Gas Condensate engineering  Dry Gas engineering except: Gas Condensate Reservoirs Characteristics GOR : 3000 – 200 000 scf/STB OGR : 300 – 5 STB/MMscf C7+ : 0.5 – 12 mol % Tc < TR < Tcricondentherm Retrograde condensation (liquid dropout). Condensate blockage (productivity loss). Condensate revenues. What’s special about gas condensate reservoirs? Fluid types Unit Conversion Units Gas Condensate engineering  Dry Gas engineering except: A ‘retrograde’ liquid phase forms in the reservoir as pressure falls below dewpoint. This liquid HC phase usually has zero or very low mobility except near-well. Retrograde condensation impacts condensate recovery and well deliverability (i.e. economics). A significant part of the income of a field may come from surface condensate (liquid) production. Surface condensate comes from the produced reservoir gas when it is processed at the surface. Most gas condensate reservoirs are produced by depletion. Typical depletion recoveries are 60 to 80% for gas and 20 to 40 % for condensate. Gas cycling can increase condensate recoveries, but will delay gas sales and/or require purchase of injection gas -- and therefore is often uneconomic. When Well BHP falls below the dewpoint, productivity can be reduced by the accumulation of liquid around the wellbore -- “condensate blockage”. This is an important consideration for most low and medium permeability condensate reservoirs.

References Examples Notes Craft and Hawkins, Petroleum Reservoir Engineering, Ch.2 Muskat, Gas Condensate Ch. 13. Gas Condensate PVT – What’s Really Important and Why? SPE Phase Behavior Monograph Chapter 2. Examples Value of Gas and Liquids: CGR - Cn+ relationship Simulation example – Depletion and Gas Cycling Notes