NZ623721B2 - Formation pressure sensing system - Google Patents
Formation pressure sensing system Download PDFInfo
- Publication number
- NZ623721B2 NZ623721B2 NZ623721A NZ62372112A NZ623721B2 NZ 623721 B2 NZ623721 B2 NZ 623721B2 NZ 623721 A NZ623721 A NZ 623721A NZ 62372112 A NZ62372112 A NZ 62372112A NZ 623721 B2 NZ623721 B2 NZ 623721B2
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- New Zealand
- Prior art keywords
- conduit
- pressure
- formation
- inlet
- fluid
- Prior art date
Links
- 230000015572 biosynthetic process Effects 0.000 title claims abstract description 142
- 238000005755 formation reaction Methods 0.000 title claims abstract description 137
- 239000012530 fluid Substances 0.000 claims abstract description 135
- 239000011440 grout Substances 0.000 claims abstract description 93
- 238000005086 pumping Methods 0.000 claims abstract description 13
- 239000000463 material Substances 0.000 claims description 45
- 239000007788 liquid Substances 0.000 claims description 22
- 239000011800 void material Substances 0.000 claims description 9
- 238000009434 installation Methods 0.000 claims description 8
- 238000005259 measurement Methods 0.000 claims description 5
- 239000002002 slurry Substances 0.000 claims 4
- 238000010926 purge Methods 0.000 claims 2
- 238000007789 sealing Methods 0.000 claims 2
- 230000035945 sensitivity Effects 0.000 claims 1
- 239000004568 cement Substances 0.000 abstract description 55
- 238000000034 method Methods 0.000 abstract description 13
- 238000004891 communication Methods 0.000 abstract description 7
- 238000002347 injection Methods 0.000 description 31
- 239000007924 injection Substances 0.000 description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 230000000875 corresponding Effects 0.000 description 5
- 239000003673 groundwater Substances 0.000 description 5
- 230000035699 permeability Effects 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 239000003245 coal Substances 0.000 description 4
- 238000009530 blood pressure measurement Methods 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 230000036571 hydration Effects 0.000 description 2
- 238000006703 hydration reaction Methods 0.000 description 2
- 230000002706 hydrostatic Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000003208 petroleum Substances 0.000 description 2
- 229920000915 polyvinyl chloride Polymers 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- HWKQNAWCHQMZHK-UHFFFAOYSA-N Trolnitrate Chemical compound [O-][N+](=O)OCCN(CCO[N+]([O-])=O)CCO[N+]([O-])=O HWKQNAWCHQMZHK-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910000278 bentonite Inorganic materials 0.000 description 1
- 239000000440 bentonite Substances 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 229910052570 clay Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001419 dependent Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000037361 pathway Effects 0.000 description 1
- 238000005500 petroleum industry Methods 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 230000003068 static Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices, or the like
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/01—Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/06—Measuring temperature or pressure
Abstract
method of installing a pressure transducer (5) in a borehole (1) to measure the fluid pressure of a geological formation. The pressure transducer is installed into the borehole at a desired depth, and then the borehole is filled with a cement grout (3). The fluid connection between the pressure transducer and the formation is opened by pumping a fluid through tubing to displace the cement grout. A process of hydrofracture can be employed to provide a communication path of fluid between the formation and the pressure transducer surrounded by the fractured grout. A pressure transducer may be cemented into the borehole along with a check and pressure relief valve (7). The pressure transducer may be installed in the tubing at a subsequent stage. ansducer and the formation is opened by pumping a fluid through tubing to displace the cement grout. A process of hydrofracture can be employed to provide a communication path of fluid between the formation and the pressure transducer surrounded by the fractured grout. A pressure transducer may be cemented into the borehole along with a check and pressure relief valve (7). The pressure transducer may be installed in the tubing at a subsequent stage.
Description
FORMATION PRESSURE SENSING SYSTEM
Related Patent Application
This international PCT patent application claims priority to Australian provisional patent
application filed 11 October 2011, and accorded application number 2011904211. The
disclosure of the Australian provisional patent application is incorporated herein by
reference.
Technical Field of the Invention
The present invention relates in general to the monitoring and measuring of fluid pressures
in geological formations, and more particularly to measuring techniques which more
accurately measure the fluid pressure in the formation at a desired elevation or depth,
without being influenced by pressures in the formation above and below the pressure
measuring apparatus.
Background of the Invention
The measurement of pressures in geological formations is often of great importance to
engineering and environmental matters. To the civil engineer, pore pressures in soils are
important in the design of foundations, slopes and retaining walls. To the hydrogeologist,
pressures in aquifers and aquicludes are a key to determining groundwater resources and
movement. To the petroleum engineer, understanding the pressure of the fluids is critical in
determining the resources and reserves of petroleum fluids.
The civil engineering industry often refers to pressure monitoring systems as piezometers.
Piezometers take a variety of forms. The most traditional piezometer involves the
placement of an open tube standpipe into a borehole with a sand or gravel pack around a
slotted tip. A bentonite seal is placed above the gravel pack and the remainder of the hole
is cemented. Variations on this theme exist with some standpipes being fitted with a filter
tip, where the filter tip is driven into a clay.
The fluid level is generally measured in standpipe piezometers by measuring the water
level therein either manually by some form of dipping system, or by the measurement of
pressure above a certain point in the standpipe. This has previously been accomplished by
measuring the required pressure to force a bubble out of a tube in the standpipe, but is
more commonly undertaken by the use of pressure transducers.
The disadvantage of the standpipe system is that the standpipe has a significant volume. To
produce a change in the volume of the fluid in the standpipe, fluid must either come out of
the formation to fill the standpipe, or pass from the standpipe into the formation. This
requires the formation to have an adequate permeability and storage characteristic to
operate with the standpipe. This pressure measuring technique also requires a very good
connection between the standpipe and the formation. In all cases, the standpipe adversely
functions to dampen the true pressures of the formation.
To overcome the volumetric problems with the use of standpipes, low volume pressure
transducers were fixed in a filter zone in a borehole or structure. Because of the inherent
instability of early electronic devices, pneumatic piezometers were developed. In the use of
pneumatic piezometers, two tubes were fitted to the transducer - one to permit the passage
of compressed air to the device, and the other to permit the return of the compressed air
after it passed through a pneumatic valve. The pressure of the fluid in the formation was
detected by the pressure required to pneumatically open the valve, as detected by the
airflow up the return tube. This type of transducer was particularly well suited to the
monitoring of earth dams as the tubing and transducers could be easily incorporated into
the earth structure.
The next major development was to use electrical transducers, particularly of a vibrating
wire type. This type of transducer exhibited better long term drift characteristics as
compared to the bridge type transducers of the same era. The vibrating wire transducers
had very low volumetric requirements to operate an internal diaphragm, and as such were
easily incorporated into filter zones within boreholes. The availability of vibrating wire
transducers made it possible to install multiple transducers into a single borehole, although
this was generally accomplished by the use of multiple levels of gravel packing and
cementing.
The next major development was the realisation that in many cases a pressure transducer
could be cemented directly into a borehole. To make this possible, the pressure sensing
diaphragm of the transducer must be isolated from the direct contact with the cement, and
the cement required adequate permeability to permit a fluid connection between the
geological formation and the transducer. With this installation method, there is always an
uncertainty as to what is connected to what, i.e. is the formation fluid at the same elevation
as the transducer in the borehole, or is the fluid in the formation at some other level in the
borehole? It has been generally assumed that the pressure measured by the transducer is
that of the formation fluid located directly adjacent to where the transducer has been
installed. This may not, however, be universally correct as, if the formation adjacent to the
transducer is extremely impermeable, and the formation further up the hole is not, then
depending on the relative permeabilities of the formations and the cement grout, the
pressure measured may not be that produced by the formation located directly adjacent to
the pressure transducer. This becomes particularly problematic if shrinkage of the cement
grout occurs, which leads to longitudinal leakage paths within the cured grout. When this
occurs, the pressure transducer can be influenced by formation pressures that exist above
and below the pressure transducer. In this event, the pressure transducer measures the
composite of all of the formation pressures to which it is exposed.
Because most exploitable aquifers have high permeability and storage characteristics, the
groundwater industry has generally managed to utilise traditional standpipes or the use of
monitoring wells. In low permeability formations, investigations have been undertaken to
consider low volume fluid pressure measuring techniques.
The petroleum industry is a field where the measurement of geological formation pressures
was traditionally accomplished by pressure measurements in test wells or production wells.
This situation has since changed dramatically with the introduction of several formation
testing tools. Permanent monitoring of formation pressures has also grown with the use of
pressure transducers which are fixed in the casing, or to the tubing, having been run into a
well and cement grouted into place.
Lastly, it has been proposed that one or more pressure sensing lines could be grouted in the
borehole formed in a coal seam to measure the fluid pressures therein. This technique is
disclosed in a technical paper published in SPE Reservoir Engineering (February 1987)
and entitled ‘Reservoir Engineering in Coal Seams: Part 2 – Observations of Gas
Movement in Coal Seams’ by Ian Gray. According to this technique, the pressure sensing
line(s) is strapped to a PVC conduit and the assembly is lowered into the borehole. The
borehole is grouted around the assembly, and the line is filled with water to prevent the
grout from flowing up the pressure sensing line. The PVC pipe can accommodate the flow
of grout therein. After the grout has set, the pressure sensing line is pressurised to fracture
the grout and create an opening to the coal seam. The pressure sensing line can be
connected to a pressure gauge or chart recorder located at the surface.
From the foregoing, it can be seen that a need exists for a fluid measuring technique that
more accurately measures the fluid pressure in the part of the formation that is at the same
depth, elevation or vicinity of the pressure sensor. A further need exists for isolating the
pressure sensor in a borehole so that it is only exposed to the fluid pressure in the
formation adjacent to the pressure sensor and not to the formation pressure at another
position in the hole. A further need exists for a method to isolate the pressure sensor in the
borehole using a cement grout between the pressure sensor and the borehole, and then
opening a communication path in the cement grout between the pressure sensor and the
wall of the borehole where the formation fluid pressure is to be measured. Yet another
need exists to undertake the installation of one or more sensors in a single cementing
operation.
Summary of the Invention
The various features of the invention permit a more reliable connection system between a
pressure sensing location within a cement grouted borehole and the transducer system used
to monitor the pressure in the surrounding geological formation. This is accomplished by
cementing a conduit fitted with a filter at its bottom end in the borehole at a desired
location. The filter is the inlet to the pressure measuring apparatus. The conduit is
pressurised with fluid to clear the conduit of any cement grout during this operation. A
valve is used to block the backflow of cement grout from the borehole back into the
conduit. The valve is preferably a check valve.
Once the cementing operation is complete, but before the cement grout has completely set,
a fluid is again introduced into the conduit. The fluid is forced out of the bottom end of the
conduit (and the filter) and displaces the cement grout to achieve a fluid connection
between the formation and the filter. The process of introducing the fluid into the conduit is
preferably accomplished in several stages. The first stage of the initial fluid injection is to
ensure the filter end of the conduit is cleaned of cement grout. The second stage of fluid
injection takes place to move the cement grout in the borehole from around the bottom end
of the conduit. The second stage is normally carried out when the cement grout has started
to set. The final fluid injection stage can be advantageously employed to ensure
connectivity in certain circumstances, and follows the full setting of the cement grout. In
this final stage, a fluid is pumped through the conduit and filter at adequate pressure to
cause the local hydrofracture of the geological formation located laterally adjacent to the
filter. As such, pressures produced by the geological formation at the filter depth are
coupled directly to the input of the pressure measuring apparatus.
In an alternative process, the fracturing of both the grout and the formation can be
accomplished following the filter washing and setting of the grout.
According to a feature of the invention, the cement grout is pumped through the borehole
formed in the formation using either a grout pipe to convey the grout from the base
upwards in the borehole, or if grouting is being undertaken from a borehole collar, a return
tube is employed.
In one embodiment of the invention suitable for any reservoir type, a pressure transducer is
installed at a desired depth in a bore to measure formation pressures at such depth. The
pressure transducer is placed between a filter and a check valve equipped with a pressure
relief valve. The check valve is of the type that opens at a predetermined pressure. The
opening pressure of the check valve is designed to prevent a standing fluid level in the
fluid monitoring zone. The installation involves the lowering of the pressure transducer
into the formation on the end of a cable, together with a conduit that is typically a small
diameter tubing pipe (typically ¼” diameter). Cement grouting of the borehole is
undertaken along with the staged process of fluid injection in the conduit to clear the filter
of grout and then displace the grout so that the filter is in communication with the
formation pressure to be measured. In certain circumstances the method can be followed
by a hydrofracture process once the grout has set.
In another embodiment of the invention the conduit run into the borehole can be
constructed with a small diameter tubing pipe connected to a larger diameter tubing section
located near the surface. The installation of the tubing pipe would normally, but not
necessarily, be strapped to a grout pipe. When located at a desired depth in the borehole,
the top of the tubing pipe is filled with fluid and fitted with a non-return valve. The non-
return valve may be automatically or manually operated to achieve a no-return behaviour.
The grouting operation for the borehole is then undertaken, whereupon the non-return
valve prevents fluid from being pushed out of the conduit due to density or pumping
pressure difference. Once grouting is complete, a small volume of fluid is pumped through
the conduit to clean the filter. This is followed by the pumping of additional fluid into the
conduit to displace the grout in the borehole radially around the inlet filter, usually when
the grout has started to set, to avoid mixing the fluid and the grout. In some cases the
method can be followed by a hydrofracture process once the grout has set. In this
embodiment, fracturing pressures are not impeded by the pressure limitations of the
downhole transducer used in the embodiment described above. Once the grout has set, the
non-return valve is removed and the pressure sensing transducer is run into the top of the
conduit. It is undesirable to permit fluid movement within the conduit as this requires the
formation to supply or receive that fluid. To avoid this and to permit the pressure
transducer to be located in its most suitable pressure range, the pressure transducer is
preferably attached to a packer which is lowered with it into the enlarged upper portion of
the conduit. The packer may then be set to block the upper end of the conduit. In this
embodiment, the transducer can be removed periodically for calibration or maintenance. It
is also possible to alter the location of the transducer within the conduit to suit the pressure
range of the device. This embodiment is ideally suited to high accuracy monitoring of
groundwater where the fluid in the conduit is a liquid (preferably water) of known density.
Preferably the density of the fluid should match that of the reservoir located in the
geological formation.
According to a further embodiment of the invention, disclosed is a method of monitoring a
fluid pressure in a subterranean formation. The method includes forming a borehole in the
subterranean formation at least to a depth where the fluid pressure is to be measured, and
then placing a conduit into the borehole to a depth so that a bottom inlet end of the conduit
is laterally adjacent a location where the formation pressure is to be measured. A non-
return valve is used in the conduit so that liquid cannot pass upwardly all the way through
the conduit. A cementitious material is placed in the borehole until the cementitious
material rises at least above the bottom inlet end of the conduit. A liquid is pumped down
the conduit through the non-return valve, out of the inlet end of the conduit and into the
cementitious material in the borehole to displace the cementitious material around the
bottom inlet end of the conduit to thereby form a fluid connection to the formation. A
pressure sensing device is coupled to the formation fluid pressure within the conduit to
measure the fluid pressure of the formation at the desired depth.
According to yet another embodiment of the invention, disclosed is a method of
monitoring a fluid pressure in a subterranean formation, which includes forming a borehole
in the subterranean formation at least to a depth where the fluid pressure is to be measured.
A pressure sensing device is connected to a bottom inlet end of a conduit so that the
pressure sensing device measures fluid pressures at the inlet end of the conduit, and the
conduit is lowered into the borehole until the inlet end of the conduit is at a depth where
the formation pressure is to be measured. The borehole is then filled with a cementitious
material to a level substantially above the inlet end of the conduit and the cementitious
material is prevented from flowing up the conduit, whereby the cementitious material
surrounds the inlet end of the conduit. The inlet end of the conduit is purged of
cementitious material by pumping a liquid down the conduit. A lateral fluid path is formed
between the inlet end of the conduit and the formation, whereby the formation pressure
forces the formation fluid to flow through the fluid path and through the inlet end of the
conduit to the pressure sensing device so that the formation fluid pressure is measured.
According to yet a further embodiment of the invention, disclosed is a method of
monitoring a fluid pressure in a subterranean formation, which includes placing a conduit
in a borehole formed in the subterranean formation so that a pressure measuring inlet of the
conduit is located at a depth where the formation pressure is to be measured. A pressure
sensing device is connected to the conduit to measure pressures at the pressure measuring
inlet of the conduit. The borehole is filled with a cementitious material above and below
the pressure measuring inlet of the conduit so that the pressure measuring inlet has a fluid
communication path outwardly to the formation, but the pressure measuring inlet of the
conduit is isolated by the cementitious material from other portions of the formation
located above and below the pressure measuring inlet of the conduit.
Brief Description of the Drawings
Further features and advantages will become apparent from the following and more
particular description of the preferred and other embodiments of the invention as illustrated
in the accompanying drawings, in which like reference characters generally refer to the
same parts, functions or elements throughout the views, and in which:
Figs. 1A-1D illustrate the sequence of installation steps of a formation pressure sensing
system according to the first embodiment, which incorporates a permanent downhole
pressure transducer.
Fig. 2 is a component diagram illustrating the details of the pressure sensor arrangement,
including a pressure sensor, a check valve and a filter.
Figs. 3A-3F illustrate the sequence of installation steps of a formation pressure sensing
system, including a hydrofracture stage, of the second embodiment of the invention where
the transducer is readily accessible from the surface.
Fig. 4 shows graphically the chronological record of pressure for a pressure transducer
such as that installed in Figs 1A-1D.
Detailed Description of the Invention
Fig. 1A illustrates a borehole (1) which has been drilled in the ground. Situated in the
borehole (1) is a grout pipe (3) for carrying a cementitious material, such as a cement
grout. Materials other than cement grout can be employed with equal effectiveness. The
grout pipe (3) is constructed with a port (4) near its base to permit the cement grout to be
deposited at the bottom of the borehole (1). Also located in the borehole (1) is a pressure
sensor arrangement comprising a connector block (9) for internally connecting together a
filter (10), a pressure transducer (5) and a check valve (7). The filter (10) can be any type
of filter, and can be of sintered metal construction to prevent formation debris from
clogging the input of the pressure transducer (5). The check valve (7) is preferably of the
type which is preset to open at a suitable differential pressure. The pressure transducer (5)
is lowered into the borehole (1) via a fluid injection pipe (8) which extends to the surface.
Moreover, the pressure transducer (5) is located in the borehole (1) at a location where the
corresponding formation fluid pressure is to be measured.
As noted above, the connector block (9) is internally cross ported to connect together the
filter (10), the pressure transducer (5) and the check valve (7). The pressure transducer (5)
is electrically connected to the surface by a cable (6) which transfers signals corresponding
to the differential pressure across the transducer (5). The pressure transducer (5) can be of
the conventional piezometer type for sensing the differential pressure across a movable
diaphragm, and providing a corresponding electrical signal output. Other types of pressure
sensors having electrical outputs can be employed with equal effectiveness. The check
valve (7) is connected to the fluid injection pipe (8) which also extends to the surface.
Prior to grouting the borehole (1) via the grout pipe (3), the fluid injection tube (8) is filled
with a liquid, such as water, under sufficient pressure that the fluid passes through the
check valve (7), the connector block (9), out of the filter (10) and into the borehole (1).
The liquid is pumped into the injection tube (8) to clear the system of any bubbles of gas
and to ensure the filter (10) is clear of any blockage which may have occurred during its
placement in the borehole (1).
Fig. 1B illustrates the borehole (1) during the grouting operation in which a cement grout
material is pumped down the grout pipe (3). The cement grout exits the grout pipe (3) via
the bottom port (4) where it fills the bottom of the borehole (1) and flows upwardly where
it temporarily reaches a level at location (11). It can be appreciated that during the grout
pumping operation, the pressure sensor arrangement is surrounded with the cement grout
material.
Fig. 1C illustrates the borehole (1) which is filled with the cement grout material. As can
be seen, the filling of the borehole (1) with the cement grout from the bottom up displaces
the liquid in the borehole (1). At this time, a small amount of liquid is pumped down the
injection tube (8) through the check valve (7) and filter (10) to clear the filter (10) of the
grout material.
Fig. 1D illustrates the next stage of the fluid injection operation which displaces the
cement grout from around the filter (10) to form a void at location (13) and to provide a
fluid connection from the formation through the parted cement grout (13) and thence back
through the filter (10) and connector block (9) to the pressure transducer (5). The injection
liquid is prevented from passing back up the injection tube (8) by the check valve (7). This
stage is preferably undertaken when the cement grout has started to set so that the addition
of the injection fluid via the filter (10) does not dilute the grout. The grout material is then
left undisturbed until fully set.
Fig. 2 illustrates the pressure transducer assembly which includes the connector block (9)
with the pressure transducer (5) screwed therein so as to be connected to the internal
porting of the connector block (9). The pressure transducer (5) is of the type where the top
of the pressure sensing member is exposed to pressure which is the reference internal
pressure of the transducer and is preferably a vacuum, or in shallow applications may be
vented by another conduit (not shown) to atmospheric pressure. The bottom of the
pressure sensing member is exposed to the fluid pressure produced by the geological
formation. The electrical output of the pressure transducer (5) is connected to an electrical
cable (6), which carries the electrical pressure signals to surface-located monitor
equipment. The electrical signals can be carried to surface-located equipment and
converted to conventional pressure readings, such as millibars, psi, etc.. The pressure
signals can also be transmitted via telemetry equipment to remote locations where the
pressures of a number of geological formations can be monitored.
A preset pressure relief type of check valve (7) is similarly screwed into the connector
block (9), as is the filter (10). The connector block (9) contains internal passages (20),
(21), (25), and (22) to provide a common connection between the components connected to
the block (9). The passage (20) is blocked by grub screws (23) and (24) to prevent
communication of the internal passages of the connector block (9) with the borehole (1).
The fluid injection pipe (8) is connected to the inlet side of the pressure relief and check
valve (7). As described above, the fluid injection pipe (8) is supplied with a fluid from up
hole pump equipment.
From the foregoing, described is an embodiment of a formation fluid pressure sensing
system in which the pressure transducer (5) is precisely located down a borehole (1) at a
location where the pressure in the geological formation is to be measured. The pressure
transducer (5) together with a filter (10) is fixed in the borehole (1) at the desired location
by placing a cement grout around the pressure transducer (5). Before the cement grout is
fully cured, a liquid is pumped down hole through a check valve (7) to clear the filter (10)
of the cement grout material. Subsequently a fluid is again pumped down the borehole (1)
through the check valve (7) to form a void or communication path between the formation
and the pressure transducer (5). The cement grout material around the void (13) isolates
the pressure transducer (5) in the borehole (1), except the laterally adjacent portion of the
geological formation where it is desired to obtain fluid pressure measurements.
Figs. 3A-3F illustrate another embodiment of the invention. In Fig. 3A, a borehole (1) is
formed in the geological formation in which it is desired to determine the fluid pressure at
a particular depth. A grout pipe (3) is installed in the borehole (1) so that the borehole (1)
can be filled with a cement grout material from the bottom. To that end, the grout pipe (3)
is constructed with a port (4) near its base through which cement grout can be pumped into
the bottom of the borehole (1). Also installed at a desired location in the borehole (1) is a
filter (10) which is connected to the bottom of a fluid injection tube (30). According to this
embodiment, the check valve (32) and the pressure transducer (5) (shown in Fig. 3F) are
not connected to the bottom end of the fluid injection tube (30). Near the top of the
borehole (1), the injection tube (30) is connected to a larger tube (31). At the surface of the
borehole (1) site, the check valve (32) and an input tube (33) are connected to the larger
tube (31). A fluid is pumped through the input tube (33), which then passes through the
check valve (32), the large tubing (31), the smaller fluid injection tube (30) and filter (10)
before passing into the borehole (1). As shown, the pumped fluid has risen in the borehole
(1) to a level (2).
Fig. 3B illustrates the next step in the method in which the cement grout is pumped down
the grout pipe (3) and out of the bottom port (4) into the bottom of the borehole (1). At this
time, the cement grout moves upwardly in the borehole (1) and reaches level (34). The
cement grout continues to be pumped into the grout pipe (3) until the borehole (1) is filled
to a desired level. The raised pressure at the filter (10) and the action of the check valve
(32) prevent either the fluid or the cement grout from passing back up the tubing (30) and
(31). As can be appreciated, any formation fluid initially in the borehole (1) is displaced
with the cement grout material.
Fig. 3C illustrates a step in the operation in which a fluid, such as water, is pumped into the
surface-located input tube (33). The fluid passes through the check valve (32) and through
the fluid injection tubing (31) and (30) to clear the filter (10) of the fresh cement grout. A
small diluted area of cement grout around the filter (10) is shown at location (12).
Fig. 3D illustrates the next stage, preferably when the cement grout at location (13) has
started to set. This prevents dilution of the cement grout around the filter (10). According
to a feature of the invention, the fluid is pumped into the surface input tube (33) so that the
fluid is forced out of the filter (10), and displaces the cement grout at location (13) around
the filter (10). The displaced cement grout forms a pocket, void or fluid pathway between
the filter (10) and that part of the borehole (1) sidewall that is laterally adjacent to the filter
(10). The filter (10) connected to the bottom end of the injection tube (30) is thus adjacent
to that part of the geological formation where the fluid pressure is to be measured.
Importantly, the cement grout confines the inlet to the pressure sensor arrangement to the
formation pressures that exist at the desired elevation. As will be described below, the inlet
to the pressure sensor arrangement is the filter (10). The filter (10) prevents cement grout
particles entering the injection tube (30), and at a later stage the ingress of any particles
with formation fluid. The filter (10) could be omitted in some cases. In this case the inlet to
the pressure sensor arrangement would be the bottom end or inlet port of the injection tube
(30). The isolation of the pressure transducer input prevents it from being influenced by
borehole fluid pressures above or below the filter (10), which would otherwise occur.
Fig. 3E illustrates the operation which is carried out after the cement grout has set. In this
case, a pressurised fluid is pumped into the surface input tube (33) to displace fluid from
the injection tubing (31) and (30), through the check valve (32) and out of the filter (10)
through the opened cement grout at location (13). The pressure of the fluid pumped into
the input tube (33) is sufficient to fracture the formation at location (40) via the void area
(13) around the filter (10). The hardened cement grout in the borehole (1) above and
below the void area (13) functions to concentrate the pressurised fluid in the annular area
of the formation surrounding the filter (10) component of the pressure sensor arrangement.
Depending on the pressure and volume of the injected fluid, the fracture zone (40) of the
geological formation can extend radially outwardly from the borehole (1) a significant
distance. After fracturing the formation, the natural pressures of the geological formation
cause the formation fluid to enter the fracture zone (40) into the void area (13), and from
the filter (10) to the pressure transducer (5) described in Fig. 3F.
Fig. 3F illustrates the borehole (1) set up for monitoring the fluid pressure around the
borehole (1) at fracture location (40). Here, the surface input tube (33) and check valve
(32) are removed from the large injection tube (31). The large injection tube (31) remains
connected to the underlying smaller tubing (30). A packer (34) carrying a pressure
transducer (5) at its bottom end is inserted into the large tube (31) and sealed therein. The
pressure transducer (5) is of the type where the top of the pressure sensing member is
exposed to the transducer internal pressure which is preferably a vacuum, or in shallow
applications to monitor an unconfined aquifer, may be advantageously connected to
atmospheric pressure via a conduit (not shown), and the bottom of the pressure sensing
member is exposed to the fluid pressure produced by the geological formation. The packer
(34) is inflated and sealed in the large tube (31) by fluid pressure delivered through a tube
(36) connected to the packer inflation tubing (35). The packer (34) effectively plugs the
large tube (31) so that the pressure in the formation can pressurise the lower injection tube
(30). To that end, the packer (34) functions as a seal to block the flow of formation liquid
in the large tube (31). The top (37) of the packer inflation tubing (35) is sealed around the
electrical cable (6) which carries the electrical signals from the pressure transducer (5). It
must be realised that the pressure transducer (5) is removable and/or relocatable within the
large tube (31). This provides the user with the advantage of servicing the transducer (5)
or relocating it to a depth suited to its pressure range. The pressure transducer (5) is
relocatable to a different depth by deflating the packer (34), and moving it together with
the attached pressure transducer (5) to a different elevation in the large tube (31). When
moved to the new depth, the packer (34) is again inflated to fix it in the large tube (31) in
the manner described above. The packer (34) is described above as an inflatable device. In
another embodiment it could be a mechanically expandable packer or a seal element which
may be slid within the injection tube (31). In the latter case a vent would need to be
incorporated into the device to permit fluid to pass through the seal when it is being
moved. As can be seen in this embodiment, the pressure sensor arrangement includes
components that are not all located in the same area, but rather are distributed in the
system.
In operation, the fluid pressure produced by the geological formation enters the pressure
sensing system through the formation fractures to the void zone (13) around the filter (10).
Again, this occurs at an elevation in the formation where it is desired to measure the
pressure. The pressure of the formation fluid rises in the injection tube (30) and exerts a
corresponding force on the bottom of the pressure sensing member of the pressure
transducer (5). The top of the pressure sensing member is held at a static pressure, and
thus the pressure transducer is able to accurately measure the formation pressure. In some
instances the transducer will be used to measure water head in a groundwater body with a
phreatic surface. In this case it is advantageous to vent the top of the pressure sensing
member to atmospheric pressure and the bottom to the local groundwater pressure.
Changes in the formation pressure, if any, are sensed by the pressure transducer (5) and
coupled by corresponding electrical signals to the surface monitoring equipment.
It should be appreciated that while reference is made in Figures 3A to 3F of a tube (30)
being of smaller size than the upper tubing (31), this is not a necessary feature of the
invention. The tubing could be of the same size provided it is large enough to take the
transducer (5) and seal. The choice of tubing sizes is dependent on the local economics of
the situation and the degree of variability in location that is required for the packer (34) and
transducer (5) combination to monitor formation fluid pressure.
Figure 4 shows a typical chronological record of pressure at the transducer (5) for the
installation described in Figures 1A to 1D. Here, the borehole (1) is filled with fluid with
an initial borehole hydrostatic pressure (51). With the pumping of cementitious grout up
hole and past the transducer (5), the pressure increases (52) to final hydrostatic pressure
(53) of the cementitious grout. As hydration takes place the fluid pressure of the
cementitious grout pressure begins to decline (54). The pressure may decline to far below
formation pressure before recovery (55) begins to reach formation pressure (56). This drop
in pressure is more severe if the cement grout has lost fluid to the formation prior to
hydration. The dotted line shows the advantageous use of fluid injection to maintain
pressure at the transducer (5) to approximate formation pressure. Here, injection is
conducted twice to reach peak pressures at (57) and (58) before the pressure asymptotes to
the final reservoir pressure.
From the foregoing, disclosed are various embodiments of geological formation pressure
sensing systems that more accurately measure the formation pressures at desired depths.
The inlet to the pressure sensing apparatus is located at a desired depth in the formation,
and isolated to pressures produced by the formation at such depth. As such, the
measurement of the formation pressure is not affected by other and different pressures that
could otherwise exist in the borehole above and below the inlet to the pressure measuring
apparatus.
While the preferred and other embodiments of the invention have been disclosed with
reference to specific formation pressure sensing systems, and associated methods and
manufacture thereof, it is to be understood that many changes in detail may be made as a
matter of engineering choices without departing from the spirit and scope of the invention,
as defined by the appended claims.
Claims (20)
1. A method of monitoring a fluid pressure in a subterranean formation, comprising: forming a borehole in the subterranean formation from a surface at least to a depth where the fluid pressure is to be measured; 5 placing a grout pipe down the borehole, said grout pipe having a port at a bottom end thereof for allowing a cementitious material to flow therethrough; placing a conduit into the borehole to a depth so that an inlet of the conduit is adjacent a location where the formation pressure is to be measured, the inlet of said conduit is located at a depth in said borehole independent of a location of the port at the 10 bottom of said grout tube during a time when said conduit is lowered into said borehole; using a non-return valve in the conduit so that liquid cannot pass upwardly all the way through the conduit; using the grout tube to place a cementitious material into the borehole until the 15 cementitious material rises at least above the inlet of the conduit; pumping a liquid down the conduit through the non-return valve, out of the inlet of the conduit and into the cementitious material in the borehole so that the liquid displaces the cementitious material around the inlet of the conduit and form a fluid connection to the formation; and 20 placing a pressure sensing device below the surface of the borehole to measure the fluid pressure of the formation at said depth.
2. The method according to Claim 1, further including pumping the liquid down the conduit to form the fluid connection to the formation before the cementitious material around the inlet of the conduit is fully set. 25
3. The method according to Claim 1, further including forming the fluid connection to the formation by the use of localised hydrofracture of the cemenitious material when fully set.
4. The method according to Claim 3, further including performing the localised hydrofracture using a liquid of sufficient pressure that the hydrofracture extends 30 through the cementitious material and into the formation.
5. The method according to Claim 1, further including pumping the liquid down the conduit to form the fluid connection to the formation before the cementitious material around the inlet of the conduit is fully set, allowing an adequate time for the cementitious material to set, and then hydrofracturing the set cementitious 5 material between the inlet of the conduit and the formation by using a pressurised liquid of sufficient pressure that the hydrofracture extends laterally through the cementitious material and into the formation.
6. The method according to any of the above Claims 1 to 5, further including using a non-return valve that is pre-loaded with a pressure relief valve, and placing the non- 10 return valve within the conduit with the pressure sensing device located below the non-return valve, whereby the pressure sensing device is in fluid connection with the formation fluid and yet isolated from the pressure above the non-return valve by an operating pressure of the pressure relief valve.
7. The method according to any of Claims 1 to 5, whereby when the cementitious 15 material is set, the pressure sensing device is introduced into the conduit and sealed in place to monitor pressure.
8. The method according to Claim 7, further including sealing the pressure sensing device into the conduit by using a packer located at a suitable location within the conduit to maximise a required range and sensitivity of measurement. 20
9. The method according to Claim 8, further including sealing the pressure sensing device to a bottom of the packer, and using a large diameter conduit located near a surface of the borehole to hold the packer and pressure sensing device, whereby the installation and replacement of the pressure sensing device and the packer is facilitated. 25
10. The method according to Claim 1, further including connecting a filter to the inlet of the conduit.
11. The method according to Claim 10, further including connecting the non-return valve, the pressure sensing device and the filter to a connector block to provide a pressure sensor arrangement, so that filtered formation fluid is supplied to the non- 30 return valve and the pressure sensing device.
12. The method according to Claim 11, further including locating the pressure sensor arrangement in the borehole at the formation location where the formation pressure is to be measured.
13. The method according to Claim 10, further including connecting the pressure 5 sensing device in the conduit at a location below the surface of the borehole so that the pressure sensing device can be removed.
14. The method according to Claim 13, further including connecting the pressure sensing device to a bottom of a packer, and setting the packer in the conduit location below the surface of the borehole. 10
15. The method according to Claim 14, further including removing the non-return valve and using the packer to prevent passage of formation fluid upwardly all the way through the conduit.
16. The method according to Claim 1, further including placing a filter at the inlet of the conduit, and pumping a liquid down the conduit through the non-return valve to 15 clear the filter of the cementitious material before setting thereof and to form a void pocket around the filter.
17. The method of claim 1, wherein said conduit is not connected to said grout pipe.
18. A method of monitoring a fluid pressure in a subterranean formation, comprising: forming a borehole in the subterranean formation at least to a depth where the fluid 20 pressure is to be measured; connecting a pressure sensing device to an inlet of a conduit so that the pressure sensing device measures fluid pressures at the inlet of the conduit, and extending an electrical cable from the pressure sensing device to a surface of the subterranean formation for monitoring of the formation pressure; 25 lowering the conduit into the borehole until the inlet of the conduit is at a depth where the formation pressure is to be measured; filling the borehole with a cementitious slurry to a level substantially above the inlet of the conduit so that cementitious slurry surrounds the inlet of the conduit; preventing the cemintitious slurry and other fluids from flowing up the conduit; 30 before the cementitious slurry hardens to a fully set state around the inlet of the conduit, purging the inlet of the conduit of cementitious material by pumping a liquid down the conduit to displace the cementitious material that is not fully set to form a pocket around the inlet of the conduit and toward the subterranean formation; after the pocket is formed around the inlet of the conduit, allowing the cementitious material around the pocket to cure to a fully set state; 5 if the pocket around the inlet of the conduit does not reach the subterranean formation, forming a lateral fluid path between the subterranean formation and the pocket, whereby a fluid flow path is formed between the subterranean formation and the inlet of the conduit, and the fluid flow path is isolated to fluid flow only from the subterranean formation located laterally adjacent to the inlet of the conduit; and 10 whereby the subterranean formation pressure forces the subterranean formation fluid to flow to the inlet of the conduit and to the pressure sensing device so that the subterranean formation fluid pressure is measured at the desired depth in the subterranean location.
19. The method of Claim 18, further including extending a grout pipe different from 15 said conduit down the borehole and passing the cementitious material down the grout pipe to fill the borehole from the bottom up.
20. A method of monitoring a fluid pressure in a subterranean formation, comprising: forming a borehole in the subterranean formation at least to a depth where the fluid 20 pressure is to be measured; lowering a conduit into the borehole until an inlet of the conduit is at a depth where the formation pressure is to be measured; filling the borehole with a cementitious material to a level substantially above the inlet of the conduit and using a non-return valve to prevent the cementitious material 25 from flowing up the conduit, whereby the cementitious material surrounds the inlet of the conduit; purging the inlet of the conduit of cementitious material by pumping a liquid down the conduit and out of the inlet of the conduit; forming a lateral fluid path between the inlet of the conduit through the 30 cementitious material and to the formation by displacing the cementitious material around the inlet of the conduit when the pumped liquid exits the conduit inlet, whereby the formation pressure forces the formation fluid to flow through the fluid path and through the inlet of the conduit; and connecting a pressure sensing device under a packer and placing the packer and pressure sensor in the conduit to block the conduit and allow the pressure sensor to 5 sense fluid pressures of the formation via the inlet of the conduit.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2011904211A AU2011904211A0 (en) | 2011-10-11 | Formation pressure sensing system | |
AU2011904211 | 2011-10-11 | ||
PCT/AU2012/001221 WO2013052996A1 (en) | 2011-10-11 | 2012-10-10 | Formation pressure sensing system |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ623721A NZ623721A (en) | 2015-03-27 |
NZ623721B2 true NZ623721B2 (en) | 2015-06-30 |
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