With global energy demand soaring, Saudi Arabia, whose abundant reserves of light oil have supplied the world for decades, is looking to unlock its huge, hard-to-tap and largely unexploited reservoirs of heavy crude. If it succeeds in overcoming the technical hurdles, the effort could significantly increase Saudi Arabia's oil reserves over the next several years, potentially adding some slack to tight energy markets. It would also be a blow to so-called peak-oil theorists who have forecast that world oil production is on the brink of peaking. Crude-oil prices have more than tripled since 2002 as increases in global demand have...