Carbonate reservoirs store more than 50% of the earth hydrocarbon reserves with mostly mixed wettability. Water injection in these reservoirs likely results in low recovery due to uneven water movement. In the past years, it has been noticed that Low Salinity Water Flooding (LSWF) regularly led to incremental recovery. Some of the possible Enhanced Oil Recovery LSWF mechanisms on the relation of the injected fluid composition and orginal reservoir fluids.In this study the effects of altering the concentration of the injected Sulphate ions on pH, CO2, calcite dissolution and its impact on oil recovery in carbonates are investigated. Ca2+, Mg2+ and SO-4 2are determining ions to the carbonate surface which impact the surface charge of the rock (Zhang, 2006). The adsorption of the determining ions having conflicting charges Ca2+ and SO4 -2 on the carbonate rock surface is dependent on the relative concentration and equilibrium. An increase in pH causes a reaction with the acidic components of the oil which improves reservoir in-situ surfactants. This study describes LSWF five spots simulation model with 4 producers and one injector. A 3D homogeneous reservoir was built using CMG simulators specifically the compositional simulator GEM. The basic data used to build the model like PVT data, crude composition, injected and connate water geochemical compositions were collected from several case studies conducted in a carbonate reservoir. From the simulation results, pH was found to increase during the interaction between low salinity brine and reservoir rocks. The results show that dissolution of carbonate minerals can occur and this will alter the composition of the injected low salinity brine, the concentration of divalent ions on rock surface and hence the potential of low salinity to improve recovery. Calcite dissolution and indirectly Anhydrite Precipitation is being accelerated and controlled by the CO2 within the residual oil. The study indicates strong bond between pH and CO2 and their effect on oil recovery while preforming LSWF. Enhancements on the injected water composition on a LSWF project based on the recommended chemical reaction controlling factors will enhance the understating of the driving mechanism of the LSWF and improve the oil recovery.

This study illustrates a comprehensive-integrated approach to identify the potential locations for future development in a sector area of a giant carbonate mature oil reservoir. The approach uses various data from several sources including reservoir surveillance, production performance, geological interpretation and numerical simulation and cohesively combines them to yield an informed decision to assess field development and management. The study area is under peripheral waterflood for more than fifty years and dominated by heterogeneity related to fracture corridors, high permeable zone, and reservoir zonation. These features leads to a preferential and uneven propagation of water flow which results in un-swept oil bearing spots using the existing wells lay-out and configuration. The reservoir management team has developed an integrated workflow to address these challenges by using several reservoir engineering methods and models including Water Encroachment, Reservoir Opportunity index, Fractional Flow Calculation, Remaining Volumetric and Water Flow Paths. The designed workflow consists of creating derived attributes that describe these models and filter the sector area to define the sweet spots. The selection and prioritization of the defined sweet spots are supported by available reservoir surveillance and production data. However, the scarcity of reservoir surveillance and production data in some areas of the sector, motivated reservoir management team to stretch the limits by capitalizing on gas wells penetrating the shallower oil reservoirs. The open-hole logs of these wells recorded thicker oil column than the preestimated column using the existing surveillance data. As a result of these efforts, a development plan was designed in order to ensure reserves depletion in the identified sweet spots by drilling new wells or sidetracking the existing wells. Despite the level of maturity, simulation forecasts indicate that the area of interest has lot of potential to sustain a high production rate.

This paper presents a generic workflow to assess direct and indirect production in reservoirs with layered contrasted permeability. The objectives are to quantify the total individual production split from those zones when compared to volumetric and evaluate the productivity efficiency. The workflow comprehensively integrates reservoir surveillance tools such as Production Logging Tools (PLTs) to perform a zonal decline analysis through analytical approach. The numerical simulation modeling is utilized to support this assessment. The paper describes a method of capitalizing the flowmeter results and correlate them with production decline to identify the volumes swept from the tighter zones of interest. The workflows identifies, as a result of this analysis, the split of the two portions of this swept volumes in the tight zones : a portion easy to identify, as it is produced directly through the logged wellbore or migrated vertically to most permeable zones to build-up on the attic portions of the reservoir. Such analysis when conducted in a specific field and coupled with simulation result is a powerful tool to decide on the actual mechanism affecting the sweep including the importance of gravity and percolation process. Consequently, strategic decision could be taken based on the options to develop the contrasted zones. This is including the decisions on wells configuration, whether it is more justified to fetch the tight zones volumes through vertical wells or to rationally exploiting the top layer through horizontal wells. The workflow was applied to real case study and showed a quantitative conclusive result, it demonstrated the equilibrium, required to maintain, in the withdrawals ratio of the contrasted zones. This equilibrium will ensure to have a better sweep of lower productivity zone.