At present one of effective tools of real reservoir systems simulation is the numerical solution of partial differential equations of multidimensional multiphase filtration theory with combination of well equations. Because of that the wells are a single source of information about reservoir systems, the realistic description of fluid flow around the wells is one of most challenging aspects of reservoir simulation. In conventional reservoir simulation there is accepted that the boundary conditions for reservoirs must be to given in the production (injection) wells and in the external (internal) boundaries. Wells are assumed to be in the gridblock centers without taking into account their exact position. It leads to neglecting of closest neighbouring cells influences and the fluid flow around an off-center wells is described incorrectly. This problem is especially important in the full-field simulators development when the reservoir systems approximate with very coarse gridblocks and reservoir produces (injected) by numerous off-center wells. In this paper the new well representation technique in the reservoir simulation is described. This technique allows to give exact off-center well position and take into account the influence from closest neighbouring gridblocks. The application of this technique is described in the explicitly and implicitly formulations. The results of calculations by using of suggested technique was matched with results of reservoir simulation by fine-grid application and showed a good agreement. In this paper there is illustrated that the implementation of this technique allows to improve the accuracy of results and considerable decrease of computing time because of that suggested technique assumes the use of coarse grids.

The production experience from the Statfjord Field on the Norwegian Continental Shelf is one of the greatest adventures in modern oil and gas history. After achieving very high oil recovery factor using a predominant drainage strategy with pressure maintenance by water and gas injection, the drainage strategy in the field has since 2007/2008 been changed to reservoir depressurization. Prior to depressurization start-up, the field has produced about 652 million Sm3 (4.1 billion bbl) oil and 187 billion Sm3 gas. Currently, the field is producing at an oil rate of approximately 5 300 Sm3/d and a gas rate of about 11 million Sm3/d. Estimates indicate that successful implementation of the new drainage strategy will continue and lead to an ultimate oil recovery of higher than 67% and a significant additional gas production, as a result of the depressurization process. In addition, the field life will be extended from 2009 to 2025, and this will contribute to lifetime extension of the attached satellite fields. The main purpose of this paper is to provide a description of the multidisciplinary approach used for evaluation and planning of the Statfjord Late Life (SFLL) with reservoir depressurization, share learnings from depressurization start-up and address challenges, uncertainties and opportunities.

No abstract