Statistical Forecast Models To Determine Retrograde Dew Pressure and C7+ Percentage of Gas Condensates on Basis of Production Test Data of Eastern Venezuelan Reservoirs
- Ilsis Marruffo (PDVSA) | Jose Maita (Universidad de Oriente) | Jesus Him (Universidad de Oriente) | Gonzalo Rojas (Universidad de Oriente)
- Document ID
- Society of Petroleum Engineers
- SPE Latin American and Caribbean Petroleum Engineering Conference, 25-28 March, Buenos Aires, Argentina
- Publication Date
- Document Type
- Conference Paper
- 2001. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 4.5 Offshore Facilities and Subsea Systems, 5.8.8 Gas-condensate reservoirs, 5.2.2 Fluid Modeling, Equations of State, 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements
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In this paper are presented correlations to determine the dew point pressure and C7+ content of gas condensate reservoirs, achieved from production parameters that we usually have in the field. To develop this correlations it were collected 146 PVT analysis informs of western Venezuela (Anaco) fields: San Joaquin: 42 ; Santa Rosa: 26 ; El Roble: 16 ; Guario: 4 ; Santa Ana: 3 ; El Toco: 3 ; Zapatos: 15 ; Mata-R: 15 ; Aguasay: 13 ; La Ceibita: 5 ; Carisito: 4. At the end it were finally used 106 to the final correlations.
The PVT tests results were validated through consistence tests: mathematical recombination and mass balance. After this steps an statistical analysis of the variables was done.
For this, statistical methods were used and they were focused on multiple no linear regressions.
At last the correlations accuracy were the following: dew point pressure showed 5.74 % of average error with a correlation coefficient of 0.82 based on 80 PVT's data, the first C7+ content correlation showed 9.59 % of average error with a correlation coefficient of 0.98 based on 81 PVT's data, the second C7+ content correlation showed 7.85 % of average error with a correlation coefficient of 0.99 based on 90 PVT's data.
The new Retrograde Dew Point correlation that was obtained improves the Nemeth and Kennedy (10) one that forecast dew point with 9.69 % of average error when it is applied on 54 Anaco's PVT analyses which had all the compositional information that it requires; with the new Anaco Dew Point Correlation the average error was 5 % for the same data. This news Anaco correlations allow to improve the characterization and exploitation plans of gas condensate reservoirs without PVT information.
Anaco area has been one of the most important venezuelan petroleum operational districts and it has a big number of gas condensate reservoirs. Due to the importance of gas exploitation in this area, is fundamental the development of research and new technologies that allow their efficient characterization and exploitation. There are two basic parameters: the dew pressure and the heavy components content (C7+), since retrograde condensation occurs when the pressure reservoir falls below it. They are not always available for this kind of reservoirs, and in order to get them it was necessary to develop correlations to estimated them based in fields parameters easily and usually availables. This parameters are: condensate API gravity, Gas/condensate production relation, in some cases separator gas gravity and reservoir temperature.
The selected PVT analyses passed the consistent tests of mathematical recombination of gas and liquid phases and the mass balance of the constant volume depletion experiment (CVD), this allow to verify that those samples were in thermodynamic equilibrium at each pressure depletion level. Finally, a nonlinear regression software was used to fit appropriate models to the data.
The collection of PVT data, included the PVT reports of the Greater Oficina area as well as the Greater Anaco Area. The total PVT data was 146 analyses. After the process of selection and validation we obtained a consistence analyses PVT data base of 114 tests that after a dispersion analysis was reduced to 106 and this results the final data base to develop statistical processes.
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