HOUSTON, Aug. 30 (Xinhua) -- The number of active drilling rigs in the United States fell by 12 to 904 this week, 144 rigs down year on year, according to the weekly data released by Baker Hughes on Friday.
According to the Houston-based oilfield services company, these active drilling rigs included 742 oil rigs operating in the U.S. oil fields, down 12; 162 gas drilling rigs, remaining level as last week.
Of the 904 rigs, 876 are land drilling ones, down 11, and 28 offshore drilling ones, remaining level as last week. The only inland water drilling rig lost in the week.
Of them, 70 are directional drilling rigs, 784 are horizontal drilling rigs and 50 are vertical drilling rigs.
The number of drilling rigs increased the most by three to 51 rigs in the state of North Dakota, while Texas lost the most with five to 441.
The number of horizontal drilling rigs this week decreased the most by 13. Horizontal drilling is one of the most renowned technologies in the petroleum industry, which has brought about a revolution in worldwide energy production.
With the combination of hydraulic fracturing and horizontal drilling, oil production has increased significantly, and this is termed as "Shale Revolution."
According to the U.S. Energy Information Administration (EIA), hydraulically fractured horizontal wells accounted for 69 percent of all oil and natural gas wells and 83 percent of the total linear footage drilled in the country.
By far, the Permian basin has been the largest source of shale oil production growth in the United States, which has become the engine of supply growth outside the Organization of the Petroleum Exporting Countries in the past years.
