Pilot Testing Issues of Chemical EOR in Large Fractured Carbonate Reservoirs

Abstract

Many world class large carbonate reservoirs leave behind at least half of the initial oil in place. Typically water injection is used to improve oil recovery while gas injection is used to maintain pressure or to promote oil gravity drainage. Immiscible gas injection, including injection of CO 2 , has been considered but not implemented on a large scale for economic reasons. Furthermore, interest in using surfactants in large carbonate reservoirs has recently flourished. As a result, we began to investigate the viability of designing and conducting a manageable pilot test program in a large fractured carbonate reservoir using a single-well, dual-completion system to evaluate the efficacy of the surfactant oil mobilization and oil capture. However, pilot testing in large reservoirs is very expensive and requires a long time to complete. These issues are less problematic in pilot testing of small and thin reservoirs in onshore field. In this paper we will present the results of a conceptual model to simulate the performance of surfactant flooding in the above-mentioned pilot test configuration. Three different model formulations, having different approaches to gridding and grid-refinement, were used. These include conventional dual-porosity, dual-permeability, and single-porosity models with variable porosity and permeability to simulate fracture-matrix interactions. Simulation of pilot tests using dual-porosity models shows that gravity is most effective during waterflood but not as effective during the surfactant injection while in the dual-permeability models, the surfactant oil recovery is greater because both gravity and viscous displacement contribute. We will explain the reasons and will indicate which model is more reliable. In general the results of this study give an insight into the viability of using surfactant injection in thick carbonate reservoirs both in the pilot and production stage.

Mechanically robust re-crosslinkable polymeric hydrogels for water management of void space conduits containing reservoirs

“…[14] Open hole fractures have been demonstrated to significantly reduce the oil recovery because the displacing fluid would bypass oil-rich unswept areas/zones. [15][16] For example, the rapid breakthrough in the Anton Irish Clearfork flood has resulted in the shut-in wells in which large void space flow conduits were generated from flooding induced and enhanced fractures. Moreover, the excess water and CO 2 production had the wells uncompetitive compared to its original high oil recovery.…”

A review of development methods and EOR technologies for carbonate reservoirs

“…Because the reserves of fractured vuggy carbonate reservoirs account for a large proportion of the world's oil reserves, the chemical assistant method based on surfactant injection (i.e., spontaneous imbibition, wetting agent, and ITF reduction) is an active research field, often used as an important method to improve the recovery of fractured vuggy carbonate reservoirs (Alvarado and Manrique 2010). By changing the wettability of the surfactants, the interfacial tension of oil/water can be effectively reduced to ultralow values, the adsorption capacity can be reduced and the absorption process can be promoted (Farhadinia and Delshad 2010;Alvarado and Manrique 2010;Kiani et al 2011).…”

Post-Surfactant $$\hbox {CO}_{2}$$ CO 2 Foam/Polymer-Enhanced Foam Flooding for Heavy Oil Recovery: Pore-Scale Visualization in Fractured Micromodel

“…Wettability and matrix block size are two major factors in fluid transfer between fractures and matrix (Kiani et al 2011). For an oil-wet fractured carbonate reservoir, injected water can flow in fractures easily and much faster than in the matrix.…”

“…Gravity drainage can produce oil if the matrix block is thick enough to overcome the negative water-oil capillary pressure. The surfactant injection in an oil-wet fractured reservoir might not be effective because of the following reasons (Kiani et al 2011): (1) Pressure gradient may be too small to displace oil from the matrix in fractured formations and (2) high permeable fractures could act like thief zones. In these cases, using mobility control agents such as foam might be considered.…”