Halliburton revealed a 23% rise in first-quarter earnings and topped Wall Street expectations, as demand for oil-rich shale formations kicked higher in the US, lifting its rig count in the region. The Houston-based oilfield services company reported net income of $627 million, or 68 cents a share, compared with a year earlier $511 million, or 56 cents. Excluding one-time items, the company earned 89 cents, ahead of average analyst estimates of 85 cents in a Thomson Reuters poll. Revenue for the three months ended March 31 was up 30% to $6.8 billion, up from $5.3 billion a year ago, matching the Street’s view. However, the company’s operating margin fell to 14.9% from 15.4%.