The tar sand and heavy oil deposits of Alberta and Saskatchewan represent a huge resource, most of which has to be recovered by in-situ methods, rather than surface mining. Oil viscosities are extremely high at normal reservoir temperatures and thermal methods of enhanced recovery, primarily steam injection and in-situ combustion, have been successfully employed on a pilot scale. Lithic sands in the Cold Lake area have been subjected to steam injection and pre- and post-steam cores are available for examination of mineral alteration reactions. A core from quartzose sands in the Lloyd-minster area, which was cut after in-situ combustion, is also available and the nature of the mineralogical reactions in these compositionally distinct rocks, subjected to a physically very different recovery scheme, can be compared and contrasted with the Cold Lake samples.
Important factors in controlling the extent of mineral alteration include the original composition and mineral distribution of the sands, the temperature and time of exposure to elevated temperature and the water-to-rock ratio. Oil recovery may be affected by mineral reactions if the timing is such that porosity-reducing reactions occur before there has been significant oil displacement. Mineral reactions may also increase porosity and produce CO2, both of which are potentially beneficial to ultimate oil recovery.
Figures & Tables
Clastic diagenesis has evolved from a very descriptive science to a much more process-oriented study. This evolution has been driven by the realization that many hydrocarbon reservoirs have significant diagenetic compotents directly affecting porosity and permeability characteristics. The prediction in time and space of reservoir characteristics affected by diagenesis can greatly reduce the risk in the search for hydrocarbon accumulations, particularly in subtle targets lacking pronounced structural expression. This publication contains three sections designed to increase understanding in the processes controlling clastic diagenesis: Conepts and Principles; Aspects of Porosity Modification; and Applications of Clastic Diagenesis in Exploration and Production. The first two sections deal with processes controlling various aspects of clastic diagenesis, and the third section applies these principles and observations to specific examples. Altogether, the three sections contain 22 chapters.