TISA® 3D Borehole Radar project

The TISA 3D Borehole Radar will be the first technique to perform 3D ground penetrating radar measurements from a single borehole. In addition, TISA 3D will be able to penetrate deeper into the surroundings of a borehole other than existing geophysical borehole survey tools currently available.

Development in 2 phases

The development of the TISA 3D Borehole Radar consists of  two  phases. Only when phase 1 is fully completed and tested, T&A will proceed to phase 2.

  1. The development of the TISA 3D prototype for the detection of metal objects in boreholes up to a depth of 100 meters.
  2. The development of the full service tool for use in boreholes up to a depth of 4.000 meters for the characterization of oil and gas reservoirs.

December 2019 TISA 3D Update

T&A Survey has finished the development and production of a new generation of the TISA 3D borehole radar system. The TISA 3D measurement system is the successor of the 3D BHR (introduced in 2001), a high resolution geophysical measurement system that delineates objects in the surroundings of a borehole until a depth of 30 meters below the surface. Recently, T&A has upgraded this system. The new TISA 3D has improved a lot compared to the 3D BHR.

Final result: a full-service TISA 3D tool

T&A’s full service tool will reach a maximum depth of 4.000 meters, and withstand anticipated temperatures as high as 150°C and pressure at 400 bar/5.800 psi. With the TISA 3D it will be possible to perform measurements up to a distance of tens of meters from the borehole, creating a fully detailed High Definition 3D image of the borehole surroundings due to its directional response capabilities.  

The new TISA 3D Borehole Radar has improved a lot compared to the 3D BHR introduced in 2001:

  • The diameter has been reduced from 160 to 135 mm. The probe can now be applied in 145 mm boreholes, for instance borings with a 160 mm OD plastic casing.
  • Reduction of the length (4,2 to 3,1 m) and weight (250 to 50 kg) of the, making it easier to operate. The probe can now be lowered into a borehole with a tripod instead of a crane.
  • Improved quality of the radar signal due to the use of synthetic materials instead of metal and a modified positioning of several parts in de probe. This has led to an increased number of possible applications.
  • More robust depth recording. The depth recording of the probe is now carried out by an encoder in the top of the tripod, instead of by measuring the water pressure in the borehole.
  • A substantial reduction of the dissipated electrical power from 50 W to 12 W. The probe can now be fed by batteries inside the probe instead of wall power that is transported through the borehole.
  • Data communication in the borehole now takes place by glass fibre cabling instead of metal coaxial cabling. In addition to the absence of a power cable in the borehole, this means that there are no metal cables left in the borehole, enhancing the radar data quality.
  • Radar electronics have been modified: the transmission of radar signals has shifted from incidental high power pulses to continuous low power sines of varying frequency. This has improved the signal to noise ratio and increased the dynamic range from 40 to 65 dB, enabling the detection of objects at larger distances.
  • Measurement speed has been increased and the duration of a measurement was reduced by a factor 10. Measurement of one borehole can now be done with a speed of 1 m/minute. The achieved resolution is 3 cm in borehole direction and 0,5 degrees azimuthally.   

The first measurements with the new system have been carried out successfully. We will report further on this at the beginning of 2020.

Advantages TISA 3D technology has the following advantages over existing tools and methods:       

  • TISA 3D can image structures tens of meters away from the wellbore - TISA 3D images up to 15 m into the formation with a resolution of 0.017- 2 m, depending on the antenna type. In highly resistive environments such as pure salt bodies, radar signal will actually penetrate for hundreds of meters.      
  • Scalability - Due to its modular nature, parts of the TISA 3D tool can be interchanged flexibly. Modules such as source and receiver antenna, communications and power can be adjusted to the application (shallow/deep, wireline/MWD). Depending on the resolution and distance of the target form the borehole various antenna frequencies are possible. 
  • A complete image of the borehole surroundings -  Compared to other borehole tools, the 3D nature of the TISA 3D measurements add an extra dimension to the target. Fractures and their networks are imaged, together with the fluids flowing through them and the steam/water fronts.       
  • Operation of the tool in various borehole conditions - The TISA 3D technology has no adherence to a specific type of drilling fluid (water-based, oil-based or synthetic) and can actually measure the degree of mud invasion in the formation. Hardening of the tool for high pressure and temperature conditions will be comparable to other borehole tools. Radar measurements are not hindered by the mechanical noise due to high pressure and vibrations.

The TISA 3D Borehole Radar technology is a promising addition to existing logging techniques in oil and gas exploration and production.

Main applications
  • Logging tool: In an exploration environment, TISA 3D can be used as an Electric Propagation Tool to detect the electrical properties of the formation.
  • Geosteering: In thin pay zones, where it is crucial to follow a specific drilling path,  TISA 3D can provide the information to steer the drill bit. The distance to the top and bottom of the reservoir can also be measured.
  • Monitoring: In production phases, where water or steam drives are used, the TISA 3D is well suited to monitor the movement of the steam/water front in 3D.

Penetration range
The penetration range of the TISA 3D system in reservoirs is 5 to 10 meters, based on average reservoir properties (see table). Penetration range increases with increasing resistivity. In ideal situations, a penetration range of 15 meters can be obtained.

The mining industry is all about knowing what's going on in the underground. Without subsurface testing, it is impossible to locate an ore body, to define exploitable reserves or to design a mine plan.

Geophysical tools used in the oil industry (such as 3D seismic techniques) have been adapted and applied in mining industry, resulting in great benefits for the exploration of mines. However useful these tools may be, none of them can compete with the TISA 3D Borehole Radar’s capacity to reveal a high-resolution contrast between different materials in the underground.

Main applications
TISA 3D provides a useful addition to existing geophysical techniques in recognizing geology for mining. It can be applied in both exploration and production phases.
In an exploration environment, TISA 3D can be applied in horizontal and vertical drillings into e.g. coal, ore and salt bodies.

Depending on the resistivity of the formation, the signals penetrate up to 20 meters around the borehole. It can be used for detecting:
  • Lateral and vertical inhomogeneities
  • Cavities
  • Faults
  • Fracture zones: length, dip and distance

Other possible applications are:
  • Locating an ore body
  • Defining exploitable reserves
  • Designing a mine plan
  • Detecting pot holes

Due to increasing scarcity in oil and gas resources, energy costs are rising and so is the demand for alternative resources. Deep geothermal energy is an alternative energy source with great advantages, which could become more and more important.

Geothermal Energy is generated by pumping up deep groundwater from a depth of 1.5 to 4.0 kilometers with a temperature of 70 to 100 degrees Celsius, in order to heat houses and/or horticulture greenhouses. After releasing its heat, the groundwater is pumped back into the groundwater reservoir. This energy source is almost inexhaustible.

Mapping deep groundwater reservoirs
In order for a geothermal project to be successful, it is important to study the geological structure and stratigraphy of the subsurface of the planned location. The research target of a geological study is to map deep groundwater reservoirs. The results of the study include a detailed description of, for example, the geometry and other properties of the reservoir. The completed study is comprised with other drillings, wire line logs and cores.

Main applications
The groundwater reservoir needs to be estimated very accurately prior to making the decision whether a geothermal system can be successfully and economically exploited. Additional information, next to the wire line logs, can be obtained by TISA 3D Borehole radar measurements. TISA 3D data can be used to delineate the location and dimensions of the reservoir and to determine the presence of impermeable cap rock on top of the groundwater reservoir. Faults and fractures can be detected.

Measurement of underground structures (concrete piles, sheet piles and foundations) are important in order to verify their exact location and dimensions and to check possible damage or degradation. After many years, the exact location of structures is often unknown and needs to be determined again.

Measurement of underground structures with conventional surface measurement techniques are operationally difficult and tend to be unreliable for several reasons:
  • The structures are positioned too deep for conventional measuring.
  • The current surface techniques prevents conducting overburden.
  • The current techniques do not provide enough resolution.
  • The existing above ground structures makes measuring difficult.

Steered Drilling
Steered drilling is a new technique for laying underground cables. As an alternative to digging trenches, it is a cost-effective method that causes fewer disturbances to the environment. As the number of cables and other objects in the shallow subsurface increases, there is more need for exploration of the drilling path. As an alternative to measurements from the surface, the high-resolution directional borehole radar can be integrated in the drilling process to explore the drilling path in advance.

 Concrete foundations are used for an increasing number of underground infrastructure projects. Various jet grout injections consolidate the soil and decrease the risks of subsidence from large surface structures. Jet grout columns vary in diameter, depending upon the injection pressure and the soil conditions. The diameter is an important property that should be quantified, especially when several grout columns are connected to form an underground concrete floor. Until now, no proven or tested techniques existed to calculate the diameter ofinjected columns. Until now, it has been almost impossible to conclude whether thejetgrout foundations provide enough stability, especially in underpinning applications.

Main applications
By integrating the TISA 3D Borehole Radar technology into the injection lance, the diameter of the column can be determined on site. The boundary between grout column and hosting medium is a sharp edge and, therefore, a good reflector for incident radar waves.

There are two ways to apply the TISA 3D in the jet grouting process. In both cases, the diameter can be measured very precisely because of the resolution of the TISA 3D method:
  • Integrating the TISA 3D in the jet grouting system. During construction of the column, the radar is located just below the injection point and the grout column diameter is measured from within the column. The injection pressure can be adjusted while the column is being made.
  • Drilling a borehole near the grout column allows the TISA 3D to measure the distance from this borehole to the edge of the column.

It is essential that any tunnel project starts with a comprehensive investigation of ground conditions. In addition, encountering unforeseen ground conditions, objects or anomalies can be costly in terms of time and materials. The TISA 3D Borehole Radar technique continuously gathers detailed information about obstacles and geological transition zones.

Main applications
TISA 3D is positioned in a horizontal borehole with a diameter of about 20 centimeters, and drilled along the planned trajectory. It measures the complete surroundings of the borehole. Rotating 360°, it gathers and processes data from all angles with special proprietary software. After processing, the raw ground penetrating radar data is combined with simultaneously collected positioning data, providing meaningful operating data.

T&A is the first geophysical survey company to successfully integrate radar electronics into a geophysical tool. It is capable of surveying the surrounding soil construction and simultaneously determining the exact position of objects from within one borehole.

Unexploded ordnance, such as aircraft bombs and artillery shells from for example World War II still can be found in the subsurface throughout Europe. These explosives are especially dangerous when touched or moved during digging, dredging or piling activities.

Detection from the surface is often not feasible, since the explosives are buried too deep. When a bomb dropped from an airplane doesn't explode touching the surface, it penetrates the upper soft peat and clay layer and stops at the first stable sand layer. In the Netherlands, this layer can be located at a depth of more than 10 meters below the surface. Due to resolution problems, detection from the surface is not an option in these cases. Measurements from a borehole are needed to solve the problem. Traditionally, these measurements are done using a magnetometer.

The main drawbacks of the magnetometer method are:
  • Limited penetration range of 1 to 2 meters.
  • The measurements contain no directional information.

Main applications
For TISA 3D Borehole Radar measurements, a borehole is drilled in a safe zone, just outside the investigation area. When it's determined that the area around this borehole is safe, the next measurement is done in an adjacent position closer to the area of investigation. This way the whole area is searched for deep explosives.

Unexploded bombs with a large metal content show a strong electrical contrast with the surrounding soil. Therefore, these objects are very good reflectors of radar waves.