Abstract
A new waterflooding process, Toe-To-Heel Waterflooding (TTHW) was developed, partly based on recently developed thermal toe-to-heel displacement processes: THAI and CAPRI. TTHW is a novel oil recovery process utilizing a horizontal producer (HP) and a vertical injector (VI). The HP has its horizontal leg located at the top of formation, while its toe is close to the VI, which is perforated at the lower part of the formation.
TTHW realizes a gravity stable displacement, where water/oil mobility ratio becomes less important, and its detrimental effect on sweep efficiency is diminished. The main advantage of TTHW process is that the water always breaks-through at the toe, following which water cut gradually increases.
A systematic investigation of the TTHW process in a Hele Shaw laboratory model mimicking a simulated porous medium showed that the process substantially improved the vertical sweep efficiency as compared to conventional waterflooding. Following these semi-quantitative tests, a more comprehensive 3-D model testing was undertaken in order to investigate the overall sweep efficiency of the process. The 3-D model consists of a metal box filled with glass beads and saturated with oil at connate water saturation; the thickness of "oil layer" is 16 cm and the length is 42 cm. Oil was displaced with a high salinity brine, either in a toe-to-heel configuration, or in a conventional array, using only vertical wells.
A staggered line drive was used, by injecting water in two vertical wells located at one side of box and producing oil through either a horizontal producer with its toe close to injection line, or by using a vertical producer located at the horizontal producer's heel position.
Several TTHW tests were carried out at different injection rates. For a given injection rate, the TTHW results were compared to those of conventional waterflooding tests. For the same amount of water injected, the ultimate oil recovery increased by a factor of up to two, as compared to that for conventional waterflooding. Numerical simulation models successfully matched the observed performance in the laboratory.
All in all, the results of laboratory investigations and numerical simulations show that the novel TTHW process is sound, and can be further optimized.
