TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper presents a new empirical correlation to predict the dewpoint pressure of gas-condensate fluids from readily available field data. The new correlation relates the dewpoint pressure of a gas-condensate fluid directly to its reservoir temperature, pseudoreduced pressure and temperature, primary separator gas-oil ratio, the primary separator pressure and temperature, and relative densities of separator gas and heptanes-plus fraction. The correlation was developed based on field and laboratory PVT analysis data of several gascondensate fluid samples representing different gas reservoirs in the Middle East. Additional data sets, not included in the development of this correlation, were used to validate the new model's accuracy. Based on the error statistical analysis results, the new model outperforms the existing correlations.
Due to instability and degradation of the conventional drilling fluids specially under high shear rate, elevated temperatures and chemically complex environments of deep and geothermal wells, it is essential to modify and develop stable batches of clay suspensions that can perform adequately under these conditions. To obtain batches, a reliable set-up should be designed and constructed to examine and measure all the properties that may possibly change under the prevailing conditions. A scaled dynamic flow loop is designed and built in the Department of Petroleum Engineering at the University of Petroleum & Minerals, Dhahran. This set-up can simulate efficiently the bottomhole condition e.g. high temperature up to 450°F, high shear rate up to 50,000 sec−1. The system pressure is maintained above the saturation pressure of water at the test temperature. Dynamic filteration rate and the corrosion rate is monitored instantaneously at wide range of bottomhole conditions. The flow parameters N&K,τ, γ etc., are obtained by measuring AP across the 3-tube viscometer using the DP 15-150 pressure differential transducers. The ambient properties are measured by Baroid multi-speed viscometer and compared with data obtained from the loop. Two batches composed of sepiolite and polymer were tested. Effective viscosity is increased significantly at high temperature for the first and second batches. The consistency and thermal stability of these fluids may be attributed to the transfer of sepiolite to smectite at high temperature and high shear.
The present method used by petroleum engineers to smooth experimental flash liberation data involves graphical technique to abram the bubblepoint volume. A trial-and-error procedure that utilizes the Y-correlation is then used to obtain the bubblepoint pressure and smooth the data below the bubblepoint pressure_ The data points above the bubblepoint pressure are smoothed using a graphical technique or least-squares regression. The smoothing technique presented in this study is a nonlinear parameter estimation approach. It smooths the data points above and below the bubblepoint pressure and determines the bubblepoint volume and bubblepoint pressure simultaneously. Other advantages of this approach are that it avoids trial-underror procedure and provides a quantitative measure of the results by calculating confidence limits on the estimated parameters. It was also demonstrated that the new correlation introduced (X-correlation) is more sensitive to the bubblepoint volume while the Y-correlation is more sensitive to the bubblepoint pressure. Introduction Pressure volume relationships are needed for many reservoir engineering calculations. One of the methods to obtain such data is to conduct a flash liberation on constant composition expansion experiment on a gas-oil mixture at a constant temperature. The analysis of the data obtained will define the bubblepoint volume, the bubblepoint pressure, the single-phase volumetric behavior at pressure above the bubble and the two-phase volumetric behavior at pressures below the bubbleprint. The experimental smoothing procedure used by petroleum engineers consist of three steps. First, the experimental data of volume versus pressure ate plotted. The bubble point volume is obtained from the intersection of the two curves of the data above and below the bubblepoint pressure. The pressure at the intersection point is considered as an initial estimated of the intersection point is considered as an initial estimate of the bubblepoint pressure which is usually refined during the smoothing process of the data below the bubblepoint pressure. The second step is to smooth the experimented data at pressures above the bubblepoint. This can be accomplished either graphically (1) or using regression techniques by fitting the relative volume versus pressure to a quadratic equation. The third step is to smooth the data at pressures below the bubblepoint. The most popular method of smoothing such data is by use of an empirical relation termed the Y -correlation2. The Y-correlation is defined as: Equation. (Available In Full Paper) Where Y is calculated from the regression line: Equation. (Available In Full Paper) In Equation (3), a 1 and a2 are the regression parameters. The properties of the Y-correlation were summarized by Standing(2) System composed almost entirely of hydrocarbons show a linear relation of Y and pressure, while systems that contain appreciable quantities of non-hydrocarbons usually give curved relation of Y and pressure. The sensitivity of the Y-correlation of Y and pressure. The sensitivity of the Y-correlation is greatest close to the bubblepoint of the system. The smoothing method outlined above has several disadvantages:Only the experimental data at pressure below the bubblepoint pressure are utilized to obtain the bubblepoint pressure.
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