LONDON—Banks raised their forecasts for the price of Brent crude, the global oil benchmark, in 2019, as the market continues to be supported by production cuts led by the Organization of the Petroleum Exporting Countries, as well as geopolitical risks to supply. Brent crude is expected to average just over $68 a barrel this year, according to a poll of 12 investment banks conducted by The Wall Street Journal in March, compared with a forecast of $67 a barrel in February. …