Petroleum Geomechanics: Excursions Into Coupled Behaviour

Abstract Heavy oil will be a major future energy source as conventional oil production rates decline. Consideration of recent trends suggests that the next decade will see acceleration of heavy oil developments. The Canadian industry and governments should be consciously poised to take full advantage of these developments. In addition, because heavy oil development is geomechanically demanding, the role of petroleum geomechanics will be vital. Are popular rock mechanics paradigms complete? No; they generally fail to consider proper coupling to the stress and pressure fields, to physicochemical factors (as in shales), and to dynamic effects. Coupling the mechanical behaviour of the rock matrix with processes such as fluid flow, dynamic excitation, fabric liquefaction, and gas solution behaviour is one of the most important innovations taking place in petroleum geomechanics research. Ongoing developments include new models to describe dynamic pressure pulsing effects, new models to describe Cold Heavy Oil Production (CHOP), and new models for shale stability that include mechano-chemical coupling. Valuable practical applications have paralleled these developments. Introduction Are current petroleum rock mechanics paradigms complete? Do existing models account for all first-order effects? Are there applications areas that have been ignored or missed? Why is geomechanics becoming a more important enabling discipline, particularly for heavy oil? Does heavy oil even have a future? This article will briefly explore some of these questions. Conventional Oil, Heavy Oil A consensus has emerged that worldwide production of conventional oil will peak in the next decade(1). Thereafter, a gradual decline in light oil production will occur (Figure 1). The decline rate may be affected by new technologies such as gravity drainage and pressure pulsing. However, given the large amount of information on the world's sedimentary basins and the low probability of finding many large, easy-to-develop deposits, it is unlikely that the production decline will ever be reversed. In the past, there have always been new basins to explore; at present, there is at least seismic data on almost all of the world's sedimentary basins, if not exploratory wells and geochemical analysis. These data now allow reasonable bounds to be placed on the size distribution of undiscovered deposits in basins throughout the world. Simply put, we are running out conventional oil because we are running out of new basins. Furthermore, the difficulty of exploitation in difficult, remote basins (Antarctic fringe, Arctic basins, deep offshore) means that only the larger finds will be developed. Are we running out of energy or oil? No; only conventional oil is potentially in short supply. This is apparent for several reasons. First, over the span of centuries, new energy sources systematically displace previous ones (e.g., cow dung, wood, charcoal, coal, oil, nuclear, natural gas, solar, hydrogen cycle); this will happen with oil. Second, conventional oil represents only a small fraction of the hydrocarbon resources in basins (Table 1); technology developments and price will permit economic access to other HC resources. Third, if demand for oil continues indefinitely, oil can be made from natural gas or coal.