A simple 3-D physical model has been developed to investigate the use of in-situ combustion in heterogeneous reservoirs. Gas over-ride phenomena is one of the major causes of instability of combustion process; gas override results in poor sweep efficiency with subsequent low oil recovery. However, the use of horizontal wells in direct line drive arrangement has shown a great deal of combustion stability and propagation by means of controlling gas override This paper has extended the scope of using horizontal wells in direct line drive configuration in heterogeneous reservoirs. Three cases of reservoir heterogeneity were investigated in this study. In the first case, a dual-layer permeability of sand was used (a high permeability layer on top and a low permeability layer on bottom); in the second case, placement of the aforementioned layers was swapped, and in the third case, a high permeability streak was sandwiched between two low permeability layers of fine sand. The results indicated that a stable combustion front has been achieved in the first two cases with a high oil recovery, however the performance of the combustion process markedly deteriorated when a high permeability streak layer was utilised as a result of a severe low temperature oxidation due to oxygen channelling through the streak, with subsequent poor sweep efficiency and in turn low oil recovery. The use of horizontal wells as producers and injectors in a line drive configuration is beneficial and effective for minimising the effect of reservoir heterogeneity to some extent. 相似文献
Combined simulation–optimization (CSO) schemes are common in the literature to solve different groundwater management problems, and CSO is particularly well-established in the coastal aquifer management literature. However, with a few exceptions, nearly all previous studies have employed the CSO approach to derive static groundwater management plans that remain unchanged during the entire management period, consequently overlooking the possible positive impacts of dynamic strategies. Dynamic strategies involve division of the planning time interval into several subintervals or periods, and adoption of revised decisions during each period based on the most recent knowledge of the groundwater system and its associated uncertainties. Problem structuring and computational challenges seem to be the main factors preventing the widespread implementation of dynamic strategies in groundwater applications. The objective of this study is to address these challenges by introducing a novel probabilistic Multiperiod CSO approach for dynamic groundwater management. This includes reformulation of the groundwater management problem so that it can be adapted to the multiperiod CSO approach, and subsequent employment of polynomial chaos expansion-based stochastic dynamic programming to obtain optimal dynamic strategies. The proposed approach is employed to provide sustainable solutions for a coastal aquifer storage and recovery facility in Oman, considering the effect of natural recharge uncertainty. It is revealed that the proposed dynamic approach results in an improved performance by taking advantage of system variations, allowing for increased groundwater abstraction, injection and hence monetary benefit compared to the commonly used static optimization approach.
Mosaicing is connecting two or more images and making a new wide area image with no visible seam-lines. Several algorithms
have been proposed to construct mosaics from image sequence where the camera motion is more or less complex. Most of these
methods are based either on the interest points matching or on theoretical corner models. This paper describes a fully automated
image-mosaicing method based on the regions and the Harris points primitives. Indeed, in order to limit the search window
of potential homologous points, for each point of interest, regions segmentation and matching steps are being performed. This
enables us to improve the reliability and the robustness of the Harris points matching process by estimating the camera motion.
The main originality of the proposed system resides in the preliminary manipulation of regions matching, thus making it possible
to estimate the rotation, the translation and the scale factor between two successive images of the input sequence. This estimation
allows an initial alignment of the images along with the framing of the interest points search window, and therefore reducing
considerably the complexity of the interest points matching algorithm. Then, the resolution of a minimization problem, altogether
considering the couples of matched-points, permits us to perform the homography. In order to improve the mosaic continuity
around junctions, radiometric corrections are applied. The validity of the herewith described method is illustrated by being
tested on several sequences of complex and challenging images captured from real-world indoor and outdoor scenes. These simulations
proved the validity of the proposed method against camera motions, illumination variations, acquirement conditions, moving
objects and image noise. To determine the importance of the regions matching stage in motion estimation, as well as for the
framing of the search window associated to a point of interest, we compared the matching points results of this described
method with those produced using the zero-mean normalized cross correlation score (without regions matching). We made this
comparison in the case of a simple motion (without the presence of a rotation around optical axis and/or a scale factor),
in the case of a rotation and in the general case of an homothety. For justifying the effectiveness of this method, we proposed
an objective assessment by defining a reconstruction error.
In this paper, we propose a novel Route Maintenance scheme for IEEE 802.11 wireless mesh networks. Despite lack of mobility and energy constraints, reactive routing protocols such as AODV and DSR suffer from frequent route breakages in 802.11 based infrastructure wireless mesh networks. In these networks, if any intermediate node fails to successfully transmit a packet to the next hop node after a certain number of retransmissions, the link layer reports a transmission problem to the network layer. Reactive routing protocols systematically consider this as a link breakage (and therefore a route breakage). Transmission failures can be caused by a number of factors e.g. interference or noise and can be transient in nature. Frequent route breakages result in significant performance degradation. The proposed mechanism considers multiple factors to differentiate between links with transient transmission problems from those links which have permanent transmission problems and takes a coherent decision on link breakage. The proposed mechanism is implemented in AODV for single-radio single-channel mesh network and an extension is incorporated in multi-radio multi-channel scenarios. Simulation results show substantial performance improvement compared to classical AODV and local route repair schemes. 相似文献
The influence of polyesters end-groups on cyclic oligoester formation is investigated using a series of hydroxy-, carboxy- and methylester-terminated aliphatic polyesters, in the presence of various ester interchange catalysts. The presence of hydroxy end-groups is the preponderant factor on cyclodepolymerization kinetics. This indicates that the main reaction is the intramolecular hydroxy–ester interchange reaction between hydroxy end-groups and ester functions in the chain. Carboxy-ester and ester–ester interchanges play a minor role, as the cycle-chain equilibrium is reached only very slowly when carboxy- or ester-terminated polyesters are reacted. High temperature and the presence of tin catalysts are also favorable factors, while, as expected, dilution shifts the equilibrium toward the formation of high yields of cyclic oligoesters. A mechanism is proposed, based on the reverse of the “coordination-insertion” mechanism established for the ring-opening polymerization of lactones. 相似文献