Well Injectivity Management during Geological Carbon Sequestration Activity

Abstract

It is well known that the saline aquifer formations are considered very reliable candidates for carbon sequestration because of their wide availability and they have good storage capacity. Due to high formation salinity, there a big concern about bore formation dry-out resulting from the salt precipitation in the form of halite (NaCl). The mutual solubility between CO₂ and brine is responsible for creating the salt deposits, this processes may take place in three ways: (1) when CO₂ dissolves in the brine it increases the brine density; (2) when CO₂ dissolves in the brine it reacts with water and forms carbonic acid (H₂CO₃); (3) H₂O dissolves or vaporizes into CO₂ stream, removing water from the brine and increasing its salinity; as the salt concentration increases, this leads to dry-out and salting-out. When the brine salinity increases, the dissolution of CO₂ will dissolve. If this phenomenon takes place, it will cause reduction in the well injectivity and this will lead to pressure build up problems. In oil industry, the formation damage i.e. reduction in the permeability is attributed to the clay swelling when it comes in contact with water. The permeability is an important property of porous media, many engineers and geologists intensively studied this property and their main concern is always about the formation damage. In this experimental work, the focus was about the well injectivity and how it can be improved. As mentioned earlier, due to high NaCl concentration, the salt will be precipitated in the near well bore and it will cause reduction in the aquifer permeability and porosity and consequently the well injectivity will be affected. The dilution of aquifer salinity by periodic pumping of the sea water (salinity 3.5%) will assist in improving the well injectivity. In this work, the studied core samples (Gray Berea sandstone and Parker sandstone) were saturated with different brine solutions (10, 15, 20 and 26.4%), the core flow tests were carried out for the above mentioned core samples before and after dilution by sea water utilizing the experimental setup, and the results are obtained. It was observed that the dilution by seawater assisted in improving the CO₂ flow rates; this means that the injectivity will be increased. The main objective is to improve the well injectivity and increase the solubility trapping mechanism.

Keywords: Aquifer salinity, porosity, permeability, CO₂ storage, well injectivity