The host rocks of shale gas accumulations act as source, seal and reservoir. They are characterized by complex pore systems with ultra-low to low interparticle permeability and low to moderate porosity. The word "shale" is used in the sense of a geological formation rather than a lithology, so shale gas reservoirs can show marked variations in rock type from claystones, marlstones and mudstones to sandstone and carbonate lithological "sweet spots". The pore space includes both intergranular and intrakerogen porosity. The density of natural fractures varies markedly, and pore throat connectivity is relatively ineffective. Moreover, in-situ gas pore volume has to take account of both free and adsorbed gas, an evaluation exercise that is complicated by pronounced variations in water salinity. All these characteristics present major challenges to the process of petrophysical evaluation. The petrophysical responses to these issues are several fold. First, a broader calibrating database of core measurements is required at key wells, especially as regards mineralogy, porosity and permeability data, tight rock analyses, total organic carbon, gas desorption isotherms, and the analysis of extracted formation waters. Second, at least in the key wells, an extended suite of logs should include an elemental analysis log, magnetic resonance imager, electrical micro-imager, and a dipole sonic log. These databases lead to a populating electrofacies scheme that takes better account of dynamic properties and fracturability. They also allow reservoir partitioning based on exclusivity of empirical interpretive algorithms, e.g. quartz content vs. producibility. These responses comprise key elements of a functional petrophysical system that encompasses fit-for-purpose interpretation methods such as a pseudo-Archie approach. This system is presented as a workflow for application in shale gas reservoirs. The benefits are especially strong in reserves reporting of these unconventional gas reservoirs. Introduction In contemporary petrophysical parlance, there are two types of reservoir: those that conform to the implicit assumptions underpinning the work of Archie (1942) and those that do not. The second category includes most of the World's reservoirs. It can be subdivided further into non-Archie conventional reservoirs and unconventional reservoirs (Worthington 2011a). Non-Archie conventional reservoirs include those with fresh formation waters, significant shale content, high capillarity, a bimodal pore system, or fractures. In other words, they infringe one or more of the Archie assumptions. Unconventional reservoirs include tight gas sands, coal seam gas reservoirs, gas hydrates, and shale gas reservoirs. Each of these infringes several of the Archie assumptions. At the limit, shale gas reservoirs infringe them all (Table 1). Yet, the interpretive challenges presented by shale gas reservoirs go even further, because gas-bearing shale deposits co-function as source, seal and reservoir. Therefore their character contains elements of all three. Thus, for example, shale gas deposits contain kerogen porosity, have very low effective permeability to gas, and yet can show a markedly variable pore character. To be successful, a petrophysical methodology for the evaluation of shale gas deposits has to be founded on approaches that sit outside the conventional range of thinking. This paper presents a synthesis of the technical challenges that face shale gas petrophysics and collates practical solutions based on what is currently known.

The host rocks of shale gas accumulations act as source, seal and reservoir. They are characterized by complex pore systems with ultra-low to low interparticle permeability and low to moderate porosity. The word ‘shale’ is used in the sense of a geological formation rather than a lithology, so shale gas reservoirs can show marked variations in rock type from claystones, marlstones and mudstones to sandstone and carbonate lithological ‘sweet spots’. The pore space includes both intergranular and intrakerogen porosity. The density of natural fractures varies markedly, and pore throat connectivity is relatively ineffective. Moreover, in-situ gas pore volume has to take account of both free and adsorbed gas, an evaluation exercise that is complicated by pronounced variations in water salinity. All these characteristics present major challenges to the process of petrophysical evaluation. The petrophysical responses to these issues are severalfold. First, a broader calibrating database of core measurements is required at key wells, especially as regards mineralogy, porosity and permeability data, shale/mudstone sample analyses, total organic carbon, gas desorption isotherms, and the analysis of extracted formation waters. Second, at least in the key wells, an extended suite of logs should include an elemental analysis log, magnetic resonance imager, electrical micro-imager, and a dipole sonic log. These databases lead to a rock-typing scheme that takes better account of dynamic properties and fracturability. They also allow reservoir partitioning based on exclusivity of empirical interpretative algorithms, e.g. quartz content vs. producibility. These responses comprise key elements of a functional petrophysical system that encompasses fit-for-purpose interpretation methods, such as a pseudo-Archie approach, i.e. the application of the Archie equations with non-intrinsic exponents. This system is presented as a workflow for application in shale gas reservoirs, for which bulk density retains a major influence on computed gas in place. The benefits of this approach are especially strong in reserves reporting of these unconventional gas reservoirs.

Potential applications of oil sands industry wastesMajid, A.; Kotlyar, L.; Sparks, B. D.

No abstract

An improved suspension-firing reactor has been constructed and a new experimental procedure developed that is able to assess the relative performances of coals and coal blends. The method measures the total combustion time of the samples by measuring the exit gas analysis from the reactor on a continuous basis. The new equipment and procedure overcome some deficiencies that were identified in an earlier suspension-firing method that was based on the extent of burnout of the sample at the end of an arrested combustion test. The presence of a synergistic effect on blending is indicated by a difference between the actual performance of the blend and that predicted by additivity from the performance of the individual coals and the composition of the blend. Three sets of binary blends and their parent coals, which have also been used in utility pf furnaces, have been tested in the suspension-firing reactor. The results have been compared with the performance at the commercial scale, as indicated by the C content of the electrostatic precipitator fly ashes. In all three cases, the performance as predicted by the suspension-firing reactor was consistent with that observed at the commercial scale. This suggests that this relatively straightforward small scale test may provide a useful route for the assessment of coals prior to purchase and for the optimization of blend performance.