U.S. patent application number 12/281848 was filed with the patent office on 2009-01-29 for tracer method and apparatus.
This patent application is currently assigned to JOHNSON MATTHEY PLC. Invention is credited to Darrell Green, David Stubbs.
Application Number | 20090025470 12/281848 |
Document ID | / |
Family ID | 36219191 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090025470 |
Kind Code |
A1 |
Green; Darrell ; et
al. |
January 29, 2009 |
TRACER METHOD AND APPARATUS
Abstract
A method of monitoring the flow of fluid within or from an oil
or gas reservoir includes inserting a solid tracer into the
reservoir. The tracer comprises at least one metal selected from
caesium, niobium, tantalum, tellurium, terbium, lanthanum, gold,
iridium, osmium, silver, platinum, palladium, rhenium, ruthenium,
rhodium, hafnium, indium, a metal of the Lanthanide series of the
periodic table, or a salt thereof. A sample of fluid within or
flowing from the reservoir is collected and analysed to determine
the amount of the tracer contained in the sample. A perforation
tool allows for insertion of the tracer within the formation.
Inventors: |
Green; Darrell; (Cleveland,
GB) ; Stubbs; David; (Cleveland, GB) |
Correspondence
Address: |
RATNERPRESTIA
P.O. BOX 980
VALLEY FORGE
PA
19482
US
|
Assignee: |
JOHNSON MATTHEY PLC
|
Family ID: |
36219191 |
Appl. No.: |
12/281848 |
Filed: |
March 5, 2007 |
PCT Filed: |
March 5, 2007 |
PCT NO: |
PCT/GB07/50099 |
371 Date: |
September 5, 2008 |
Current U.S.
Class: |
73/152.18 ;
166/55 |
Current CPC
Class: |
E21B 43/117 20130101;
E21B 47/11 20200501 |
Class at
Publication: |
73/152.18 ;
166/55 |
International
Class: |
E21B 47/10 20060101
E21B047/10; E21B 29/00 20060101 E21B029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2006 |
GB |
0604451.5 |
Claims
1. A method of monitoring the flow of fluid within or from a
reservoir comprising the steps of inserting in said reservoir a
solid tracer comprising at least one non-radioactive metal selected
from the group consisting of caesium, niobium, tantalum, tellurium,
terbium, lanthanum, gold, iridium, osmium, silver, platinum,
palladium, rhenium, ruthenium, rhodium, hafnium, indium, a metal of
the Lanthanide series of the periodic table, and a salt thereof,
thereafter collecting a sample of fluid within or flowing from the
reservoir and analysing said sample to determine an amount of said
tracer contained in the sample, wherein the tracer is inserted into
the reservoir by means of a perforation tool.
2. A method as claimed in claim 1, wherein the tracer comprises
caesium, niobium, tantalum, tellurium, terbium, europium, platinum
or rhodium or a salt thereof.
3. A method as claimed in claim 1, wherein the tracer comprises a
water-soluble salt of at least one of said non-radioactive
metals.
4. A method as claimed in claim 1, wherein the tracer comprises a
hydrocarbon-soluble salt of at least one of said non-radioactive
metals.
5. A method as claimed in claim 1, wherein the tracer comprises at
least one of said non-radioactive metals in elemental form.
6. A method as claimed in claim 1, wherein the tracer is in a
physical form of a disc, rod, wire or coating.
7. A method as claimed in claim 1, wherein the tracer is in a form
of finely divided particles of said non-radioactive metal or of a
salt of the at least one non-radioactive metal.
8. A method as claimed in claim 7, wherein the particles are formed
into a shaped unit.
9. A method as claimed in claim 1, wherein the reservoir is a
subterranean oil and/or natural gas reservoir.
10. (canceled)
11. A perforation tool comprising an elongate body having a central
longitudinal axis, a control means, deployment means and at least
one explosive charge mounted on or within said body and associated
with detonation means, said charge being arranged to direct energy
explosively and outwardly from the elongate body upon detonation,
and at least one tracer material mounted on or within said body
within the path of said explosive energy, wherein the tracer
material is solid and comprises at least one non-radioactive metal
selected from the group consisting of caesium, niobium, tantalum,
tellurium, terbium, lanthanum, gold, iridium, osmium, silver,
platinum, palladium, rhenium, ruthenium, rhodium, hafnium, indium,
a metal of the Lanthanide series of the periodic table, and a salt
thereof.
12. A perforation tool as claimed in claim 11, wherein the tracer
comprises caesium, niobium, tantalum, tellurium, terbium, europium,
platinum or rhodium or a salt thereof.
13. A perforation tool as claimed in claim 11, wherein the tracer
comprises a water-soluble salt of at least one of said
non-radioactive metals.
14. A perforation tool as claimed in claim 11, wherein the tracer
comprises a hydrocarbon-soluble salt of at least one of said
non-radioactive metals.
15. A perforation tool as claimed in claim 11, wherein the tracer
comprises at least one of said non-radioactive metals in elemental
form.
16. A perforation tool as claimed in claim 11, wherein the tool
comprises an outer sleeve covering the explosive charges and
wherein the tracer is located in one or more indentations formed in
the outer sleeve aligned with one or more of the explosive
charges.
17. A perforation tool as claimed in claim 11, wherein the tracer
is located spaced away from a charge between said charge and an
outer sleeve of said tool in the intended path of the explosive
blast so that at least some of the tracer material is carried into
the reservoir formation with the explosive gases when the charge is
detonated.
Description
[0001] The present invention relates to a method for tracing
fluids, particularly fluids flowing within a well such as from an
oil or gas reservoir, and to a perforation tool suitable for
introducing a tracer into such a reservoir.
[0002] It is common in the oil exploration and recovery industry to
place tracers within a well in order to determine the flow of fluid
from the well or from a particular section of it. When the tracer
is incorporated in the fluid flowing from the well, it may be
detected in the fluid by analysis of the fluid arriving at the
well-head. For example, U.S. Pat. No. 3,623,842 describes a method
of determining fluid saturations in reservoirs by injecting at
least two tracers having different partition coefficients between
fluid phases (e.g. oil and water) into the formation and monitoring
the appearance of the two tracers in the produced fluids. This
example uses ethyl acetate as a tracer chemical. Radioactive
tracers have been widely used for many years in well-monitoring
applications. As an example, see U.S. Pat. No. 5,077,471, in which
radioactive tracers are injected into a perforated well-bore,
sealed and then monitored for decay to indicate the fluid flow from
the formation.
[0003] One problem encountered with the use of radioactive tracers
is that their transport and use is highly regulated, leading to
greater expense and difficulty with their use. In addition, it has
become quite common to use tracers associated with a perforation
tool, in which the tracer is fired by explosive devices located
around the tool into the formation to perforate the formation and
thereby to embed the tracer in the formation. Since explosive
devices are also highly controlled, it has become very difficult to
arrange the transport of devices incorporating both radioactive
sources and explosives. Although non-radioactive tracers, i.e.
chemical tracers, may be used, these require careful selection to
ensure that they are sufficiently soluble in the phase to be
monitored and that they are readily detectable at low
concentrations. The high limit of detection of many chemicals makes
them unsuitable for use as tracers. U.S. Pat. No. 4,755,469
describes the use of rare metal tracers for tracing oil and
associated reservoir fluids by mixing an oil-dispersible rare metal
salt with oil or an oil-like composition, injecting the dissolved
tracer composition it into a subterranean reservoir and analysing
oil fluids produced from a different part of the reservoir for the
presence of the rare metal to determine whether the oil mixed with
the tracer has been produced from the reservoir.
[0004] It is an object of the present invention to provide a tracer
and a method of monitoring fluids flowing from a reservoir using
the tracer which overcomes some of the problems with the existing
tracers and methods.
[0005] According to the invention, we provide a method of
monitoring the flow of fluid within or from a reservoir comprising
the steps of inserting in said reservoir a solid non-radioactive
tracer comprising at least one metal selected from caesium,
niobium, tantalum, tellurium, terbium, lanthanum, gold, iridium,
osmium, silver, platinum, palladium, rhenium, ruthenium, rhodium,
hafnium, indium a metal of the Lanthanide series of the periodic
table, or a salt thereof, thereafter collecting a sample of fluid
within or flowing from the reservoir and analysing said sample to
determine the amount of said tracer contained in the sample. From
the presence or absence of tracer in the sample, its amount and
other parameters such as sample size, timing of the sample
collection etc, information about the fluid flow within the
reservoir may be gathered. The reservoir is normally a subterranean
oil and/or natural gas reservoir. The fluid flowing within the
reservoir normally contains oil, natural gas, water and solids such
as sand or other particles.
[0006] According to a second aspect of the invention we provide a
perforation tool comprising an elongate body having a central
longitudinal axis, a control means, deployment means and at least
one explosive charge mounted on or within said body and associated
with detonation means, said charge being arranged to direct energy
explosively, outwardly, and, preferably transversely, along a path
with respect to the elongate body upon detonation, and at least one
tracer material mounted on or within said body within the path of
said explosive energy, characterised in that the tracer material
comprises at least one non-radioactive metal selected from caesium,
niobium, tantalum, tellurium, terbium, lanthanum, gold, iridium,
osmium, silver, platinum, palladium, rhenium, ruthenium, rhodium,
hafnium, indium a metal of the Lanthanide series of the periodic
table, or a salt thereof.
[0007] The tracer comprises at least one non-radioactive metal
selected from caesium, niobium, tantalum, tellurium, terbium,
lanthanum, gold, iridium, osmium, silver, platinum, palladium,
rhenium, ruthenium, rhodium, hafnium, indium a metal of the
Lanthanide series of the periodic table, or a salt thereof. The
metals of the Lanthanide series comprise the elements of atomic
numbers from 57 to 71. Preferred metals include niobium, tantalum,
tellurium, terbium, europium, platinum and rhodium, and especially
preferred are niobium, tantalum, tellurium, terbium and europium.
These metals are not naturally abundant and have a low detection
limit using standard elemental analysis methods such as
inductively-coupled plasma-mass spectroscopy (ICP-MS).
[0008] Many of the metals naturally contain more than one isotope.
By non-radioactive, we mean that the metals used in the tracer do
not contain a greater proportion of radioactive isotopes than found
in the naturally occurring metal, i.e. they have not been enriched
with radioactive isotopes. Some of the metals may contain unstable
radioactive isotopes in their natural state but the emission of
radioactivity is very low, and they are unsuitable for use as
radioactive tracers at the dilutions typically used without
enrichment with one or more radioactive isotopes. Normally for use
as a radioactive tracer a metal is treated, e.g. by bombardment
with neutrons in a nuclear reactor, to enrich the composition of
isotopes with unstable, radioactive isotopes which can emit
detectable radiation. The metals used in the tracers of the present
inventive method may have a composition of isotopes which is not
naturally occurring, by enrichment with one or more stable
non-radioactive isotopes to assist identification of the metal,
particularly by mass-spectrometry.
[0009] In one preferred embodiment, the tracer or tracers may be
formed of the selected metal or metals in elemental form.
Alternatively the tracer may be supplied as salts of the metals.
When used as salts, inorganic anions are preferred, particularly, a
low-mass anion such as nitride or carbide in order to increase the
amount of tracer metal in a given mass of tracer composition.
[0010] A tracer in elemental form may be conveniently supplied as a
discrete tracer unit such as a disc, wire or rod or as a coating
for placement in or attachment to a reservoir perforator gun
(perforation tool). Alternatively the tracer metal may be moulded
to fit around an explosive charge. The salts may be supplied as
pressed discs or in another form. More than one metal may be used
in a tracer. When more than one metal is used as a tracer they may
be simply mixed or alloyed. Alternatively more than one discrete
tracer unit, e.g. metallic disc, may be used in the same location
or different tracers may be placed in different locations.
[0011] The tracer may take the physical form of a moulded metal
shape such as a disc, wire or rod or may comprise finely divided
particles of metal or as a salt of the metal. The particles may be
formed into a shape, such as a tablet or disk, e.g. by pressing,
extruding, granulating or other method, optionally using a binder.
The tablet may further comprise other materials such as a diluent
(i.e. a non-traceable material) to add mass, and/or a dispersant to
aid dispersal and/or dissolution of the particles into the fluid to
be traced. The tablet or other shape may be encased in a protective
coating, preferably of a soluble or permeable material.
[0012] For insertion of a tracer by means of a perforator gun, it
is preferred to form the tracer metal into a disc for placement
into a perforation gun apparatus, either in an external scallop or
in close proximity to the explosive charge. Typically a disc may
contain from about 0.1 g-20 g especially 5-20 g of metal,
preferably from about 8 to 12 g. The tracer may be associated with
each explosive charge or only some of them. Preferably the amount
of tracer used in a well section provides from about 20 to about
500 g (more preferably between about 50 and 200 g) of tracer
metal.
[0013] The sample of fluid may be taken from the top of the well or
may be withdrawn from within a well using a suitable well tool. The
sample may be analysed by any suitable means to determine the
amount of tracer present. There are many suitable methods for the
detection and measurement of metals in a sample by elemental
analysis. One suitable method is inductively coupled plasma mass
spectrometry (ICP-MS) calibrated for the metal used in the tracer.
The collected fluid sample may be aspirated into the plasma,
optionally after a treatment to separate the phases or to
concentrate the sample. Alternatively, when the sample is a
hydrocarbon such as crude oil, the sample may be ashed and then
extracted into acid which may then be introduced into the plasma.
Inductively-coupled plasma atomic emission spectrometry (ICP-AES)
is also a suitable elemental analysis method to determine the metal
tracer content of the sample. We have found that it is beneficial
to dilute the sample in a suitable solvent, preferably with the
addition of a complexing agent. The complexing agent maintains the
tracer metals in solution and avoids loss of tracer on surfaces
within the analytical apparatus. When metal tracers stick to
surfaces within the apparatus, they may be leached into successive
samples passing through the apparatus and lead to inaccurate
estimates of tracer within the sample. Any suitable complexing
agent may be used, provided it does not interfere with the analysis
of the tracers and forms a stable complex with the metal in the
selected solvent. Suitable complexing agents include quaternary
ammonium compounds. For the analysis of tracers in organic solution
we have found that quaternary ammonium compounds having long-chain
or bulky alkyl groups are very suitable, for example
methyltrioctylammonium chloride, sold commercially as ALIQUAT.TM.
336.
[0014] In a preferred method for analysing an oil sample for a
tracer, an internal standard is added to the sample which is
believed to contain the tracer and diluted with a solvent
containing a complexing agent. The resulting solution is then
analysed by ICP-MS configured for organics operation.
[0015] Alternatively, X-ray fluorescence spectroscopy may be used
to determine the amount of fluorescence emitted by the sample at
one or more characteristic frequencies when irradiated by X-rays.
All of these methods are widely used in analysis and may be
operated by the skilled person in a suitable manner. Alternative
methods of elemental analysis may also be used, as would be known
to the skilled analyst. Such methods may include chemical analysis,
atomic absorption spectroscopy, the use of metal sensitive
electrodes, voltammetry etc but these methods are likely to be less
sensitive than the preferred instrumental analysis methods
described above and so are less preferred.
[0016] It is preferred to analyse a blank sample from the well
(i.e. a sample taken before tracer was inserted in the reservoir)
in order to determine the amount of the selected tracer metal
occurring naturally in the fluids. When the tracer is to be
detected in a water-based fluid such as produced water, for
example, then the sample preparation may differ from that used for
an organic sample; e.g. by evaporating the sample rather than
ashing.
[0017] The above-described methods are generally capable of
quantitatively determining the amount of metal found in a sample,
with suitable calibration. However, it should be recognised that
the tracer technique itself may not be quantitative because,
especially when the tracer is forced into the reservoir formation
by a perforation gun, at least some of the metal may stick to the
formation in an unpredictable manner. Therefore the method may be
most useful for determining the presence or absence of flow from a
particular region of the reservoir.
[0018] The tracer method of the invention may be varied according
to conventional methodologies used in the industry. Therefore, two
or more tracers may be combined in a predetermined ratio in order
to produce a unique tracer composition for marking a particular
well or section of a well. It may be desired to determine the flow
of tracer from a particular part of a well or reservoir. In this
case a single reservoir may be marked by inserting different
tracers or combinations of tracers in different locations in order
to determine the part of the reservoir from which a particular
sample has originated or flowed through.
[0019] The tracer may be inserted in the reservoir by one or more
different methods. A preferred method comprises associating the
tracer with a part of a perforation tool or perforation gun. The
placement of tracers into the formation using a perforation tool
(also known as a perforation gun) is already known. A perforation
tool is used in the oil and gas drilling, exploration and recovery
industry for perforating a well, i.e. for forming channels or
perforations extending from a well-bore into the reservoir
formation. Each channel or perforation is formed by detonating an
explosive charge carried on a tool located in the well. The
explosive energy is directed into the well casing (if the well has
been cased) or the side of the well to penetrate the formation so
that the well casing or well bore side is perforated allowing
communication with the formation in the region of the tool. The
perforations form channels through which reservoir fluids may flow
out of the formation and into the well bore, thereby to flow to the
surface of the well for recovery. Perforation tools vary in their
size and design according to the result they are to achieve and any
description herein of perforation tools is given as general
background and not intended to limit the invention. Perforation
tools are equipment already known and used in the oil exploration
industry, and so a skilled designer of such tools is able to
construct a tool suitable for use in the present invention. The
tool is typically of generally cylindrical shape and has a length
typically of between about 0.5 and about 10 metres. Typically the
perforation tool carries more than one charge, usually arranged
around the circumference of the tool or gun. The number of charges
carried on a perforation tool varies but typically may be between
about 2 and about 12 charges per foot (300 mm), normally arranged
in a pattern, e.g. approximately helically, along the length of the
tool. The explosive charge, detonation means, deployment means and
control means comprise materials and apparatus which are known in
the industry. For example, the charge is normally shaped to direct
the explosive energy along the desired path relative to the body of
the perforation tool. The detonator is usually an electrically
operated detonator. Control means may comprise a microprocessor and
associated control program mounted within the perforation tool or
an associated tool or the tool may be controlled directly by means
of signals carried to the tool from an operator, normally located
at the head of the well. The signals may be carried along a cable
connecting the tool and the well-head. The tool is normally
deployed by lowering it down a well suspended on a wire or string
before, during or after completion of a well.
[0020] The tool generally has an outer sleeve covering the
explosive charges. When a perforation tool is used to insert tracer
into a formation, the tracer may be placed into indentations or
"scallops" formed in the outer sleeve, usually directly over one or
more of the explosive charges carried by the tool. The tracer
compounds may be held in place by an adhesive or a covering film,
such as an epoxy resin covering. Alternatively the tracer compounds
may be located within the outer sleeve or casing of the perforation
tool, for example in contact with an inner sleeve within the gun.
It is preferred that the tracer materials are not placed in contact
with the explosive charges in order to avoid destabilising the
charges by redirecting the angle of the blast. The tracer is
therefore placed spaced away from the charge in the path of the
blast so that at least some of the tracer material is carried into
the reservoir formation with the explosive gases when the charge is
detonated. It is likely that some of the tracer is vaporised in the
explosion and then condenses within the formation. At least some of
the tracer particles are then carried out of the formation with the
flow of fluids released by the perforation of the formation by the
explosive charge. The tracer or tracers may be placed in the gun or
perforation tool in the form of shaped units as described
hereinbefore or coated onto a part of a perforator gun.
Alternatively the tracer metal may be moulded to fit around an
explosive charge.
[0021] It is not necessary to dissolve the tracer in the fluid to
be traced; it is sufficient in many circumstances to disperse
particles of the metal or salt in the fluid so that the finely
divided metal particles flow with the fluid. A metal salt tracer
may be selected to be soluble in the fluid which is to be traced.
For example when the tracer is for use in monitoring flows of oil
in an oil well, then an oil-soluble metal salt may be selected,
e.g. a salt of an organic acid, particularly a long-chain fatty
acid. When the tracer is for use in a water-based system, e.g. for
tracing water pumped into a well, then it is preferred to use a
water-soluble salt of the tracer metal(s) such as a sulphate,
nitrate or halide. Alternatively a solid tracer comprising a
soluble salt of the metal is placed in the well and is then
dissolved in the water flowing within the well. The method of the
invention is for the placement of solid tracers comprising
non-radioactive metals in a reservoir for tracing the flow of
fluids in and from a well bored into the reservoir. It is known
from U.S. Pat. No. 5,711,900 and U.S. Pat. No. 6,001,280 to use as
a tracer a solution of a gadolinium salt of a carboxylic acid. The
deployment of tracer solutions as disclosed in those references is
not within the scope of the present invention.
[0022] The invention will be further described in the following
examples with reference to the drawing which is:
[0023] FIG. 1 a graph showing the concentration of Nb and Ta found
in a sample of reservoir fluids against time when the sample was
taken.
PREPARATION OF REAGENTS
[0024] The following reagents were used: [0025] ICP standard
solutions of 1000 mg/ml Nb, Ta, Y, Tl, La, (supplied by Inorganic
ventures, Aldrich and VWR) [0026] Multi element precious metals
standard containing 100 mg/ml Au, Ir, Os, Pt, Pd, Pt, Re, Rh and Ru
(supplied by Alfa-Aesar). [0027] Dilution solution for stock
standards, 10% w/v Aliquat.TM. 336, 10% v/v ethyl hexanol in MIBK
[0028] Dilution solution for samples, 1% w/v Aliquat 336, 5% v/v
ethyl hexanol in Lotoxane.TM. solvent.
[0029] 1 .mu.g/ml stock standards were prepared by diluting 50
.mu.l aliquots of the 1000 .mu.g/ml and 500 .mu.l of the 100
.mu.g/ml ICP standards to 50 ml with stock standard dilution
solution.
[0030] The following 1 mg/ml combined stock solutions were
prepared:
1) Nb+Ta
2) La+In
3) Au, Ir, Os, Pt, Pd, Pt, Re, Rh+Ru
[0031] 4) Y+Tl internal standard
[0032] A 0.1 mg/ml combined standard was the prepared by combining
1 ml aliquots of stock solutions 1, 2 and 3 and diluting to 10 ml
with stock standard dilution solution.
[0033] Instrumentation: ICP-MS, Thermo X Series II fitted with
organics kit, peltier cooled spray chamber, micromist low flow
nebuliser (Glass Expansion), extra mass flow controller for
addition of oxygen into the plasma and platinum cones. The
instrument was initially set up with a standard aqueous
introduction system and a detector cross-calibration and full
system tune were preformed. An instrument performance check was
then performed to confirm that the instrument was performing within
the manufacturers acceptance limits. The organics kit was then
fitted and the instrument stabilised on isopropanol. A blank
solution containing internal standard was aspirated. The oxygen
flow was adjusted until the green carbon emission was removed and
the ICP-MS optics were then optimised on the low and high mass
internal standards.
Calibration
[0034] High level calibration standards were prepared by combining
aliquots of stock solutions 1, 2 and 3, plus 500 .mu.l of internal
std solution and 1 g of base oil and diluting to 10 g with sample
dilution solution. Low level calibration standards were prepared by
adding aliquots of the 0.1 .mu.g/ml combined standard, 1 g of base
oil and 500 .mu.l of internal std solution and diluting to 10 g
with sample dilution solution. The instrument was calibrated using
the prepared high-level and low-level calibration standards.
Instrument response was linear over the calibration range 0-20 ng/g
with a relative standard deviation of less than 2%.
Detection Limits
[0035] The detection limits for the metals was determined as
3.times. standard deviation (limit of detection, LOD) and 10.times.
standard deviation (limit of quantification, LOQ) of the results of
ten repeated determinations of a measuring a 100 pg/g standard
solution. The highest LOD and LOQ was found for La at 35 pg/g and
117 pg/g respectively.
EXAMPLE 1
[0036] A 1 g sample of crude oil was spiked with 50 .mu.l of 0.1
.mu.g/ml combined standard. 500 .mu.l of internal standard solution
was added and diluted to 10 g with sample dilution solution. This
gives a spike of 0.5 ng/g in the final solution (equivalent to 5
ng/g in the 1 g sample). To establish a base level an un-spiked
sample was prepared in the same way. The samples were analysed
using the calibrated ICP-MS instrument and the results are shown in
Table 1.
[0037] The concentration of each of the metals found in the
background (i.e. the un-spiked sample) is shown together with the
percentage of added metal tracer found in the spiked sample after
subtraction of the background level. The results show that recovery
of the metal tracer elements was between 80 and 110%. Values
greater than 100% are believed to be caused by the spiked sample
responding better in the plasma than the calibration samples, an
effect which may be due to the different viscosity of the sample
and calibration solutions.
TABLE-US-00001 TABLE 1 Spike Background Recovery Element (pg/g) (%)
Nb 718 82 Ru 41 103 Rh 67 105 Pd 521 105 In 78 105 La 8763 104 Ta
44 95 Re 38 107 Os 26 108 Ir 104 84 Pt 23 110 Au 121 112
EXAMPLE 2
[0038] 12 g of niobium carbide powder was mixed with a
microcrystalline wax binder and formed into 40 disk-shaped tablets,
each approximately 10 mm diameter and 2 mm thick by pressing. The
tablets were placed into indentations, known as scallops, in the
outer surface of the casing of a perforation tool and covered in an
epoxy material. A second batch of 40 tablets containing a total of
12 g of tantalum carbide mixed with the wax binder was prepared in
the same way and the tablets were placed into the scallops of a
second perforation tool. The perforation tools were of a standard
type, each being provided with a plurality of explosive charges
arranged to fire outwardly from the perforation tool in a
predetermined direction upon operation of the tool. The perforation
tools were placed down a well into different locations in the
formation of an oil reservoir and fired to perforate the formation.
When the reservoir fluids had reached the surface, samples of the
reservoir fluid were collected every 30 minutes. The samples were
later analysed using the ICP-MS method described above. The results
are plotted in FIG. 1 as the concentration of Nb and Ta found in a
sample against time when the sample was taken. The plot shows that
both Nb and Ta have been detected confirming that both perforation
tools fired and that fluid is flowing up the well from the
locations of each of the perforation tools. This confirms that the
perforation tool successfully perforated the formation and that
fluid flowed from fissures in the formation opened by the operation
of the tool The Ta peak appears to lag behind the Nb peak by a
short time and this is believed to confirm that the tool containing
the Ta tracer was placed further from the well-head than the tool
containing the Nb tracer.
* * * * *