Study on the Performance Degradation of Sandstone under Acidification

Abstract

In most oilfields, acid fracturing is widely used for oil production. Understanding the relationship between the individual factors (i.e., carbonate rock types, acid rock reaction kinetics, and deterioration of rock mechanical properties) can provide practical guidelines that can be used for the design and optimization of acid fracturing operation. This paper takes hydrochloric acid, acetic acid, and citric acid as the main research objects and carries out acidification experiments on sandstone in Changqing Oilfield, China. In addition, the effects of tribasic, dibasic, and monobasic acids on the mechanical properties of sandstone were studied. Results show that in this study area, the most obvious effect was seen with the use of dibasic acids (hydrochloric acid + acetic acid), which effectively reduced the sample quality, uniaxial compressive strength, and elastic modulus. Citric acid and Mg promote the conversion of amorphous calcium carbonate to high-crystallinity calcite, forming a white precipitate. Furthermore, it is found by scanning electron microscopy analysis that experimental group 5 (hydrochloric acid + acetic acid) has the most ideal rock erosion effect. Inductively coupled plasma emission spectrometry analysis shows that the acid rock is present in the solution. X-ray diffraction qualitative analysis of the composition and concentration of ions shows that the formation of white precipitates is citric acid and Mg promotes the conversion of amorphous calcium carbonate to high-crystallinity calcite, forming a white precipitate. The findings of this study can help to better understand the erosion, failure state, and failure mechanism of different acid types on sandstone, which may provide certain references and guidelines for sandstone acid fracturing oil production.

Research on how acidification affects the coal's microscopic pore structure in the Guizhou mining region

“…Acidizing technology refers to the restoration or enhancement of the permeability of formation pores and cracks through the dissolving and erosioning action of acid on rock cement or blockages in formation pores and cracks, and so on. This technology shows obvious penetration‐enhancing effects in carbonate, sandstone, and shale reservoirs and is therefore widely used in oil, natural gas, and shale gas extraction applications 9–11 . In the field of coal, gas pressure and ground stress increase with the increase in mining depth, the permeability of coal rock decreases, and gas is difficult to desorbed from the reservoir, leading to a significantly higher threat of gas dynamic hazards.…”

Research on the Optimization for Acidification Modification Scheme Considering Coal’s Wettability Based on the AHP–TOPSIS Method

“…In the past decades, physical permeability improvement measures, such as hydraulic fracturing, hydraulic punching, and hydraulic slitting, had been widely used in CBM mining, and they all played a positive role in increasing the permeability of seams and reducing impact ground pressure. − However, in long-term practice, it is found that hydraulic permeability enhancement measures are difficult to form cross-link networks in rich-mineral seams with low permeability and cannot deal with the minerals filled in seams. , Acidification technology, which could improve the permeability of reservoirs through injecting acid solvent to dissolve minerals, has been widely used in the field of oil and shale gas to increase their production. − Drawing on the application of acidification technology in other fields, some researchers did some acidification experiments in the field of CBM extraction and found that acidification technology could be used in seams to dissolve minerals, unblock the pore fracture, and convert the structure of coal, thereby changing its physical and chemical properties. Zha et al treated coal samples with different acid solvents and found that the content of minerals in coal reduced substantially and the permeability increased after acidification.…”

“… 13 , 14 Acidification technology, which could improve the permeability of reservoirs through injecting acid solvent to dissolve minerals, has been widely used in the field of oil and shale gas to increase their production. 15 − 17 Drawing on the application of acidification technology in other fields, some researchers did some acidification experiments in the field of CBM extraction and found that acidification technology could be used in seams to dissolve minerals, unblock the pore fracture, and convert the structure of coal, thereby changing its physical and chemical properties. Zha et al 18 treated coal samples with different acid solvents and found that the content of minerals in coal reduced substantially and the permeability increased after acidification.…”

Damage Characterization and Permeability Variation of Acidified Rock: A Theoretical and Experimental Study

“…The rising effective stress inhibits the flow of coal seam gas and hinders gas extraction. To improve the effect of gas extraction in coal seams, pressure relief and permeability enhancement measures can be adopted on roof strata. , However, due to the geological evolution over time, pore fractures in reservoirs were blocked by minerals such as calcite, montmorillonite, and hematite. − Physical permeability enhancement methods fail to alleviate this situation. Acidification, a multiphase chemical reaction occurring at the liquid–solid interface, can unblock pores and strengthen the development of the pore-fracture system of rock formation through chemical dissolution. − Its process can be roughly divided into three phases: the movement of H + in the acid fluid system to the rock surface, the adsorption of H + on the rock surface and the chemical reaction, and the departure of the products from the rock surface at the reaction end (Figure ).…”