Some Experiences With a Critical Reservoir Fluid

Abstract

Some Experiences With a Critical Reservoir Fluid W.W. Huang W.W. Huang Unocal Science and Technology Div., Unocal Corp. Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Las Vegas, Nevada, September 1985. Paper Number: SPE-14415-MS https://doi.org/10.2118/14415-MS Published: September 22 1985 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Huang, W.W. "Some Experiences With a Critical Reservoir Fluid." Paper presented at the SPE Annual Technical Conference and Exhibition, Las Vegas, Nevada, September 1985. doi: https://doi.org/10.2118/14415-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 SPE MemberAbstractFluid properties and composition in a naturally occurring near critical reservoir show significant variations between samples. Highly undersaturated volatile oil and rich condensate gas coexist in the same reservoir without a gas-oil contact. Producing gas-oil ratios (GOR) at undersaturated Producing gas-oil ratios (GOR) at undersaturated reservoir conditions have been observed to vary up to more than two fold among wells. An equation of state (EOS) reservoir simulator was used to predict performance of nitrogen injection into this performance of nitrogen injection into this reservoir where fluid variation is the rule, not the exception. Phase behavior of the fluid samples predicted by the EOS is sensitive to their plus predicted by the EOS is sensitive to their plus fraction characterizations. Estimated characterization parameters such as Watson's factor and Whitson's molar distribution parameter a differ among the reservoir samples. Values of these characterization parameters decline generally with producing GOR of the sampled well, indicating producing GOR of the sampled well, indicating richer fluids tend to be more paraffinic and higher in heavier components. Variations in heptanes plus (C7+) properties correlate better with product GOR than with depth. Saturation pressure does not exhibit clear correlations with GOR or depth. It is difficult to explain by the qravity- thermodynamic equilibrium theory of Schulie and Hirschberg'. To account for observed GOR variation in the field, reservoir fluids are thought to vary areally rather than vertically in the oil/gas column.An EOS tuned for one sample usually gives unsatisfactory predictions of phase behavior of other samples. Describing these property variations and the effect of injected nitrogen with an EOS becomes a challenging task. This study uses calculated Watson characterization factor in regression to improve the match of extensive PVT cell data and to treat changing fluid characterization. This procedure was found to improve the PVT match procedure was found to improve the PVT match significantly when the common regression practices yield unsatisfactory results and extended analyses of the plus fraction are unavailable.This paper addresses compositional grading occurred in the near-critical reservoir and a method to account for it in an EOS reservoir model. Interfacial tension effects associated with the critical fluid are also discussed briefly.IntroductionNumerous references have appeared in recent years about methods of phase equilibrium calculation suitable for near-critical conditions. However, very few naturally occurring reservoir fluids were reported to date as close to critical point. It is well known that near critical point. It is well known that near critical conditions, including those for multiple contact miscability, impose numerous problems on flash calculations and saturation pressure determination. Numerical problems include, for example, slow convergence rates, false solutions, and for Newton Raphson's method, sensitivity to the initial estimate. Alonso and Nectoux reported a rich condensate gas reservoir, whose temperature is 13 degrees F from its critical temperature. They investigated interfacial tension (IFT) reduction as the critical point is approached. No composition variation with depth was indicated. The Statfjord reservoir fluid in the Brent field is believed to exhibit variation in composition and properties, such that changing critical properties, such that changing critical temperatures cross over the reservoir temperature. Hirschberg derives thermodynamic conditions for strong segregation which accounts for compositional grading with depth. He found that light oils showing significant compositional grading will be close to critical conditions. Keywords: saturation pressure, specific gravity, critical point, fraction, fluid variation, composition, calculation, equation, correlation, gor Subjects: Fluid Characterization, Phase behavior and PVT measurements This content is only available via PDF. 1985. Society of Petroleum Engineers You can access this article if you purchase or spend a download.