Investigation of Increased Gas-Oil Ratios in Ain Dar Field

摘要

Reservoir and production engineers have observed an increase in gas oil ratios (GOR) with increasing watercuts in north Ain Dar (ANDR), away from the gas-cap area. Several of these wells now show GORs approaching 1,000 scf/stb. The original GOR in this area is ~570 scf/stb. This variation in GOR has a direct impact on wellbore hydraulics and on the well production rates. A study was initiated to investigate the cause(s) of this abnormal increase in GOR in this area. One hypothesis for the increased GOR is that the excess gas is being produced from the brine. To ascertain this hypothesis, both subsurface and surface oil, water and gas samples were collected and analyzed. Samples were collected from several wells with different (high) water cuts and from the gas-cap area. The analyses included the determination of gas oil ratio (GOR), gas water ratio (GWR), fluid compositions and material-balance calculations. While brine as a possible source of excess gas was the prime focus of this project, other sources such as gas-cap leak off, carbon dioxide solubility in water, gas metering problems were also be investigated. The results of this study indicate that the gas-oil ratio increases with increased watercuts. However, the increase is not enough to explain the values observed in the field. One possible suspect is gas metering with orifice plates. These possible causes of increased GORs will be highlighted in the paper.