Abstract

Shell Oil Company conducted an oil shale thermal conduction pilot in the Piceance Basin of Colorado during 1997 and 1998. Six heaters and one producer were arranged in a single unconfined hexagonal seven spot pattern to test the viability of the Shell's proprietary in-situ conversion process (ICP) in oil shale under field conditions and to substantiate the in-house experiments that produced high quality crude. The pilot succeeded in meeting all of the intended objectives. The history match of the production data, however, encountered some technical challenges and hindered the full interpretation of test results.

This paper presents the results and findings of a new history match study of the pilot. This simulation succeeded in achieving a good match of the production data by the identification of (1) borehole reflux heat loss, and (2) production impairment from scale build-up and the proper adjustment of well skin effects in the model. It also confirmed that the ICP performance observed in laboratory could be used as a good proxy for ICP in field.

Introduction

The Green River formation in Colorado, Utah and Wyoming, USA is the largest oil shale basin in the world. It has been estimated that oil resource within the Green River formation is in the range of 500 to 1,100 billion barrels of recoverable oil using a cut-off of 15 gallons per ton (gpt) (Bartis, 2005). The Piceance Basin in Colorado is the largest single deposit in the Green River formation accounting for two-thirds of the Green River oil shale resource. In the heart of the Piceance Basin, oil shale thickness exceeds 1000 ft and has an average richness of 25 gpt resulting in a resource density of up to 2.5 million barrels per acre (Figure 1) (Picha et al., 2008). That is by far the most dense hydrocarbon resource in the world (Dammer, 2005).

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