DPS - Downhole P&S Sonde

The Geovista DPS P&S sonde logs P & S wave velocities within the borehole environment. It comes with

one transmitter and two receiver modules. The energy source of the transmitter operates as a dipole

source. Each receiver contains two transducers, one for the detection of the compression waves (P) and

the other for the detection of the shear waves (S). Each transducer responds to different frequencies.

The sonde is stopped at selected depths where acoustic data is acquired in different modes that allow

the determination of these P and S velocities. This is done without the need for clamping and this meth-

od gives better accuracy and resolution than other seismic methods. In situations where the P & S veloc-

Specifications:

Diameter : 51 mm

Length: 485 or 585 cm (Varies depending on which isolator section is used).

TX –RX1 spacing: Typically 200 / 300 cm depending on length of first isolator section (other lengths available).

TX –RX2 spacing: Typically 300 / 400 cm depending on length of first isolator section (other lengths available).

Sampling density: 2000 samples/wave

Resolution: 16 bits.

Sampling interval: 2.5, 5, 10, 20, or 40 µs - independently selectable.

Signal gain: Adjustable between 0 to 24 dB /channel.

Pressure rating: 5 MPa (50 bar)

The performance of the system is engineered to give good results in the slower

formations encountered at shallow depths while also performing well in deeper

formations with higher velocities. The data acquired by the system is recorded

in the industry standard SEG2 file format, allowing many commercially available

packages to read the data. GeoVista also provides a software interpretation

package to determine the P & S velocities.

GeoVista GeoVista GeoVista GeoVista www.geovista.co.uk

Logging Sondes

U N I T 1 0 , C A E F FW T B U S I N E S S P A R K , G L A N C O NW Y , L L 2 8 5 S P , U K WEB S I TE : ht tp : / /www.geovis ta .co.uk

PHONE : +44 (0)1492 57 33 99 F AX : +44 (0)1492 58 11 77 E -MA I L : geovis ta@geovis ta .co.uk

Two receivers are placed acous�cally isolated from each other. Each receiver contains two types of sensors:

1. Piezo electric device. This is to detect the P waves

2. Geophone sensor: This is to detect the S waves

Acous�c Isola�on

As in the diagram below, the tool is designed with acous c isolators between the receivers, transmi!er and logging

head. This is needed to ensure no direct acous c wave propaga on occurs in the tool.

GeoVista GeoVista GeoVista GeoVista www.geovista.co.uk

Logging Sondes

U N I T 1 0 , C A E F FW T B U S I N E S S P A R K , G L A N C O NW Y , L L 2 8 5 S P , U K WEB S I TE : ht tp : / /www.geovis ta .co.uk

PHONE : +44 (0)1492 57 33 99 F AX : +44 (0)1492 58 11 77 E -MA I L : geovis ta@geovis ta .co.uk

The spacing between the two receivers is fixed at one metre and cannot be changed. The spacing between the energy

source and the receivers can be adjusted by subs tu ng different length isolators.

The downhole source is made up of an electrically triggered actuator that acts like a hammer.

This operates as a dipole source, in that the energy source is direc onal. It can produce acous c energy in two direc-

ons, these direc ons being 180 degrees out of phase. In both cases, the energy pulse is directly perpendicular to the

wall of the borehole.

Processing So ware

Geovista provide as an op on a processing package that can take the acquired data and allow the user to process and

view the data. This so.ware can help in:

• Filtering

• Individual level analysis

• Picking of first arrival points

• Accep ng/rejec ng points

• Export of data

• Wave view analysis

• Stacking

• Depth graph display

• Auto func ons

• Calcula on of signal velocity