DETERMINING THE STATIC AND FLOWING PRESSURES OF A GAS WELL

The ability of this reservoir to deliver a certain quantity of gas depends both on the inflow performance relationship and the flowing-bottom-hole pressure. The flowing bottom-hole pressure on its part depends on the separator pressure and the configuration of the piping system.

In order to determine the deliverability of the total well system, it is necessary to calculate all the parameters and pressure drops. Static and flowing

PRESSURE DROP DUE TO FLUID FLOWS

pressures are What I’m really concerned about, and methods for determining pressure drops in tubing for single-phase gas flow and for multiphase gas-liquid flow. Inflow and outflow performance curves must be determined.

Well, the static and flowing pressure at the formation must be known in order to predict the productivity or absolute open flow potential of gas wells. The preferred method is to measure the pressure with a bottom-hole pressure gauge. It is often impractical or too expensive to measure static or flowing bottom-hole pressures with bottom-hole gauges. However, for many problems, a sufficiently pressure and temperature, formation temperature, and well depth. The static pressure is equal to the weight of the column of gas. In the case of flowing wells, the gas column weight and friction effects must be evaluated and summed up.

There are several ways to determine the pressure either static or flowing.

STATIC BOTTOM-HOLE PRESSURE:

The estimation of static bottom-hole pressure from surface measurement only involves calculating the additive pressure exerted by the weight of the static fluid column. There are three well known techniques to calculate the pressure.

Average Temperature and Deviation Factor Method.

This is the simplest method most people use, and the only thing to consider is that pressure and temperature must be the average. This equation comes from the equation of state of real gases. The temeprature profile in the shut-in gas well is shown,

TEMPERATURE PROFILE IN A STATIC WELL

that is not quite straight line but, because of circulation within the well, it tends to be higher thanindicated by a straight line connecting the surface and reservoir temperatures.

Thus, the static condition is a special case of the general vertical flow equation.

Sukkar and Cornell Method:

One of the easiest methods to use for estimating bottom-hole pressure is that of Sukkar and Cornell, whose work has the advantage of improved accuracy and also permits calculations of bottom-hole pressures with out a trial-and-error procedure. Knowing the speudoreduced temperature and pressure must be compulsory in order to determine the Z factor.

Cullender and Smith Method:

Starting with a more realistic approach that gas deviation factor is a function of both temperature and pressure, they changed the units and rearranged in the following form.

CULLENDER AND SMITH METHOD

FLOWING BOTTOM-HOLE PRESSURE:

The flowing bottom-hole pressure of a gas well is the sum of the flowing wellhead pressure, the pressure exerted by the weight of the gas column, the kinetic energy change, and the energy losses resulting from friction. As the kinetic energy change is usually very small (about 0.1%) compared to the other energies, it is usuallyfns. This leaves the general mechanical energy equatin in a simple form, for the situation of no heat loss from gas to surroundings and no work performed by the system.

ANNULAR FLOW:

In most instances, gas wells are produced through rtubing (usually 2to 3.5 in ID). Occasionally, however, a well may be produced through the casing-tubing annulus. The tubing flow equations may be used for annular flow, provided proper account is taken of the flow diameter variable.

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