The Effect of Silica Dissolution on Reservoir Properties during Alkaline-Surfactant-Polymer (ASP) Flooding

Chemical flooding is one of the effective methods to recover large volumes of oil from sandstone formations after primary depletion. However, silica dissolution often occurs during Alkaline-Surfactant-Polymer (ASP) flooding, affecting the petro-physical properties of the formation. To address this issue, samples from Berea sandstone formations were treated with various brine solutions, through static tube tests and core flooding experiments. Analytical tests such as DR/2800 spectrophotometer and scanning electron microscope were used to evaluate the silica solubility and the alteration in mineral content. The results indicated that the silicate contents decreased after the saturation due to silica solubility in the solution. Increasing brine salinity to 40,000ppm and introducing Magnesium and Calcium ions to the solution, reduces the silicate contents by 5.03 % and 7.32 %. Moreover, saturating the samples with ASP solution, further reduced the silicate contents by 14.86 %. This reduction is associated with a relative increase in silica solubility and pH of the solution. Silica dissolution affects the pore microstructure, which resulted in increasing the porosity and pore volume after the core flooding. The injection of the ASP solution increased the porosity by 5.83%, thus the pore volume increased from 17.72 to 18.76cc. This is associated with the high silica solubility and the increase of solution pH in the ASP solution. The permeability of the samples generally reduced after the core flooding, due to the silica solubility. However, injecting the ASP solution, resulted in a major reduction of the permeability by more than 75%. These changes in the petro-physical properties can lead to severe formation damage, and affect hydrocarbon production. This study assists in understanding the impact of silica dissolution during ASP treatment and addresses the factors involved. Efficient utilization of chemical flooding can help mitigating silicate scaling within the formation, and extend field productivity.

Carbonation of minerals and slags under high pressure in an autoclave

Introduction/purpose: Carbonation of minerals (olivine and wollastonite) and secondary materials such as slag under high pressure in autoclaves has high importance due to environmetal problems. Methods: The most important for this process is to have a good knowledge of the behavior of carbon dioxide in water solution under high pressure, the precipitation of silica, dissolution of metals such as nickel and magnesium as well as subsequent filtration. Results: The carbonation process of olivine und slag under high pressure (from 40 to 80 bar) in an autoclave was successfully performed at 175°C, with and without additivies. Conclusion: A comparative analysis has confirmed better carbonation of slag (max. 300 kg/ton) in comparison to that of olivine (max. 70 kg/ton) under the same conditions.

Bottom-water temperature controls on biogenic silica dissolution and recycling in surficial deep-sea sediments

This study calculated the dissolution rates of biogenic silica deposited on the seafloor and the silicic acid benthic flux for 22 Ocean Drilling Program sites. Simple models developed for two host sediment types – detrital and carbonate – were used to explain the variability of biogenic opal dissolution and recycling under present-day low (−0.3 to 2.14 °C) bottom-water temperatures. The kinetic constants describing silicic acid release and silica saturation concentration increased systematically with increasing bottom-water temperatures. When these temperature effects were incorporated into the diagenetic models, the prediction of dissolution rates and diffusive fluxes was more robust. This demonstrates that temperature acts as a primary control that decreases the relative degree of pore-water saturation with opal while increasing the silica concentration. The correlation between the dissolution rate and benthic flux with temperature was pronounced at sites where biogenic opal is accommodated in surficial sediments mostly comprised of biogenic carbonates. This is because the dissolution of carbonates provides the alkalinity necessary for both silica dissolution and clay formation; thus strongly reducing the retarding influence of clays on opal dissolution. Conversely, the silica exchange rates were modified by presence of aluminosilicates, which led to a higher burial efficiency for opal in detrital- than in carbonate-dominated benthic layers. Though model prediction of first-order silica early transformation suggests likely effects from surface temperatures (0–4 °C) on opal-CT precipitation over short geological times (