Richardson, W. C., M. K. Beladi, and C. H. Wu. "Steam Distillation Studies for the Kern River Field." SPE Reservoir Evaluation & Engineering 3, no. 01 (2000): 13–22. http://dx.doi.org/10.2118/60909-pa.
Abstract:
Summary The interactions of heavy oil and injected steam in the mature steamflood at the Kern River Field have been extensively studied to gain insight into the effect of steam on compositional changes of oil during the recovery process and to provide input for compositional thermal simulation. Steam distillation behavior of this 13°API California oil between 300 and 467°F under a variety of process conditions, along with extensive analysis of distilled hydrocarbons were incorporated to give a more in-depth description of what is happening to the oil and what changes are occurring in the distillates or produced oil. This information was further integrated with analysis of the field distillate, "casing blow," to infer what is happening in the field. The results show that steam distillation is temperature dependent and more important than originally thought. The data developed in this study are a basis for improvement of numerical thermal models with potential for better designed steamfloods and reservoir management. The results may also impact certain logging techniques used in steamfloods and possible heavy oil upgrading techniques. Kern River oil is more than 10% distillable at 300°F and 15% distillable at 400°F in dynamic laboratory steam distillation tests at steam throughputs of four times the initial volume of oil. Distillate physical properties of density, viscosity, molecular weight, and hydrocarbon composition of the distillates changed significantly. Distillate properties increased in value with increasing steam throughput, and at higher temperatures. This information is important in the tuning of equations of state, including hydrocarbon-water interaction parameters for compositional thermal simulation. Analysis of the field distillate, "casing blow," showed properties similar to laboratory distillates at low steam throughputs. The observation of a light field distillate production in a mature steamflood compared to laboratory measurements implies that the casing system temperature is a major controlling factor in "casing blow" composition and quantity. Background The phase equilibrium behavior of reservoir fluids is an important phenomenon in petroleum production, particularly in enhanced oil recovery processes. However, phase behavior for heavy oils (<15°API) under steamflood has generally been felt to be unimportant or a minimal effect to be neglected.1 A major question exists about whether the phases and fluids in a steamflood are in equilibrium or not. Proper modeling of a reservoir production process would be expected to include knowledge of the phases and their equilibrium compositions. In heavy oil, devoid of significant C1 to C6 composition, it has been sufficient to treat the oil as a dead oil or a nonvolatile phase for steamflood modeling purposes. A history match numerical study2 of steamflood performance in the Kern River Field treated the oil as nonvolatile, and was conducted without the inclusion of hydrocarbon compositional effects. Through the classic works of Willman et al.,3 Volek and Pryor,4 and Closmann and Seba,5 steam distillation has been shown to be an important component mechanism in the overall steamflooding process.6–10 The practical limit of how much of a reservoir fluid can be distilled, is obtained in dynamic steam distillation experiments developed by Brown and Wu,11,12 extended by Hseuh, Hong, and Duerksen,13,14 and refined by Wu and co-workers.15,16 This body of work demonstrates that steam distillation is an operative mechanism in laboratory models, but it has been difficult to translate this to a quantitative contribution to the field recovery process of steamflooding. Laboratory steam distillation experiments have generally been conducted as dynamic tests, that may or may not be near equilibrium. Experiments near equilibrium with extensive analysis of the phases will yield values for the vapor-liquid equilibrium (VLE) ratios (K values), another way of assessing the importance of compositional changes in steamflooding. A major recent steam distillation study by Northrup and Venkatesan17 has been completed on the South Belridge oil. Compositional data from simple distillation and laboratory steamfloods of oils in the range 13 to 33°API, including Kern River oil, has recently been reported.18 The current report is an extension of that work to include analyses of produced field samples for the Kern River steamflood. Compositional reservoir simulators demand greater emphasis on obtaining more crude oil compositional data, which would be used as input into an equation of state (EOS) or to calculate equilibrium ratios, K values. An appreciable amount of incremental oil19,20 could be recovered by steamflooding due to steam distillation depending on the composition of the crude oil. The present work establishes laboratory data to facilitate such efforts. The EOS approach and table look-up for two-phase K values are applied in thermal numerical simulation models, even though they do not fully represent three-phase separation (steam distillation). A three-component system approximation was used by Coats and Smart21 to incorporate steam distillation effects by adding water as a component in the vapor phase. The compositional variations due to steam distillation cannot be fully described by Coats' model. A difficulty in this model is the lack of three-phase laboratory steam distillation data for high-temperature and high-pressure conditions. A future goal of this research is to obtain three-phase laboratory steam distillation data to better understand the effects of water and its vapor on the hydrocarbon separation processes at high-temperature and high-pressure conditions. This includes the investigation on both the pure hydrocarbon component/water systems and crude oil/water systems. The three-phase equilibrium ratios or K values determined from these laboratory investigations are necessary to accurately describe the effects of steam distillation in mathematical reservoir simulation. Experiment Steam Distillation Cell and Procedures. In order to describe the existing laboratory procedures, Fig. 1 is presented. This experimental setup is used to perform three different types of tests:Static system pressure test (SPT).Dynamic distillation test (DDT).Stagewise isochoric distillation test (SWID). The experimental apparatus is composed of the injection assembly (Ruska pumps and the gas bottles), the distillation cell assembly, the withdrawal assembly (condenser, separator) and the automation/data acquisition assembly. The steam distillation apparatus has been extensively described elsewhere.22