How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?
- C. Shah Kabir (Chevron ETC) | Julian J. Pop (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- December 2007
- Document Type
- Journal Paper
- 644 - 656
- 2007. Society of Petroleum Engineers
- 5.2.1 Phase Behavior and PVT Measurements, 5.2 Reservoir Fluid Dynamics, 4.3.3 Aspaltenes, 4.1.5 Processing Equipment, 5.6.1 Open hole/cased hole log analysis, 4.6 Natural Gas, 5.2.2 Fluid Modeling, Equations of State, 5.8.8 Gas-condensate reservoirs, 4.6.3 Gas to liquids, 4.2 Pipelines, Flowlines and Risers, 5.6.4 Drillstem/Well Testing, 4.6.2 Liquified Natural Gas (LNG), 5.1.5 Geologic Modeling, 4.1.2 Separation and Treating
- 8 in the last 30 days
- 1,569 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Collection and analysis of gas/condensate-fluid samples presents considerable challenges. This is because downhole sampling of a gas/condensate fluid—unlike its oil counterpart—does not guarantee the retrieval of a single-phase fluid. The same is true for surface sampling because of incomplete surface and/or downhole separation. Given this reality, the pressure/volume/temperature (PVT) analysis of any fluid sample with an equation-of-state (EOS) model demands that the results are verified with independent measurements.
Our analyses of many samples show that a good correspondence exists between the PVT-derived gradient and that obtained from wellbore-flow modeling of production-test data. Older-generation formation testers (those from before 1990), although yielding comparable results, had larger error bars because of system limitations in repeatability of both pressure and depth measurements.
We developed a yield/temperature correlation to fill in the information void for reservoirs that fall within the bounds of measured data over a large geographic area. Correlating CO2 with formation temperature was a stepping stone to the yield/temperature relationship. This approach is applicable for the analysis of both single-reservoir and multireservoir samples, which is particularly useful when rapid assessment is needed over large regions.
The presence of a compositional gradient in reservoirs containing hydrocarbon columns has long been recognized since Sage and Lacey (1939) published their seminal work. Segregation of asphaltenes causes compositional grading in oil (20-30°API) columns. In contrast, compositional grading in light-hydrocarbon (> 35°API) columns occurs for near-critical fluids or, more appropriately, for fluids close to the spinodal curve (Lira-Galeana 1992). Equilibrium between gravitational and chemical forces of various hydrocarbon components results in a variable saturation pressure in a fluid column (Schulte 1980; Riemens et al. 1988; Wheaton 1991). According to Hirschberg (1988), the time to reach such an equilibrium (10 million to 1 billion years) is comparable to the geologic time of a typical reservoir.
A number of authors have reported field experiences with compositional grading in gas/condensate reservoirs (Creek and Schrader 1985; Smith et al. 2004; Ghorayeb et al. 2003). Ordinarily, the equilibrium approach appears to explain gradients observed in the field. In reality, however, heat flux can potentially prevent attaining true equilibrium in a hydrocarbon column because of the temperature gradient in a reservoir (Pedersen and Lindeloff 2003; Hoier and Whitson 2001; Ghorayeb and Firoozabadi 2000a and 2000b; Firoozabadi 1999). Irreversible thermodynamics appears to explain compositional grading in most systems. In this study, we will assume that thermal diffusion does not play a dominant role in distributing hydrocarbon components in the fluid columns studied.
|File Size||3 MB||Number of Pages||13|
Abramowitz, M. and Stegun, I.A. 1964. Handbook of Mathematical FunctionsWith Formulas, Graphs, and Mathematical Tables. Washington, DC: NationalBureau of Standards Applied Mathematics Series #55, Department ofCommerce.
Beck, J.E. and Arnold, K.J. 1977. Parameter Estimation in Engineering andScience. Wiley Series in Probability and Mathematical Statistics.New York City: John Wiley and Sons.
Bevington, P.R. and Robinson, D.K. 1992. Data Reduction and ErrorAnalysis for the Physical Sciences. New York City: WCB/McGraw-Hill.
Brown, A. 2003. Improved Interpretation of Wireline Pressure Data. AAPGBulletin 87 (2): 295-311.
Creek, J.L. and Schrader, M.L. 1985. East Painter Reservoir: An Example ofa Compositional Gradient From a Gravitional Field. Paper SPE 14411presented at the SPE Annual Technical Conference and Exhibition, Las Vegas,Nevada, 22-26 September. DOI: 10.2118/14411-MS.
Firoozabadi, A. 1999. Thermodynamics of Hydrocarbon Reservoir, 58,New York City: McGraw-Hill.
Franks, S.G. and Forester, R.W. 1984. Relationships Among SecondaryPorosity, Pore-Filled Chemistry and Carbon Dioxide. Texas Gulf Coast. AAPGMemoir 32: 63-79.
Ghorayeb, K., Firoozabadi, A., and Anraku, T. 2003. Interpretation of the Unusual FluidDistribution in the Yufutsu Gas-Condensate Field. SPEJ 8 (2):114-123. SPE: 84953-PA. DOI: 10.2118/84953-PA.
Ghorayeb, K. and Firoozabadi, A. 2000a. Modeling Multicomponent Diffusion andConvection in Porous Media. SPEJ 5 (2): 158-171. SPE:62168-PA. DOI: 10.2118/62168-PA.
Ghorayeb, K. and Firoozabadi, A. 2000b. Numerical Study of Natural Convectionand Diffusion in Fractured Porous Media. SPEJ 5 (1): 12-20.SPE: 51347-PA. DOI: 10.2118/51347-PA.
Gray, A.E. 1978. User's Manual for API 14B, SSCSV Sizing ComputerProgram, 2nd ed. API, Appendix B, 38, Dallas: American PetroleumInstitute.
Hanafy, H.H. and Mahgoub, I.S. 2005. Methodology of Investigating theCompositional Gradient Within the Hydrocarbon Column. Paper SPE 95760presented at the SPE Annual Technical Conference and Exhibition, Dallas, 9-12October. DOI: 10.2118/95760-MS.
Hirschberg, A. 1988. Role ofAsphaltenes in Compositional Grading of a Reservoir's Fluid Column.JPT 40 (1): 89-94. SPE: 13171-PA. DOI: 10.2118/13171-PA.
Hoier, L. and Whitson, C.H. 2001.Compositional Grading?Theory andPractice. SPEREE 4 (6): 525-535. SPE: 74714-PA. DOI:10.2118/74714-PA.
Isobe, T., Feigelson E.D., Akritas, M.G., and Babu, G.J. 1990. LinearRegression in Astronomy, I. The Astrophysical J. 364:104-113.
Kabir, C.S. and Hasan, A.R. 2006. Simplified Wellbore Flow Modeling inGas/Condensate Systems. SPEPO 21 (1): 89-97. SPE: 89754-PA.DOI: 10.2118/89754-PA.
Kabir, C.S., Gorell, S.B., Portillo, M.E., and Cullick, A.S. 2007. Decision Making With UncertaintyWhile Developing Multiple Gas/Condensate Reservoirs: Well Count and PipelineOptimization. SPEREE 10 (3): 251-259. SPE-95528-PA. DOI:10.2118/95528-PA.
Larter, S.R., Aplin, A.C., Corbett, P.W.M. et al. 1997. Reservoir Geochemistry: A LinkBetween Reservoir Geology and Engineering? SPERE 12 (1):12-17. SPE: 28849-PA. DOI: 10.2118/28849-PA.
Lira-Galeana, C. 1992. Discussion of Treatment of Variations of Compositionwith Depth in Gas-Condensate Reservoirs. SPERE 7 (1): 158.
Lundegard, P.D. and Land, L.T. 1986. Carbon Dioxide and Organic Acids: TheirRole in Porosity Enhancement and Cementation,
Paleogene of the Texas Gulf Coast. In Roles of Organic Matter in SedimentDiagenesis (ed. D.L. Gautier) SEPM Spec. Publ. 38: 129-146.
Meisingset, M.M. 1999. Uncertainties in Reservoir FluidDescription for Reservoir Modeling. SPEREE 2 (5): 431-435.SPE: 57886-PA. DOI: 10.2118/57886-PA.
Montel, F. and Gouel, P.L. 1985. Prediction of Compositional Gradingin a Reservoir Fluid Column. Paper SPE 14410 presented the SPE AnnualTechnical Conference and Exhibition, Las Vegas, Nevada, 22-25 September. DOI:10.2118/14410-MS.
Montel, F., Bickert, J., Hy-Billiot, J., and Royer, M. 2003. Pressure and Compositional Gradientsin Reservoirs. Paper SPE 85668 presented at the Nigeria AnnualInternational Conference and Exhibition, Abuja, Nigeria, 4-6 August. DOI:10.2118/85668-MS.
Orear, J. 1982. Least Squares When Both Variables Have Uncertainties.American J. of Physics 50 (10): 912.
Pedersen, K.S. and Lindeloff, N. 2003. Simulations of CompositionalGradients in Hydrocarbon Reservoirs Under the Influence of a TemperatureGradient. Paper SPE 84364 presented at the SPE Annual Technical Conferenceand Exhibition, Denver, 5-8 October. DOI: 10.2118/84364-MS.
Peng, D-Y. and Robinson, D.B. 1976. A New Two-Constant Equation of State.Industrial Engineering Chemistry Fundamentals 15 (1):59-64.
PVTP user's manual. 2007. Petroleum Experts, Edinburgh, UK.
Riemens, W.G., Schulte, A.M., and de Jong, L.N.J. 1988. Birba Field PVT Variations Along theHydrocarbon Column and Confirmatory Field Tests. JPT 40 (1):83-88. SPE: 13719-PA. DOI: 10.2118/13719-PA.
Sage, B.N. and Lacey, W.N. 1939. Gravitational Concentration Gradients inStatic Columns of Hydrocarbon Fluids. Trans., AIME, 132:120-131.
Schlumberger, 1984. Paris: Application Document—Schlumberger RepeatFormation Tester.
Schoell, M., Jenden, P.D., Beeunas, M.A., and Coleman, D.D. 1993. Isotope Analyses of Gases in GasField and Gas Storage Operations. Paper SPE 26171 presented at the SPE GasTechnology Symposium, Calgary, 28-30 June. DOI: 10.2118/26171-MS.
Schulte, A.M. 1980. Compositional Variations Within aHydrocarbon Column Due to Gravity. Paper SPE 9235 presented at the SPEAnnual Technical Conference and Exhibition, Dallas, 21-24 September. DOI:10.2118/9235-MS.
Smith, R.W., Bard, W.A., Guerini, A., Lugo, C., and Yernez, I. 2004. Equation of State of a Complex FluidColumn and Prediction of Contacts in Orocual Field, Venezuela.SPEREE 7 (4): 297-307. SPE: 88869-PA. DOI:10.2118/88869-PA.
Stewart, G. and Ayestaran, L. 1982. The Interpretation of VerticalPressure Gradients Measured at Observation Wells. Paper SPE 11132 presentedat the SPE Fall Technical Conference and Exhibition, New Orleans, 26-29September. DOI: 11132-MS.
Wheaton, R. 1991. Treatment ofVariations of Composition With Depth in Gas-Condensate Reservoirs.SPERE 6 (2): 239-244. SPE: 18267-PA. DOI: 10.2118/18267-PA.