Emulsion System with Nanoparticles for Selective and Reversible Water Shut-Off in Mature Sandstone Reservoirs Offshore

Abstract

Results of laboratory research conducted in the framework of laboratory program developed jointly by a technology provider and an offshore oil-gas fields operator are presented in this paper. The laboratory program included optimal list of experiments for testing physical and technological properties of the physico-chemical water shut-off agent, resulting in a ready-for-pilot solution at minimum cost and time. The studied water shut-off agent is an emulsion system with nanoparticles (ESN), which is an inverse emulsion augmented by the synergy of natural and artificial surfactants with supercharged silicon dioxide nanoparticles. The ESN consists of three liquid components: sea water, diesel and nanoparticle-based surfactant. One of the main tasks of this research was to study such features of the ESN as selectivity of blocking impact to water-bearing zones and reversibility of blocking effect in the oil-bearing zones of sandstone reservoirs in the Lower Miocene (2950 psi and 91°C) and Late Oligocene (3900 psi and 107°C) hydrocarbon formations. As a basic requirement from the operator, the ESN had to be stable at the said reservoir conditions and compatible with reservoir and process fluids. Besides that, the operator wanted to confirm that the ESN is an easy-to-handle water shut-off agent in the offshore environment, meaning that it can be prepared with ordinary equipment available at the vessel, all components are liquids easily mixed to each other at ambient conditions and ready-to-use composition properties do not change in time within the operation offshore. Thus, the laboratory program was executed in three successive stages, divided based on the experiment conditions: ambient; pressure & temperature; modeled reservoir conditions. In result, the ESN performed as stable and compatible water shut-off agent and met all requirements of the operator. In the series of core floods, conducted on eight sandstone cores of different permeability and saturation, it was confirmed that the ESN selectively and fully blocks water-saturated cores, while the oil-saturated cores permeability decreased slightly with clear tendency to full recovery under the flow of hydrocarbons.