Effect of Chemical Treatment Upon Formation Clays is Revealed by Improved SEM Technique

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract A number of commonly used stimulation and clay stabilization treatments have been investigated using an improved and more definite Scanning Electron Microscope technique. This technique involves photographing individual groups of clay platelets within a sandstone specimen at high magnification using the Scanning Electron Microscope and then chemically treating the sample. Following the treatment, the same set of platelets is located and again photographed under identical conditions of framing and magnification. By comparing the two SEM photographs, in addition to Energy Dispersive X-ray analysis of the platelets before and after treatment, it is platelets before and after treatment, it is possible to detect even minute changes in the possible to detect even minute changes in the structure and chemical composition of the clay minerals. The SEM technique used in these studies is described in detail. Systems studied include clay stabilizing agents such as hydroxy aluminum and zirconium oxychloride. The effect of various acids including hydrochloric acid, Mud Acid and Self-Generating Mud Acid have also been investigated. These studies clearly show how chemical treatments modify the clays present within the rock. Test results indicate that clay stabilizing agents work by either ion exchange or topochemical reactions. Hydrolyzable metal ions such as zirconium and hydroxy aluminum may not form the same kind of layer on the surface of the clay, but both materials effectively desensitize the clays. Core test data correlates well with SEM. Introduction Swelling and migration of clay minerals in sandstone formations has long been a problem in oil and gas production. Dispersed problem in oil and gas production. Dispersed or swollen clays can plug-the narrow pore openings within the formation, thus restricting both liquid and gas flow. It is believed that dispersion and migration of formation clays isoactually a greater problem than clay swelling. The dispersion of a small amount of non-swelling but migratory clay can cause a much greater reduction in permeability than an identical quantity of a swelling clay. Kaolinite and illite are two of the most commonly occurring non-swelling migratory clays, while montmorillonite is the most common swelling clay. Various treatments have been developed to prevent or minimize swelling and migration prevent or minimize swelling and migration tendencies of formation clays.

Stimulation of High-Temperature Sandstone Formations From West Africa With Chelating Agent-Based Fluids

“…In sandstones, Gdanski and Shuchart (1998) have shown that essentially all clays are unstable in HCl above 149°C. Therefore, other techniques for solving the hightemperature acidizing dilemma have included the borate retardedacid fluid developed by Thomas et al (1976) as well as the use of organic acid/hydrofluoric acid (HF) blends (Van Domelen and Jennings 1995;Shuchart 1997).…”