But analysts cautioned the deal would put pressure on Shell's balance sheet at a time the company is already planning substantial spending.
The deal will increase Shell's daily gas production in North America by about 7.5 percent and give it access to a swathe of the Marcellus Shale, the northeastern US rock formation that is one of the crucial sources of future US gas production.
Shale gas accounts for between 15 percent and 20 percent of US gas production but is expected to quadruple in coming years, touching off a scramble among producers large and small for access to resources.
A Shell spokeswoman said the company was not commenting on how it intended to finance the purchase. Shell had $8.45 billion cash and equivalents on its balance sheet at March 31 and generated nearly $4.8 billion in cash flow from operating activities in the first quarter.
"Although this is a good move it will put further pressure on the balance sheet, which is weakening with the high level of organic capital expenditure the group has committed to, and this has seen the balance sheet weaken over the past two years," Panmure Gordon analyst Peter Hitchens said in a note.
Hitchens said that weakened balance sheet would keep Shell from increasing its dividend over the next two years.
Shell shares fell in the early hours of trading before rebounding and were up 0.25 percent at 0934 GMT, outperforming declines in oil and gas indices.
"These acreage additions form part of an on-going strategy, which also includes divestments, with an objective to grow and to upgrade the quality of Shell's North America tight gas portfolio," Shell Chief Executive Peter Voser said. East controls 650,000 net acres (2,600 square kilometers) in the Marcellus Shale, and 1.05 million net acres overall.
The rush for acreage has been met, however, with persistent weakness in gas prices. Front month gas prices are down more than 22 percent this year, though after a steady decline they began to form a bottom in late March.
Shale gas is also harder and more expensive to extract, given that it comes from rock and not traditional reservoirs, further pinching margins.
Shell said closing the deal was subject to customary regulatory approvals. Besides its majority owners, East counts private equity firm Kohlberg Kravis Roberts & Co. as an investor and Jefferies & Co. as an adviser.
The acquisition came hours after the US government said it would review Shell's plans to begin drilling exploratory wells off Alaska this summer, delaying the project.
The already controversial project has faced increased scrutiny in recent weeks in the wake of the massive BP oil spill in the Gulf of Mexico.
"The news (on East) masks other bad news for Shell," Theodoor Gilissen Bankiers analyst Peter Heijen said in a research note. "That the delay falls right in the summer, just as drilling can happen there, is extra bad."
