[Click on images to obtain larger pictures]
Version 3.1
A high pressure, direct strain measuring borehole dilatometer inflated by
oil or gas pressure. Strain is determined across three diameters in the same
plane. The instrument is placed in H size pockets formed by conventional
rotary coring.
A combined hose and cable assembly connects the instrument to a pressure source and readout unit. When oil is used a second hose is fitted to allow gas purging of the hydraulic fluid after completion of a test.
The output of the instrument is an RS232 signal for connecting to the serial port of a computer. Software is supplied to log data on an IBM PC or compatible computer.
The instrument includes an electronic compass so that the orientation of the axes of measurement is known.
|
PARAMETER |
VALUE |
Diameter, length |
95 mm, 2.03 metres |
| Expanding length | 575 mm |
| Length to diameter ratio | 6.2:1 |
| Rated Pressure | 20 MPa, 200 bars |
| Maximum pressure | 30 MPa, 300 bars |
| Displacement Measuring
|
Six equi-spaced full bridge strain gauged cantilever springs in the same horizontal plane. The output is a function of the radius of the membrane. This allows the diameter of the borehole at three axes to be known. |
| Strain Range | Each displacement follower has a range that translates to a 45% diametric expansion of a nominal 99mm borehole, a volumetric expansion of approximately 80%. |
| Pressure measuring system | Two downhole strain gauged diaphragm pressure cells |
| Inflation method | Hydraulic oil and hand pump or compressed gas and hand regulator |
| Electronics package | Plug-in. Contains microprocessor controlled multiplexer, fluxgate magnetometer compass, l6 bit analogue to digital convertor and RS232 transmitter. |
| Resolution | 1 kPa in pressure, 1 micron (equivalent to 2.1 x 10-5 in strain, shear moduli up to 4 GPa measured, 5° in azimuth |
| Membrane. | The standard membrane is a 6mm thick
nitrile rubber sleeve which is the pressure container, which in turn is protected
by an 18 strip stainless steel sheath.
The upper and lower ends of the rubber membrane are reinforced with a short cone of steel fingers to resist axial extrusion. In weaker materials the standard membrane can be replaced with a membrane whose ends are reinforced with strands of kevlar. This offers sufficient resistance to axial extrusion without the need for steel cones. |
| Membrane protection | Stainless steel, l8 strip, chinese lantern |
| Coupling thread | BW pin thread to BS 4019:Part 1:1974 and DCDMA Standards |
| Connections to surface | 13 mm high pressure hose which contains an electrical cable. If gas inflation is used then the outer cover of the hose is pricked as a precaution against leakage. For oil inflation an optional 11 mm return hose is supplied for gas purge. RS232 output, one scan of all sensors every 10 seconds |
| Electrical Interface Unit. | The instrument connects to a small control box which provides power to the instrument and buffers the RS232 signal. Two isolated RS232 outputs are provided. To assist the operator to control the inflating pressure accurately the Unit monitors the output of an in-line pressure transducer and gives a continuous reading on a digital panel meter. |
| Hose length | 100 metres in one length is standard. Longer hose lengths can be supplied up to about 250 metres. Hose is wound on a drum, mounted vertical, on a windlass. For instruments intended for use on wireline systems, extension cables with couplers can be supplied. In this case the first coupler is usually at 2 metres only, just clear of the instrument. The extension cable can be any length up to 250 metres. |
| Power Requirements. | The instrument and Interface Unit are powered from a single 12 volt vehicle battery which may also be used to power the computer, either directly or via a socket on the Interface Unit. |
| Hand Pump. | A hand operated oil pump is provided which can be used to inflate the instrument to a pressure of 20MPa. |
| Handling | The instrument is heavy and is shipped in a stripped down form inside a custom made case. For working with the instruments on site a pipe vice is supplied mounted to purpose built frame. When assembled the frame becomes a very rigid platform. |
| Handling Frame dimensions | 1.2 m long, 0·85 m wide, 0·90 m high (assembled) |
| Weights | Downhole instrument 75 kg including couplers
and calibration cylinders
215 m Hose on drum and windlass 72 kg 215m Oil return line on drum 45 kg Hand hydraulic pump 19 kg |
| Software. | A suite of programs is provided to log the data from the instrument and display the pressure versus displacement curve in real time. The program provides a text file of the instrument output converted to engineering units for analysis by common spreadsheet programs or the separate analysis program. |
| Recovery from dry hole | The hydraulic instrument can be purged of oil using gas pressure |
| Flushing | Holes are provided at the top of the instrument so that a flow of mud or air can be passed to remove any material fallen in on top. |
| Disconnection | If, despite the above, the instrument becomes stuck in the borehole then there is a left hand thread part way down the instrument which allows disconnection of the rod adapter and cable. Recovery by over coring is then possible. |
| Cambridge Insitu Little Eversden Cambridge, CB3 7HE ENGLAND |
Telephone: +44 (0) 1223 26236l
FAX: +44 (0) 1223 263947 E-mail: Caminsitu@aol.com |
