The oversupply of gas and gas liquids, largely due to the advent of new drilling methods such as hydraulic fracturing, has also hurt prices.
Many companies have announced plans to build new pipelines, but stricter regulations and environmental concerns have delayed the completion of several projects.
"Copano is already executing on a substantial backlog of expansion projects for which it has secured customer commitments and is exploring a significant amount of projects incremental to these," said Kinder Morgan Chief Executive Richard Kinder.
Kinder is also the chief executive and co-founder of Kinder Morgan, which sold its Tennessee Gas Pipeline and a 50 percent stake in El Paso NaturalGas pipeline to Kinder Morgan Energy for about $6.22 billion in August.
Kinder Morgan in May won U.S. approval for its $23 billion acquisition of rival El Paso Corp.
Kinder Morgan Energy said late on Tuesday it would offer 0.4563 of its unit for each share of Copano. The ratio translates into a price of $40.91 per share - a 23.5 percent premium to Copano's Tuesday close of $33.13.
Thomson Reuters StarMine's intrinsic valuation model suggests Copano should be trading at $22.44. The models take into account analyst estimates for growth, usually over five years, and then model the typical growth trajectory of companies over a longer period of time.
Shares of Houston-based Kinder Morgan Energy closed at $89.66 on Tuesday on the New York Stock Exchange.
Including debt, the total deal value is about $5 billion, Kinder Morgan Energy said.
"As a result of this acquisition, we will be able to pursue incremental development in the Eagle Ford Shale play in south Texas, gain entry into the Barnett Shale Combo in north Texas and the Mississippi Lime and Woodford Shales in Oklahoma," CEO Kinder said.
Copano owns an interest in or operates about 6,900 miles of pipelines with capacity of 2.7 billion cubic feet per day (bcf/d) of gas and nine processing plants with more than 1 bcf/d capacity.
Kinder Morgan Energy owns an interest in or runs about 46,000 miles of pipelines that transport gas, gasoline, crude oil and other products, while its 180 terminals store petroleum products, chemicals and such other products.
The acquisition will add at least 10 cents per unit to Kinder Morgan Energy's earnings for at least the next five years beginning 2014, the company said.
Kinder Morgan Energy said TPG, to which Copano had sold 10.33 million convertible preferred units at $29.05 each, has agreed to support the deal,which is expected to close in the third quarter.
Kinder Morgan Energy expects to retain the "vast majority" of 415 people employed by Copano, which was founded in 1992 by John Eckel Jr, who served as its chief executive until his death in November 2009.
Citi advised Kinder Morgan Energy, while Weil Gotshal & Manges and Bracewell & Giuliani acted as legal counsel. Barclays Capital and Jefferies & Co were the financial advisers to Copano, with Wachtell, Lipton, Rosen & Katz acting as its legal counsel.