Search

For many years, the most common acid practice for sandstone acidizing is based on mud acid and dolomite formations using hydrochloric acid. During various stages of sandstone acidizing, different acids react with different minerals, and interactions of minerals with acids are an origin for precipitation reactions, which can be possibly deleterious as they may reduce reservoir permeability. During this research, the effects of chelates on pore size distribution, mineralogy, and grain size distribution have been investigated. Various chelates (GLDA, HEDTA, EDTA) were examined to react with different Berea Sandstone samples at a temperature of 180 °F and under 1000 psi confining pressure. Experimental techniques and analysis like Tescan Integrated Mineral Analysis (TIMA), were implemented in this research to understand the effect of chelates on Berea Sandstone. These results are related to elemental mass, element deportment, mineral mass, mineral locking, grain size distribution, and particle size distribution of the core samples reacted with different chelating agents. It has been found that all the chelating agents are effective in increasing the porosity and dissolving the cations from the Berea sandstone core sample. HEDTA proved to be more effective in dissolving quartz as compared to other chelates. GLDA proved to be more effective in the dissolution of rutile and zircon minerals. The significance of this research is the application of environment-friendly chelating agents to sandstone formation. Moreover, the detailed mineral analysis revealed that the most number of particles were dissolved by HEDTA.

Matrix acidizing is usually conducted on sandstone reservoirs to increase hydrocarbon production. Mineralogy plays an important role in designing acidizing treatments to enhance the production of oil and gas from sandstone reservoirs. The most common acid in practice to acidize sandstone formation is mud acid after the pre-flush acid stage. The main aim of the pre-flush acid stage is to dissolve positive ions like calcium, potassium, sodium, etc, which can cause precipitation reactions during the mud acid stage. This research is aimed to investigate the reaction mechanism of a new pre-flush acid combination (hydrochloric acid and acetic acid) with sandstone formation. Core flooding experiments were performed to react acid with the core samples (6 in x 1.5 in) under high pressure and temperature (HPHT) conditions (80 °C and 1000 psia). Analytical techniques such as Tescan Integrated Mineral Analysis (TIMA) have been used to illustrate the effect of these acids on sandstone formation. TIMA analysis showed that the new acid combination was effective in dissolving various minerals (ankerite, magnetite) and cations (calcium, magnesium, sodium, and iron). 15% HCl proved to be more effective in the dissolution of different particles from sandstone core samples. It dissolved 32.8% of the initial number of particles present inside the sample while the dissolving power of 5% CH3COOH:10% HCl is 26.7%. Subsequently, the number of pores increased by the application of 15% HCl is 22% while that by 5%CH3COOH:10% HCl is 21.8%. Density analysis showed that both acid combinations removed heavy particles effectively, whereas 5% CH3COOH:10% HCl proved more efficient in dissolving calcium ions which is very important for pre-flush acidizing.

Abstract Stimulation of the sandstone reservoir requires a mixture of acids such as mud acid, which assist in enlarging the microscopic paths by dissolving the siliceous fines or clays near the well-bore region. As a result, the formation permeability and porosity can be enhanced. In deeper wells, the temperature exceeds 200 °F, at these temperature ranges, problems can arise. For example, the use of mud acid mixtures can lead to issues like precipitations, corrosion, early consumption of acids, leading to lesser acid efficiency. In this study, the core flooding apparatus was used for acidizing experiments, designed to dissolve minerals and to analyze the changes in petrophysical parameters such as porosity, permeability, and mineralogy. Conventional and tight sandstone core samples were acidized using different chelating acids such as Hydroxyethylethylenediaminetriacetic acid (HEDTA), Ethylenediaminetetraacetic acid (EDTA) and Glutamic acid (GLDA) at high-temperature conditions. Analytical studies (mineral mass, pore size distribution, topology, grain size distribution, and density distribution were conducted using Tescan Integrated Mineral Analysis (TIMA). The obtained results showed that chelating agent HEDTA created more pore spaces in the core samples and is effective in dissolving positive ions. Also, the permeability was observed to be doubled by its application which could be effective in alteration of pore topology of the sandstone cores.