The Jasmine Field began production in 2005 with initial estimated recoverable reserves of 7 MMbbls.
A generalised methodology is described for the complete modelling of multi-lateral well performance by using a network pressure solver in a numerical simulator to solve for the interaction between well branch inflows and completion pressure drops. The paper illustrates the importance of taking into account well trajectory, completion diameter and the positioning of the artificial lift, for heavy oil multi-laterals. The results of a design study for a multi-lateral well in an 11 API oil reservoir are outlined, and the necessity for economic ranking of results, in light of significant differences in well costs, highlighted. Introduction Horizontal wells highlighted the requirement for better reservoir description, to both understand well performance, and to improve well placement. In general however, most completion issues concerned what type of liner to run and how best to clean-up the well. Multi-lateral wells add an additional level of complexity, in that well branch interactions now also need to be taken into account. These are functions of branch inflow performance, and completion performance between the sandface and well junction points, and both factors need to be considered when designing the well, particularly in low pressure heavy oil environments. Recently published papers about multi-lateral completion design have tended to concentrate mainly on the mechanical aspects of achieving isolation between well branches. Analytical modelling of multi-lateral well performance is becoming well documented, but these papers have mainly concentrated on the interference effects of multiple well branches in the same formation. The paper by Salas however, introduces the requirement to include completion pressure drops in the well design, which was achieved with an in-house analytical model, and mentions the importance of artificial lift positioning for low pressure reservoirs. This present paper describes a methodology for modelling the complete performance of multi-lateral wells, and illustrates the effects of completion design on well performance in a heavy oil reservoir. This has been used to optimise the multi-lateral well design for a reservoir containing 11 API crude. Multi-Lateral Well Performance Prediction In view of the low pressures generally encountered in heavy oil reservoirs, a modelling technique is needed which accounts for the branch inflows, completion pressure drops up to the junction nodes, pump positioning and artificial lift performance, to accurately model multi-lateral well behaviour. The technique developed by Gallivan has been used in this work. The multi-lateral well interactions which need to be accounted for are illustrated in figure 1. The methodology involves coupling branch inflow performance from a numerical simulator, with vertical flow performance tables developed for each part of the completion, using a network pressure solver. The artificial lift performance can also be modelled and input via tables, to allow the well model to predict surface flowrates. This option is commercially available, although not specifically designed for multilateral wells. However, by treating each multi-lateral branch as an individual well, and manifolding the laterals together via the lift curves, the network solver will equilibrate the drawdowns in each branch, and accurately model branch and total well inflows. The requirement for careful simulator gridding, to ensure accurate modelling of (normally horizontal) branch inflows has been well recognised in the literature". Careful tuning of the network, and short initial timesteps are usually required to get stable solutions.
This paper demonstrates the requirement for incorporating completion and artificial lift considerations into multi-lateral well design, and describes a methodology for rigorously predicting the performance of these wells. In this low pressure, heavy oil reservoir, herringbone multi-laterals are favoured over dual and tri-lateral wells, due to the impact of positioning the artificial lift closer to the sandface. Economic ranking is required to compare performance of different well types, due to significant differences in well costs. The optimal development scenario for drainage of three infill locations, consists of a long herringbone multi-lateral plus a conventional horizontal well. Introduction The reservoir, situated on the Eastern shores of Lake Maracaibo, has been producing 12 API crude since 1958. Current reservoir pressures around 830 psi. coupled with insitu viscosity of 170 cp and high water cuts in many areas, mean that new vertical wells produce under 100 stb/d, and are now uneconomic. Additionally, expanding population density in the area makes finding new drilling sites problematical. New technology is being investigated as a means of enhancing productivity. A recent internal report identified 3 possible infill locations, without water production problems, and concluded that drilling horizontal wells would be economic. The proximity of the locations (figure 1) raised the possibility of draining all three from the same surface location, either by individual, or multi-lateral wells. This paper describes the methodology adopted for accurate simulation of the different multi-lateral configurations, and the use of simple economics to rank the well performances. Reservoir Model The reservoir comprises two main channel sand bodies, Unit 2 (upper) and Unit 1, both of which average around 35 feet thick in the zone of interest, and are separated by a 40 feet shale. The proposed drilling locations (figure 1) comprise one well in each sand in the A location, and a well in Unit 1 in the B location; these will be referred to as wells A(1), A(2) and B(2), respectively. The top of unit 2 lies at 3880 feet in the A location, and is some 100 feet lower at B. Reservoir permeability averages 400 md in Unit 2 and 500 md in Unit 1, with 35% porosity and 30% water saturation in both sands; The Kv/Kh ratio has been estimated as 0.15 from core data. Well to well correlation of the channel is good, and steering the horizontal section in the reasonably competent sand is not expected to pose problems. Numerical simulation models (figure 2) have been constructed, initially of the A area, and later with the B area added, to allow modeling of the multi-laterals. The model contains 18x23x11 cells in the X, Y and Z directions (4554 cells), and uses fine grids, with dimensions fulfilling Peaceman's criteria, to allow accurate modeling of the branch inflows. Existing vertical wells have been included, to properly model the influence of the offset producers. Multi-lateral Performance Modeling A review of the literature showed that a number of papers have been published in recent years, dealing with analytical modeling of multi-lateral wells, but that these mostly concentrated on the interference effects of multiple well branches in the same formation; the paper by Salas mentions that well trajectory impacts on artificial lift efficiency, but does not quantify the effect. In view of the low reservoir pressures here, it was felt that a modeling technique that accounted for both the artificial lift positioning, and the interaction between the different well branches, would have to be used to get realistic results. P. 379
Les résultats de la recherche de l'Auteur de cet article confirment pleinement la thèse de M. Gordon (1964) selon laquelle il faut opérer une distinction radicale entre intégration culturelle et intégration structurelle des migrants dans les sociétés d'arrivée. L'auteur montre aussi l'importance que revêt l'affiliation religieuse dans la vie des groupes immigrés ainsi que le fait que la nature et le type d'institution religieuse & a g r a v e ; laquelle s'affilie le migrant peut avoir une importance considérable pour promouvoir ou freiner son adaptation dans la société d'arrivée. Cette recherche apporte ainsi une contribution au débat & a g r a v e ; propos du caractère relevant ou irrelevant de la religion dans le processus d'adaptation des migrants. Elle le fait & a g r a v e ; partir d'un matériel empirique mais en allant plus loin que la simple description.The question of the part played by religion in the adjustment of immigrants to the host society is one which in the body of sociological literature can be traced back at least as far as Weber. It is a factor which is frequently mentioned in studies of immigrant communities, but generally only descriptively, research focus usually being on the more quantifiable factors, such as &dquo; age at arrival,&dquo; &dquo; education,&dquo; &dquo; geographical dispersion &dquo; etc. Focus on such factors has been such that Mol had no hesitation in stating that : &dquo;
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