Patterson-UTI Energy Inc. PTEN announced Thursday that it had reached an agreement with NexTier Oilfield Solutions Inc..NEX to merge in a stock-for-stock transaction with an enterprise valuation of $5.4 billion. NexTier stockholders will receive 0.7522 shares of Patterson UTI for every share they own under the board approved deal. About 55% of the combined business will be owned by Patterson-UTI, and 45% by NexTier. The deal, which is expected to be completed in the fourth quarter of this year, will create a world-class drilling and well completions company with 172 superspec drilling rigs as well as a wells finishing business with…