The Tengiz field is a giant oil field producing 530 thousand BOPD from about 70 naturally flowing wells. Continued reservoir pressure depletion and the current surface gathering system pressure have necessitated the need for better prediction of the onset of liquid loading and consideration of mitigation strategies. Active surveillance programs and system integrity efforts have contributed to frequent well shut-ins and some challenges during well restarts. Additionally, the flow back of higher density drilling and completion fluids is becoming more difficult, especially in low pressure areas of the field, and in wells experiencing large fluid losses during drilling or workover.
Steady-state tools are used extensively for well modeling and production forecasting in Tengiz, with historically good results. However it was realized that the steady-state models would be unable to predict unstable production behavior expected to come with continued reservoir pressure decline. Hence, the asset team decided to use a transient flow simulator for a better understanding of these conditions.
This paper describes the selection of the candidate wells, calibration and validation of the transient models and the design of a representative ‘hypothetical’ well which was used to evaluate the minimum conditions for well flow during normal well operations as well as restart pressures post well shut-ins. The impact of various factors including wellhead pressure, productivity index (PI), reservoir pressure, water cut, gas-to-oil ratio (GOR), tubing size and well deviation on loading conditions were evaluated. The study results have provided invaluable information to evaluate mitigation options for liquid loading.