDGE (e.g., March 1999 and March 2000 issues). DIFFERENCES BETWEEN EXPLORATION AND RESERVOIR GEOPHYSICS There are several specific differences between exploration geophysics and reservoir geophysics, as the term is usually intended. These include the assumption that well control is available within the area of the geophysical survey, that a well- designed geophysical survey can be conducted at a level of detail that will be useful, and that some understanding of the rock physics is available for interpretation. Well control In exploration, we often require extrapolating well data from far outside the area of interest, crossing faults, sequence bound- aries, and occasionally worse discontinuities. The availability of “analogs” is an important component of exploration, and the level of confidence on the resulting interpretation is necessar- ily limited. In reservoir geophysics, it is generally assumed that a reservoir is already under production (or at least at a late stage of development) and that wells are available for analysis. These wells provide a variety of information. From the petro- physicist, we receive edited and interpreted well log data, de- scribing the lithology (including the mineralogy, porosity, and ∗Michigan Technological University, Department of Geological Engineering and Sciences, Houghton, Michigan 49931. E-mail: wayne@mtu.edu. c© 2001 Society of Exploration Geophysicists. All rights reserved. perhaps even the morphology of the pore spaces), the fluid content (sometimes related to logged conditions, sometimes to virgin reservoir conditions), and detailed depth constraints on geologic horizons. From the production and reservoir engi- neers, we receive an estimate of the proximity to boundaries, aquifers, or other features of interest. The reservoir engineer can also provide a good estimate of the total volume of the reservoir, and the asset team relates this to the geologic inter- pretation, determining the need for surveys at increased reso- lution. From a combination of sources, we obtain additional in- formation about the in-situ conditions of the reservoir, includ- ing the formation temperature, pressure, and the properties of the oil, gas, and brine. The geophysicist should be familiar with the usefulness and limitations of petrophysical and reservoir- engineering studies, and should be able to ask intelligent ques- tions of the experts in those fields. But the geophysicist need not become an expert in those areas in order to work with the specialists and to design a new experiment to solve reservoir problems. A good introduction to reservoir development and engi- neering practices, accessible to geophysicists as well as non- technical personnel, can be found in Van Dyke (1997); a clas- sical text in reservoir engineering is that by Craft and Hawkins (1991, revised). Other petroleum engineering texts often ap- preciated by geophysicists include ones by Dake (1978), Jahn et al. (1998) and Cossé (1993). A detailed reference work for petroleum engineering is Bradley (1987). Good references for well logging and formation evaluation include Dewan (1983) and Asquith (1982). Rock physics control One of the major questions a geophysicist is asked, or should ask independently, is this: Will the geophysical technique be- ing proposed be able to differentiate between the competing reservoir models sufficiently well to be worth the effort and cost? The answer lies not just in the geophysical model, but in the rock physics—or the “seismic petrophysics”—of the reser- voir rock and neighboring formations (Pennington, 1997). The presence of wells and the possibility that some core samples are available greatly improve the capability of the reservoir geo- physicist to address this question. Logs, particularly sonic logs 25 26 Geophysics in the new millennium of compressional and shear velocities combined with image logs providing fracture information, can be used (carefully) to provide basic seismic properties, which in turn are mod- eled for varying lithologic character, fluid content, and in-situ conditions (such as pore pressure). The core samples can be used to provide the basis for a theoretical framework, or mea- surements on them can be used (again, carefully) to provide the same basic seismic properties. The geophysicist must al- ways be on the alert for accidental misuse of the input data, and concerned with scaling properties, particularly the possi- bility that physical effects observed at one scale (such as the squirt flow mechanism for saturated rocks at high frequen- cies) not be mistakenly applied at other scales. Sometimes, a little knowledge can be a dangerous weapon; an incomplete evaluation of the seismic petrophysical aspects of the forma- tion can lead either to incorrect results or interpretations (see one pitfall demonstrated and accounted for in Dvorkin et al., 1999). A number of the fundamental papers dealing with rock physics and seismic response can be found in the compilations by Nur and Wang (1989) and Wang and Nur (1992); a summary of rock physics formulas and their use is presented by Mavko et al. (1998). Survey design Once a field has been discovered, developed, and under pro- duction for some time, quite a bit of information is available to the geophysicist to design a geophysical survey in such a man- ner as to maximize the likelihood that the data collected will optimize the interpretation. That is, if the goal of the survey is to define the structural limits of the field, a 3-D seismic survey can be designed with that in mind. If, however, the goal of the survey is to define the extent of a gas zone, the geophysicist may be able to use log data, seismic petrophysical modeling, and old (legacy) seismic data to determine whether a certain offset range is required to differentiate between the water and gas zones. If highly accurate well ties or wavelet-phase con- trol are needed, an appropriately placed vertical seismic pro- file (VSP) may be designed. Or, if an acquisition footprint had been observed in a previously acquired seismic data set and that footprint obscured the attributes used to define the reservoir target, the geophysicist can design the new survey to eliminate the troublesome artifacts. In short, the fact that the target is well known gives the reservoir geophysicist a distinct advan- tage over the exploration geophysicist by allowing the survey to be designed in a more enlightened manner than a typical exploration survey ever can be. It is often easier to justify the expense of a properly conducted seismic survey for reservoir characterization purposes because the financial impact of the survey can be calculated with greater confidence and the finan- cial returns realized more quickly than is typically the case for exploration seismic surveys. Procedures for planning 3-D seismic surveys have been un- dergoing rapid change over the past few years, but good intro- ductions to the subject are available in books by Evans (1997), Stone (1994), and Liner (1999). Some recent studies demon- strating the incorporation of seismic data, well-log control, and VSP results and production information where available, and for which much of the data are publicly available, are found in Hardage et al. (1994, 1996, 1999). 3-D SEISMIC Most reservoir geophysics is based on reflection seismic data, although a wide variety of other techniques are employed reg- ularly on specific projects. Almost all seismic data collected for reservoir studies is high-fold 3-D vertical-receiver data; how- ever, the use of converted-wave data with multiple component geophones on land and on the sea floor, and multicomponent source (on land) is increasing. In particular, in order to image below gas clouds that obscure P-wave imaging of reservoirs, converted waves are now being used, and the technology to obtain multiple-component data from the ocean bottom is con- tinually improving. The importance of fractures in many reser- voir development schemes has led to a number of experimental programs for multicomponent sources and receivers in an ef- fort to identify shear-wave splitting (and other features) asso- ciated with high fracture density. Some of these techniques will find continually increasing application in the future, but at the present, most surface seismic studies designed to characterize existing reservoirs are high-quality 3-D vertical-component- receiver surveys. Many good case histories of the use of 3-D seismic data for reservoir development purposes can be found in the collection by Weimer and Davis (1996). Case histories using 3-D seismic for unconventional reservoir characterization purposes include MacBeth and Li (1999) and Lynn et al. (1999). A current ex- ample for the use of converted waves in ocean-bottom surveys over a poor-data area (the result of a gas chimney) is provided by Thomsen et al. (1997). Attributes In most exploration and reservoir seismic surveys, the main objectives are (in order) to correctly image the structure in time and depth, and to correctly characterize the amplitudes of the reflections in both the stacked and prestack domains. From these data, a host of additional features can be derived, and used in interpretation. Collectively, these features are re- ferred to as seismic attributes (Taner et al. 1979). The simplest attribute, and the one most widely used, is seismic amplitude, and it is usually reported as the maximum (positive or nega- tive) amplitude value at each common midpoint (CMP) along a horizon picked from a 3-D volume. It is fortunate that, in many cases, the amplitude of a reflection corresponds directly to the porosity of the underlying formation, or perhaps to the den- sity (and compressibility) of the fluid occupying pore spaces in that formation. The assumption is that amplitude is pro- portional to RO, and the simple convolutional model is often appropriate for interpretation of the data in such cases. But it isn’t always this simple, and many mistakes of interpretation have occurred by making this assumption. For one thing, the convolutional model may not be appropriate for use in many instances, particularly if the offset dependence of a reflection is important in its interpretation. Likewise, the interpretation of porosity or fluid properties as the cause of a true impedance change is often overly optimistic, especially in sands containing clays or in rocks with fractures. The use of seismic attributes extends well beyond simple amplitudes. Most of the “original” seismic attributes were based on the Hilbert transform and consisted of the instan- taneous amplitude (or amplitude of the wave envelope), the Geophysics in the new millennium 29 et al., 1998). Both techniques of hydraulic-fracture monitoring have become nearly routine in the industry (that is, they are no longer experimental) and can be applied where appropriate. SUMMARY As geophysical techniques have matured over the years, they have provided an increasingly fine level of detail and are now used almost routinely for many purposes related to reservoir production. The most widely used technique, just as in explo- ration, is reflection seismic, where it is almost exclusively 3-D. Emerging techniques, having successfully proven their capa- bilities but in various stages of commercial availability, include crosswell, forward and reverse VSP, single-well imaging, and passive seismic monitoring (gravity, electromagnetic, and other techniques are described elsewhere in this issue). The distinct advantage provided to reservoir geophysics over exploration geophysics lies in the quantity and quality of existing data on the reservoir target, enabling surveys to be focused on specific targets and allowing calibration (necessary in order to have confidence in the results, as well as to improve imaging) of the geophysical observations to the formation. As geophysical techniques become more familiar to the engineer, and as en- gineering practices become more familiar to the geophysicist, continuing and increased use of reservoir geophysical tech- niques can be expected. ACKNOWLEDGMENTS This paper was prepared with support provided by a con- tract from the U.S. Department of Energy through the National Petroleum Technology Office in Tulsa, Oklahoma, DE-AC26- 98BC15135, “Calibration of Seismic Attributes for Reservoir Characterization,” under project manager Purna Halder. REFERENCES Asquith, G., 1982, Basic well log analysis for geologists: Am. Assn. Petr. Geol. Bradley, H. B., 1987, Petroleum engineering handbook: Soc. Petr. Eng. Castillo, D. A., and Wright, C. A., 1995, Tiltmeter hydraulic fracture imaging enhancement project: Progress report: 65th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 1565–1566. Chen, Q., and Sidney, S., 1997, Seismic attribute technology for reser- voir forecasting and monitoring: The Leading Edge, 16, 445–456. Cossé, R., 1993, Basics of reservoir engineering: Gulf Publ. Co. Craft, B. C., Hawkins, M., revised by Terry, R. E., 1991, Applied petroleum reservoir engineering: Prentice Hall, Inc. Dake, L. P., 1978, Fundamentals of reservoir engineering: Elsevier Sci- ence Publ. Co. Davis, S. D., and Pennington, W. D., 1989, Induced seismic deformation in the Cogdell oil field of west Texas: Bull. Seis. Soc. Am., 79, 1477– 1494. Dewan, J. T., 1983, Essentials of modern open-hole log interpretation: PennWell Publ. Co. Dubrule, O., 1998, Geostatistics in petroleum geology: Am. Assn. Petr. Geol. Dvorkin, J., Moos, D., Packwood, J. L., and Nur, A. M., 1999, Identifying patchy saturation from well logs: Geophysics, 64, 1756– 1759. Evans, B. J., 1997, A handbook for seismic data acquisition in explo- ration: Soc. Expl. Geophys. Hardage, B. A., Levey, R. A., Pendleton, V., Simmons, J., and Edson, R., 1994, A 3-D seismic case history evaluating fluvially deposited thin- bed reservoirs in a gas-producing property: Geophysics, 59, 1650– 1665. Hardage, B. A., Carr, D. L., Lancaster, D. E., Simmons, J. L., Hamilton, D. S., Elphick, R. Y., Oliver, K. L., and Johns, R. A., 1996, 3-D seismic imaging and seismic attribute analysis of genetic sequences deposited in low-accommodation conditions: Geophysics, 61, 1351– 1362. Hardage, B. A., Pendleton, V. M., Major, R. P., Asquith, G. B., Schultz- Ela, D., and Lancaster, D. E., 1999, Using petrophysics and cross- section balancing to interpret complex structure in a limited-quality 3-D seismic image: Geophysics, 64, 1760–1773. Hirsche, K., Boerner, S. Kalkomey, C., and Gastaldi, C., 1998, Avoiding pitfalls in geostatistical reservoir characterization: A survival guide: The Leading Edge, 17, 493–504. Hornby, B. E., Murphy, W. F., Liu, H.-L., and Hsu, K., 1992, Reservoir sonics: A North Sea case study: Geophysics, 57, 146–160. Houston, L. M., and Kinsland, G. L., 1998, Minimal-effort time-lapse seismic monitoring: exploiting the relationship between acquisition and imaging in time-lapse data: The Leading Edge, 17, 1440–1443. Isaaks, E. H., and Srivastava, R. M., 1989, An introduction to applied geostatistics: Oxford Univ. Press. Jahn, F., Cook, M., and Graham, M., 1998, Hydrocarbon exploration and production: Elsevier Science Publ. Co. Jensen, J. L., Lake, L. W., Corbett, P. W. M., and Goggin, D. J., 1997, Statistics for petroleum engineers and geoscientists: Prentice-Hall Inc. Kalkomey, C. T., 1997, Potential risks when using seismic attributes as predictors of reservoir properties: The Leading Edge, 16, 247–251. Kovach, R. L., 1974, Source mechanisms for Wilmington oil field, Cal- ifornia, subsidence earthquakes: Bull. Seis. Soc. Am., 64, 699. Lazaratos, S. K., Harris, J. M., Rector, J. W., and van Schaaczk, M., 1995, High-resolution crosswell imaging of a west Texas carbonate reservoir: Part 4: Reflection imaging: Geophysics, 60, 702–711. Li, Y., Cheng, D. H., and Toksöz, M. N., 1998, Seismic monitoring of the growth of a hydraulic fracture zone at Fenton Hill, New Mexico: Geophysics, 63, 120–131. Liner, C. L., 1999, Elements of 3-D seismology: PennWell Publ. Co. Lynn, H. B., Campagna, D., Simon, K. M., and Beckham, W. E., 1999, Relationship of P-wave seismic attributes, azimuthal anisotropy, and commercial gas pay in 3-D P-wave multiazimuth data, Rulison field, Piceance basin, Colorado: Geophysics, 64, 1293–1311. MacBeth, C., and Li, X-Y., 1999, AVD—An emerging new marine tech- nology for reservoir characterization: Acquisition and application: Geophysics, 64, 1153–1159. Marfurt, K. J., Kirlin, R. L., Farmer, S. L., and Bahorich, M. S., 1998, 3-D seismic attributes using a semblance-based coherency algorithm: Geophysics, 63, 1150–1165. Mavko, G., Mukerji, T., and Dvorkin, J., 1998, The rock physics hand- book: Cambridge Univ. Press. McGarr, A., 1991, On a possible connection between three major earth- quakes in California and oil production: Bull. Seis. Soc. Am., 81, 948–970. Nur, A. M., and Wang, Z., 1989, Seismic and acoustic velocities in reservoir rocks, 1: Experimental studies: Soc. Expl. Geophys. Partyka, G., Gridley, J., and Lopez, J., 1999, Interpretational applica- tions of spectral decomposition in reservoir characterization: The Leading Edge, 18, 353–360. Paulsson, B., Fairborn, J., and Fuller, B., 1997, Single well seismic imag- ing and reverse VSP applications for the downhole seismic vibrator: 67th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 2029. Pennington, W. D., 1997, Seismic petrophysics—An applied science for reservoir geophysics; The Leading Edge, 16, 241–244. Pennington, W. D., Davis, S. D., Carlson, S. M., Dupree, J., and Ewing, T. E., 1986, The evolution of seismic barriers and asperities caused by the depressuring of fault planes in oil and gas fields of south Texas: Bull. Seis. Soc. Am., 78, 939–948. Phillips, W. S., Fairbanks, T. D., Rutledge, J. T., and Anderson, D. W., 1998, Induced microearthquake patterns and oil-producing fracture systems in the Austin chalk: Tectonophysics, 289, 153–169. Poupon, M., Azbel, K., and Ingram, J. E., 1999, Integrating seismic facies and petro-acoustic modeling: World Oil, June, 75–80. Raleigh, C. B., Healy, J. H., and Bredehoeft, J. D., 1976, An experiment in earthquake control at Rangely, Colorado: Science, 191, 1230–1236. Rutledge, J. T., Fairbanks, T. D., Albright, J. N., Boade, R. R., Dangerfield, J., and Landa, G. H., 1994, Reservoir microseismicity at the Ekofisk oil field, in Rock mechanics in petroleum engineering, Proceedings of Eurock ’94: Balkema Publishers, 589–596. Segall, P., 1989, Earthquakes triggered by fluid extraction: Geology, 17, 942–946. Sheriff, R. E., Ed., 1992, Reservoir geophysics: Soc. Expl. Geophys. Stone, D. G., 1994, Designing seismic surveys in two and three dimen- sions: Soc. Expl. Geophys. Taner, M. T., Koehler, F., and Sheriff, R. E., 1979, Complex seismic trace analysis: Geophysics, 44, 1041–1063. Teufel, L. W., and Rhett, D. W., 1992, Failure of chalk during water- flooding of the Ekofisk field: SPE paper 24911, presented at 67th Soc. Petr. Eng. Ann. Tech. Conf. Thomsen, L. A., Barkved, O., Haggard, B., Kommedal, J., and Rosland, 30 Geophysics in the new millennium B., 1997, Converted-wave imaging of Valhall reservoir: 59th Mtg., Eur. Assoc. Expl. Geophys., Extended Abstracts, B048. Van Dyke, K., 1997, Fundamentals of petroleum: University of Texas at Austin Petroleum Extension Service. Wang, Z., and Nur, A. M., 1992, Seismic and acoustic velocities in reser- voir rocks, 2: Theoretical and model studies: Soc. Expl. Geophys. Weimer, P., and Davis, T. L., 1996, Applications of 3-D seismic data to exploration and development: Am. Assn. Petr. Geol. and Soc. Expl. Geophys. Yarus, J. M., and Chambers, R. L., 1995, Stochastic modeling and geostatistics—Principles, methods, and case studies: Am. Assn. Petr. Geol.
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