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Abstract A general method has been developed to compute steam distillation yield and to quantify oil quality changes during steam injection. It was found that steam distillation data from the literature can be correlated with the steam distillation yield obtained from the DOE crude oil assays. The common basis for comparison was the equivalent normal boiling point. Blending of distilled components with the initial oil results in API gravity changes similar to those observed in several laboratory and field operations.
Introduction In steam injection the principal mechanisms responsible for additional oil recovery are thermal expansion of oil, visosity reduction and steam distillation. Steam distillation yields can be significant, even for heavy crudes. In reservoirs containing light oil, steam distillation is the major mechanism contributing towards improved recovery.
Steam distillation is the main mechanism which reduces the residual oil saturation behind the hot water front during a steamflood. At a given steam injection pressure or temperature, the residual oil saturation is essentially composition dependent. An increase of 2 degrees to 4 degrees API in the gravity of produced oil has been observed both during laboratory produced oil has been observed both during laboratory experiments and field tests. The residual oil in the steam zone has a high content of heavy components. Similar observations have been made during in-situ combustion field tests.
A major objective of this study is to investigate changes in quality of produced oil compared to the initial oil. Existing laboratory and field data will be interpreted in the light of the findings.
Quantification for oil quality changes during steam injection requires understanding of the major phenomena associated with the process. Steam distills lighter components, leaving behind heavier residuum. Blending of the lighter distilled components with the initial oil results in produced oil with higher API gravity. The main objective is to quantify these phenomena. For a given steam distillation condition, questions which phenomena. For a given steam distillation condition, questions which should be answered are:
* What is the steam distillation yield?* What is the quality or API gravity of the distillate?* How much heavier does the residuum become?* What API gravity change can be expected when the distilled components are mixed with the initial oil?
The Department of Energy (DOE) Crude Oil Analysis Data Bank will serve as the main source of information. A basis of correlating the DOE data with steam distillation data will be established. The results will be verified by comparison with experimental data published in the literature.
DISTILLATION DATA The DOE Crude Oil Analysis Data Bank contains crude oil assays for all major reservoirs in the United States. These crude oil analyses were obtained by the Bureau of Mines routine method distillation. Table 1 shows the distillation cuts and the calculated equivalent normal boiling points (ENBP).
Data from 454 California crude oil samples from the DOE Crude Oil Data Bank were analyzed. Fig. 1 shows the cumulative distillation yield as a function of API gravity for Cut Number 12. The distillation temperature is 437 degrees F at a pressure of 40 mmHg. The ENBP is 635 degrees F. A linear relation was pressure of 40 mmHg. The ENBP is 635 degrees F. A linear relation was found to fit the data:
(1)
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