Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
1999-11-23
2001-05-01
Schoeppel, Roger (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S264000, C175S059000, C073S061410, C073S064550, C073S019010
Reexamination Certificate
active
06223822
ABSTRACT:
The invention relates to sampling apparatus for use downhole in acquiring samples of volatile components dissolved in downhole fluids, and to an associated method.
BACKGROUND OF THE INVENTION
Acquiring samples representative of downhole fluids is an important aspect of determining the economic value of an hydrocarbon formation. However where a volatile gas is dissolved in the fluid, the sample taken downhole may under-represent the proportion of the volatile gas within the fluid due to its reaction with the material from which sampling apparatus is made. This leads to an underestimate of the proportion of volatile gas.
There is a particular problem where hydrogen sulphide (H
2
S) is dissolved in the fluid. H
2
S is highly corrosive and toxic and any underestimate of the proportion of this gas within the fluid can affect the economics of well production, as pipework will need to be replaced sooner than expected. Underestimate of the presence of corrosive gases such as H
2
S is having an effect on the economies of well production. In the last decade, it here has been observed that the proportion of H
2
S within hydrocarbon formations is increasing, partly as a result of accessing deeper formations.
Attempts to address this problem have included coating metal sampling apparatus with inert layers or the use of glass bottles to collect the samples of fluid. However these are relatively expensive and prevent the use of existing hardware. It is an objection of the present invention to provide apparatus and method for sampling downhole fluid which reduces the underestimation of volatile gases in hydrocarbons.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, a wellbore fluid sampling device is provided comprising a main body to be suspended into a hydrocarbon well, said body having at least one fluid inlet port to engage with a wall of the well, at least one conduit guiding fluid into the main body and a gas extraction system associated with said at least one conduit for essentially exclusively separating from said wellbore fluid at least part of a predetermined volatile non-hydrocarbon component dissolved in said wellbore fluid entering said at least one conduit.
The gas extraction system is preferably a material capable of binding the volatile component of the wellbore fluid. However, in another variant of the invention, it is also envisaged to use a selectively permeable membrane or interface as extraction system.
The preferred volatile component to be extracted from the wellbore fluid is H
2
S.
The method may further comprise retrieving the gas extraction system to the surface after sampling to permit analysis of the non-volatile components fixed in the system.
A preferred analysis of the material which the volatile component is bound to involves pyrolysis followed by mass spectrometry, by which the quantity of the non-volatile components fixed by the binding material can be determined.
According to a further aspect of the present invention, there is provided a method of quantitatively sampling volatile components dissolved in wellbore fluids, comprising the steps of lowering a sampling tool into a wellbore; bringing an inlet port of said tool into close contact with a subterranean formation; guiding said wellbore fluid from said subterranean formation into said tool; exposing said wellbore fluid to a gas extraction system for essentially exclusively separating from said wellbore fluid a predetermined volatile non-hydrocarbon component dissolved in said wellbore fluid; at least partially separating said volatile non-hydrocarbon component from said wellbore fluid; and storing said separated volatile component as non-volatile samples within said tool.
The gas extraction system may be placed within the hollow body, or in a supplementary chamber having an inlet and an outlet which is attached to the body and through which the fluid passes to enter the hollow body.
Where a supplementary chamber is used, preferably inlet and the outlet are provided with filters to prevent loss of binding material within the gas extraction system. Preferably the filters are formed from material which is inert to downhole fluids and to the binding material, and typically may comprise polytetrafluoroethylene (PTFE).
The hollow body has a fixed volume and as such the quantity of fluid sampled is known. This allows quantitative analysis of the volatile components to be performed. Thus a fluid can be sampled whilst downhole to ascertain the presence and percentage of selected volatile components in the fluid by selecting an appropriate binding material within the gas extraction system which material will preferentially react with the volatile component from the downhole fluid.
Such an sampling device allows gases dissolved within downhole fluids such as drilling fluid, oil or gas, to be fixed in a nonvolatile form within a binding material matrix for later analysis.
Typically the binding material is selected so as to secure H
2
S in non-volatile form.
For other gases which can occur downhole, such as carbon dioxide nitrogen, a binding material has to be chosen from those material which stabilises the respective gas. E.g., a strong alkali reactant for carbon dioxide.
The binding material may comprise one or combinations of the following materials, namely: metals, and in particular transition metals such as iron (Fe), molybdenum (Mo) and zinc (Zn), and metal oxides and in particular transition metal oxides such as iron oxide Fe
3
O
4
, zinc oxide ZnO and tungsten oxide WO
3
.
Metals and metal oxides may be doped, for example copper oxide doped tin oxide SnO
2
/CuO and gold doped tungsten oxide W
0
3
/Au.
Apart from metals and metal oxides, organic materials such as amines may be used, particularly where they exist as an organic solid at downhole temperatures.
Other compounds which may be used as the binding material include iron (III) EDTA complex in an aqueous alkaline solution for oxidising hydrogen sulphide to elemental sulphur and R
1
R
2
XYR
3
R
4
compounds, where X and Y are carbon or nitrogen atoms and any two of the R groups contain electronegative groups, for example fumaronitrile.
By analysing the quantity of iron sulphide FeS
2
present for a known volume of downhole fluid sampled by the sampling device, the amount of H
2
S dissolved in the downhole fluid can be determined. Thus quantitative analysis of H
2
S can be achieved by choosing a binding material which reacts with H
2
S to form an inert sulphur containing compound.
The use of Fe
3
O
4
as the binding material within the gas extraction system allows this to be done, since Fe
3
O
4
fixes sulphur contained within H
2
S into an inert non-volatile form of iron sulphide according to the following equation:
Fe
3
O
4
+6H
2
S→3FeS
2
+4H
2
O+2H
2
The properties of the fluid and the temperatures experienced downhole will affect the choice of the binding material. Thus for example where high temperatures are present downhole, the binding material may desirably be tungsten oxide WO
3
.
Preferably the binding material is in the form of generally spherical particles, or a powder, so as to present a large surface area to the fluids to be tested. Preferably the particles have a diameter in the range of 0.1 mm to 10 mm, and more preferably in the range of 0.1 mm to 1 mm, so as to ensure there is no significant pressure drop across the binding material within the device.
By making the gas extraction chamber compatible with existing downhole equipment, the tool according to the invention can be achieved by retrofitting to existing apparatus, and allows re-use of existing hardware so achieving cost savings.
The device may further comprise attachment means to secure it to a wireline so that it can be lowered downhole when sampling is required, and after sampling, raised again to surface.
These and other features of the invention, preferred embodiments and variants thereof, possible applications and advantages will become appreciated and understood by those skilled in the art from the following detailed description an
Batzer William B.
Schlumberger Technology Corporation
Schoeppel Roger
Wang William L.
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