Experimental and Theoretical Assessment of Using Propane to Remediate Liquid Buildup in Condensate Reservoirs

Abstract

Abstract This paper presents the results of an assessment of condensate phase behavior issues in the near-wellbore region. Constant composition expansion (CCE) studies were conducted to measure the retrograde liquid deposit data for a real reservoir fluid. Subsequently, the effect of adding light hydrocarbon gases on the vaporization of condensed liquid was studied. An equation of state (EOS) model was developed based on the measured data and was used to evaluate the experimentally observed phase behavior characteristics of the condensate fluid. Results indicate that although carbon dioxide can influence the liquid extraction properties of the condensate wellstream to some extent, the use of propane allows the system conditions to be supercritical conditions for most typical reservoir fluids at reservoir temperature and pressure. This allows for an enhanced liquid extraction capability, which subsequently improves wellbore extraction. Introduction It is well known that during gas-condensate production, liquid condensation and subsequent deposition occur in the near-wellbore region when the flowing pressure falls below the dewpoint pressure of the reservoir fluid.1 The condensed liquid increases the fluid saturation in the near-wellbore formation (Fig. 1) and, therefore, has the potential to decrease the gas-relative permeability. Fig. 2 presents a schematic interpretation of gas-relative permeability changes as a function of liquid saturation around the near-wellbore region. Numerous studies have focused on the experimental verification of the influence of liquid dropout on gas-relative permeability.2–7 It has been noted that reducing gas-relative permeability decreases the productivity of the well and is generally more pronounced in low-permeability formations. In some instances, the gas productivity may decrease to uneconomic levels.8,9 Methods to address this problem include hydraulic fracturing10 to bypass the "condensate ring," pressure maintenance by removing liquids and recycling gas, as well as injecting supercritical CO2 into the near-wellbore region. In this process, the CO2 extracts the condensed liquids in the near-wellbore region and, consequently, increases the productivity upon bringing the well back on-line. Experimental results show a significant improvement in gas-relative permeability of the condensate reservoir by injecting methanol.7 In this paper, we assess the experimental and theoretical thermodynamics of using propane to extract liquid dropout in the near-wellbore region. The use of propane should allow the system conditions to be in supercritical conditions for most typical reservoir fluids at reservoir temperature and pressure conditions. Fluid Characterization A typical rich gas-condensate system was considered for this project. The key properties of this fluid are summarized in Table 1. As can be seen, the gas-liquid ratio (GLR) is 3685 scf/STL and the measured dewpoint pressure of the system is 10,035 psia. The stock-tank liquid (STL) API is 33. The molecular composition of the system up to C7+ is presented in Table 2.