Rick Gdanski

Newly discovered equilibrium controls HF stoichiometry

This paper describes the discovery of a chemical equilibrium between silicon fluorides, aluminum fluorides, and HCl that controls the reactivity ratios or stoichiometry of the primary and secondary reactions of HF acid that allows accurate modeling of effluent compositions in laboratory flow tests and is consistent with returns analyses from HF treatments.

Kinetics of Tertiary Reaction of HF on Alumino-Silicates

The standard description of HF acidizing chemistry clearly demonstrates a primary and secondary reaction of HF with alumino-silicates. 1 Field experience has taught our industry that possible precipitation during the secondary reaction can adversely affect treatment success. 2 This statement has been particularly true in formations with high K-feldspar content or formations having temperatures above 300°F. Recent work has also reported the existence of a third, or tertiary reaction of HF with alumino-silicates. 3 This paper reports how the rate law and kinetics for this tertiary reaction are determined on kaolinite and feldspar over a broad temperature range. This document also discusses the discovery of how most clays were thermally unstable to HCI at temperatures above 250°F. These findings were made possible by recently applied experimental techniques including 19 FNMR Spectroscopy, 3 fractional pore volume flow experiments. 4 and an accurate knowledge of the HF stoichiometry. 5 The tertiary reaction of aluminum fluorides. AlF x (where x is the average F/Al ratio). with clay was slow below 200°F and was dominated by HCI decomposition of the clay above 250°F. The tertiary reaction required the presence and consumption of acid to proceed. Feldspars were very stable in HCI at all temperatures while every clay tested had a temperature above which it was easily decomposed by HCI. Ion-exchanging clays tended to be the least stable of the clays, while kaolinite was the most stable clay.

Encapsulated Scale Inhibitor for Use in Fracturing Treatments

This paper describes the development and testing of a solid, encapsulated scale inhibitor for use in fracturing treatments. Data from laboratory and field tests are reported. Laboratory testing with a continuous flow apparatus has yielded inhibitor release rates under dynamic conditions. The inhibitor was tested to determine the minimum inhibitor concentration required to inhibit the formation of CaCO 3 , CaSO 4 , and BaSO 4 scales in brine. Laboratory data were used to determine the parameters of a mathematical model to predict the long-term release rate of the inhibitor. Data from a treated well are compared with predictions of the model. Release-rate testing in a continuous-flow apparatus shows that an encapsulated solid derivative of a phosphonate inhibitor has a sustained release profile. Temperature (100° to 225°F) and brine strength have a small effect on the release-rate profile. Coating the solid derivative makes it compatible with metal-crosslinked fracturing fluids. The coating has a short-term effect on the release-rate profile. The composition of the solid derivative has the greatest effect on its long-term release-rate profile. A comparison between the mathematical model proposed to describe the long-term release rate of the inhibitor and actual data collected from a treated well shows a large discrepancy, likely because most of the inhibitor is not in contact with the water being produced from this well.

Modeling Acid Returns Profiles After HF Acidizing Treatments

A comprehensive hydrofluoric acid (HF) acidizing radial-flow model describes deep-matrix mixing and backproduction of spent acidizing fluids. The model has matched published ioninc returns profiles of several HF acidizing treatments. A hypothetical HF acidizing treatment was modeled that demonstrated approximately two treatment volumes of aqueous production are required to recover most of the original treating fluid. The full-length paper contains four case studies where published field acid returns were matched with the simulator.