Abstract

A new practical method is proposed to estimate pressure drop for multiphase flow in tubing.

It needs only two steady state production tests (i.e. two triples of bottom hole flowing pressure, well head flowing pressure, stock tank oil flowrate) plus some basic information such as the tubing inner diameter.

The pressure drop is simply expressed by an equation where only the following parameters are present: bottom hole flowing pressure (Pwf)wellhead flowing pressure (Pwh), tubing diameter (D) and oil rate stock tank (Qo). The equation has the form:

(Equation)

where A and B are numerical coefficients to be determined with the available production tests data.

The equation is theoretically obtained, without any PVT or tubing roughness values, starting from the equations of multiphase vertical fluid flow in tubing, and introducing some simplifications that are acceptable for field calculations.

The method has been tested by using more than a hundred wells operating under a large variety of conditions. The error of the bottom hole flowing pressure calculated with such a method is usually below 3%, definitely acceptable for the majority of the well performance problems. The method has also been validated for gas wells, with an error below 1%.

Of course the method has limitations: the input data have to be steady state with approximately constant GOR and WC. Finally, to better describe wells affected by liquid accumulation phenomena, a small extension of the equation above has been developed which further increases the accuracy.

Introduction

The steady state pressure drop calculations of production tubing is important for several studies, including the following:

  1. estimate the optimum tubing size for the wells,

  2. determine the best artificial method,

  3. calculate the production rates after a workover,

  4. calculate the production rates for different separator pressures or choke sizes.

Unfortunately, the dynamic multiphase flow in pipe is extremely difficult to model. In the last decades many papers have been published on the subject and important industrial models are now commercialized for both steady state and transient flow. At present one of the most popular dynamic models is Olga.

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