On the Quality of Data From Standard Gas-Condensate PVT Experiments

Abstract

SPE Members*Now with BHP Petroleum Pty. Ltd. Abstract From an analysis of the constant volume depletion experiments performed on 80gas-condensates, it is concluded that serious problems exist in the detection of the actual volume of retrograde liquid in the PVT cell. The measured liquid volume is usually only a fraction of that required to give realistic liquid densities. The frequently observed concave shape of the retrograde liquid saturation curve close to the dew point is not real and is the result of experimental error. It is recommended that the data quality be improved by directly measuring the retrograde liquid density because it provides an excellent control over the liquid saturation, especially when this saturation is low. The properties of the fluid initially in the PVT cell are normally determined mathematically. However, this often only approximates the true properties and deviations can have consequences for the derived liquid properties. The direct measurement of the composition and propertie scan easily solve this problem and is therefore strongly recommended. The analysis of the experiments leads to the following statements for constant volume depletion experiments . liquid densities are monotonically decreasing with pressure . B: and R: are both monotonically increasing with pressure. Here B: is defined as the inverted partial density of the C5+ component fraction in the liquid, while R: is the mass ratio of the C4- fraction over the C5+ mass fraction. Introduction The importance of a good knowledge of the phase behaviour and compositional properties of reservoir fluids for the development of gas-condensate reservoirs and the subsequent processing of the well stream is widely recognised. Substantial financial investment is made on the acquisition of reliable samples of a reservoir fluid and on measuring the phase behaviour or PVT propertiest. Great reliance is placed directly on the resulting data and often even more on a derived equation of state'mathematical representation. In this paper we address the subject of the quality of experimental PVT data obtained from the standard experiment performed on gas-condensates, the constant volume depletion(CVD). The experiment is related directly to the way the information is applied by reservoir engineers (reservoir material balance calculations and numerical reservoir simulations) and also serves to provide a set of data on which to base the development of a mathematical model of the fluid. This so called equation of state model is then used for all kinds of purposes, eg separator design, gas processing plant design, compositional simulations, vertical performance calculation setc. Recently a variation of the black oil PVT representation in terms of masses of pseudocomponents was presented which derives its parameters directly from experimental data without the need for equation of state simulations of separator systems etc., and which allows black oil reservoir simulations to be conducted with improved accuracy, especially for gas-condensates. P. 525^

A New and Rigorous Equation for Modeling Gas Condensate Well Deliverability Including an Experimental Study of Revaporization of Retrograde Condensate

“…Although many authors have proposed numerous methods to calculate the black-oil-type properties of the reservoir fluid with depressurization [11][12][13] , herein the fluid properties are obtained with a commercial PVT software attached to the compositional simulator, CompIV released by the former SSI Company, USA. The calculated results are shown in Fig.2 through Fig.4.…”

Comparative Study of Empirical Correlations and Equations of State Effectiveness for Compressibility Factor of Natural Gas Determination

“…The values of the parameters , , * for pure components are given in (Brusilovsky, 1992 (Drohm, 1988).…”

“…It also needs special equipment and human resources. The authors of (Drohm, 1988) discussed also the problem of quality of experimental PVT data obtained from the experiments performed on gas condensates.…”

Novel Microfluidic Device for Dew Point Pressure Measurement of Retrograde Gas Condensates

“…In gas condensate reservoirs, accumulation of condensate dropout (also known as condensate blockage) can reduce the effective gas permeability in the near-wellbore region. , If the flowing pressure is not maintained above the dew point pressure, condensate blockage can cause a significant decline in well productivity . Therefore, accurately determining the dew point pressure of gas condensates is arguably the most important thermodynamic parameter for evaluating reserve and planning production from a condensate field …”

“…3 Therefore, accurately determining the dew point pressure of gas condensates is arguably the most important thermodynamic parameter for evaluating reserve and planning production from a condensate field. 4 The retrograde condensation can be explained by looking at the phase behavior of gas condensates. Figure 1a illustrates the phase diagram of a typical gas condensatea multicomponent mixture of light and heavy hydrocarbon molecules.…”