<p>A lightweight cement grout for filing an annular cavity formed between to an internal longitudinal tubular member inserted in an external longitudinal tubular member includes Portland cement in an amount ranging between 250 and 550 kg per cubic meter of the cement grout; water in amount ranging between 145 and 375 liters per cubic meter of the cement grout; and a foaming agent in a quantity sufficient to adjust the wet density of the cement grout to a value ranging between 600 and 1000 kg per cubic meter.</p>
