How Repeatable will Libra Pre-Salt PRM Permanent Reservoir Monitoring be ? A Full Wave Elastic and Acoustic Study

Abstract

Mero (Libra NW) is a field with high Gas Oil Rate (GOR) and high CO2 content, therefore the produced gas is reinjected in the reservoirs and the reservoir management strategy revolved around mitigating gas to maximize oil production within the limitations of surface gas reinjection capability. The reservoirs are thick but present 4 orders of magnitude in the variations of permeability (Fig. 1 left), including presence of high porosity/high permeability units that we anticipate will channel part of the gas injection, but are generally impossible to map from 3D seismic. The production strategy put in place by Libra Join Project Team (JPT) to address this setting combines several technologies that combine together with others such as HiSep CO2 separation: An injection strategy combining Water Alternating Gas (WAG) to slow the gas, with injection of gas into the most porous parts of aquifers in order to delay the increase of GOR around the producers. The use of intelligent well completions with several levels that can be de-activated in order to limit the amount of gas injected or produced in various zones. A monitoring strategy combining the usage of tracers with high-quality 4D in order to detect and track the gas fronts. Firstly, combining the two first strategies should provide efficiency in reactive reservoir management, adressing the risks induced by locally strong values of respectively high horizontal (Kh) or vertical (Kv) permeability (Fig. 1 right).