A Pseudo-Radial Pressure Model for Near-Wellbore Condensate Banking Prediction

A new pseudo-radial pressure model for inflow performance analysis and near-wellbore condensate banking deliverability is developed. Analysis of condensate banking and evolution in near wellbore region (i.e. zone 3) has been extensively studied. The new zone 4 region identified in this work will help in delineating the limit of retrograde condensation and the onset of revapourisation. Revapourisation after retrograde condensation is usually not accounted for in most field applications. However, in mature fields such as the Oredo field investigated in this study, revapourisation and near wellbore dynamics play an important role in optimising production from the field. The results of the newly formulated model captured the transient retrograde revapourisation near the wellbore for the well X studied in this work.

Studying the impact of carbon dioxide on phase transitions of gas-condensate systems and dispersion of retrograde condensate

The paper studies the effect of carbon dioxide on the phase transitions within gas-condensate systems and defines its role on the evaporation of retrograde condensate isolated in formation due to the decreasing pressure during development process. Based on the experiments carried out by special methodology in рVT bomb, the essence of various impact of carbon dioxide amount in the content of gas-condensate mixture on the physico-chemical and thermo-dynamic parameters of the system depending on the temperature interval revealed. As a result of experiments, it was defined that the increase of carbon dioxide within gas-condensate mixture raises the content of dispersed condensate in gas phase. Moreover, the increase of CO2 in gas phase leads to the growth of gas amount dissolved in a unit volume of condensate as well. It is shown that the effect of carbon dioxide on the pressure of retrograde condensation within gas-condensate system cannot be definitely estimated. The pressure of retrograde condensation within such mixtures may be different in various temperature diapasons due to the change of the features and critical parameters of the system.

PREDICTION OF CONDENSATE BANKING WITH RELATIVE PERMEABILITY TO OIL – GAS AND SATURATION IN A GAS CONDENSATE RESERVOIR

Gas condensate fields are quite lucrative fields because of the highly economic value of condensates. However, the development of these fields is often difficult due to retrograde condensation resulting to condensate banking in the immediate vicinity of the wellbore. In many cases, adequate characterization and prediction of condensate banks are often difficult leading to poor technical decisions in the management of such fields. This study will present a simulation performed with Eclipse300 compositional simulator on a gas condensate reservoir with three case study wells- a gas injector (INJ1) and two producers (PROD1 and PROD2) to predict condensate banking. Rock and fluid properties at laboratory condition were simulated to reservoir conditions and a comparative method of analysis was used to efficiently diagnose the presence of condensate banks in the affected grid-blocks. Relative Permeability to Condensate and gas and saturation curves shows condensate banks region. The result shows that PROD2 was greatly affected by condensate banking while PROD1 remained unaffected during the investigation. Other factors were analyzed and the results reveal that the nature and composition of condensates can significantly affect condensate banking in the immediate vicinity of the wellbore. Also, it was observed that efficient production from condensate reservoir requires the pressure to be kept above dew point pressure so as to minimize the effect and the tendency of retrograde condensation. Keywords: Condensate Banking, Phase Production, Relative Permeability, Relative Saturation, Retrograde Condensation

Study the effect of nitrogen gas on phase behavior of gas condensate systems and dispersion of retrograde condensate

The effect of nitrogen gas on the phase transformation of gas condensate systems and its efficiency as a «working agent» for the production of precipitated retrograde condensate has been analyzed. Experimental studies on the pVT bomb based on a special methodology have clarified some contradictions that still exist in this area. Thus, the physical-thermodynamic nature of the different ways effect of nitrogen gas on the retrograde condensation pressure of the formation system or the stability of its dispersed state depending on the temperature range is explained. The research surveys are also studied the effect of nitrogen gas on gas phase dispersion in the precipitated retrograde condensate and liquid-gas interfacial exchange processes under different thermo-baric conditions. It was defined that if nitrogen gas is used to develop the wellbore zone of a gas condensate well, its efficiency should be specified depending on the degree of wellbore saturation with retrograde condensate, the amount of nitrogen in the working agent, formation temperature and number of cycles affecting the wellbore.

An evaluation on phase behaviors of gas condensate reservoir in cyclic gas injection

Maintaining the reservoir pressure by gas injection is frequently adopted in the development of gas condensate reservoir. The aim of this work is to investigate the phase behavior of condensate oil and remaining condensate gas in the formation under gas injection. The DZT gas condensate reservoir in East China is taken as an example. The multiple contact calculation based on cell-to-cell method and phase equilibrium calculations based on PR Equation of State (EOS) were utilized to evaluate the displacement mechanism and phase behavior change. The research results show that different pure gas has different miscible mechanism in the displacement of condensate oil: vaporizing gas drive for N2 and CH4; condensing gas drive for CO2 and C2H6. Meanwhile, there is a vaporing gas drive rather than a condensing gas drive for injecting produced gas. When the condensate oil is mixed with 0.44 mole fraction of produced gas, the phase behavior of the petroleum mixture reverses, and the condensate oil is converted to condensate gas. About the reinjection of produced gas, the enrichment ability of hydrocarbons is better than that of no-hydrocarbons. After injecting produced gas, retrograde condensation is more difficult to occur, and the remaining condensate gas develops toward dry gas.

ENHANCEMENT OF CONDENSATE RECOVERY FACTOR FROM DEPLETED GAS CONDENSATE FIELDS

The efficiency of gas condensate fields additional development at the final stage was investigated. The feature of condensed hydrocarbon production at low reservoir pressures is analyzed and the effectiveness of methods for increasing condensate recovery from depleted gas condensate fields is considered. The theoretical model of the simplified depleted gas condensate field with homogeneous volume and reservoir properties is developed. The study involves processes of the gas condensate recovery from depleted gas condensate fields enhancement through the injection of dry hydrocarbon gas, nitrogen, carbon dioxide gas into a bed, fringe of the propane-butane fraction with its transfer along the bed through nitrogen and by flooding are investigated using the hydrodynamic simulator Eclipse 300. The effectiveness of various placements of injection wells and the active reservoir water effect on the gas condensate field exploitation are outlined. The research proved that the placement of injection wells in the contour zone is the most effective when reservoir water active contour is available. In general, the introduction of methods for condensate recovery enhancement in gas condensate fields with high level of condensate should be carried out from the beginning of the field exploitation to prevent the loss of hydrocarbons because of retrograde condensation. The effect of introducing methods for the condensate recovery enhancement is relatively inconsiderable in the depleted gas condensate fields. Carbon dioxide turned out to be displacing agent. Its injection in the contour part of the field is recommended, in particular, this value will be even higher if the active water bed is not available.