Estimation of Saturation Pressure Through Wellbore Measurements (2004)

Estimation of Saturation Pressure Through Wellbore Measurements Millan Arcia Einstein; Millan Arcia Einstein PDVSA Search for other works by this author on: This Site Google Scholar F. Rodriguez; F. Rodriguez PDVSA Search for other works by this author on: This Site Google Scholar W. Madail W. Madail PDVSA Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Houston, Texas, September 2004. Paper Number: SPE-90186-MS https://doi.org/10.2118/90186-MS Published: September 26 2004 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Get Permissions Search Site Citation Einstein, Millan Arcia, Rodriguez, F., and W. Madail. "Estimation of Saturation Pressure Through Wellbore Measurements." Paper presented at the SPE Annual Technical Conference and Exhibition, Houston, Texas, September 2004. doi: https://doi.org/10.2118/90186-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractReliable fluid property data is always required in reservoir description. Normally, the most accurate fluid data is available from PVT studies, based on surface or bottomhole collected fluid samples. Specifically for Gas Condensate systems, fluid sample reliability poses a strong challenge mainly due to thermodynamic-instability-related problems. Very often, due to the extremely low liquid to gas ratio, even in high yield fluids, inaccuracies related to surface sampling links to erroneous results in PVT data. Despite recent advances in pressure compensate bottomhole fluid samples, temperature dependency yielding to phase envelope migration poses a strong challenge.Tedious and time consuming laboratory procedures adversely impact field operations and hence final operating costs. Without implying to substitute laboratory results, a simplistic approach has been developed to determine saturation pressure based on easily acquired downhole wellbore data. The method involves basic flowing pressure versus depth sensor-gauge-data to estimate the dynamic gradient derivative, and offers a fast, reliable, and inexpensive approach to identify saturation pressure, fluid segregation and convection events in under saturated reservoirs. Actual PVT and dynamic gradient data belonging to gas condensate reservoirs were used. Measured saturation pressure was available for two of the three wells evaluated. The fluid data was validated and reproduced by means of the PVTi Eclipse module. PVT consistency verification was performed via, well completion, and production data, mass balance and thermodynamic stability checks. Results suggest good match between the PVT and dynamic gradient derived saturation pressure values.IntroductionAccurate and reliable fluid property data is vital for proper reservoir management and production optimization of oil and gas reservoirs. In reservoir studies, it is normally used data obtained from laboratory analysis of actual fluid samples recovered from the reservoir.Obtaining representative fluid samples from a gas condensate well is difficult due to condensation of liquid fractions in or near the wellbore, and instabilities caused by thermodynamic fluid changes in the vertical and horizontal flow regions. Large errors in estimating the dew point and in predicting performance of condensate systems can occur due to the non-representative nature of the samples and tedious-time-consuming laboratory procedures. Calculations can be made for estimating the dew point pressure using the equilibrium constants (K-values) but this method also requires fluid composition from representative samples. The modern approach is to mathematically predict the phase equilibria using the Equation of State (EOS). However, EOS method also requires detailed laboratory analysis on a representative sample and this data is often of poor quality or is not available at all.In this paper, we present a simple method for a reliable and accurate estimation of the dew point pressure for gas condensate systems. The method consists of recording the dynamic pressure profile of a producing well using a sensitive pressure gauge. The recorded pressure (versus depth and time) is analyzed to establish pressure gradients, density and gradient derivative in the wellbore and this, in turn, is interpreted in terms of condensation, segregation, fluid convection and flow regime identification in the wellbore. The pressure at which the condensation first appears is the estimated dew point for the gas condensate system.PVT ValidationTwo PVT and three pressure versus depth data sets were used in this study. Sampling conditions are shown in Table 1 whereas fluid description is shown in Tables 2 and 3. These data belongs to wells located in Eastern Venezuelan Eocene formations (See Figure 1). Besides a complex fluid column, these reservoirs are originally at high pressure and temperature in excess of 10.000 psi and 300 °F respectively. A general description for the fluid samples is shown in Table 1.As can be observed, these samples belong to undersaturated gas condensate reservoirs with gravity ranging from 36 to 38 °API. The samples were collected early in the life of the reservoir, at the initial stages of production, from the high-pressure separator and later recombined at the laboratory, to the gas/liquid ratio of the produced fluid. The dew point pressure for the recombined samples ranged between 7800 and 8300 psi at reservoir temperature 303 and 305 °F respectively, hence remaining in single phase at reservoir conditions. Keywords: reservoir surveillance, composition, gradient, venezuela, derivative plot, condensate system, condensation, estimation, pvt measurement, fluid sample Subjects: Well & Reservoir Surveillance and Monitoring, Fluid Characterization, Phase behavior and PVT measurements This content is only available via PDF. 2004. Society of Petroleum Engineers You can access this article if you purchase or spend a download.