In-depth Water Diversion Using Sodium Silicate – Preparation for Single Well Field Pilot on Snorre

摘要

The waterflood sweep efficiency can be increased considerably by in-depth placement of a blocking agent. Sodium silicate is one of the few PLONOR chemicals applicable for water control. This paper highlights key results obtained from a research program on qualifying sodium silicate for offshore application. The main findings of this work can be summarized as follows: 1. Sodium silicate is an alkaline liquid containing nano-size particles with water-like viscosity and good buffer capacity. 2. Sodium silicate can be diluted in brines with a low divalent ion concentration addressing the need of a sufficiently large preflush. 3. Upon reaction, triggered by an activator, sodium silicate forms silicate aggregates and gel which reduce permeability. 4. The reaction rate is controlled by the formation temperature and the sodium silicate concentrations, and ranges from minutes to several months. 5. The gelation kinetic has been successfully implemented in a simulation model. 6. Coreflood experiments demonstrated both a good injectivity of non-reacted sodium silicate and dynamic reaction rates similar to bulk reaction rates. 7. Interpretations of coreflood experiments unfold the effect of cation exchange. 8. The flow behaviour of reacted silicate aggregates is understood by classical theory on fine particle transport through porous medium, which includes a velocity dependent deposition rate. It is concluded that large volumes of sodium silicate can be injected into offshore oil reservoirs. Prior to the injection, a preflush is needed and the silicate is to be diluted in desalinated water. The permeability reduction can be obtained either during dynamic injection or shut-in period. The design parameters involve temperature, velocity and concentration gradients.