5.C PRESSURE CORRECTION

5.C.1 CORRECTION METHODS5.C.1.A FLOW CORRELATIONS FOR OILDUNS & ROS CORRELATIONThe Duns & Ros correlation is developed for vertical flow of gas and liquid mixtures in wells. For water contents less than 10%, the Duns-Ros correlation (with a correction factor) has been reported to work well.

HAGEDORN & BROWN CORRELATIONThis correlation was developed using data obtained from a 1500-ft vertical well. Tubing diameters ranging from 1-2 in. The correlation is used extensively throughout the industry and is recommended inwells with minimal flow regime effects.

ORKISZEWSKI CORRELATIONDeveloped using work from both Duns & Ross and Hagedorn & Brown.

10% H2O

5.C.1 CORRECTION METHODS5.C.1.A FLOW CORRELATIONS FOR OILBEGGS & BRILL CORRELATIONThe Beggs & Brill correlation is developed for tubing strings in inclined wells and pipelines for hilly terrain. This correlation resulted from experiments using air and water as test fluids over a wide range of parameters.

MUKHERJEE-BRILLDeveloped experimentally using 1.5″ steel pipe inclined at several angles. Thisincludes downhill flow as a flow regime. This is recommended for inclined or horizontal wells.

DUKLER-EATONBased on 2600 laboratory and field tests to generate an expression for frictional pressure losses along pipelines. It can be used for horizontal flow.

5.C.1 CORRECTION METHODS5.C.1.B FLOW CORRELATIONS FOR GASCULLENDER & SMITH:

This correlation is based on gas properties as defined by the PVT, and ageneral friction factor calculated using the Colebrook and White equation.

Note that when handling a condensate case with equivalent gas gravity and total rates, the proper gradient and rates are used in Cullender and Smith to account for the presence of condensate. The presence of water can be accommodated, based on a constant water to gas production ratio.

5.C.1 CORRECTION METHODS5.C.1.C LIFT CURVESLift curves usually provide the pressure drop between the well head and lift curve depth.

External lift curves are discrete data. When using them the pressure drop calculations are performed by interpolations in the lift curve table in each of the required dimensions.

Therefore it is recommended to provide as many lift curves as possible to cover the widest possible range of situations such as varying rates, phase ratios and well head pressures.

5.C.2 GENERAL CALCULATION METHOD

In vertical multiphase flow calculations the pipe is divided into small depth increments. The pressure loss in each increment is determined in a reiterative process using average pressure and temperature values to calculate fluid properties.

Multiphase cases are treated using multiphase flow correlations. In the event that the interpreter has identified more than one phase rate, Perrine’s method* is usually used.

Pressure drop correlations are valid under dynamic conditions only, not during build-ups or fall-offs.

*Perrine’s method: Basically replaces the single-phase compressibility by the multiphase compressibility so that each fluid is analyzed separately using the concept of mobility.

5.C.3 CORRECTING GAUGE DATA VS.CORRECTING MODEL

Correcting the data: When the intake pressure model has been defined, the interpretation engineer will decide during extraction to make the pressure correction to whatever depth is desired. There is an option to create a new pressure gauge with the corrected pressure.

Correcting the model: Conversely, when the intake pressure model has been defined, the interpretation engineer will decide that when generating the model the model response will be corrected to gauge depth.

The downhole rates are calculated by the model and will therefore incorporate wellbore storage effects. This ensures that, with significant friction, there will be no discontinuity in the corrected model when the surface rate changes.

5.D PHASE REDISTRIBUTION

6.A VERTICAL FULLY PENETRATING WELL

Let’s consider that a well has a constant skin when the additional pressure drop, or Δpskin.

In addition to mechanical skin damage, many other parameters cause either loss or gain in well productivity. These parameters include:1. Wells completed in part of the pay zone.2. Near-wellbore turbulence3. Perforated density4. Slant wells

6.A.1 CONSTANT SKIN

6.A VERTICAL FULLY PENETRATING WELL6.A.2 RATE DEPENDENT SKIN

st=s + Dqsc where

st = total skin factors = true skin factorD = rate-dependent skin factor, mmscfd-1

qsc = gas flow rate, mmscfd

6.A VERTICAL FULLY PENETRATING WELL6.A.3 TIME DEPENDENT SKIN

When it is progressively damaged over its producing life, the skin may change in time.