The Performance Characteristics of Waterdrive Gas Reservoirs off the South-East Coast of Trinidad

Sustained production is needed to satisfy the contractual demands of both Trinidad's domestic and LNG markets. To unlock the value of existing fields on production, comprehending the case histories of produced water drive reservoirs is necessary. This study analyses production, reservoir and well data to understand trends in 12 water drive gas reservoirs from production to abandonment. These reservoirs were produced by 16 wells, from 5 fields located off the South East coast of Trinidad. From the analysis, relative permeability Corey exponents were matched to fractional flow curves in a numerical simulator. The Buckley-Leverett-Wedge (B-L-W) technique was applied to predict the flooding order of the reservoirs, but was not found to be reliable because of its inability to compensate for layering and thick reservoir intervals. Nevertheless, the shape of the relative permeability curves could be used in some cases to identify a general grain size distribution. The endpoint values of the water curves in particular were correlated with the water-wettabilities of the reservoirs. It was discovered that Recovery Factor (RF) before Water Breakthrough (WBT) was better with the high production rate reservoirs. Meanwhile improvement in RF after WBT depended on having a higher initial gas column. The pre-WBT result may have been caused by successfully outrunning the aquifer. The effect of increasing aquifer size was to lower RFs. Single well completion reservoirs' WGR profiles depended on completion orientation. Vertical completions experienced WBT between 80 and 85 percent RF compared to horizontal and deviated wells at greater than 95 percent RF. At conditions close to abandonment by water-out, phenomena such as liquid loading and condensate blocking were prevalent in a few reservoirs based on production trending. A study limitation that may have led to incorrect conclusions was the inability to keep all other variables constant whilst manipulating only one. This could be remedied by a study with a larger number of reservoirs.

Energy Control in the Depletion of Gas Condensate Reservoirs with Different Permeabilities

Energy control (i. e. pressure control) has an obvious effect on development effect in the depletion of gas condensate reservoir. Phase change behavior and characteristics of the relative pemeability in gas condensate reservoirs were displayed in this paper, then pressure and condensate distribution were showed through reservoir simulation. Finally, the influence of the pressure drop on condensate distribution and condensate oil production in gas condensate reservoirs with different permeabilities was studied. Results show that: First, in high / moderate permeability gas condensate reservoirs, the pressure and the condensate blocking will extend to further reservoir, while the pressure and condensate just appear in the vicinity of wellbore in low permeability gas condensate reservoirs. Second, the influence of pressure drop on condensate distribution in high permeability gas condensate reservoirs is obvious, the condensate blocking extends with the increasing of the pressure drop, and condensate extent can be controlled by optimizing a rational pressure drop, while the influence is inconspicuous in low permeability gas condensate reservoirs. Third, the influence of pressure drop on condensate oil production in high / moderate permeability gas condensate reservoirs is conspicuous, a rational pressure drop exists, while the influence is indistinct in low permeability or tight gas condensate reservoirs, before the retrograde condensation, a low pressure drop should be adopted in a long term until the bottom hole flowing pressure drops below the dew point pressure, when the condensate blocking forms, well stimulation is advised before developing by pressure control.

Modeling the Effect of Reduced Liquid-Wetting on Spontaneous Imbibition for Condensate Blocking Applications

In this paper, we present our interpretation for some of the unexpected experimental results that we obtained during 3D spontaneous imbibition experiments. We treated carbonate rocks with flourochemical polymers where we altered the wettability towards reduced liquid-wetting. The expected result is a reduced imbibition rate as a result of reduced capillary forces. Although the early imbibition rate decreased, we observed an increase in rate at late imbibition time resulting in a higher liquid saturation in the altered rock. We used numerical modeling to interpret the result and show that this observation actually represents the target wettability state we should be seeking in some applications.