Horizontal wells are being used to develop the  vast resources of these four leading uncon- ventional plays, and this theme portion will  discuss the technologies — especially those  proprietary to and patented by Core Lab — that are making these successes possible. A total of 35,676 wells were drilled in the  U.S. in 2013, and the designs of approxi- mately 24,000 of those wells included hori- zontal trajectories. More horizontal wells were  drilled in the United States than in all the petroleum  provinces in the rest of the world combined. Thousands more horizontal wells were drilled in Canada. Statoil is drill- ing horizontal wells offshore Brazil and is using horizontal well technology to develop heavy oil reserves in the North Sea Grane field.  Core believes that the number of horizontal wells will continue to increase world- wide. More horizontal wells will be used to develop unconventional reservoirs, and  they will be used to develop conventional reservoirs, as Energy XXI is doing in the  shallow waters of the Gulf of Mexico today. In a decade, Core projects horizontal  wells will outnumber vertical wells worldwide. Figure 1 shows the locations of the largest unconventional tight-oil and wet-gas  developments in the U.S. The Bakken, Eagle Ford, Marcellus, and Permian Basin  developments produce more than 3,000,000 barrels of oil and NGLs per day, almost  30% of the U.S. total. More than 100 petroleum companies are involved in these  plays, ranging in size from Exxon-Mobil, Chevron, BP, Shell, and ConocoPhillips  to the smallest independent operator. The level of interest has attracted billions of  dollars of foreign oil company capital as well.  The difficulties in producing economical quantities of hydrocarbons from unconventional  reservoirs are providing opportunities for Core Lab to develop innovative technologies  that can be applied to maximizing initial and daily hydrocarbon production while maxi- mizing the total Estimated Ultimate Recovery (EUR) rates from tight-oil reservoirs.  Figure 1. Locations of the largest  unconventional tight-oil and wet-gas developments in the U.S.