Thermal Alterations of Asphaltenes in Peace River Tars

Abstract

ABSTRACT In 1973-74 Shell Canada Limited and Shell Explorer Limited conducted a steam injectivity and productivity test in the Peace River Bullhead sand.1 The test comprised several phases. Cold production was started on September 12, 1973. Steam injection into the same well commenced on November 29, 1973 and ended on February 6, 1974. After a 54-day soak period, backflow began on April 1, 1974 and ended on October 1, 1974. A total of 122,000 barrels of steam were injected at rates as high as 2366 B/D at less than fracturing pressure. After 175 days of back-flowing, approximately 29,900 barrels of tar were produced at an oil/steam ratio of 0.23. Temperatures as high as 311°C (591°F) were observed in the formation. On the basis of results from this test, an expanded pilot has been proposed for Peace River.2,3 In support of the above effort, laboratory work was undertaken in order to obtain mobility data for Peace River tar in its parent core material at temperatures and stress conditions simulating reservoir zones downstream of a steam condensation front. Because of possible effects on flow properties, the asphaltene and maltene components of produced tars were examined. Both the quantity and degree of thermal alteration of the asphaltenes were considered, in order to assess the influence of these factors on observed flow behavior. Based on information learned in these studies, a series of flow experiments was undertaken and will be reported in our following paper.4 Mineral-free tar was obtained from Peace River core material by means of separation procedures which minimized compositional changes of the native tar. Experimental extraction procedures and resulting tar properties for Batches 1, 2, and 5 are described in Reference 4. The maximum temperature to which these extracted tars were exposed was 70°C (158°F).