The global oil and natural gas industry will need to drill more than 670,000 wells from 2014 through 2020 to meet demand forecasts, according to consultant Douglas-Westwood (DW).

The firm's "World Development Drilling & Production Forecast" said more than 79,00 wells were drilled worldwide in 2013. However, by 2020, annual well numbers would need to exceed 106,000 to meet a 17% growth surge in demand.

"As the easiest-to-access oil and gas reserves deplete, each year we have to drill more and more wells for less and less production per well," said Chairman John Westwood. "Over the period, numbers of development wells drilled need to grow 35% to enable oil and gas production to meet an expected demand growth of 17%.

"This effect is most marked onshore, where by 2020 we expect production to grow by 15%, whereas offshore production should grow at 21% due to developments in deepwater."

DW geologist Matt Cook, who led the modeling forecast, said the 114 deepwater development wells that were drilled in 2013 should increase to more than 400 deepwater wells by 2018. "Meanwhile, production will grow from 6,000 boe/d to 9,500 boe/d."

The demand expectations vary from country to country, said senior analyst Matt Loffman.

"Driven by onshore unconventional liquids production, the U.S. has gained approximately 2,000 b/d crude in addition to almost 500 boe/d of gas in the past two years," he said. "As rigs are focused on oil-targeted wells in the future, onshore oil well completions are set for a 36% increase by 2020."

However, in Norway, which also has plentiful supplies of gas, oil production is expected to increase slightly over the next six years.

"This will be led by improved recovery from existing fields and greenfield projects such as the Goliat and Johan Sverdrup fields," said analyst Andy Jenkins. "DW forecast gas production will increase to 19,500 boe/d from 18,400 boe/d off the back of substantial investment and a number of planned projects in the Barents Sea. Such redevelopments will see the number of well completions sit around the 200 mark into the 2020s."

Traditionally productive regions are in decline and face a variety of futures, according to DW.

"Shallow water oil production is struggling for growth, despite high levels of investment, while many aging onshore regions require redevelopment and must turn to unconventionals, as North America has, in order to stand a chance of long-term growth. However, global oil and gas supplies and accordingly, the drilling industry, will remain dominated by onshore activity, accounting for 97% of well completions and 71% of global output."