Evaluation of Recovery Performance of Miscible Displacement and WAG

摘要

Recent advances in well design and production techniques have brought considerable attention to exploitation of tight (low permeability, absolute permeability <1 mD) oil resources. Drilling of long horizontal wells and deployment of hydraulic fractures along these wells (multi-fractured horizontal wells) can substantially improve the primary production rates from such reservoirs. Nevertheless, the low effective permeability of the formation to oil hinders the sustainability of favorable oil rates and at some point applying some EOR technique becomes inevitable. In the current study, CO2 miscible flooding and WAG processes in a tight oil reservoir are investigated. Although several studies have investigated different aspects of the process in conventional oil plays, the design of an effective scheme in tight oil formations is more complex. These complexities are related to the proper design of the fractures (half-length, permeability, direction (transverse vs. longitudinal), etc.) and their relative arrangement in producers and injectors and the operational constraints on each well or segment of the well. In this work, we utilize an innovative EOR scheme design where multi-fractured horizontal wells are used for both injection and production, and the hydraulic fracturing stages are staggered to delay breakthrough and improve sweep efficiency. For a set of defined parameters, compositional simulations are conducted to optimize the WAG ratio and cycle length and injection starting point (in time) for the model. The recovery associated with EOR is compared with its corresponding base case model in which all wells are producing under primary recovery for the whole life of the reservoir. The results of this study show that the primary recovery factors (5-15%) can be increased to 25-35% under optimum flooding conditions, considering a reasonable economic framework.