Shell is making a quiet but pointed return to Angola’s offshore oil patch, signing a deal to acquire a 35% stake in two deepwater blocks from a Chevron subsidiary, as international majors circle a country trying to arrest a long production slide. The agreement gives Shell a minority interest in assets operated by Cabinda Gulf Oil Co., Chevron’s Angolan unit. Financial terms were not disclosed, but Shell said the deal has government approval and is moving through final legal steps. The farm-in follows an exclusive exploration agreement…