Guidelines for Choosing Compositional and Black-Oil Models for Volatile Oil and Gas-Condensate Reservoirs (2000)

Guidelines for Choosing Compositional and Black-Oil Models for Volatile Oil and Gas-Condensate Reservoirs Øivind Fevang; Øivind Fevang PERA Search for other works by this author on: This Site Google Scholar Kameshwar Singh; Kameshwar Singh NTNU Search for other works by this author on: This Site Google Scholar Curtis H. Whitson Curtis H. Whitson NTNU/PERA Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 2000. Paper Number: SPE-63087-MS https://doi.org/10.2118/63087-MS Published: October 01 2000 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Fevang, Øivind, Singh, Kameshwar, and Curtis H. Whitson. "Guidelines for Choosing Compositional and Black-Oil Models for Volatile Oil and Gas-Condensate Reservoirs." Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 2000. doi: https://doi.org/10.2118/63087-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractThis paper provides specific guidelines for choosing the PVT model, black-oil or equation of state (EOS), for full-field reservoir simulation of volatile/near-critical oil and gas condensate fluid systems produced by depletion and/or gas injection.In the paper we have used a "generic" reservoir from the North Sea containing a fluid system with compositional grading from a medium-rich gas condensate upstructure, through an undersaturated critical mixture at the gas-oil contact, to a volatile oil downstructure.A component pseudoization procedure is described which involves a stepwise automated regression from the original 22-component EOS. We found that a six-component pseudoized EOS model described the reservoir fluid system with good accuracy and, for the most part, this EOS model was used in the study.Methods are proposed for generating consistent black-oil PVT tables for this complex fluid system. The methods are based on consistent initialization and accurate in-place surface gas and surface oil volumes when compared with initialization with an EOS model. We also discuss the trade-off between accurate initialization and accurate depletion performance (oil and gas recoveries).Each "reservoir" is simulated using black-oil and compositional models for various depletion and gas injection cases. The simulated performance for the two PVT models is compared for fluid systems ranging from a medium rich gas condensate to a critical fluid, to slightly volatile oils. The initial reservoir fluid composition is either constant with depth or exhibits a vertical compositional gradient. Scenarios both with saturated and undersaturated GOC are considered. The reservoir performance for the two PVT models is also compared for different permeability distributions.Reservoir simulation results show that the black-oil model can be used for all depletion cases if the black-oil PVT data are generated properly. In most gas injection cases, the black-oil model is not recommended—with only a few exceptions.We also show that black-oil simulations using solution oil/gas ratio equal to zero (rs=0) does not always define a conservative ("P10") sensitivity for gas injection processes. If gravity segregation is strong, the incremental loss of oil recovery due to "zero vaporization" is more than offset by exaggerated density differences caused by erroneous gas densities.IntroductionReservoir simulation is a versatile tool for reservoir engineering. Usually CPU-time is the limiting factor when the simulation model is made. The objective of this paper is to provide guidelines for choosing black-oil or compositional reservoir simulators. The paper also recommends procedures for generation of black-oil PVT tables and for initialization of black-oil and pseudoized EOS simulation models. Furthermore, a stepwise component pseudoization procedure in order to minimize the number of component when a compositional simulator is required.Simulated production performance both for injection and depletion from black-oil and compositional are compared for a variety of reservoir fluids ranging a medium rich gas condensate to a critical fluid, to slightly volatile. Both reservoirs with constant composition and compositional grading reservoir with depth have been simulated.Selection of Reservoir Fluid SystemA fluid sample was selected from a North Sea field. The reservoir is slightly undersaturated with an initial reservoir pressure of 490 bara at the "reference" depth of 4640 m MSL. The selected reference sample contains 8.6 mol-% C7+, it has a two-stage GOR of 1100 Sm3/Sm3 and a dewpoint of 452 bara at 163°C. Table 1 gives the reference fluid composition (Fig. 1).22-Component SRK EOS ModelThe Pedersen et al. SRK1 EOS characterization method was used to generate the "base" EOS model. Decanes-plus was split into 9 fractions using the EOS simulation program PVTsim. Keywords: reservoir simulation, compositional gradient, black-oil pvt table, eos model, volatile oil, black-oil model, production rate, experiment, pvt measurement, recovery Subjects: Fluid Characterization, Reservoir Simulation, Phase behavior and PVT measurements This content is only available via PDF. 2000. Society of Petroleum Engineers You can access this article if you purchase or spend a download.