PITTSBURGH — Shell Oil Co. is still actively exploring a plan to build a huge natural gas processing plant in Western Pennsylvania, and may have selected engineering firms to do feasibility studies.

In March 2012, Shell chose a possible site in Beaver County for the so-called ethane cracking, or cracker, plant. It would convert ethane from Marcellus and Utica Shale natural gas into more profitable chemicals such as ethylene, which are used to produce everything from plastics to tires to antifreeze.

But Shell has cautioned that a final decision on whether to build the multibillion dollar plant wouldn’t be made for several years. While some reports suggested that the project might be canceled, The Associated Press found that Shell still has scores of people working on the assessment.

Shell has an option to buy the industrial site in Monaca that’s now owned by Horsehead Corp.

Horsehead CEO Jim Hensler said Shell continues to be “extremely active” at the site, with “about 70 people crawling all over” it.

Shell spokeswoman Kimberly Wendon said that “our evaluation of the site continues” and that the process “typically takes several years to complete.”

There also are other signs Shell is seriously considering the project.

Gulfport Energy Corp. said that it signed a contract to provide Shell with raw natural gas for the project, if it gets built.

Last month Chemical Week, an industry publication, reported that Shell has chosen two multinational engineering firms to do feasibility and pre-project planning. Executive Vice President Graham van’t Hoff told the publication that Bechtel Corp. and Linde AG of Germany would do the preliminary work.