What has happened in 30 years

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Ian Gray started work at his new company, Sigra Pty Ltd, in 1994. Throughout much of its existence Sigra has had a background of the coal industry of Queensland, and overseas. For a period this morphed into providing exploration services to the coal seam gas industry including drills stem testing, isotherm and gas content measurement. New methods have been developed for this purpose. One important aspect of this was predicting whether coal seams would increase or decrease in permeability with drainage. This is called Stress Path Analysis and for it to be done properly requires the measurement of coal properties, stress, shrinkage behaviour and isotherms. Sigra has built the tools to measure these.

As the exploration phase of CSG declined these skills were re-used in dealing with gassy mines in Queensland, New South Wales and in China, Russia and Kazakhstan. One of the big problems to be dealt with is that of outbursting, the expulsion of gas and coal from the working face. The company has addressed this fully in several projects supported by the Australian Coal Industry Research Program though implementation always lags new knowledge. Work into rock bursting has also been important.

The knowledge of ground fluids has also been used in dealing with major cut slopes on roadworks and is currently in test work for pumped hydro and compressed air storage projects that we hope will be part of our energy storage solution. One development in the area of ground fluids is to enable the installation of multiple piezometers into deep (1000 m) holes with testable connections to the formation and isolation within the borehole.

An area of major development by Sigra has been in that of rock stress measurement. This started with the original IST2D two-dimensional overcore system which has now been used up to 1600 m in depth and in over 2000 successful measurements. This has been augmented by hydrofracture and hydrojacking, the use of borehole breakout and the new development of a core ovality system to determine the stress difference orthogonal to the core. In the last three years, Sigra has developed its IST3D three-dimensional overcore system. These techniques form a powerful suite to determine rock stress. They have been used in ten countries in projects from deep lithium in Serbia to copper in Arizona. Sigra has also developed methods to analyse stress throughout a complex rock mass The first paper describing the use of tectonic strain to describe stress was written in 2000.

Another area where Sigra has extensively worked is in the area of rock properties. It undertook this work as a result of having to work out stresses in the highly anisotropic and nonlinear sandstones of Sydney. The methods developed included those to measure these properties in a triaxial test rig, which was designed and manufactured by Sigra and by hydrostatic testing of rock fragments. Sigra has adapted shear test methods adapted from Russian practice and separately developed the measurement of plasticity in uniaxial testing. The measurement of poroelasticity is also important in some applications. Sigra’s laboratory provides quality measurement for its projects.

Drilling has always been important to the company, not least because it is vital to the measurements that Sigra performs in the ground. The developments in this area have been in directional drilling with a rotary steering tool now under trial and drilling electronics well developed. This is for directional measurement, the determination of rock type from drilling an open hole and testing within the hole. This suite of tools are designed for coal and are therefore intrinsically safe but can also be used for metalliferous and civil engineering purposes. There are also well control systems used in exploration and managed pressure drilling from underground mines and tunnels.

Sigra’s jobs have had a background of underground coal and have progressed through coal seam gas, slope stability, mine exploration and design to site investigation for the big civil projects such as road and rail tunnels and now underground energy storage projects which include storage of hydrogen in solution mined salt caverns.

Sigra has shown its ability to adapt to changing times with an ever developing suite of technology virtually all of which is developed in-house. The fact that it has worked in different industries, each with their particular methods and strengths, means that Sigra has a breadth of experience and can adapt between these and cross disciplines with ease.

The company looks forward to the challenges of the next 30 years.