Upload
vanessa-ada-eloka
View
243
Download
0
Embed Size (px)
Citation preview
STUDENTS INDUSTRIAL WORK EXPERIENCE
SCHEME (SIWES)
WITH
STERLING OIL EXPLORATION AND ENERGY
PRODUCTION CO. LTD.
Supervisor: Prepared by:
Mr. Lincoln Bassey Eloka V. Adaeze
OUTLINE
ABSTRACT
1. DRILLING AND COMPLETIONS
1.1 INTRODUCTION
1.2 DRILLING
1.2.1 Typical Casing Profile
1.2.2 Getting Ready to Spud
1.2.3 Spudding
1.2.4 Running the Surface Casing
1.2.5 Running the Intermediate Casing
1.2.6 Running the Production Casing
1.2.7 Running the Production Liner
1.3 COMPLETIONS
1.3.1 Single String with Single Packer
1.3.2 Dual String with Multiple Packers
1.3.3 Single String with Multiple Packers- Selective Zone
1.3.4 Christmas (Xmas) Tree
2. PETROLEUM GEOLOGY
2.1 INTRODUCTION
2.2 FORMATIONS IN THE NIGER DELTA
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 2
3. MDT PRESSURE GRADIENT SURVEY
3.1 DETERMINATION OF FLUID TYPE AND
CONTACTS FROM PRESSURE-DEPTH PLOTS
3.1.1 Introduction
3.1.2 Objectives
3.1.3 Evaluation
3.1.3.1 OKW-A Reservoir
3.1.3.2 OKW-B Reservoir
3.1.3.3 OKW-C Reservoir
3.1.3.4 E7000 Reservoir
3.1.3.5 E7500 Reservoir
3.1.3.6 E8000 Reservoir
3.1.4 Conclusion
4. PRESSURE VOLUME TEMPERATURE
4.1 PVT ANALYSIS OF FLUID SAMPLES GOTTEN
FROM AGU FIELD
4.1.1 Introduction
4.1.2 Objectives
4.1.3 Results
4.1.4 Conclusion
5. APPENDIX
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 3
ABSTRACT
Sterling Oil Exploration and Energy Production Co. Ltd (SEEPCO) is an oil company
involved in the exploration and production of hydrocarbons in Nigeria. Presently, they
operate on two blocks; Okwuibome field located in OML 143, Kwale, Delta State and
Agu field located in OPL 277, Owerri, Imo State.
During the training period, I was assigned to two different departments; operations
department and subsurface department. This report is divided into four sections; drilling
and completions, petroleum geology, modular formation dynamics tester (MDT) pressure
gradient survey and pressure volume temperature (PVT) analysis, based on my
assignments in Sterling.
The drilling and completions section contains information about Sterling’s wells, the
drilling process applied and the typical casing profile Sterling uses. Also, the type of
completions that were used to complete Sterling’s wells along with sketches of the
completion strings. The petroleum geology section contains information on the geology of
the Niger Delta and the formations in the Niger Delta.
The modular formation dynamics tester (MDT) pressure gradient survey involved the use
of pressure data to plot graphs which were used to locate the oil, water and/or gas zones
along with the location of the oil-water contact and/or gas-oil contacts if any.
The pressure volume temperature (PVT) analysis used PVT data gotten from the
laboratory to determine the bubble point pressure of the reservoir, formation volume
factor, solution gas oil ratio, viscosity and composition of the reservoir fluid.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 4
1. DRILLING AND COMPLETION
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 5
1.1 INTRODUCTION
Sterling uses rotary rigs to drill her wells. Two rotary rigs were assigned; Durga-1 and
Durga-2. These rigs were operated by BOGEL (the drilling service company). Durga-1
was used to drill four completions in the II pack sands. Two of the completions were
vertical wells while the other two were horizontal wells and they were all shallow sands.
Durga-2 drilled two vertical and one dually completed well, making four completions in
IV pack sands. Durga-2 which is used for drilling high pressure and high temperature
zones was used to drill these wells because the IV pack sands are deep with high pressure
and temperature.
Rotary drilling consists of two types of rotating systems that can be used; rotary table
system and top drive system. The top drive system was used to drill all Sterling’s wells
except OKW-9 where the rotary table system was used.
1.2 DRILLING
The companies involved in the drilling operations include;
Drilling contractors
Mud contractors
Mud loggers
Cement contractors
Logging company
The drilling contractors consist of the tool pusher, tour pusher, driller, assistant driller,
floor men, derrick man, and derrick pusher. The mud contractors are in charge of mixing
mud. The mud logger monitors drilling parameters like depth, rate of penetration,
cuttings analyses and so on. The cement contractors are in charge of cementing the casing
to the borehole wall. The logging company performs all well logging operations while
drilling.
At the planning stages of drilling Sterling’s wells, the drilling engineer, with input from
the Geo-scientist, petrophysicists, reservoir engineers and production engineers decided
on the strategy to adopt for the appraisal drilling of proposed wells.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 6
1.2.1 Typical Casing profile
The hole drilled for each casing must be large enough to easily fit the casing inside it,
allowing room for cement between the outside of the casing and the hole. Also, the inside
diameter of the first casing string must be large enough to fit the second bit that will be
used to continue drilling.
Usually, a well contains multiple intervals of casing successively placed within the
previous casing run. The following casing profiles were used for Sterling’s wells design;
Conductor casing
Surface casing
Intermediate casing
Production casing
Production liner
During drilling of the well(s) the logging tool is run in hole to measure formation
parameters, along with the MDT tool. The MDT takes pressure measurements and
pressurized fluid samples. These fluid samples are taken to the laboratory for Pressure-
Volume-Temperature analysis. The DST tool on the other hand is run in a cased hole
section along with the perforating gun. When the gun perforates the casing, the DST tool
measures the formation’s flow pressure.
1.2.2 Getting Ready to Spud
Drilling land wells begin with digging a cellar which can be from 3-15feet. The primary
purpose of the cellar is to align the Christmas tree at relative ground level. This allows for
easier access to the valves, choke, and other equipment. The first string of pipe is called
the conductor pipe or drive pipe which is usually 30” for Sterling’s wells.
Below are the steps taken preparatory to drilling and completion of wells;
1.2.3 Spudding
A large diameter hole is drilled to a specified depth generally relatively shallow,
such as 1 ft or 200 ft.
The pipe is driven into the ground to the point of refusal.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 7
1.2.4 Running the Surface Casing
After drilling 26” surface hole, the 20” surface casing is run to a specified depth
to isolate any fresh water, salt water, and oil or gas zones within that depth range
of the formation. Cement is circulated to surface of the 20” surface casing.
1.2.5 Running the Intermediate Casing
After the 17 ½” hole has been drilled, 13-3/8” intermediate casing casing is run in
the hole and cemented to a predetermined depth to ensure a good cement bond is
obtained between the surface casing and the intermediate casing.
1.2.6 Running the Production Casing
The 12 ¼” hole is drilled and 9-5/8”production casing is run and cemented in
place.
1.2.7 Running the Production Liner
The production liner is run to the total depth of the well. When the 6” hole is
drilled, the 4 ½” production liner is installed and cemented in place.
See figure below
30” conductor casing
cement
Casing shoe
26” hole
20” surface casing
17 ½” hole
13 3/8” intermediate casing
12 ¼” hole
9 5/8” production casing
6” hole
4 ½” production liner
Figure: typical casing profile
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 8
1.3 COMPLETIONS
Well completion is composed of tubular, tools and equipments placed in a wellbore to convey, pump or control the production or injection of fluids. Wells can be completed as;
Open hole or cased hole Single string completions, dual string completions, single selective completions
etc Naturally flowing or artificially flowing wells
Openhole completions are feasible only in reservoirs with sufficient formation strength to prevent caving or sloughing; such as carbonate reservoirs. Cased hole completions are feasible in reservoirs without sufficient formation strength such as sandstone reservoirs which are unconsolidated. Cased hole involve using a set of casing set through the producing reservoir and cemented in place. Fluid flow is established by perforating the casing and cement sheath, thereby opening and connecting the reservoir to the wellbore.Sterling does cased hole completions because formation structure in the Niger delta is sand stone. The tubing configurations used includes the following;
Single string with single packer Dual string with multiple packers Single string with multiple packers- Selective Zone
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 9
1.3.1 Single String with Single Packer
This is a single string flow conduit. There is both tubing and annulus flow. The packer is
run in hole, installed in place and pressure tested, and then the tubing string is run in-
between the packer. The packer holds the tubing string in place and establishes hydraulic
separation between the tubing string and the casing or liner.
Flow Coupling
Selective Landing Nipple
Tubing Seal Divider
Sliding Sleeve
Packer
No-Go Nipple
Figure: single string with single packer
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 10
1.3.2 Dual String with Multiple Packers
In the dual string with multiple packers, several zones can be lifted simultaneously. In the figure below, the fluids in the upper zone is produced through the short string which is 2-7/8” OD while the fluids in the lower zone is produced through the long string which is 3-½” OD. The dual string is usually placed in the 9-5/8” production casing.
Sliding Sleeve
No-Go Nipple
Packer
Flow Coupling
Selective Landing Nipple
Blast Joint
Polished Nipple
Tubing Seal Divider
Packer
No-Go Nipple
Figure: dual string with multiple packers
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 11
1.3.3 Single String with Multiple Packers- Selective Zone
In the single string with multiple packers, the zones can be produced one at a time or they can be co-mingled depending on government regulations or the quality of the fluids. If the zones are to be produced one at a time, the producing sections can be opened or closed by shifting the sliding sleeve, using wireline services.
Sliding Sleeve
Packer
Sliding Sleeve
Flow Coupling
Selective Landing Nipple
Blast Joint
Selective Landing Nipple
Packer
Flow Coupling
Blast Joint
Selective Landing Nipple
Packer
No-Go Nipple
Figure: single selective string with multiple packers
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 12
1.3.4 Christmas (Xmas) TreeAt the top of the well completions is the Christmas tree which is an assembly of valves, spools, pressure gauges and choke. The tree prevents the release of oil and gas from the well into the environment, directs flow of oil and gas from the well.
Figure: the production Christmas tree
The swab valve provides vertical access to the wellbore, see figure above. The surface
choke is used to control fluid flow rate or downstream system pressure. Wing valves are
incorporated into the wings of a Christmas tree to provide access to the production tubing
for production and well control purposes. The two wings featured in the Christmas tree
include a production wing connected to the surface production facilities, and a kill wing
that may be used for well control or treatment purposes.
A correctly functioning master valve is so important that two master valves are fitted to
the Christmas tree. The upper master valve is used on a routine basis, with the lower
master valve providing backup in the event that the normal service valve is leaking and
needs replacement.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 13
The production string is the primary conduit through which reservoir fluids are produced
to surface. The production string is typically assembled with tubing and completion
components in a way that suits the wellbore conditions and the production method. An
important function of the production string is to protect the primary wellbore tubulars,
including the casing and liner, from corrosion and erosion by the reservoir fluid.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 14
2. PETROLEUM GEOLOGY
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 15
2.1 INTRODUCTION
Hydrocarbon originates from micro-organisms in the seas, river, lakes and land. When
these organisms die, they deposit at the bottom of the sea where they form organic matter
as sediments.
As more of these micro-organisms die, they are deposited on the previous sediments
during which pressure and temperature increases. This increase creates a reducing
environment during which oxygen is stripped from the sediments and they become
compacted thereby forming sedimentary rocks.
Hydrocarbons are mostly found in anticlinal structures; as a result, they are sought out by
geologists who explore for oil and gas. Since oil and gas are less dense than water, they
tend to migrate upward through permeable rock. When rock is folded into an anticline
and capped by an overlying impermeable rock, then oil and gas will migrate up the slope
of the fold to the crest and accumulate there.
Some hydrocarbon traps are created by faulting. Some of the faults in the Niger Delta are;
Rollover anticline
Listric fault: this is a spoon shaped fault.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 16
Collapsed crest: this is where compressional forces push a block of rock upward
Growth fault: this is a situation where the hanging wall is thicker than the footwall
Counter regional fault: this is a C-shaped fault
Antithetic fault: this is a fault where the hanging wall dips to the north
Synthetic fault: this is a situation where the hanging wall dips to the south
2.2 FORMATIONS IN THE NIGER DELTA
There are three formations in the Niger Delta;
Benin formation
Agbada formation
Akata formation
The Benin formation contains unconsolidated fine beach sand basically. The gamma ray
reading in this formation is low because sand contains little or no radioactive particles.
This sand also contains fresh water which has high resistivity and can be mistaken for
hydrocarbon, but hydrocarbon can not be found in the benin formation because it is
separated from Agbada formation by a very thick shale called the upper agbada shale.
Agbada formation is where the hydrocarbon is trapped. In this formation, there is sand
and shale intercalation and the water in Agbada formation is saline resulting in low
resistivity. Therefore if high resistivity is encountered in Agbada, it is usually perceived
to be hydrocarbon.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 17
The Akata formation is where the hydrocarbon is formed before it migrates up to the
Agbada formation. This formation consists mainly of marine shales and the pressure and
temperature here is very high because of its position.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 18
3. MDT PRESSURE GRADIENT SURVEY
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 19
3.1 DETERMINATION OF FLUID TYPE AND CONTACTS FROM PRESSURE-DEPTH PLOTS
3.1.1 Introduction
Okwuibome field is located in OML 143 and is situated in the northern depositional belt
of the Niger Delta.
Sterling has drilled some wells in the field. Okw-A well was completed in IID sands
while Okw-C and Okw-B wells were completed in IVA-1 sand. The three wells were
completed up dip of the reservoir.
Hydrocarbon from the IID reservoir has 19°API gravity with Gas Oil Ratio (GOR) of
about 6scf/bbl. The reservoir quality of the IID sands is good with a porosity ranging
from 26 to 28%, and the oil is relatively viscous.
IVA-1 reservoir has 49° API gravity with Gas Oil Ratio (GOR) of about 2000scf/bbl. The
reservoir quality for the IVA-1 sand is also good with the porosity ranging from 23 to
25% and an effective permeability of 148 Darcy, the oil here is not as viscous as the oil in
the IID sand. The initial pressures for OKW B and C are 4774.63psia and 5158psia
respectively.
Agu main field on the other hand is in Block OPL-277 which is located in Imo state. Agu
2 and Agu 3 appraisal wells were drilled which encountered several sands including
sands E7000, E7500 and E8000. The reservoir’s porosity is within the range of 25% to
32%, and permeability in the range of 5 to 6 Darcy. The oil gravity is between 22 and 26
degrees API gravity, with a very low GOR of 200 to 260scf/stb, although a high GOR
was encountered in E8000.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 20
Modular Formation Dynamics Tester (MDT) survey and sampling were carried out on
three wells; OKW-A, OKW-B and OKW-C in Okwuibome field and on three wells;
E7000, E7500, E8000 in Agu field. The purpose of carrying out this survey was to
identify the fluids in the reservoir and their contacts, as well as obtain fluid samples for
Pressure Volume Temperature (PVT) analysis.
Formation testers were introduced about 55 years ago for the sole purpose of sampling
fluids in the well. The formation tester was first introduced by Schlumberger, later oil
servicing companies such as Baker Hughes, Halliburton etc. produced their own versions.
When this tool was first introduced in 1955, it was specifically supposed to collect
reservoir fluid samples but could only collect one sample per trip in the well. It was later
replaced by the formation interval tester and then the repeat formation tester in 1975,
(See Figure 1). Presently, Schlumberger’s MDT tool offers significant improvements in
pressure measurement with the introduction of the combinable quartz gauge (CQG) and it
also offers improved sampling capabilities.
Figure 1: The transition of formation testers over the years
The Schlumberger MDT tool was used for pressure survey and fluid sampling in OKW-
A, B, C and E7000, E7500 and E8000 wells respectively. The results from this survey
were compared with logs that were measured while drilling. Some of the logs used were
the gamma ray log, resistivity log, etc. The gamma ray curve provides lithology
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 21
information such as sandstones and shales. Low gamma ray reading indicates sandstone
while high gamma ray reading depicts shales. Hydrocarbons from petrophysical
interpretation of the composite logs (gamma ray curve, resistivity curve, neutron-density
curve, etc) always exist in the sands/sandstone.
Resistivity curve gives an idea of fluid types contained in the sandstone. Since water is a
conductor of electricity and hydrocarbons are insulators, the resistivity reading in a water
zone is usually lower than the resistivity reading in a hydrocarbon zone. So, wherever
there is a drop in resistivity in a sandstone region, it means that that point is a
hydrocarbon-water contact/oil-water contact.
The neutron-density curve on the other hand indicates the exact type of hydrocarbon in
the sandstone by measuring their densities. The densities of the hydrocarbons have
opposite effects on these two measurements. As a result, the two measurements are
plotted on a graph in such a way that the two curves overlap in the water-bearing zone. In
the gas zone, there is a large separation with neutron on the right and density on the left.
This separation is called the gas separation. In the oil zone, the two curves nearly overlap
each other while in shales, the separation that occurs is the inverse of what happens in the
gas zone. Here the neutron curve shifts to the left while the density curve shifts to the
right.
3.1.2 Objectives
Identify fluids from their pressure gradients.
Determine the position of the gas/oil and oil/water contacts from pressure-depth
plots.
Evaluate samples obtained for PVT analysis.
3.1.3 Evaluation
3.1.3.1 OKW-A Reservoir: the pressure plot of well OKW-A showed OWC at 1691m
TVD SS and the pressure gradients calculated were 0.404psi/ft for oil and 0.438psi/ft for
water. The pressure gradients are close because the density of the oil is almost up to that
of the water. This trend is seen on the pressure plot, as the plot is almost linear. From the
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 22
pressure gradient calculated, the oil is heavy oil. On the gamma ray curve, from 1679m to
1772m shows sandstone because of the low gamma ray reading in that section. The
resistivity curve at that section indicates a resistivity drop at 1691.2m and since
hydrocarbon has a higher resistivity than water, it means that the OWC is at 1691.2m (see
figure 2). The neutron-density curve at that section shows that the density of the oil is
close to that of water because the overlapping of the curves is almost the same.
Figure 2: MDT for OKW-A Reservoir
3.1.3.2 OKW-B Reservoir: the pressure plots showed OWC at 3130m TVD SS in
OKW-B and the pressure gradients calculated were 0.149psi/ft for gas, 0.215psi/ft for oil
and 0.457psi/ft for water. From the pressure gradients calculated, the gas is gas
condensate which is a low density mixture of hydrocarbon liquids e.g. pentane, hexane,
heptanes, etc, while the oil is volatile oil. On the gamma ray curve, from 3118m to
3154m is sandstone because of the high gamma ray reading in that section. On the
resistivity curve, from that section, there is a sharp resistivity drop at 3134.5m. This can
only mean that from that point of the resistivity drop downwards is a water zone.
Therefore, the OWC is at 3134.5m. (see Figure 3). The neutron-density curve for OKW-
B is not accurate because of the scaling that was used.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 23
Figure 3: MDT for OKW-B Reservoir
3.1.3.3 OKW-C Reservoir: the pressure plots showed the OWC at 3159m in OKW-C
and the pressure gradients calculated were at 0.234psi/ft for oil and 0.42psi/ft for water.
The pressure gradient for oil shows that it is volatile oil which is oil that evaporates
rapidly and doesn’t leave stains. It can also be called clean oil or good quality oil. On the
gamma ray curve, from 3152m to 3196m is sandstone because of the high gamma ray
reading in that section. On the resistivity curve, from that section, there is a sharp
resistivity drop at 3166.5m. This means that from the point of the resistivity drop
downwards is water zone. Therefore, the OWC is at 3166.5m. (see Figure 4). The
neutron-density curve for OKW-C is not accurate because of the scaling that was used.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 24
Figure 4: MDT for OKW-C reservoir
3.1.3.4 E7000 Reservoir: Based on the MDT pressure measurement, the gas and water
gradient were determined as 0.089 and 0.45 psi/ft. The gradient calculated for the gas
classifies it as dry gas. In the oil column, a pressure gradient of 0.39 psi/ft was
determined from fluid sample. This gradient value indicates that the oil is heavy oil, see
figure 5. The MDT data was unable to infer contacts due to poor pressure data obtained
in the oil column.
Figure 5: MDT for E7500 reservoir
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 25
3.1.3.5 E7500 Reservoir: Three fluids were present in this sand (gas, oil and water). The
gradients were calculated from the pressure plots to be 0.05, 0.36, and 0.43 psi/ft, for gas,
oil and water respectively. These gradients show that the gas is dry gas and the oil is
black oil. The GOC was at 1768 m-ss and OWC was at 1774 m-ss.
Figure 6: MDT for E7500 reservoir
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 26
3.1.3.6 E8000 Reservoir
Two fluids were present in this sand (oil and water). Based on the slopes generated from
the pressure plots, the fluid gradients were calculated as 0.36, and 0.45 psi/ft, for oil and
water respectively. The gradient for the oil defined it as heavy oil. The fluid contact
within the reservoir was defined as, OWC at 1815 m-ss.
Figure 7: MDT for E8000 reservoir
3.1.4 Conclusion
The pressure gradient calculated from the plots helped in identifying the fluid types present in the reservoir, which gave knowledge of the hydrocarbon categorization. It is important for the water contact to be known during the early stages of field development.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 27
4. PRESSURE VOLUME TEMPERATURE ANALYSIS
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 28
4.1 PVT ANALYSIS OF FLUID SAMPLES GOTTEN FROM AGU FIELD
4.1.1 Introduction
MDT samples were taken from Agu 2 and Agu 3 in reservoir E7000, E7500 and E8000
for laboratory PVT analyses. From the site, Schlumberger transported the reservoir fluids
which they had collected in their pressurized sample chamber to Reservoir Fluid
Laboratory (in PH) for full PVT analysis. At the laboratory, the samples were transferred
from Schlumberger’s sample chambers to the RFL (Reservoir Fluid Laboratory) cylinder
in order to relieve Sterling of the rental charges that would have been incurred. After the
transfer, the following tests were performed on the reservoir fluid sample:
differential liberation test
flash expansion test
viscosity test
compositional analysis
pressure-volume relation
These tests help in determining reservoir fluid properties which are very important in
petroleum engineering computations such as material balance calculations, reserve
estimates, inflow performance calculations and numerical reservoir simulations. Some of
these reservoir fluid properties include;
oil formation volume factor
solution gas oil ratio
viscosity
4.1.2 Objectives
To determine the;
bubble point pressure of the reservoir, formation volume factor and solution gas
oil ratio
viscosity
composition of the reservoir fluid
4.1.3 Results
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 29
The differential liberation test simulates the behavior of the reservoir fluids in-situ during
pressure depletion. Table 1 shows the results of the differential liberation test for
reservoir E7000 with initial pressure at 2514psia and bubble point pressure at 1832psia. It
can also be seen that for every pressure change, the formation volume factor, gas volume
factor, deviation factor, solution gas oil ratio, liberated gas oil ratio, specific gravity gas,
gas viscosity and liquid phase density were measured.
Pressure
(psia) FVF (Bo)
Gas Volume Factor
(bbl/mscf)Z
(Z = PV/NRT)Solution
GOR (scf/stb)
Liberated Gas-oil Ratio
(scf/stb)
Specific Gravity Gas
(Air = 1.0000)
Gas Viscosity
(cp)
Liquid Phase
Density (gm/cm3)
5000 1.104 215 0.8504
4500 1.106 215 0.849
4000 1.108 215 0.8473
3500 1.11 215 0.8454
3000 1.113 215 0.8434
Pi 2514 1.116 215 0.8412
2000 1.12 215 0.8384
Pb 1832 1.121 215 0 0.8375
1500 1.103 1.936 0.934 181 34 0.568 0.01473 0.8475
1200 1.09 2.431 0.938 146 69 0.5677 0.01417 0.8535
900 1.079 3.261 0.944 111 104 0.5683 0.01367 0.8583
600 1.067 4.938 0.953 74 141 0.57 0.01324 0.8637
300 1.054 10.061 0.971 35 180 0.5741 0.01289 0.8695
100 1.046 30.758 0.989 12 203 0.588 0.01268 0.8733
15 1.034 207.324 1 0 215 0.6146 0.01254 0.8821
DIFFERENTIAL LIBERATION TEST AT 157°F
Table 1
The PVT parameters used on the field depends on the surface separation conditions,
therefore, the result of the differential liberation test was adjusted to surface separator
conditions at 300psia and 100°F because the highest shrinkage factor was achieved at this
pressure and temperature during the separator flash expansion test.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 30
Table 2 shows the adjusted values for the oil formation volume factor (FVF) and solution
gas oil ratio for reservoir E7000.
Pressure, psi
FVF, bbl/stb
Solution GOR, scf/stb
2514 1.115 212
1832 1.120 212
1500 1.102 178
1200 1.089 143
900 1.078 108
600 1.066 71
300 1.053 32
100 1.045 9
15 1.033 0
ADJUSTED VALUES
Table 2
The values were adjusted using the Lee and Gonzalez method which is represented by the
equation below:
Bo = Bod [Bobf/Bobd]
Rs = Rsif – (Rsid - Rsd) [Bobf/Bobd]
For reservoir E7000,
Bobf = 1.120bbl/stb
Bobd = 1.121bbl/stb
Rsif = 212scf/stb
Rsid = 215scf/stb
Where,
Bofb = Separator flash formation volume factor
Bodb = Bubble Point Oil formation volume factor from differential liberation
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 31
Bod = Formation volume factor at pressure from differential liberation
Bo = Adjusted formation volume factor
Rsif = Separator flash solution gas oil ratio
Rsid = differential liberation solution gas oil ratio
Rsd = Solution gas oil ratio at pressure from differential liberation
Rs = Adjusted solution gas oil ratio
The formation volume factor and solution gas oil ratio of reservoir E7000 was plotted
against pressure in figure 1. This plot shows that Bo increases slightly as the pressure is
reduced from initial to bubble point pressure which is due to the fact that the liquid
expands and since the compressibility of the undersaturated oil reservoir is low, the
expansion is relatively small.
Figure 1: figure showing the formation volume factor and solution gas oil ratio of
reservoir E7000
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 32
The oil can dissolve more gas if available, then the initial value of the solution gas oil
ratio must remain constant at 212 (scf/stb) until the pressure drops to the bubble point,
when the oil becomes saturated. See figure 1.
The initial value of the oil formation volume factor, Boi is 1.115rb/stb which increases to
1.120rb/stb at the bubble point pressure. This means that initially 1.115rb/stb of oil plus
its dissolved gas will produce one stb of oil. This ratio is actually favorable since Boi is
close to unity which indicates that the oil contains hardly any dissolved gas and reservoir
volumes are approximately equal to surface volumes. The initial solution gas oil ratio is
relatively low at 212scf/stb which indicates that the oil in reservoir sand A is black oil.
To show the effect of viscosity on the oil with respect to the solution gas oil ratio, the
viscosity values were plotted against pressure as shown in figure 2;
Figure 2: Viscosity-pressure relationship for reservoir E7000
At the initial pressure, the viscosity of the oil is low because it is undersaturated with gas
at this point, but at bubble point pressure, the viscosity increases which is as a result of
the fact that the gas comes out of solution with the oil thereby reducing the oil’s mobility.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 33
The differential liberation test was also performed on the E7500 reservoir fluid samples
that were taken to the laboratory. Table 2 below shows the details of the test.
Pressure (psia) FVF (Bo)
Gas Volume Factor (bbl/mscf)
Z (Z = PV/NRT)
Solution GOR (scf/stb)
Liberated Gas-oil Ratio (scf/stb)
Specific Gravity Gas (Air = 1.0000)
Gas Viscosity (cp)
Liquid Phase Density (gm/cm3)
5000 1.107 246 0.8525
4500 1.109 246 0.8510
4000 1.111 246 0.8492
3500 1.114 246 0.8472
3000 1.117 246 0.8450
Pi 2572 1.120 246 0.8428
Pb 2105 1.123 246 0 0.8402
1800 1.112 1.572 0.907 213 33 0.5746 0.01551 0.8449
1500 1.099 1.907 0.917 178 68 0.5693 0.01482 0.8508
1200 1.087 2.413 0.928 144 102 0.5690 0.01423 0.8560
900 1.075 3.252 0.938 108 137 0.5677 0.01372 0.8616
600 1.063 4.950 0.952 73 173 0.5684 0.01328 0.8672
300 1.051 10.088 0.970 36 210 0.5629 0.01293 0.8725
100 1.044 30.882 0.990 13 233 0.5862 0.01277 0.8757
15 1.034 207.996 1.000 0 246 0.6084 0.01259 0.8822
DIFFERENTIAL LIBERATION AT 159°F
Table 3
The result of the differential liberation test was adjusted to surface separator conditions at
300psia and 100°F because a higher shrinkage factor was achieved at this pressure and
temperature during the separator flash expansion test. However, the values of the
formation volume factor and the solution gas oil ratio had to be adjusted to meet surface
separator conditions. For this reservoir,
Bobf = 1.119bbl/stb
Bobd = 1.123bbl/stb
Rsif = 241scf/stb
Rsid = 246scf/stb
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 34
These values were used to calculate the adjustment is shown in table 4;
Pressure, psia
FVF, bbl/stb
Solution GOR, scf/stb
2572 1.116 241
2105 1.119 241
1800 1.108 208
1500 1.095 173
1200 1.083 139
900 1.071 103600 1.059 69300 1.047 32100 1.040 915 1.030 0
ADJUSTED VALUES
Table 4
In reservoir E7500, as the pressure is reduced from initial to bubble point pressure, Bo
increases slightly. This effect is due to the fact that the liquid expands and since the
compressibility of the undersaturated oil reservoir is low, the expansion is relatively
small. It can therefore be deduced that the initial formation volume factor of 1.116rb/stb
of oil plus its dissolved gas will produce one stb of oil as shown in figure 3.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 35
Figure 3: figure showing the formation volume factor and solution gas oil ratio of
reservoir E7500
Furthermore, the oil is undersaturated with gas, which means it could dissolve more gas if
it were available, then the initial value of the solution gas oil ratio must remain constant
at 241 (scf/stb) until the pressure drops to the bubble point, when the oil becomes
saturated, see figure 2. The oil in reservoir E7000 is black oil because the initial solution
gas oil ratio is low and within the GOR range for black oil.
The viscosity of the E7500 sample was measured and a graph of viscosity against
pressure was plotted as shown in figure 4.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 36
Figure 4: Viscosity-pressure relationship for reservoir E7500
The viscosity pressure relationship in figure 4 exhibits a similar trend with E7000
reservoir but the rate at which the viscosity increases in E7500 is lower. This is because
the solution gas oil ratio of the oil in reservoir E7500 is higher than that of reservoir
E7000.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 37
Finally, a differential liberation test was conducted for the E8000 reservoir fluid sample.
Table 3 shows the results of this test in detail.
Pressure (psia) FVF (Bo)
Gas Volume Factor (bbl/mscf)
Z (Z = PV/NRT)
Solution GOR
(scf/stb)
Liberated Gas-oil Ratio (scf/stb)
Specific Gravity Gas
(Air = 1.0000)
Gas Viscosity
(cp)
Liquid Phase Density
(gm/cm3)
5000 1.965 1854 0.6012
4820 1.971 1854 0.5992
4520 1.982 1854 0.5959
4128 1.997 1854 0.5914
Pi 3887 2.008 1854 0.5882
Pb 3514 2.026 1854 0 0.5830
3000 1.817 0.827 0.793 1455 399 0.7591 0.02344 0.6137
2500 1.675 0.995 0.794 1161 693 0.7337 0.01996 0.6377
2000 1.561 1.274 0.814 920 934 0.7195 0.01722 0.6602
1500 1.463 1.750 0.839 709 1145 0.7079 0.01523 0.6822
1000 1.376 2.707 0.865 522 1332 0.7254 0.01376 0.7037
500 1.292 5.665 0.905 342 1512 0.7949 0.01247 0.7252
110 1.188 27.381 0.962 158 1696 1.1956 0.01054 0.7459
15 1.070 208.381 1.000 0 1854 2.436 0.0077 0.7525
DIFFERENTIAL LIBERATION AT 161°F
Table 5
The values of the formation volume factor and solution gas oil ratio were adjusted to
surface separator conditions at 300psia and 100°F which resulted in the values shown in
table 6. The values that were used to calculate the adjustment for this reservoir are as
follows;
Bobf = 1.770bbl/stb
Bobd = 2.026bbl/stb
Rsif = 1476scf/stb
Rsid = 1854scf/stb
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 38
Pressure, psia
FVF, bbl/stb
Solution GOR, scf/stb
3887 1.754 1476
3514 1.770 1476
3000 1.587 1127
2500 1.463 871
2000 1.364 660
1500 1.278 476
1000 1.202 312
500 1.129 155
110 1.038 0
15 0.935 0
ADJUSTED VALUES
These adjusted values were then plotted against pressure as shown in figure 5;
Figure 5: figure showing the formation volume factor and solution gas oil ratio of
reservoir E8000
In reservoir E8000, the change in the formation volume factor is from 1.754bbl/stb to
1.770bbl/stb which means that 1.754 reservoir barrel of oil plus its dissolved gas will
produce one stb of oil, see figure 5. Also, in this reservoir sand, Boi is not close to one and
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 39
this implies that there might be a significant amount of gas dissolved in the oil, so the
reservoir has to be conditioned properly to ensure that a representative fluid sample is
obtained. But on the other hand, the farther away Boi is from one, the more volatile the
oil.
In this same reservoir, Rsi is constant at 1476scf/stb from the initial pressure to the bubble
point pressure. This is because the oil is undersaturated with gas and has the capacity to
dissolve more gas, (figure 5). The solution gas oil ratio is relatively high at 1476scf/stb
which indicates that the oil present in the reservoir sand is volatile oil.
In addition, a graph of viscosity versus pressure was plotted using the measured viscosity
values of the sample and the corresponding pressure. See figure 6;
Figure 6: Viscosity-pressure relationship for reservoir E8000
The viscosity of E8000 at initial pressure and at bubble point pressure is almost the same.
This could be a result of the high solution gas oil ratio, so even at bubble point pressure
the gas that leaves the oil will have very little effect on the viscosity change of the
remaining oil.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 40
4.1.4 Conclusion
The results of the PVT analysis are important in completion designs- how the completion
strings will react to the produced fluids. On the other hand, it helps in deciding the type
of surface facilities to be used for separation when the fluid is eventually produced to
surface.
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 41
5. APPENDIX
Tools
Flow coupling
Selective landing nipple
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 42
Flow couplings are designed to inhibit erosion caused by flow turbulence. Flow couplings should be installed above and below landing nipples or any other restriction that may cause turbulent flow.
Selective landing nipple is a completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile designed to be run in series throughout the wellbore.
Sliding sleeve
Tubing seal divider
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 43
The sliding sleeve is comprised of full-opening devices with an inner sleeve that can be opened or closed, using standard wireline methods to provide communication between the tubing and the tubing/casing annulus.
The tubing seal divider is designed to disconnect the tubing string without disturbing the packer setting.
No-go landing nipple
Blast joint
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 44
No-go landing nipple is a nipple that incorporates a reduced diameter internal profile that provides a positive indication of seating by preventing the tool or device to be set from passing through the nipple.
Blast joints are installed in the tubing opposite perforation wells with two or more zones. The blast joints are sized to help prevent tubing damage from the jetting action of the zone perforations.
Packer
Students Industrial Work Experience Scheme (SIWES) with SEEPCO 06/2011 to 10/2011: Adaeze Eloka 45
A packer is a downhole device used in every completion to isolate the annulus from the production conduit, enabling controlled production, injection or treatment. A typical packer assembly incorporates a means of securing the packer against the casing or liner wall, such as a slip arrangement, and a means of creating a reliable hydraulic seal to isolate the annulus, typically by means of an expandable elastomeric element.
Packers are classified by application, setting method and possible retrievability.