BP has started to simplify its portfolio and cut costs, and will make fewer but better choices in which projects to invest, chief executive Meg O’Neill said on Thursday. “We are taking concrete action to grow long-term value for shareholders: simplifying our portfolio, reducing costs, maintaining tight discipline on capex and strengthening the balance sheet,” O’Neill, the first female CEO of a Big Oil company, wrote in a LinkedIn post to reflect on the first 100 days as top executive of BP. “We need to be deliberate…