Sandstone Acidizing Using a Low-Reaction Acid System

Abstract

Sandstone acidizing is the process of removing the damage from sandstone reservoirs to restore the well productivity/injectivity to its original or expected rates. It differs from carbonate acidizing in which a substantial portion of the rock is dissolved. Stimulating sandstone with mud acid HF/HCl may cause many problems as sandstone is a clastic sedimentary rock that consists mainly of quartz, silica minerals, feldspars, clays, and minor quantities of zeolite and chlorites. When conventional mud acid reacts with rock some sensitive components of sandstone get cemented by silica, calcite, or iron oxides. This happens due to the different precipitation reactions that take place and form fluosilicates, calcium fluorides, silica-gel filming, and even colloidal silica-gel compounds. In this work, two chelating agents, hydroxyethylenediaminetetraacetic acid (HEDTA) and diethylenetriaminepentaacetic acid (DTPA), were used to stimulate Berea sandstone cores. Berea sandstone cores were scanned using the XRD to quantify their mineralogical composition. Different pore volumes of 0.6M HEDTA and 0.6M DTPA were used as a preflush followed by different concentrations of HF as a main flush. For the post-flush stage, ammonium chloride was used to flow back the cores and measure their permeability. The levels of calcium, magnesium, aluminum, and iron ions in the effluent samples were measured using inductively coupled plasma (ICP) to assess the ability of each chemical to leach these different ions. Both HEDTA and DTPA showed a strong capability of chelating calcium, iron, and magnesium ions from the sandstone cores while the amounts of chelated aluminum ions were quite small. Once starting the injection of the used chelating agents, the permeability of the core got enhanced gradually. The higher amounts of the chelating agents resulted in better the cores permeability. However, DTPA showed a better permeability enhancement than HEDTA due to its stronger ability to chelate the calcium, iron, magnesium, and aluminum ions. Adding HF as the main flush initiates different reactions with the clay and silica minerals of the Berea sandstone cores. This caused a reduction in the permeability due to the formation of some precipitates such as fluosilicates and calcium fluorides. Therefore, it is recommended to use a very low concentration of HF while treating the Berea sandstone.

Synthesis and Corrosion Inhibition Performance of Mannich Bases on Mild Steel in Lactic Acid Media

“…From constant K ads , the adsorption free energy ΔG ads can be determined as follows 45 = G RT K ln(55. 5 ) ads ads (17) where R is the universal gas constant, T is the thermodynamic temperature, and 55.5 is the molar concentration of water. 45 The calculated ΔG ads values of DTZA and DPZA in a 363 K environment are −34.62 and −28.90 kJ•mol −1 , respectively.…”

“…In practice, a mud acid-treated oil well normally undergoes rapid decline after an initial increase in oil production. Therefore, recently, chelating acid systems, which can realize high efficiency and rapid, uniform, and prolonged validity period of acidification, have been developed and have attracted significant attention. , Recent field applications proved that compared with conventional mud acid acidification, organic chelating acid can simplify the acidification process, reduce the total cost by decreasing the injected acid volume, and achieve a significantly increased production . Organic phosphonic acid, gluconic acid, lactic acid, etc., could be used as chelating acids.…”

Applications of Chelating Agents in the Upstream Oil and Gas Industry: A Review

“…Gomaa et al optimized the utilization of chelating agents in sandstone acidizing. DTPA and HEDTA were tested at different conditions using Berea sandstone cores.…”

Research on high efficiency and retarded autogenous mud acid for plugging removal in a sandstone reservoir—Example of Bai 823 well area

“…In 2003, Rodoplu et al developed a mathematical model of "two acids and three minerals" to reflect the change of permeability, and the experimental results verified the validity of the model and the good agreement with the experimental results. 21 In 2005, Xie et al 22 further applied the small-scale model developed by Li et al 23 to study the conditions for earthworm pore formation during sandstone acidification, and the results showed that sandstone reservoirs with strong inhomogeneity are favorable for earthworm pore formation at low injection rates. A similar study was done by Morgenthaler et al Similar studies on the effect of inhomogeneity showed that the effect of inhomogeneity on permeability in small-scale lithology is greater than the effect of petrographic mineralogy on permeability.…”