Device and method for determining the orientation of fractures in a geological formation

A device and method are provided for determining, from a well, the orientation of fractures in a geological formation having a fracture zone. The device includes a tubular element connected to a hydraulic fluid source and having at least one flow orifice through which the fluid may escape. This device further includes: PA1 (a) at least one chamber through which the fluid may flow from the tubular element towards the fracture, this chamber being in communication with the flow orifice, PA1 (b) at least one mobile orientation element situated substantially at the same depth as the fracture zone, this element being articulated about the tubular element and being adapted for moving by rotation towards a final position following discharge of the fluid from the chamber towards the fracture zone, and PA1 (c) an arrangement for locating the final position of said orientation element, this position being in relation with the orientation of the fracture.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a device and method for measuring the 
orientation of the fractures or drains in a geological formation. 
It applies to the field of fossile energy production and more particularly 
to the stimulation of reservoirs and relates both to vertical wells and to 
deflected wells. 
2. Description of the Prior Art 
Hydraulic formation fracturing consists in cracking the productive rock by 
increasing a fluid pressure in the well and maintaining the crack thus 
created open. It develops along a plane whose orientation depends on the 
forces exerted on the reservoir: 
the main vertical force due to the weight of the sediments (.sigma..sub.1), 
the main horizontal stresses which depend in particular on the tectonics of 
the side (.sigma..sub.2 and .sigma..sub.3). 
The fracture plane develops perpendicularly to the lowest of these three 
stresses the fracture will in general be horizontal at a small depth (less 
than 600 m), the vertical stress being smaller than the two horizontal 
stresses, and vertical for greater depths, fracturing being perpendicular 
to the smallest of the two horizontal stresses. 
Hydraulic fracturing is sometimes used for connecting two wells at the 
level of a geological formation, for example for carrying out the 
underground gasification of a cold air whose permeability is too low to 
provide, between the two wells, the gas flow rate required for maintaining 
back combustion. 
It is also used for providing the connection between two wells in the case 
of high enthalpy geothermy, or for seeking better scavenging of an oil 
deposit by forming a drain which distributes the injection of water 
charged with chemical additives. 
For all these methods, knowledge of the direction taken by the fracture 
created is essential. If such knowledge is indispensable when it is a 
question of using the fracture for connecting the two wells together, it 
is not less important for a simple stimulation where only an improvement 
in the productivity of the well is sought; in fact, if the fracture is 
directed towards the oil-water limit, it will cause premature submersion 
of the well which will cause its closure, instead of the expected increase 
in oil production. 
It is known to seek the direction of a fracture by observing the wall of a 
well through an oriented television camera, or by using the technique of 
printing packer. A sealing member or packer equipped with a deformable 
membrane is lowered and anchored in the layer before and after fracturing. 
The fracture is visible on the membrane of the packer which has an 
orientation detection device. 
These methods can only apply to uncased wells and imposes bringing the well 
to a long halt for putting in the apparatus and for their withdrowal. 
It is also known to determine the fracture direction by an acoustic 
detection of the advance of the fracture, this detection can be remotely 
achieved when the well is not outfit and preferably uncased at less than 
100 m from the fractured well. 
Geophones or accelerometers applied against the wall detect noises related 
to the fracturing. However, the availability of such a listening well is 
fairly uncertain and, in addition, with the present interpretation 
methods, a direction even approximative of the fracture cannot be derived 
from the numerous noises recorded, for the time being. 
SUMMARY OF THE INVENTION 
The device of the present invention overcomes these drawbacks, for its 
purpose is to determine, at the beginning and/or during fracturing, a 
fracture direction from a well not only cased and perforated but also an 
uncovered well and to limit the loss of time on the well by easy, rapid 
and inexpensive setting up, the apparatus forming in fact part of the 
fracturing packing itself and requires no additional manoeuvers. 
The object of the invention is also to determine the values of the stress. 
The invention provides a device for determining the orientation of 
fractures and drains in a geological formation having a substantially 
vertical or oblique fracture zone from a well, this device including a 
tubular element whose cross section is substantially circular, said 
tubular element being connected to a hydraulic fluid source and having at 
least one flow orifice through which the fluid may escape. 
This device comprises more particularly in combination: 
(a) at least one chamber through which said fluid may flow from said 
tubular element towards the fracture, this chamber being in communication 
with said flow orifice, 
(b) at least one mobile orientation element situated substantially at the 
same depth as the fracture zone, being mounted for rotation about said 
tubular element and being adapted for moving by rotation to a second final 
position following discharge of said fluid from said chamber to the 
fracture zone, and 
(c) means for detecting or measuring said final position of said 
orientation element, said final position being in relation with the 
orientation of the fracture. 
The invention also provides a method for determining the orientation of 
fractures or drains in a geological formation having a substantially 
vertical or oblique fracture zone, from a well. In this method, a 
hydraulic fluid is introduced into a tubular element having at least one 
flow orifice, the fluid is caused to flow through a mobile orientation 
element situated substantially at the same depth as the fracture zone 
while letting the fluid escape through at least one outlet orifice in a 
direction, preferably inclined with respect to the axis of the well, so as 
to cause said orientation element to move by rotation as far as a final 
position in relation with the orientation of the fracture and said 
position is located. 
The orientation element may be moved in line with the fracture and then be 
in a position in direct relation with the orientation of the fracture, or 
it may be moved towards a position which may or may not be facing the 
fracture if the device is provided with a return member, for example, 
which may be correlated, through calibration for example, with the 
orientation of a fracture. 
In another embodiment of the invention, said tubular element includes at 
least one flow orifice situated substantially along at least one 
generatrix. It may also comprise at least two diametrically opposite 
mobile orientation elements. 
In a particularly advantageous embodiment, the device includes a tubular 
element with at least one flow orifice disposed along a generatrix, at 
least one fixed blade disposed parallel to the axis of said element and 
situated in the immediate vicinity of said flow orifice, at least one 
mobile blade disposed parallel to the axis of the tubular element, said 
mobile blade being separated from said fixed blade by said flow orifice, 
said mobile blade being articulated about said element while defining a 
chamber with said fixed blade, said chamber being in communication with 
said flow orifice, said mobile blade being adapted for moving by rotation 
from an initial position defined by a return member to said final position 
corresponding to discharge of said fluid from said chamber towards said 
fracture zone. 
The hydraulic fluid injected may be advantageously water, or a viscous 
liquid which may contain chemical additives even propping agents, such as 
sand or zirconium balls for example. 
The pumping rate allowing the device to operate is between 0.1 and a few 
tens of m.sup.3 per minute and preferably between 1 and 2 m.sup.3 per 
minute. 
For determining the direction of a fracture, it is necessary first of all 
to determine the orientation, i.e. the angular position .theta. of the 
mobile part or window directed towards the fracture with respect to a 
reference generatrix of the probe fixed to the end of the tubular element. 
Then the angle of this reference generatrix of the probe is determined with 
respect to a geographical reference which may be either the magnetic or 
geographic North, or a vertical reference plane passing through the axis 
of the well or of the probe, that is to say either the azimuth .alpha. in 
the case of vertical wells, or in the case of deflected wells the azimuth 
.alpha., the slant i and the angle of rotation u between the planes 
defined by the axis of the well (or of the probe) and the reference 
generatrix, on the one hand, and the vertical direction and the axis of 
the well on the other. 
The azimuth .alpha. is the angle formed between the projection of the 
direction of the magnetic North on the horizontal plane and the projection 
of the axis of the well of the probe on the horizontal plane. 
The slant i is the angle which the axis of the well forms with the vertical 
whereas the angle of rotation u is formed between the vertical plane 
passing through the axis of the probe and the plane passing through the 
reference generatrix and the axis of the probe. 
The above described means for measuring these different angles are known 
and will not be described in detail. A combination thereof however answers 
the problem raised, namely the measurement of the orientation of the 
mobile part with respect to the position of a reference generatrix of the 
probe and consequently the direction of the fracture can be determined. 
Thus the value of an angle .theta.+ or -.alpha. is measured in the case of 
a vertical well and .theta., .alpha., i, u in the case of a deflected 
well. 
The angle .theta. may be obtained, in all cases, by at least one proximity 
sensor associated for example with small magnets. 
In addition, if the well is vertical, in the presence of a non magnetic 
medium, a magnetic compass may be used for measuring .alpha. and in the 
presence of a magnetic medium a gyroscope. 
On the other hand, if the well is deflected, in a non magnetic environment, 
a compass or magnetometers may be used for determining the angle .alpha. 
and inclinometers for the angle i, and in a magnetic medium, a gyroscope 
and inclinometers. 
If furthermore, the azimuth .alpha. and the slant i are known which are 
constant values which only depend on the drilling, only the angle u is 
measured, by means of a transverse pendulum cooperating with a 
potentiometric track or by means of two or three static accelerometers. It 
is then combined with the angle .theta. under the form u+ or -.theta.. 
The locating means may then include the probe with its different measuring 
apparatus, this probe being: 
(a) adapted to the fixed tubular element and operating with an electronic 
memory, 
(b) connected to the surface through a logging cable and resting for 
example on a seat. The electric cable conveys the information to the 
surface, 
(c) connected to an electric bottom connector, known per se, the connection 
being formed once the assembly has been lowered to the level of the 
fracture. 
The compass, the inclinometers and the static accelerometers are fixed to 
the probe (fixed part) whereas the instrument measuring the angular 
position is formed of a fixed part having at least one proximity sensor 
fixed to the probe or to the tubular element, this sensor cooperating with 
a mobile, part, formed by a plurality of magnets, disposed for example on 
the mobile orientation element.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The reference 20 in FIG. 2 designates a deflected or vertical oil well and 
the reference 21 the device of the invention for detecting the orientation 
of a fracture 5 to be created or present in a geological formation 5a. 
In this well 20, a casing 1 is positioned in a way known per se. It has a 
zone 4 which has been perforated by known means and which is placed in the 
immediate vicinity of the geological layer 5a containing the fracture 5 or 
in which it is desired to form a fracture 5. Of course, the perforations 4 
are formed in the different radial directions. In the different Figures 
only the perforations 4 have been shown which are adjacent the fracture 
and through which there will be a flow of fluid. At the depth of 
geological formations containing oil or gas, the fractures will be rather 
substantially vertical or oblique with respect to the longitudinal axis of 
the well. 
The device 21 of the invention is positioned at the surface on a tubular 
element 2 before being lowered into the well. This tubular element 2 is 
pierced with at least one flow orifice 6 in its lower part. Device 21 is 
formed of a rotating element or cage mounted on bearings 12a and 12b 
providing easy rotation of cage 11 about the tubular element 2. This 
rotating element 11 in the form of a volume of revolution is located 
substantially at the same level as the fracture zone and is in 
communication with the flow orifice 6. It defines a chamber 22 and has at 
its periphery an outlet orifice 13 in the form of a slit or hole or a 
plurality of holes disposed substantially along a generatrix of the volume 
of revolution or in the immediate vicinity of the generatrix. This orifice 
13 forms a mobile orientation element. 
Advantageously (FIG. 2), the element 11 may include, for promoting rotation 
thereof, at least one blade 25 situated in the immediate vicinity of 
orifice 13 between the tubular element 2 and cage 11 and whose length is 
such that this blade does not touch the tubular element 2. Excellent 
results are obtained when element 11 has two diametrically opposite 
blades. 
Furthermore, the rotating element 11 includes a plurality of magnets 14, 
for example, which form the mobile part and which are associated with at 
least one proximity detector or sensor 15 connected by a connection 29 to 
the electric cable 9. This sensor is fixed to probe 10. The other 
apparatus 8, such as a compass, accelerometers, inclinometers, 
magnometers, and gyroscope are disposed on the probe. In this embodiment 
only the magnets 14 are fixed to the mobile element 11 and the measuring 
system (15, 8) may be raised by cable 9 with probe 10. 
The orifices 4, 13 and 6 are therefore substantially at the same depth as 
the fracture 5 whose direction it is desired to determine. 
A packer 3a provides sealing upstream of device 21 between casings 1 and 2 
as well as centering of the installation. 
Another packer 3b may possibly provide sealing downstream if the space 
between the rotary element 11 and casing 1 or the wall of the well proved 
to be too great. 
The detection or locating means (probe with its measuring instruments) is 
lowered by an electric cable 9 controlled from the surface substantially 
below the fractured zone and comes into contact with a stop 7 forming a 
seat. 
The probe thus comes off the base of the tubular element 2. Sealing may 
also be provided through a satisfactory tension of cable 9 from the 
surface. 
In FIGS. 1 and 2, chamber 22 is annular and closed, possibly by the 
detection means. The tubular element 2 includes at least one radial 
orifice 6. 
The information is either treated at the surface or stored and treated 
after the probe 10 has been raised to the surface where the operations are 
also carried out for controlling and monitoring the pumping of the 
hydraulic fluid delivered by a pump, for example from the surface. 
Means of a known type not shown in the Figure, housed in the probe allow 
the value of the stress to be determined. 
In FIG. 2, taken through plane AA, the tubular element 2 includes two 
diametrically opposite flow orifices 6 and the rotary element 22 also has 
two diametrically opposite outlet orifices 13. 
This configuration facilitates the drive torque for the mobile assembly. At 
least one means 23 (restriction lip for example) may be advantageously 
provided on the external edge of orifice 13 for introducing a dissymmetric 
pressure loss in the path of the fluid. 
In another embodiment illustrated in FIGS. 3 and 3A (section through BB), 
chamber 22 is cylindrical and the base of cage 11 provides sealing. 
Cage 11 may possibly include blades 25 facilitating rotation thereof and is 
supported by at least two reinforcement elements 26, attached to the fixed 
tubular element 2, the cage resting on a guide member 27 such as a pointed 
projection. The reinforcement elements 26 and the guide member 27 also 
maintain the cage in position at the time of pumping and react to the 
effects of the pressure of the fluid on the base of the cage. 
Magnets 14 are disposed on cage 11 and the proximity sensors 15, fixed to 
the tubular element 2, are connected by a connection 24 to a male 
connector 28a to which a female connector 28b of cable 9 is coupled. 
Thus, the above described rotation measurement system and magnets 14 are 
lowered at the same time as the tubular element and the measurement 
signal, taken over by the bottom electric connector (28a, 28b) is 
transmitted to the surface by cable 9. 
In another embodiment shown in FIGS. 4 and 5 (section through CC) the 
rotary element 11 mounted on bearings 12a and 12b includes two mobile 
blades 17 of rectangular shape for example and diametrically opposite, 
whereas the tubular element 2 has two flow orifices in the immediate 
proximity of which are situated two diametrically opposite fixed blades 
16. 
A return member 18 of known type holds the mobile blades 17 in a 
reproducible and perfectly known rest position, that is to say that they 
substantially face the fixed blades 16 while being separated by the flow 
orifice 6. 
A butt 19 may possibly stop the action of the return member 18 (FIG. 5). 
Without departing from the scope of the present invention, the form of the 
free and mobile blades or of the fluid flow and outlet orifices may by 
modified or the fixed blades may be omitted as well as the return members 
such as illustrated in FIG. 6. 
The operation of the device, illustrated in FIG. 1, is as follows: 
Into a cased and perforated well 20, vertical for example, or into an 
uncased well a tubular element 2 is lowered equipped with two sealing 
members and the flow orifices 6 of which will come substantially at the 
level of the fractured layer. 
The rotary element 11 which is screwed substantially facing the zone to be 
fractured 5 is lowered on this element 2. The sealing packer 3a is then 
anchored to the casing above the zone. Then the measuring element 10 which 
will be positioned against the stop 7 is lowered by means of the electric 
cable 9. The initial position .alpha. of the system is determined. 
A pressurized hydraulic fluid (gel) is fed by the surface pumping 
installations at a flow rate of 1 m.sup.3 /min which flows first of all 
inside the tubular element 2, then flows into the chamber 22 through the 
flow orifices 6 and is finally discharged to the fracture zone by moving 
the mobile orientation element (mobile blades, FIG. 4: 17,; FIG. 1: 11 and 
13) which will be positioned opposite the fracture, thus indicating a 
final direction corresponding to the direction of the fracture, or the 
angular position .theta.. 
This direction is then measured by the system of magnets 14 and proximity 
sensors 15 and the information is stored or sent to the surface for 
processing (determination of the magnitude .theta.+ or -.alpha.). 
It is possible if required to carry out a second measurement by releasing 
the seal and by lowering the assembly of devices 2, 21 to a depth where a 
second fracture zone is to be studied and by repeating the above described 
operation. 
When the operation is finished, it only remains to raise the measuring 
elements 10 by means of cable 9, which frees an optimum passage through 
the casing 2. 
As regards the device illustrated in FIG. 3, the rotational measuring 
systems are lowered at the same time as the tubular element. After the 
sealing elements 3a and/or 3b have been anchored and the parameters 
.alpha. if the well is vertical and u if the well is deflected have been 
measured, the bottom electric connector 22b is lowered by means of cable 9 
and this connector 28b is coupled to the measuring device. The fluid is 
then pumped and the angular position (rotation) of the rotary element 13, 
11 indicating the direction of the fracture is measured.