Influence Of Desorption Research Articles

A new production analysis method for shale gas well based on the evaluation of decline parameters in advance

Production forecasting for multi-fractured horizontal well (MFHW) in shale gas reservoir is of vital importance to the evaluation of development potential.In this paper, we develop a new method to predict production of the MFHW under constant bottom-hole Pressure (BHP) condition. Based on the analytical model, well's life cycle is divided into two stages, in which the decline models are established, respectively. According to these models, the decline exponent is a function of fluid properties, the pressure drawdown strategy and heterogeneous completion. It can be directly calculated without production data matching. Influence of desorption on decline exponent, calculation of “initial pressure” during boundary dominated flow (BDF) period, are discussed. A workflow is established to perform production forecasting for a MFHW with complex fracture configuration and constant BHP in shale reservoir. A preliminary scheme is also developed to extend the workflow to variable BHP condition. Results indicate that a special hyperbolic model in which decline exponent changes as pressure drops, can be employed to forecast production during BDF. A constant decline exponent may result in an underestimation/overestimation well production, especially, in the BDF period. This new method can be used to explore how each factor impacts well productivity rigorously. Compared with conventional methods, it is of higher accuracy when making production forecast, especially for wells with short history.

Numerical computation for nonlinear unsteady percolation of shale gas and prediction of production

According to the reality of the marine shale reservoirs in South China, multi-scale gas flow in the shale reservoirs with special pore structure characteristics is considered. By using the Knudsen number, it is judged that the dominant pattern of flow in shale porous media is slip flow, and it is pointed out that the process of gas transport is an isothermal process. On the basis of multiscale Beskok-Karniadakis flow model, the corresponding second-order approximation correction is given and the mathematic model of nonlinear unsteady radial percolation is established for the tight shale gas wells. The problem is simplified by applying the Boltzmann transformation and an explicit iteration scheme to solve the pressure is presented by numerical discrete technique. The distribution curves of pressure with time and space are obtained for the case of the constant pressure at the inner boundary. The variation of output over time is predicted and the influence of desorption, slippage and diffusion on the production is analyzed.

Productivity Evaluation Study of Shale Gas Reservoirs

The seepage mechanism of unconventional gas is very complex, and has a unique seepage mechanism and dynamic flow characteristics. It is difficult to use conventional gas production capacity to predict recoverable reserves. In this paper, starting from fluid mechanics, based on reservoir characteristics of the shale gas fracturing, a composite model of shale gas reservoirs was established, and stable production time was determined. We analyzed the effects of inside and outside zone permeability, the radius, pressure gradient, desorption influence of the compression factor and reservoir thickness, etc., and the established a shale gas well productivity equation refer to Vogel equation. The results show that: area permeability, penetration outside the area, zone radius, reservoir thickness and desorption compression factor were sensitive to shale gas production capacity; skin factor and the pressure gradient is not sensitive factor; through reliability analysis, the productivity formula which was referred to Vogel equation can determine the production capacity of shale gas wells quickly and accurately.

Influence of desorption and sorption of water on the purity of perfluorooctanoic acid

The composition of impurities in perfluorooctanoic acid (PFOA) was measured and determined to be notably different between lots. Since the purity of PFOA varied, the accuracy of prepared calibration solution concentrations was reduced. In this study, factors influencing the purity were investigated using a Karl Fischer titrator and a LC/MS to support the development of reference materials. The results showed variances of water and isomer/homologue contents under different ambient conditions during sample handling. Moreover, these variances, especially for water, greatly affected the purity of PFOA (0.95–0.99 kg kg−1). Therefore, PFOA of reliable purity should be used for the preparation of calibration solutions.

Influence of desorption and contact time on sediment‐water distribution of spiked polychlorinated biphenyls and polycyclic aromatic hydrocarbons: Relation with in situ distribution

The long-term sediment-water distribution of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), spiked to Lake Ketelmeer (The Netherlands) sediment, was studied using a gas-purge technique. Contact times varied from 2 to 1,461 d for the PCBs and from 5 to 100 d for the PAHs. Purge-induced desorption experiments lasted 300 to > 4,000 h. The initial distribution coefficients that were observed during the first part of the experiment were close to literature values for distribution after short contact times. The distribution coefficients increased during the purge-induced desorption experiments. The final distribution coefficients that were observed during the last part of the experiment were one to two orders of magnitude higher than the initial values and were close to distribution coefficients reported earlier for in situ PCBs and PAHs present in a field-contaminated sediment for years to decades. The change in distribution coefficients during a gas-purge experiment may resemble the long-term change in a field sediment. Final distribution coefficients seem to be a more relevant measure for the distribution coefficients of hydrophobic organic chemicals in aged field sediments than values obtained after short contact times.

Influence of desorption on the composition of high-temperature superconducting thin films during magnetron sputtering

Results are presented of investigations to study how desorption caused by interaction between the surface of condensation and the plasma particles affects the composition of thin films of Y-Ba-Cu-O high-temperature superconductors during magnetron sputtering. An analysis of the current-voltage characteristics of Langmuir probes was used to determine the floating potential of the substrate at various working gas pressures. Electron Auger spectroscopy was used to determine the atomic composition of films obtained at various substrate bias voltages. It was established that during magnetron sputtering of Y-Ba-Cu-O films the formation of the condensate composition may be strongly influenced by selective desorption of components from the substrate and the surrounding structural elements as a result of bombardment by plasma ions accelerated in the floating potential field.

Influence of desorption on the indoor concentration of toxic gases

A theoretical model is developed which considers the influence of both deposition and desorption processes on the indoor concentration of toxic gases. The model is based on a simplification of the Langmuir theory. Model parameters for NH 3, Cl 2, the nerve agent sarin, and a simulant for the nerve agent VX are calculated from available experiments with common indoor materials. The adaptation of parameters seems to work well for low to moderate exposure. The model is then used to study concentrations of the nerve agent sarin in ordinary buildings after a hypothetical attack. Desorption results in a residual indoor concentration over an extended period, and, in contrast to a non-desorbing gas, the indoor exposure ∫ τ 0 c i d t of a desorbing gas can therefore approach the outdoor exposure given sufficient time. For several indoor materials this approach is slow, especially under conditions of low ventilation. A very high deposition and a low desorption of sarin to/from unpainted concrete is found, thus demonstrating that rooms of unpainted concrete offers good protection against sarin.