Modeling Condensate Banking in Lean Gas Condensate Reservoirs

摘要

Gas condensate reservoirs show a complex behavior when they are produced below dew point pressure under isothermal conditions, due to the presence of a two-phase system, and the appearance of a condensate banking phenomena. Recent gas condensate field discoveries in Peru exhibited initial reservoir pressures slightly higher than dew point; as PVT reports indicated that retrograde liquid saturation would not exceed 4%, condensate drop-out was not presumed to be a significant problem affecting well productivity and production performance, and indeed, strategies to face this problem have been currently delayed Initial multirate tests run in the Peruvian gas condensate fields did show only a slightly indication of liquid drop-out in NIA formation (less than 5%), but some features of the existence of condensate banking were noticed in NOI and ENE reservoirs. As a consequence, it is worth to study the condensate drop-out phenomena as in many cases, it causes a permanent reduction in well productivity, and eventually, in recovery factor, even though is partially compensated by capillary number effects. An integrated approach to model the condensate banking phenomena at well and fullfield scales, over the time, in Peruvian gas condensate fields is proposed by the combination of two powerful tools: well testing analysis and numerical compositional simulation; while the transient testing analysis, supported by a deconvolution algorithm, is used to evaluate “snapshots” of the three or four regions representing the various mobility zones around the wellbore, the compositional simulation allows predicting how the condensate banking will evolve in the future, and how this phenomena will affect production performance. Preliminary results predict a reduction of gas and oil production and recovery between 3% and 5%.