Journal of Unconventional Oil and Gas Resources最新文献

Source-rock reservoirs are fine-grained petroleum source rocks from which liquid and gaseous hydrocarbons may be produced following fracture stimulation. A major factor that allows such a source rock to function well as a reservoir is its organic matter – specifically the quantity, quality and thermal maturity of that organic matter as it occurs within the source-rock reservoir. Here we review the published literature to assess the current status of geochemical measurement and data interpretation of organic matter in these reservoirs, and how workers have applied this information in the exploration for this reservoir type. Our focus is on the chemical and geochemical characteristics of source-rock reservoirs, with emphasis on the isotopic and molecular characteristics of their hydrocarbon fluids and solid organic matter. Special consideration is given to geochemical analytical methods particularly appropriate to the organic matter in this reservoir type. Our discussions of published studies focus on three areas: (a) source rock characteristics – organic matter quantity, quality and maturity; (b) thermally-induced cracking of kerogen, oil, condensate and gas; and (c) natural gas stable carbon isotopic anomalies often observed in shale plays. Conceptual approaches and practical applications are addressed in equal measure, and our assessment of future directions and unsolved problems is provided.

The coal seam gas (CSG) industry is globally of potentially great importance economically. This study exemplifies the complex relationship between land use and management, groundwater impact and associated water treatment especially in relation to Queensland where a significant increase in the amount of gas extracted over the past 6 years has occurred. In order to effectively manage the environmental impact of the CSG industry it is necessary to appropriately understand the nature of the gas deposits, methods for gas collection, the physicochemical composition of the by-product associated water and the technologies available for water remediation. Australia is mainly considered arid and semi-arid and thus there is a need to not only beneficially reuse water resources but also protect existing ground water reservoirs such as the Great Artesian Basin (GAB). This paper focussed primarily on the Surat Basin located in Queensland and northern New South Wales. The mechanism for CSG formation, relation to local geological features, extraction approach and the potential impact/benefits of associated water was discussed. An outline of the current legislative requirements on physical and chemical properties of associated water in the Surat Basin was also provided, as well as the current treatment technologies used by the major CSG companies. This review was of significance in relation to the formulation of the most appropriate and cost effective management of associated water, while simultaneously preserving existing water resources and the environment.

Nigerian bitumen paraffinic hydrocarbon (PH) fraction was analyzed to establish the characteristics which might aid the developmental processes of the natural resource. Bitumen samples extracted from the oil sands were deasphalted and paraffinic hydrocarbons (PHs) eluted by column chromatography. The organic components of the PHs were investigated using Fourier transform infrared (FT-IR) spectrometry and Gas chromatography (GC); elemental concentration was determined using Atomic absorption spectrometry, while physical properties by standard methods. The IR spectra showed mainly the presence of CH(CH₃) and CH(CH₂) functional groups, indicating high purity of the samples. Thirty-one organic compounds were identified and quantified by GC. The PHs had a mean carbon preference index value of 1.035, indicating that the PHs were thermally matured and of petrogenic origin. Principal component analysis using the organics’ concentrations as variables indicated that the compounds had similar chemical properties, common sources, and/or maturation age. Elemental concentrations of the PHs were generally low compared with other fraction of Nigerian bitumen and were confirmed by their T-test values which indicated significant difference. Elemental cluster analysis showed two groups which were fairly correlated indicating similar sources and/or chemical affinity. The PHs V/Ni ratio 0.10–1.88 (1.12 was close to that of Nigerian bitumen 0.45–2.28 (1.12) which was higher than the average value (0.16) obtained for Nigerian crude oil, while V/V + Ni ratio 0.09–0.65 (0.50) obtained in this study is also close to 0.31–070 (0.50) obtained for Nigerian bitumen. Color of the PHs ranged from colorless to off-white. Values of the analyzed physical parameters confirmed that the PHs contained relatively high concentration of carbon and would tend to burn slower in the combustion chamber of an engine. The study also provided useful information on conversion mechanism and environmental implications of the development of the fossil fuel.

Natural gas hydrates have been investigated as a potential resource for commercially producing gas since the 1990s. Based on the latest available data for the Shenhu area of the South China Sea (SH7), a practical two-dimensional model has been constructed to investigate the gas production potential and the distributions of different physical properties in alternating formations by selecting a proper perforated interval favouring borehole stability and gas production. The effects of overburden and underburden permeability on gas production are intensively discussed. The simulation results indicate that the initial hydrate dissociation mainly occurs among the upper gas hydrate bearing-sediments (GHBS) with a high permeability but that in the later period, it is mainly distributed among the bottom low permeability GHBS. In addition, an obvious hydrate re-formation can be observed in the middle GHBS, and the dilution effect in the bottom low permeability GHBS is stronger than that in the upper space with high permeability. A comparative study showed that the GHBS in the Shenhu area with only one permeable burden (overburden or underburden) is not the most promising target for depressurisation.

Natural gas is a very important energy source. The production, processing and transportation of natural gas can be affected significantly by gas hydrates. Pipeline blockages due to hydrate formation causes operational problems and a decrease in production performance. This paper presents an improved artificial neural network (ANN) method to predict the hydrate formation temperature (HFT) for a wide range of gas mixtures. A new approach was used to define the variables for formation of a hydrate structure according to each species presented in natural gas mixtures. This approach resulted in a strong network with a precise prediction, especially in the case of sour gases.

This study also presents a detailed comparison of the results predicted by this ANN model with those of other correlations and thermodynamics-based models for an estimation of the HFT. The results showed that the proposed ANN model predictions are in much better agreement with the experimental data than the existing models and correlations. Finally, outlier detection was performed on the entire data set to identify any defective measurements of the experimental data.

Numerical model results of heavy oil production through multi-stage radio-frequency electromagnetic (RF EM) heating from a well after fracturing and re-fracturing operations are given in this paper. We consider the inflow of heavy oil to the well through two perpendicular fractures filled with propping agent. The conductivity of fractures is substantially greater than the conductivity of the reservoir but the dielectric and thermal properties of the reservoir and fractures are considered identical. In the expression used for heat distribution, a correction for near-field is introduced, which is shown to improve the accuracy of the temperature distribution around the well. The calculations for different powers of EM emitters and length of fractures are also considered and compared to the base case (cold oil) production.

In the work described in this paper, we developed simulations of methane production and supercritical carbon dioxide injection that consider competitive sorption of methane (CH₄) and carbon dioxide (CO₂) on both organic matter and the clay mineral montmorillonite. We used the results of these simulations to assess the potential for storage of CO₂ in a hydraulically fractured shale gas reservoir and for enhanced recovery of CH₄. Assuming equal volume fractions of organic matter and montmorillonite, amounts of CO₂ adsorbed on both materials were comparable, while methane desorption from clays was greater than desorption from organic material. CO₂ injection simultaneous to CH₄ production in two separate wells enhanced the contribution of methane desorption from 3535 to 6401 metric tons, while storing 82 metric kilotons of CO₂.

For decades, scientists and engineers have been investigating and describing storage and transport mechanisms in geological porous media such as reservoir rocks. This effort has resulted in the development of concepts such as single-phase and multi-phase flow, which describe the storage and transport of fluids in conventional reservoir rock types such as sandstones and carbonates. However, many of these concepts are not directly applicable to unconventional reservoirs. For example, shale gas reservoirs consist of organic-rich lithotypes, which have high compressibility, very small pore throats, low porosities and extremely low and anisotropic permeabilities, and relatively low gas storage capacities. The models developed to describe conventional reservoirs do not accurately describe the hydrocarbon transport processes involved in these rocks.

In this part A of the review paper, we aim to provide a concise and complete review on characterizing the fluid transport processes in unconventional reservoirs. We will examine processes occurring at various spatial scales, ranging from fracture flow on the centimeter scale down to slip-flow on the nanometer scale. Due to the softer nature of tight shales, many processes, such as slip-flow and the pore-throat compressibility, will have to be considered as coupled. We also develop a detailed description of the coupling between slip-flow, which is a fluid dynamic effect, and the pore-throat compressibility, which is a poroelastic effect, in unconventional reservoirs, and interpret experimental observations in light of this description.

Furthermore, we discuss in detail how these transport properties depend on organic content, clay content and type, amount of pre-adsorbed water and pore compressibility.