CO₂ Foam for Enhanced Oil Recovery Applications

CO2-foam yields improved sweep efficiency in enhanced oil recovery (EOR) applications over that of polymers to avoid potential polymer-induced formation damage. In addition to carbon sequestration in underground formations, CO2 foam has low water content, which also reduces formation damage in water-sensitive formations and allows for fast cleanup. However, foam stability diminishes in harsh environments such as those with high salinity and temperature and when in contact with crude oil. This chapter highlights the different foam-generation mechanisms and the deterioration effect of crude oil on CO2-foam stability. More specifically, this chapter investigates using nanoparticles and viscosifiers to improve foam stability. Further, the effects of different nanoparticles, including aluminum oxide, copper oxide, and low-cost nanoparticles such as silicon dioxide, will be demonstrated. Field applications of viscoelastic surfactants and polymers in foam systems are also reviewed. The controlling factor for these different systems is the foam stability and improved oil recovery

Removing Ilmenite-Based Filter Cakes Using Hydrochloric Acid and Chelating Agent – Experimental Study

Ilmenite is often used as a weighting agent in drilling fluids to increase the fluid density, but the formation of a filter cake on the borehole wall can impact cementing operations and reduce well productivity. To remove the filter cake, various techniques can be employed such as chemical treatments, mechanical methods, or a combination of both. The goal of this study is to evaluate the effectiveness of chemical removal of ilmenite-based filter cake using 7.5 wt.% hydrochloric acid (HCl) and hydroxyethyl ethylenediamine triacetic acid (HEDTA) – chelating agent. The filter cakes were generated using API filter press under harsh conditions of 300 psi pressure and 250°F temperature. Sandstone cores (2.5-in. diameter and 1-in. thickness) were utilized to replicate the formation during filtration experiments. The filtrate fluid was collected and the sandstone cores with filter cakes were scanned using computerized tomography (CT) technology. Immediately after that, the cores and filter cakes were soaked with HCl–HEDTA solution for 6 hours, followed by CT-scanning the cores and remaining filter cakes again. After acidizing, the effluent solution was analyzed using inductively coupled plasma (ICP). Scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) was used to analyze the dried filter cakes and remaining residue. The results showed that, the use of 7.5 wt.% HCl was effective in partially removing the ilmenite-based filter cake. Additionally, the use of HEDTA showed limited effect on the efficiency of filter cake removal, but it effectively prevented corrosion problems during the treatment. This study presents useful findings on removing ilmenite-based filter cake with a low acid concentration and reducing the risk of corrosion issues

Insights on Potential Formation Damage Mechanisms Associated with the Use of Gel Breakers in Hydraulic Fracturing

Hydraulic fracturing using water-soluble polymers has been extensively used to enhance the productivity of oil and gas wells. However, the production enhancement can be significantly impaired due to polymer residue generated within the proppant pack in the created fractures. This work describes an approach to establish a suitable fracturing fluid cleanup process by characterizing broken polymer residues generated from the use of different gel breaker types. Commonly used gel breakers such as inorganic oxidizers (bromate and persulfate salts), specific enzymes, and acids were evaluated in this work. The influence of each gel breaker was examined using High-Pressure/High-Temperature (HP/HT) rheometer, aging cells, zeta potential, Gel Permeation Chromatography (GPC), and Environmental Scanning Electron Microscope/Energy Dispersive X-ray Spectroscopy (ESEM/EDS). Experiments were performed on a carboxymethylhydroxypropyl guar (CMHPG) fracturing fluid at temperatures up to 300 °F. The developed GPC methodology showed that the size of the broken polymer chains was mainly dependent on the type of gel breakers used. Moreover, laboratory tests have revealed that some gel breakers may negatively influence the performance of polymeric clay stabilizers. Additionally, this work showed damaging precipitations that can be generated due to the interactions of gel breakers with H2S

New insights into guar gum as environmentally friendly polymer for enhanced oil recovery in high-salinity and high-temperature sandstone reservoirs

Chemical enhanced oil recovery (EOR) processes are usually used as additives for hydrocarbon production due to its simplicity and relatively reasonable additional production costs. Polymer flooding uses polymer solutions to increase oil recovery by decreasing the water/oil mobility ratio by increasing the viscosity of the displacing water. The commonly used synthetic water-soluble polymer in EOR application is partially hydrolyzed polyacrylamide (HPAM). However, synthetic polymers in general are not attractive because of high cost, environmental concerns, limitation in high temperature, and high-salinity environment. Guar gum is an environmentally friendly natural water-soluble polymer available in large quantities in many countries and widely used in various applications in the oil and gas industry especially in drilling fluids and hydraulic fracturing operations; however, very limited studies investigated on guar as a polymer for EOR and no any study investigated on its uses in high-temperature and high -salinity reservoirs. The objective of this study is to confirm the use of guar gum as a natural polymer for EOR applications in sandstone reservoirs and investigate its applicability for high-temperature and high-salinity reservoirs. The study experimentally investigated rheological characteristics of a natural polymer obtained from guar gum with consideration of high temperature (up to 210 °F) and high salinity (up to 20% NaCl) and tested the guar solution as EOR polymer. The results of this study show that the guar solution can be used as an environmentally friendly polymer to enhance oil recovery. Based on the results, it can be concluded that guar gum shows shear-thinning behavior and strongly susceptible to microbial degradation but also shows a very good properties stability in high temperature and salinity, where in low shear rate case, about 100 cp viscosity can be achieved at 210 °F for polymer prepared in deionized water. Guar polymer shows good viscosity in the presence of 20% NaCl where the viscosity is acceptable for temperature less than 190 °F. Also, the flooding experiment shows that the recovery factor can be increased by 16%.Petroleum Engineerin