Microseismic monitoring – illuminating reservoirs from a different angle of view

What is microseismic monitoring?
Microseismic monitoring makes use of the fact that man-made interferences in the natural subsurface conditions causes mechanical instabilities usually resulting in the emission of microseismic signals. In the context of reservoir exploitation those fracturing processes can be triggered by changes of the reservoir pressure due to depletion or hydraulic stimulation, for example.

Microseismic events can be precisely located and characterized with a relatively small network of typically less than 10 monitoring instruments. During stimulation jobs thousands of events may occur within a few days forming a three-dimensional image of the enhanced permeability zone. Microseismic analysis hence provides a detailed picture of flow pathways within the reservoir.

During the past two decades the development of the microseismic technology has been solely pushed by geothermal R & D. It has become an indispensable key technology for opening up a vast energy resource, the so-called Hot-Fractured-Rock or Enhanced Geothermal Systems.

Field implementations
“Without microseismic monitoring we would not have a clue about the dimensions and the orientation of our reservoir,” says Doone Wyborn, Executive Director of Geodynamics Limited. The Habanero geothermal field of Geodynamics in the Australian Cooper Basin has been continuously monitored since early 2005. Despite the extreme weather conditions in the Australian outback, the monitoring system has been operated in a self-sustaining mode without any failures or downtimes.

Equipped with a satellite link, monitoring can be performed in real-time from any place in the world via Internet. Typically, this is only done during critical operations such as reservoir stimulation treatments when the microseismic response of the reservoir is used as a decision making tool. By watching the impact of stimulation in real-time reservoir engineers are enabled to conduct pinpoint treatments with optimal efficiency.

During regular production periods the system is usually operated in a low-cost memory mode where data is collected over a longer period of time before it gets processed and analyzed in a batch mode. To date, the Habanero reservoir is mapped by nearly 50,000 microseismic events covering an area of several square kilometers. “From the microseismic image we have learned where we need to drill our production wells and where we rather stay away from,” explains Doone Wyborn. “Only recently we have drilled another well into the reservoir and found exactly what our microseismic consultants from Q-con have predicted. Economic exploitation of the Habanero field is unthinkable without seismic monitoring.”

Also in the oil and gas industry this technology attracts more and more attention. The application in tight gas and naturally fractured reservoirs has a huge potential. “We have only started using Q-con’s microseismic monitoring systems during the last years and I am impressed finding a mature technology which has been nearly completely ignored by the oil and gas industry.” says Simon Chipperfield from Santos Ltd (Australia).