Shell Canada has experienced significant deposition of solid sulfur during the production of dry sour gas from several of its deep carbonate pools located in Southern Alberta. In several cases, wells have become completely plugged with sulfur in the reservoir within several months. Accurate prediction and effective management of the sulfur deposition are crucial to the economic viability of these fields. A new analytical model has been developed for predicting sulfur deposition associated with sour gas production in naturally fractured reservoirs. Key features of the model include incorporation of reservoir temperature profiles and the concept of critical velocity, which accounts for dynamic effects, resulting in a zone of reduced deposition close to the wellbore. The model has been used to successfully match and predict sulfur deposition in several sour gas producers. The modeling results have been used as a design basis for downhole sulfur treatments and clean-out operations, the optimization of well completions and off-take rates to minimize the impact of sulfur deposition, and the development of new well designs and operating strategies for sulfur producers.

CO2 is one of the hazardous greenhouse gases causing significant changes to the environment. The sequestering of CO2 in a suitable geological media can be a feasible method to avoid the negative effects of CO2 emissions into the atmosphere. A numerical model was developed regarding CO2 sequestration in a deep saline aquifer. A compositional numerical model using CMG software (GEM) was employed to study the ability of the selected aquifer to accept and retain large quantities of CO2 injected in a supercritical state for long periods of time (up to 200 years). Supercritical CO2 is a one-state fluid which exhibits both gas- and liquid-like properties. In this study, supercritical CO2 was sequestered in three forms in a deep saline aquifer. It was assumed to be supplied in an isothermal condition during the injection and sequestration processes and we ignored porosity and permeability changes due to mineralization. Also, CO2 adsorption was not considered in our numerical model. Gas bubble formation, dissolution of CO2 in brine and precipitation of CO2 with calcite mineral in aquifers have been discussed. The CO2 gas bubble displaces the formation water with immiscible behaviour. During and after displacement, the gravitational effects cause the CO2 to rise and accumulate under the caprock. Both vertical and horizontal permeability ratios and initial pressure conditions were the most dominating parameters affecting CO2 saturation in the three layers, whereas the CO2 injection rate influenced CO2 saturation in layers two and three since CO2 was injected from layer three at the bottom of the reservoir. Introduction CO2 sequestration is the capture of, separation and long-term storage of CO2 in underground reservoirs for environmental purposes. CO2 is one of the hazardous greenhouse gases causing significant changes in global temperature and sea levels(1), which could have negative consequences for people in many parts of the world. Scenarios for stabilizing atmospheric CO2 at reasonable levels will eventually require substantial cuts in overall emissions over the next few decades(1,2). If usage of fossil fuels is to continue at current levels while avoiding undesirable climate change, technical means need to be found to reduce the carbon dioxide emitted to the atmosphere in the production and consumption of fossil fuels(3). CO2 sequestration can be regarded as one possible solution for reducing CO2 emissions in a form where they will not reach the atmosphere. Disposal environments for CO2 sequestration can be divided into four different categories. Oceans, terrestrial basins, a biological environment and geologic formations are the candidates for the disposal of CO2. Among these alternatives, geologic formations can be regarded as the best possible environment to sequester CO2 because of the fact that the storage of CO2 in geologic formations is a self-containing and volumetrically efficient process. In geologic formations, CO2 can be sequestered in porous or non-porous media. Depleted oil and gas reservoirs, aquifers and coal beds can be categorized as porous media, whereas salt caverns and lined rock caverns can be regarded as types of non-porous media.

Enormous volumes of gas (.30 Tcf ) are contained within the deepest portions of the Western Canada Foreland Basin, where tight gas-saturated Cretaceous sandstones grade updip into porous water-saturated sandstones. Production has occurred from coarse-grained shoreline sands both near the updip gas-water interface, such as those found in the Elmworth Field, and from low-porosity-permeability reservoirs found deeper in the basin. These basin-centred gas (BCG) reservoirs are characterized by regionally pervasive gas-saturated lithologies, abnormal pressures and no downdip water contact, and occur in low-permeability reservoirs. The keys to Shell's exploration success were an understanding of the stratigraphy, sedimentology and rock properties of the basin, the development of structural, petrophysical and geomechanical models, development of an understanding of the desiccation or dewatering process, the distribution of water within the basin and how the pressure regime evolved, interpretation of 3D seismic, and an aggressive land strategy. The evaluation of structural leads was aided when seismic and geomechanical modelling were combined, thereby aiding in the prediction of zones with a higher probability of encountering favourable reservoir producibility characteristics, that is, areas where a well developed, well connected open fracture network is expected. This multidisciplinary approach has resulted in economic success in regions once thought to be non-productive, and where it was once said, 'People go broke chasing the Nikanassin'.

In the current high oil / low gas price North American environment, and considering the new options available for well completions technology in unconventional reservoirs, recent industry activities have turned their focus to the areas of Liquid Rich Shales (LRS) and Light Tight Oil (LTO) along with unconventional tight and shale gas (UG). Integrated workflows are important to the successful execution of this portfolio, i.e. systematic methodologies to screen and appraise opportunities, and cutting edge integrated technologies must be viewed as key enablers. It is also important to maintain a life-cycle mindset and leverage economies of scale to execute projects faster and more efficiently. This paper will discuss some of the advances and best practices that Shell has in each of the following disciplines, the value of R&D and applied technologies as well as integrated workflows used for exploration, appraisal and development of UG, LRS, and LTO plays: • Geological screening and sweet-spotting • Geomechanics evaluation and modeling • Reservoir engineering, including PVT sampling and characterization • Completions, stimulations and diagnostics • Artificial lift and operational considerations