Gas Cap Monitoring in high flow rate, low porosity clastic reservoirs in Colombia gives big economic returns

Abstract

Abstract Cased hole neutron logging has been around for a long time and is often used to monitor gas movement in reservoirs behind pipe. This often works well in high porosity reservoirs but is rarely successful in low porosity reservoirs. In Colombia, there are high flow rate reservoirs with significant permeability, that have low porosity (5-6 PU). The challenge was to monitor gas cap expansion, fluid movement due to re-injection, and voidage. At the same time the objective was to identify low GOR intervals behind pipe for possible recompletion. A number of different examples are shown to illustrate both the technique and the economic benefit of the monitoring program. Many of these wells contributed significant additional oil from bypassed zones that were initially thought to be dry gas. In some wells, the instantaneous incremental production was over 10,000 BOPD from a single recompletion. Gas cap monitoring in very low porosity reservoirs in Colombia proved to be not only feasible, but extremely profitable by differentiating dry gas zones from low GOR zones.