The Cassia, Flamboyant, Immortelle, Mahogany, and Amherstia fields currently produce over 1.4 bcf/d for the Trinidad domestic gas market and Atlantic LNG Projects (Trains I and II). By early 2004 the gas rate should increase to about 2 bcf/d when two new projects start-up. These fields, plus the older Teak field are located in the Columbus Basin off the southeast coast of Trinidad.
The six fields have produced gas from 35 reservoirs, which are at depths from 5084 ft tvdss to 13,000 ft tvdss, and with initial pressures from 2305 psi to 7420 psi. The fluid samples and production data show that the gases are condensates. The gas is a mixture of biogenic and thermogenic gas, and the initial condensate yields vary from 1 b/MMscf up to 50 b/MMscf. For most fields, it was found that the condensate yield increased with depth or reservoir pressure.
The reservoirs exhibit a number of production mechanisms, including volumetric, volumetric with compartmentalization, and water-drive (weak to strong aquifers) (with or without compartmentalization). The paper reviews the condensate recovery factors, and produced yield trends for the different reservoirs and the different production mechanisms. It was also observed that for many of the waterdrive reservoirs that the condensate yield increased in late-life when water breakthrough occurred.
An analytical approach was used to predict whether near wellbore condensate banking would occur in the Trinidad reservoirs. The model and field data both showed that near wellbore condensate banking was not a major issue in these reservoirs because of the high permeabilities and low drawdowns. However, banking could occur in some low permeability reservoirs or if a well was produced with a large drawdown.