Looking to increase its exposure to the booming U.S. oil industry, New York City-based private equity firm Arsenal Capital Partners has made a pair of purchases in oil-field chemicals, each for an undisclosed amount. It purchased Kel-Tech, a Midland, Texas-based supplier of oil-field and drilling chemicals around the Permian Basin in western Texas. It also bought Thomas, Okla.-based Danlin Industries, which provides chemicals to oil and gas firms across nine central states. Arsenal says the purchases build on its late-2013 acquisition of Flowchem, which supplies chemicals used in the operation of oil pipelines. In the ongoing U.S. shale boom, oil-field chemicals firms have become attractive acquisition targets. Last October, Solvay purchased Chemlogics for $1.3 billion.