Investigation of Increased Gas-Oil Ratios in Ain Dar Field

摘要

Reservoir and production engineers have observed an increasein gas oil ratios (GOR) with increasing watercuts in north AinDar (ANDR), away from the gas-cap area. Several of thesewells now show GORs approaching 1,000 scf/stb. The originalGOR in this area is ~570 scf/stb. This variation in GOR has adirect impact on wellbore hydraulics and on the wellproduction rates. A study was initiated to investigate thecause(s) of this abnormal increase in GOR in this area.One hypothesis for the increased GOR is that the excessgas is being produced from the brine. To ascertain thishypothesis, both subsurface and surface oil, water and gassamples were collected and analyzed. Samples were collectedfrom several wells with different (high) water cuts and fromthe gas-cap area. The analyses included the determination ofgas oil ratio (GOR), gas water ratio (GWR), fluidcompositions and material-balance calculations. While brineas a possible source of excess gas was the prime focus of thisproject, other sources such as gas-cap leak off, carbon dioxidesolubility in water, gas metering problems were also beinvestigated. The results of this study indicate that the gas-oilratio increases with increased watercuts. However, theincrease is not enough to explain the values observed in thefield. One possible suspect is gas metering with orifice plates.These possible causes of increased GORs will be highlightedin the paper.