Improving waterflooding sweep efficiency is one of the most important actions in brown fields supported by water injection. The main cause of water injection poor sweep efficiency has been historically associated to the presence of heterogeneity in reservoir, which in some cases leads to preferential flow paths between injectors and producers. This results in early water breakthrough and recirculation of injected water. In order to mitigate this effect, Eni applied on a large scale an innovative water conformance technology involving the addition of Thermally Activated Polymers (TAP) to the injected water. These polymers react at defined temperature by increasing their dimension and obstructing matrix pores in high permeable and watered out layers. As a consequence, injected water results forced to find alternative flow-paths and hence to displace unswept oil areas in lower permeability channels. From a production point of view, the improvement in sweep efficiency by deep conformance control leads to the reduction of water production and the maintenance of an economical oil production rate.
This paper will focus on the recent application on a mature onshore oil field characterized by a sandstone formation with interbedded shales and a good contrast of permeability, as confirmed by PLT analysis. A first pilot test was already performed in 2009 with positive results, highlighting a reduction of production water cut and an increase in oil rate. In that framework, the involved producer showed also an increase of water salinity, indicating that the contribution of the different sand bodies was changing thanks to water conformance application.
Given the positive results of this first pilot, a new application was recently performed in 2016 on a larger scale, involving two injectors and a total of 7 main connected producers. A screening of water injectors was performed to select the best candidates for the application of the considered technology, based on a comprehensive analysis of production data, pressure and water salinity trends, and finally confirmed by PLT campaign results. The field implementation as well as preliminary results of TAP injection are presented in the paper.
