LPG characterization and production quantification for oil and gas reservoirs

摘要

Liquefied petroleum gas (LPG) refers to the gas extracted and liquefied from the separator gas in a processing plant and mainly consists of propane (C3) and butane (C4). Many offshore projects have restrictions on flaring gases and special fiscal terms make extracted liquids significantly more valuable than oil and condensate in some cases, which in turn impact the economics of many projects.This paper for the first time systematically investigates LPG characterization and production quantification coupled together with reservoir simulation. Detailed calculations of LPG yields from both gas cap and solution gas are given. LPG yield of fluid is a function of the initial gas-oil ratio (GOR), gas specific gravity, and separator condition: LPG yield, which is lower in the gas cap compared to the solution gas of the same reservoir, has a good correlation with gas specific gravity and is impacted by separator conditions.The concept of LPG-produced GOR correlation curve is introduced and applied together with gas production rate to predict LPG production. Correlation curves depend on reservoir fluid properties and development strategies. Generated from flashing the mixtures of different proportions of oil and gas samples, LPG-produced GOR correlation curve has a good agreement with the results from reservoir compositional simulation and can be coupled with various forecasting tools in reservoir engineering. Lean gas injection has an insignificant impact on LPG recovery but can substantially improve the recovery of total liquid (oil and condensate). The paper also shows that lumping C3 and C4 as one pseudo-component is suitable.