Slow down, you have at least until the second half of 2016, maybe longer depending on the approval process. Figure how much your tax will be (or consult a tax accountant) so you have a real number to work with; remember the gain will be long-term and you can spread it out over 2015 and 2016 by selling some in each year. Also, review the rest of your portfolio and clean out any losers--you can buy them back after the wash-sale rule expires if you really want them, but ITM, the losses will help offset your gain.
Since you're already invested in a natgas company that owns pipelines, consider buying midstream natgas mlp's or their GP's--most report losses for tax purposes that may offset some of your gain even though you'll receive cash distributions (you'll have to deal with K-1's, but doing that is usually cheaper than paying income taxes).
Last, take comfort that you have a GAIN! After the last few days, you are in the minority.