Emeraude vapeur — an offshore steam pilot

Abstract

The Emeraude field is located offshore Zaïre (Congo), on the West African coast. Very adverse conditions apply to this field: water depth is 65 m, depth of reservoirs is shallow (200–500 m) and they consist of silt layers alternating with thin fractured limestone beds. In addition these very heterogeneous reservoirs are strongly depleted and oil is viscous (0.1 Pa s (100 cp) at reservoir conditions). In 1980, a steam-drive pilot was decided in order to estimate a recovery rate and an oil-steam ratio on two superimposed and independent reservoirs. The adverse environmental conditions required original solutions: tilted conductor pipes, a tilted rig, and adapted pumping units on one platform because of reservoir shallowness and steam production equipment on a second platform because of the distance to the shore. Steam injection started in March 1985, after 18 months of preliminary tests (injection and interference tests) and of primary production. A clear significant response in oil production has been noticed in some wells. After two years of steam injection, the incremental recovery rate is promising and the oil-steam ratio is 0.28 V V −1 in the pilot area. Some wells outside this area show an oil rate increase. Numerical simulations of the pilot behaviour were made with a thermal pseudo-compositional simulator.