CHAPTER ONE
INTRODUCTION
1.0 Background of Study
In the production system, Pressure drop
has been a major issue in the field. These pressure drops could be
experienced as a result of valves and fittings
installed, due to friction along pipe sections or in lifting fluid up to a certain level.
As these pressure drops are identified,
and the economic flow rate of a reservoir fluid is known, pumps may be
employed to reduce the effect of pressure drop and maintain a given
fluid flow rate for good economic recovery. These pump applications are
usually analysed to determine an optimum Hydraulic pump requirement for a
given fluid system and pipe diameter. It can form one of the basic
aspect to be considered during well completion in selecting production
tubing diameter.
In general, a pump is a device used to
transport liquids, gases, and slurries. However,the term pump is usually
used to refer to liquid handling equipment. The purpose of the pump is
to provide a certain pressure at certain flowrate of a process stream.
The pressure requirement is dictated by the process andpiping involved,
while the flow rate is controlled by the required capacity in
thedownhole units.
At least one out of every 10 barrels of
oillifted in the world’s oil and gas operations are produced using an
ElectricSubmersible Pump (ESP). Typical installationsproduce liquids in
the 2,000 to 20,000 bpd range,making the ESP an effective and economical
meansof lifting large volumes of fluids from great depthsunder a
variety of well conditions.
There are several types of pumps used
for liquid handling. However, these can bedivided into two general
forms: positive displacement pumps (including reciprocatingpiston pump
and the rotary gear pump), and centrifugal pumps. The selection of
thepump type depends on many factor including the flow rate, the
pressure, the nature ofthe liquid, power supply, and operating type
(continuous or intermittent).
The power requirement for a mechanical system, like pumps and compressors, isgiven by the general mechanical balance equation:
P = -mWs = m 1.1
All terms in this equation take their normal meaning with m being
the mass flow rate,and α a coefficient used to take into account the
velocity profile inside the pipe (forlaminar α = 0.5, while for
turbulent α = 1). The required work (or power) given by Pis
the total work that needs to be delivered to the fluid. This work will
be drawn froma motor (operated with electricity or engines). The
conversion between the motor andpump power is not complete and an
efficiency is defined to describe the powerconversion. The efficiency is
given by:
1.2
The input power can be measured from the source. For example, if the pump is
operated with electricity, the input power will be I×V (current times voltage). Theoutlet power can be determined using Equation (1.1).
1. Static head (Δzterm): the height to which the fluid will be pumped.
2. Pressure head ( term): the pressure
to which the fluid will be delivered (ina pressurized vessel for
example). The pressure units must be converted to lengthunits using
relation.
3. System or dynamic head (F term): the energy lost due to friction in pipes, valves,fittings, etc.
1.1. Statement Of The Problem
It is important to accurately predict
the pressure drop accross a production system. This has been a difficult
task in the oil and gas industry as the production system in real life
is not homogenous (single phase) as assumed in most theories. The reason
for this is that the two-phase flow is complex and difficult to
analyze. Ideally, gas moves at a much higher velocity than the liquid.
As a result, the down hole flowing pressure of the liquid-gas mixture is
greater than the corresponding pressure corrected for down hole
temperature and pressure and this could be calculated from the produced
gas-liquid ratio.
This pressure drop in a flowing
(production) system could be identified using different existing
correlations. Some of these correlations are empirical, mechanistic or
numerical. Hagedorn and Brown is the most widely used correlation for
vertical wells (Schoham, 2006). In planning well completion the tubing
diameter that will give less pressure drop hence much liquid production
can be selected by the use of multiphase correlation.
It is also very necessary to plan for
pumps in tubing size selection should need arise on future production
for pumping of the reservoir fluid to optimize production.
1.2. Objectives
- Determine the Hydraulic Horse Power Requirement needed to maintain production of reservoir fluid within economic limit.
The above objective can be achieved by
using two-phase pressure drop correlations to determine pressure drop in
selected production tubing used in the Niger Delta.
1.3. Scope of The Work
The determination of pressure drop using
the selected two-phase correlations using production tubings used most
often in the Niger Delta.