U.S. shale producers are drilling at the highest rate in 18 months but have left a record number of wells unfinished in the largest oilfield in the country – a sign that output may not rise as swiftly as drilling activity would indicate. Rising U.S. shale output has rattled OPEC’s most influential exporter Saudi Arabia and pushed oil prices to a near four-month low on Wednesday. U.S. production gains are frustrating Saudi-led attempts by the world’s top oil exporters to cut supply, drain record-high inventories and lift prices. Investors watch data on the number of rigs deployed in North American oil and gas fields as a leading indicator for output. But the rising rig count and frenetic drilling activity in the Permian Basin in West Texas is not all about pumping oil. [RIG/U] During […]