Sigra was founded as an Australian company by Dr Ian Gray. It became operational in April 1994, and Dr Gray remains Managing Director.
Initially the company served the coal mining industry in a consulting role, and through research and development as part of the Australian Coal Industry Research Program.
This work was undertaken on aspects of drilling and gas drainage including:
- Torque and drag behaviour
- Drill rod testing and design with the application of underground directional drilling
- Well control as applied to underground gas drainage boreholes
- Safety shut off valves for gas drainage ranges
- Flow meters for gas drainage monitoring
The consulting work involved aspects of coal mine safety, particularly in respect of:
- Gas drainage
- Dealing with hydrogen sulphide
It also involved some geotechnical work for metalliferous mines, and in using the company’s stiff torque and drag model to design the trajectory of pipeline boreholes for the civil engineering industry. In the early years Sigra also provided support to the University of Queensland and its multi-disciplinary Coal Seam Methane research project, funded by the Queensland Electricity Commission. Several postgraduate students worked with Sigra as part of this alliance.
Gradually Sigra built up technology for itself, which was of more economic importance to the company than funded research. This started in 1996 with its overcore stress measurement system (IST), capable of being used to 2000 m depth in HQ coring. The survey system in this tool originally included hand built magnetometers and accelerometers. Currently “off the shelf” integrated circuit units are used as they are more cost effective, but it is worth noting that the original units remain more accurate, indicating the high standard of Sigra’s design.
This was followed by the development of inflatable packers and their accompanying reinforced rubber technology.
The company became increasingly involved in field measurement with multiple stress measurement projects. From these came the evolution of the tectonic strain theory to explain the varying stresses measured through sedimentary strata. This concept has been almost universally adopted by the mining and petroleum industries.
Sigra also undertook several jobs to measure permeability of coal seams from underground. These were followed by interference tests from surface. The decision was made to build Sigra’s own drill stem test tools, which were designed especially for use in conjunction with the HQ coring system. This, and the IST tool for stress measurement, became key tools in investigations for mines.
In 2000 the coal industry went into recession. This impacted upon the company, and in particular some research and development projects had simply to be shelved or abandoned. A notable loss during the period was the directional hammer system. Work was however made up in other areas. One of these was to build well control systems for use with down- the- hole hammer simultaneous casing drilling operations for use at Lihir gold mine in Papua New Guinea. This work was successfully completed, and then combined with the choke system that had been developed for underground drilling, to build a line of small, lightweight well control systems for coring operations. Sigra still sells these systems.
In 2002 Sigra was approached by Anglo Coal Australia to deal with an urgent problem at Dartbrook Colliery, New South Wales. Here the gas drainage flows from borehole had reduced by more than an order of magnitude in the new longwall areas. Sigra undertook testing and confirmed a drop in permeability due to the presence of dawsonite in the cleating. To overcome this problem, Sigra initiated hydrofracture from underground boreholes in the coal to stimulate flow from seams.
With the advent of the coal seam gas industry Sigra became a key supplier of well testing services to that industry. This dominated the company’s field operations for some time. Its prime clients in this area were Queensland Gas Company and Arrow, plus many of the smaller players since amalgamated into larger companies. The new industry also required well path design for directional boreholes in coal. This was another need met by Sigra.
Through the development of its field loggers, Sigra supplied equipment to a number of companies; notably, several hundred have been supplied to BHP Billiton in the Illawarra, New South Wales, to collect data from the field. The radio connection on these, and their ability to work with vibrating wire sensors, made them unique for some time. These were later enhanced by connection via the cellular telephone network as it expanded. Their development continues to this day, with both enhanced hardware, and a data acquisition and processing service.
One of the main uses of the field data acquisition systems has been to monitor pressure sensors installed to monitor reservoir or aquifer pressures, in the mining and coal seam gas industries. Another use was in the installation of cemented – in stress change cells to monitor the changes in stress brought about by mining, or fluid withdrawal with drainage.
It became apparent fairly quickly, that while Sigra supplied loggers and pressure transducers for reservoir monitoring, very few of our clients could actually install working systems at the correct location and with sufficient connectivity to the formation to be monitored. For this reason Sigra undertook research and development into cementing transducers in the ground, and ensuring that a connection could be made between these and the formation to be monitored. This has required the development of an entire cementing technology, from the rheology of grout design, to modelling its behaviour and actually pumping it into the ground.
While the work on gas continued, the areas of geomechanics and groundwater became growing parts of the company’s activities.
In the groundwater fields two major projects stand out. In 2003 Sigra was engaged to determine what potential inflows could occur to Moranbah North Mine in Queensland, in the advent of flooding of the nearby Isaac River. This study involved drilling and testing three angled boreholes to see what the directional permeability might be over a goaf area. The goaf was in fact found to be remarkably consolidated, and the only measure recommended to control ingress of water was to rip surface fractures caused by subsidence and to fill them with bentonite. This was a practical, economic solution that has withstood the test of several major inundations which have since occurred.
The other important groundwater project commenced in 2008. It involved a major landslide on an extension of the Centenary Highway at SpringfieldLakes, close to Brisbane. Here the Queensland Department of Transport and Main Roads requested Sigra’s assistance in working out the groundwater regime, and in draining the cut slopes so as to improve their stability. This is an ongoing project that has required extensive monitoring using Sigra’s equipment and in the use of pumping wells. These are required to evaluate the groundwater regime, and for groundwater control.
In the field of geomechanics Sigra’s operations branched in two ways. One of these is in the area of mine rock mechanics while the other is in the field of reservoir engineering. Sometimes these two have merged. A notable example of the latter is in the area of deep gassy coal mines. Here rock mechanics is needed for the purpose of determining the direction of the longwall panels, rock support design, and to provide a basis for assessing the caving behaviour on extraction. It is also required in the determination of reservoir behaviour.
Underpinned by the original work on the subject by Dr Ian Gray in the early 1980s, Sigra has developed its stress path analysis to determine how the effective stresses in coal seams and other adsorbative reservoirs change with the removal of fluids; in this case, water and gas, where the latter leads to shrinkage of the coal. This is important because the permeability of coals is very dependent on the effective stress that they are subject to.
Of recent times Sigra has undertaken several studies to determine the stresses in the coal and in the surrounding rocks. These matter in designing drainage or production systems. If it is necessary to drill holes, and possibly stimulate using hydrofracture, then the stability of the holes is paramount. If they cannot be drilled in coal because they fail to stay open, then it may be necessary to move them to the adjacent roof or floor rocks. In this case it is necessary to connect the borehole to the coal using hydrofracture. This again requires a detailed knowledge of rock stress and strength. Sigra has undertaken several studies of this nature. The most notable of these has been for Vale at the Belvedere lease, near Moura in Central Queensland.
On this project, the stress work has been underpinned by Sigra’s IST stress measurement system. It has been augmented by borehole breakout analysis and Sigra’s capability to undertake hydrofracture testing for stress measurement. Using this combined information we have characterised the stress fields over several lease areas. Some of these have involved about 50 to 100 in situ stress measurements using the IST system, some hundreds of borehole breakout determinations, and detailed examination of seismic data to determine faulting.
To support the field work Sigra has progressively developed its laboratory services to cover rock testing, so that the modulus of the rock from stress measurements can be correctly determined. It also tests coals triaxially to determine modulus under confined conditions. We have also developed a coal laboratory which is used to measure isotherm and shrinkage behaviour, in addition to more normal analyses.
In 2012 Sigra built, tested and proved its Gas Content Without Coring System (GCWC). This enables the gas content of strata to be determined while drilling an open hole under overbalanced conditions. This is a very important development as it provides a means for determining the gas content of virtually all rocks that are not vuggy or hugely over pressured. It has been proven in coal bearing formations.
In addition to services, Sigra has a well established product range. Notable are its:
- Field data acquisition systems
- Well control systems
- Cyclonic separators
Sigra has always been prepared to work in the international arena. Recent examples are:
- The first stage of a consulting project to improve mining practices in a gold mine in Eastern Siberia
- Stress measurements at a diamond mine in Africa
- It is supplying gas-water separators to overseas clients
- Sigra has an ongoing relationship with Agapito Associates to meet the US market for stress measurement, using the IST system