Estimation has been made of the applicability and reliability of five well known oil well pressure drop prediction methods and for each method guidelines are presented concerning their accuracy as a function of flowrate, tubing size, liquid velocity, water cut and wellbore angle of deviation. New methods are presented for modelling pressure loss in retrograde gas-condensate wells. These methods employ redefined flow pattern map boundaries based upon the utilization of available well test data and are superior in accuracy to existing multi-flow regime and no-flow regime, methods of interest. Fourteen crude oil compositions, five retrograde gas-condensate compositions and a total of 102 well test pressure surveys from a wide range of North Sea field are used to ascertain the suitability of the correlations. The fluid PVT properties are generated by the Peng Robinson equation of state and the Schmidt Wenzel equation of state is employed for improved liquid density predictions. Generally, the predictions compare most favorably with laboratory measured data. In addition, full consideration of transient heat-transfer to the formation is included in the modelling.
Well performance modelling is important for many crude oil and retrograde gas-condensate well design calculations ranging from the sizing of production facilities to the optimum size of tubing strings. It is also important to anticipate production problems resulting from liquid condensation, particularly when the fluid is a rich gas-condensate mixture.
Many different models and correlations are available in the literature for the purpose of predicting the multiphase flow of hydrocarbon mixtures in vertical and inclined wells. Unfortunately, however, the choice of the appropriate method for a particular situation has historically been an area of great controversy. Thus, the objective of this paper is to evaluate the accuracy and engineering applicability of existing multiphase flow pressure loss prediction methods for both crude oil and retrograde gas-condensate wells. Using the available North Sea well test data it has also been possible to develop new pressure loss prediction methods.
All pressure gradient correlations may be grouped into one of the following four categories:
Single phase correlations.
Correlations which do not recognise the existence of phase slippage or distinct flow regimes.
Correlations which consider phase slippage but do not recognise the existence of distinct flow regimes.
Multi-flow regime correlations which use flow pattern maps and consider phase slippage.
The general pressure gradient equation which forms the basis of all the correlations is given by:
= + +
............(1)
P. 457^
