Abstract

JOB Pertamina-Seaunion Energy (Limau) Ltd. drilled its first horizontal well in the Q-51 Block of the Limau Oil Field, South Sumatra, Indonesia in September, 1999. The primary objective was to improve production performance and oil recovery from a mature oil field that faces escalating water cuts and production decline. The reservoirs are massive stacked channel / alluvial sandstones, with excellent porosity and permeability, occurring in thick, stackedsand sequences. Water coning in vertical wells has been partially controlled in recent years with reverse coning installations (dual oil-leg/water-leg completions).

Reservoir numerical simulation modeling was used to history match existing vertical wells and to forecast production from possible horizontal well locations across the top of the remaining oil pay. A detailed drilling plan was prepared for drilling a horizontal sidetrack through a "window" cut in the casing of an existing vertical well. The well was successfully drilled and a 215-meter horizontal section of excellent oil pay was completed open-hole, with an uncemented pre-perforated liner.

The well produced clean oil during the first five weeks of production; however, after that, the watercut steadily increased. A bottomhole flowing and shut-in pressure survey was conducted and the test analysis indicated that the pressure drawdown was very low, that only 5-10% of the total pay section was effectively producing, and that the wellbore skin was negative. Later, a mud clean-out job and production logging survey was performed, which showed no improvement and that all of the production was coming from a short section at the toe of the well. It was concluded that the wellbore has encountered a very high permeability layer that is causing the water problem and that it may be possible to close this off. It was also concluded that a completion method allowing more isolation control of the wellbore should be utilized on future horizontal wells of this nature.