Effect of dilute acid treatment on adhesion properties of Longmaxi black shale

Abstract

Properties of shale in an acid environment are important when acid or CO 2 is injected into geologic formations as a working fluid for enhanced oil and gas recovery, hydraulic fracturing and reduced fracture initiation pressure. It has previously been shown that acid fluids can enhance the formation conductivity and decrease the hardness of shale. However, less is known about the effect of dilute acid on the adhesion properties of shale. In the study, shale samples are characterized in detail with advanced analysis. Adhesion properties of shale via dilute acid treatment were revealed by atomic force microscopy (AFM) for the first time. Results indicate that acid treatment can greatly enhance adhesion forces of the shale surface. After acid treatment, the average adhesion forces show a platform-like growth with an increase in loading force. Through analysis of results from AFM, scanning electron microscopy, and X-ray diffraction, we affirm that the enhanced adhesion forces are mainly from increased specific surface area and reduced elastic modulus. The results presented in this work help understand the adhesion properties of shale oil/gas present in an acidic environment, which have great significance in unconventional resources development.

Modification of Microscopic Properties of Shale by Carbonic Acid Treatment: Implications for CO2-Based Fracturing in Shale Formations

“…Adhesion force is an intrinsic property of materials, which is relatively stable for the homogeneous surface. The intermolecular interaction related to adhesion force can be chemical bonding, van der Waals forces, and electrostatic force. , With proper modification on the AFM tip, the interactive forces measured can provide quantitative insight into the adsorption behavior of oil and gas. − Until now, research on the adhesion properties of shale at the nanoscale is still in its early infancy, and there has not been a unified understanding in adhesion properties of shale for the inherent heterogeneity. ,,, …”

“…45−47 Until now, research on the adhesion properties of shale at the nanoscale is still in its early infancy, and there has not been a unified understanding in adhesion properties of shale for the inherent heterogeneity. 36,41,45,47 In this study, preexperiments are performed on the silicon substrate to ensure the stability of the instrument (as shown in Figure S4) and the adhesion force is almost consistent under different conditions. We innovatively divided the surface into quartz and nonquartz regions according to the EDS mapping results (Figure 5) and measured the adhesion force.…”

Evolution of Shale Microstructure under in Situ Heat Treatment: Synchrotron Small-Angle X-ray Scattering

“…1,10,15,16 Chem-ical stimulation refers to the transformation of the shale inorganic mineral matrix or OM by using acids, oxidants, or metabolites of microorganisms. 12,17 Heat treatment technology can be further categorized according to different methods into resistance heating, high-temperature steam injection, and electromagnetic heating. 13,18,19 Fracturing technology improves the connectivity of the reservoir by forming artificial fracture networks through mechanical stress.…”

“…Shale has a complex pore structure and is often accompanied by narrow pore throats, which hinders the migration and diffusion of methane gas. − Methane gas in shale reservoirs is largely adsorbed on the surface of organic matter (OM) and clay aggregates, and free gas is sealed in the narrow throat intergranular pores and natural fractures. , Based on the above characteristics, reservoir stimulation and production technologies utilized include fracturing technology, chemical reservoir stimulation, and heat treatment technology. − …”

“…For fracturing technology, the commonly used fracturing medium is water, although other fluids like liquefied petroleum gas (LPG), CO 2 , can also be used to help shale gas production to be more environmentally friendly and efficient. ,,, Chemical stimulation refers to the transformation of the shale inorganic mineral matrix or OM by using acids, oxidants, or metabolites of microorganisms. , Heat treatment technology can be further categorized according to different methods into resistance heating, high-temperature steam injection, and electromagnetic heating. ,, …”