Tight gas sands, coal-bed methane, and gas shales are commonly called unconventional reservoirs. Tight gas sands (TGS) are often described as formations with an expected average permeability of 0.1mD or less. Gas production rates from TGS reservoirs are usually low due to poor permeability. As such, state-of-the-art technology must be used to economically develop the resource. TGS formations need to be hydraulically fractured in order to enhance the gas production rates. A majority of these reservoirs can be described as thick, multilayered gas systems. Many reservoirs are hundreds of feet thick and some are thousands of feet thick. The technology used to complete and stimulate thick, tight gas reservoirs is quite complex. It is often difficult to determine the optimum completion and stimulating techniques in thick reservoirs. The optimum methods are functions of many parameters, such as depth, pressure, temperature, in-situ stress and the number of layers. In multilayered reservoirs, it is important to include several sand layers in a single completion. The petroleum literature contains information on the various diversion techniques involved in the completion of these multilayered reservoirs. In this research, we have deduced and evaluated eight possible techniques that have been used in the oil and gas industry to divert multilayered fracture treatments in layered reservoirs. We have developed decision charts, economic analyses and computer programs that will assist completion engineers in determining which of the diversion methods are feasible for a given well stimulation. Our computer programs have been tested using case histories from the petroleum literature with results expressed in this thesis. A limited entry design program has also being developed from this research to calculate the fluid distribution into different layers when fracture treating multilayered tight gas reservoirs using the limited entry technique. The research is aimed at providing decision tools which will eventually be input into an expert advisor for well completions in tight gas reservoirs worldwide.

Reserves estimation in unconventional (low/ultra-low permeability) reservoirs has become a topic of increased interest as more of these resources are being developed, especially in North America. The estimation of reserves in unconventional reservoirs is challenging due to the long transient flow period exhibited by the production data. The use of conventional methods (i.e., Arps' decline curves) to estimate reserves is often times inaccurate and leads to the overestimation of reserves because these models are only (theoretically) applicable for the boundary-dominated flow regime. The premise of this work is to present and demonstrate a methodology which continuously estimates the ultimate recovery during the producing life of a well in order to generate a time-dependent profile of the estimated ultimate recovery (EUR). The "objective" is to estimate the final EUR value(s) from several complimentary analyses. In this work we present the "Continuous EUR Method" to estimate reserves for unconventional gas reservoirs using a rate-time analysis approach. This work offers a coherent process to reduce the uncertainty in reserves estimation for unconventional gas reservoirs by quantifying "upper" and "lower" limits of EUR prior to the onset of boundary-dominated flow. We propose the use of traditional and new rate-time relations to establish the "upper" limit for EUR. We clearly demonstrate that rate-time relations which better represent the transient and transitional flow regimes (in particular the power law exponential rate decline relation) often lead to a more accurate "upper" limit for reserves estimates — earlier in the producing life of a well (as compared to conventional ("Arps") relations). Furthermore, we propose a straight line extrapolation technique to offer a conservative estimate of maximum produced gas which we use as the "lower" limit for EUR. The EUR values estimated using this technique continually increase with time, eventually reaching a maximum value. We successfully demonstrate the methodology by applying the approach to 43 field examples producing from 7 different tight sandstone and shale gas reservoirs. We show that the difference between the "upper" and "lower" limit of reserves decreases with time and converges to the "true" value of reserves during the latter producing life of a well.

Tight gas reservoirs are those reservoirs where the matrix has a low permeability range (k < 0.1 md). The literature documents laboratory experiments under restressed conditions that show stress dependent rock properties are more significant in tighter rocks. For gas reservoirs, real gas properties are also sensitive to variations of pressure, and the correct description of gas flow must include pressure-dependent gas properties. Under these circumstances the resulting equation for real gas flow is a second order, non-linear, partial differential equation. Non-linearities include pressure-dependence of gas viscosity, gas compressibility, reservoir permeability and reservoir porosity. This paper investigates dynamic permeability change as a function of net overburden stress in tight gas reservoirs. The gas reservoir simulator used for this work included pressure-dependent reservoir permeability. Radial flow cases are analyzed using this simulator. During this study we found that from analysis of production data alone, it is impossible to determine the correct permeability value for tight gas reservoirs with pressure-dependent permeability. For the cases studied, the transient performance was similar for both constant permeability and pressure-dependent permeability. This similarity causes constant permeability and pressure-dependent permeability to be indistinguishable, based on analysis of transient performance data. It was found that the productivity index decreases when pressure-dependent permeability is more significant. Finally, this study verified that the method of Ibrahim et al.28 under estimates original gas in place (OGIP) for tight gas reservoirs with pressure-dependent permeability.

As the demand for energy worldwide increases, the oil and gas industry will need to increase recovery from unconventional gas reservoirs (UGR). UGRs include Tight Gas Sand (TGS), coalbed methane and gas shales. To economically produce UGRs, one must have adequate product price and one must use the most current technology. TGS reservoirs require stimulation as a part of the completion, so improvement of completion practices is very important. We did a thorough literature review to extract knowledge and experience about completion and stimulation technologies used in TGS reservoirs. We developed the principal design and two modules of a computer program called Tight Gas Sand Advisor (TGS Advisor), which can be used to assist engineers in making decisions while completing and stimulating TGS reservoirs. The modules include Perforation Selection and Proppant Selection. Based on input well/reservoir parameters these subroutines provide unambiguous recommendations concerning which perforation strategy(s) and what proppant(s) are applicable for a given well. The most crucial parameters from completion best-practices analyses and consultations with experts are built into TGS Advisor's logic, which mimics human expert's decision-making process. TGS Advisor's recommended procedures for successful completions will facilitate TGS development and improve economical performance of TGS reservoirs.

Tight gas sands, coal-bed methane, and gas shales are commonly called unconventional reservoirs. Tight gas sands (TGS) are often described as formations with an expected average permeability of 0.1mD or less. Gas production rates from TGS reservoirs are usually low due to poor permeability. As such, state-of-the-art technology must be used to economically develop the resource. TGS formations need to be hydraulically fractured in order to enhance the gas production rates. A majority of these reservoirs can be described as thick, multilayered gas systems. Many reservoirs are hundreds of feet thick and some are thousands of feet thick. The technology used to complete and stimulate thick, tight gas reservoirs is quite complex. It is often difficult to determine the optimum completion and stimulating techniques in thick reservoirs. The optimum methods are functions of many parameters, such as depth, pressure, temperature, in-situ stress and the number of layers. In multilayered reservoirs, it is important to include several sand layers in a single completion. The petroleum literature contains information on the various diversion techniques involved in the completion of these multilayered reservoirs. In this research, we have deduced and evaluated eight possible techniques that have been used in the oil and gas industry to divert multilayered fracture treatments in layered reservoirs. We have developed decision charts, economic analyses and computer programs that will assist completion engineers in determining which of the diversion methods are feasible for a given well stimulation. Our computer programs have been tested using case histories from the petroleum literature with results expressed in this thesis. A limited entry design program has also being developed from this research to calculate the fluid distribution into different layers when fracture treating multilayered tight gas reservoirs using the limited entry technique. The research is aimed at providing decision tools which will eventually be input into an expert advisor for well completions in tight gas reservoirs worldwide.

Universiẗat, FB Chemie, Diss.--Hamburg, 2005. / Auch als elektronische Ressource. Zsfassung in engl. Sprache.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves.

As devise sizes approach the nanoscale, novel device geometries and materials are considered, and new types of essential physics becomes important and new physical switching mechanism are considered, and as our intuitive understanding of device behavior is stretched accordingly, increasing first-principles simulation is required to understand and predict device behavior. To this end, initially I worked to capture the richness of the confinement and transport physics in quantum-wire devices. I developed an efficient fully three dimensional atomistic quantum transport simulator within a nearest-neighbor atomistic tight-binding framework. However, I soon adapted this work to the study of transport in graphene mono-layer and bilayer nano-ribbons. Motivated by proposals for use of nano-ribbons to create band gaps in otherwise gapless graphene monolayers, I studied the effects of edge disorder in such graphene nano-ribbon FETs. I found that ribbon widths sufficiently narrow to produce useful bandgaps, would also lead to an extreme sensitivity to ribbon-edge roughness and associated performance degradation and device-to-device variability. Going beyond conventional switching but staying with the graphene material system, to model electron-hole condensation in two graphene monolayers separated by a tunnel dielectric potentially beyond room temperature, I developed a self-consistent atomistic tight-binding treatment of the required interlayer exchange interaction within non-local Hartree-Fock mean-field theory. Such condensation, associated many-body enhanced interlayer current flow, and gate-control thereof is the basis for the beyond-CMOS Bilayer-pseudoSpin Field Effect Transistor (BiSFET) proposed by colleagues. I studied the effect of various system parameters and on interlayer charge imbalance on the strength of the condensate state. I also modeled the critical current, the maximum interlayer current that can be supported by the condensate, its detailed dependence on the nature and strength of the required interlayer bare tunneling and on charge imbalance. The results presented here are expected to be used to refine devices models of the BiSFET, and may serve as guides to experiments to observe such a condensate state. / text

It is common for field models of tight gas reservoirs to include several wells with hydraulic fractures. These hydraulic fractures can be very long, extending for more than a thousand feet. A hydraulic fracture width is usually no more than about 0.02 ft. The combination of the above factors leads to the conclusion that there is a need to model hydraulic fractures in coarse grid blocks for these field models since it may be impractical to simulate these models using fine grids. In this dissertation, a method was developed to simulate a reservoir model with a single hydraulic fracture that passes through several coarse gridblocks. This method was tested and a numerical error was quantified that occurs at early time due to the use of coarse grid blocks. In addition, in this work, rules were developed and tested on using uniform fine grids to simulate a reservoir model with a single hydraulic fracture. Results were compared with the results from simulations using non-uniform fine grids.

This project is a research into the effect of gas condensate damage in hydraulically fractured wells. It is the result of a problem encountered in producing a low permeability formation from a well in South Texas owned by the El Paso Production Company. The well was producing a gas condensate reservoir and questions were raised about how much drop in flowing bottomhole pressure below dewpoint would be appropriate. Condensate damage in the hydraulic fracture was expected to be of significant effect. Previous attempts to answer these questions have been from the perspective of a radial model. Condensate builds up in the reservoir as the reservoir pressure drops below the dewpoint pressure. As a result, the gas moving to the wellbore becomes leaner. With respect to the study by El-Banbi and McCain, the gas production rate may stabilize, or possibly increase, after the period of initial decline. This is controlled primarily by the condensate saturation near the wellbore. This current work has a totally different approach. The effects of reservoir depletion are minimized by introduction of an injector well with fluid composition the same as the original reservoir fluid. It also assumes an infinite conductivity hydraulic fracture and uses a linear model. During the research, gas condensate simulations were performed using a commercial simulator (CMG). The results of this research are a step forward in helping to improve the management of gas condensate reservoirs by understanding the mechanics of liquid build-up. It also provides methodology for quantifying the condensate damage that impairs linear flow of gas into the hydraulic fracture.