Development of Aluminum-Based Dissolvable Alloys for Hydraulic Fracturing Applications

Downhole tools made of dissolvable alloys (DAs) are getting more attractive, especially with the difficulties that arise from drilling wellbores with longer lateral distances. To date, most of the DAs are based on Al alloys (AAs) or Mg alloys, which offer undesirable mechanical properties. This work aims to develop a series of new Al-based DAs, providing high material strength and fast corrosion rates, for hydraulic fracturing applications. Given the enormous possibilities in tunning the structures and compositions of potential DAs, a literature review was first done to summarize the effects of various alloying elements on the microstructures, mechanical properties, and corrosion resistance of AAs. The main chemistry in downhole environments is KCl while the abundant electrochemical data of AAs are in NaCl electrolytes. In order to maximize the available electrochemical data of AAs, the effect of the associate cation type (K+ vs. Na+) on the corrosion of selected alloys was investigated by comparing the electrochemical values obtained under the same Cl- molar concentration of KCl vs. NaCl solutions. To facilitate the design and elemental selection, Taguchi's method was utilized to change the chemistry of a commercial alloy (AA 7075) by adding various elements (such as Cu, Ga, Ag, Sn, In, Zn, Cr, and Zr). Scheil-Gulliver model was used to predict the potential phases formed as well as their amounts. Based on the review and simulation results, a few candidate alloys were targeted which were anticipated to potentially yield high mechanical properties and active corrosion behavior. It is believed that the experimental and simulation methods employed in the work will facilitate the development of the most promising DA compositions for downhole applications.