CASE 11 Surface monitoring of hydraulic fracking and delineation of fracture zones

LandTech’s LT-FS sensor is the only surface sensor in the market which can record microseismic events (even negative magnitudes!) from many Km down even microseisms generated during hydraulic fracking of a reservoir. This sensor has an external diameter of 50mm allowing it to be installed into small and shallow boreholes, hence reducing the cost of installation. At the end of December 2011, Stream Oil & Gas Ltd had planned to apply the technique of hydraulic acid fracturing in Well D-12 of the Delvina block, aiming to increase the rate at which natural gas is produced from this wellbore. In the frame of this, LandTech was asked to monitor and study the possible microseismic and seismic activity on this area, which is related to the hydraulic fracturing, by using a supplementary surface network of seismic stations. The scope was to drive a horizontal well towards regions crossing major fractures and faults in order to increase the production rate.

A microseismic network consisting of 16 LandTech’s LT-FS sensors was installed on the surface around the well (D12) which was used for the hydraulic fracturing experiment.

Passive seismic case study

Surface passive network

The network delineated very clearly the pattern of the induced microseismicity using only the surface sensors and without the need of an observation well. As it can be judged from the following figure all the events are concentrated within a zone at the fracking depth.

Passive seismic case study

Epicenters of the recorded induced events

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Recorded hypoocenters, red line indicates fluid injection level

In addition the location of the induced microseisms all the corresponding focal mechanisms for all the events were also determined depicting accurately the directions of the fracture zones as it can be seen in the following figures.

Passive seismic case study

The possible faults/fractures as proposed by the focal mechanisms have been superimposed on the map (lines). Most of the faults are reverse and show a North-South and Northwest-Southeast trend being in good correlation with the known thrust faults in the area. There are also a couple of strike-slip (or oblique reverse) faults that trends from Northeast to Southwest and are located at the northern part of the area that is covered by seismic events, about 900m and 550 meters from Well D-12.

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The recorded events related to hydraulic fracturing applied to Well D-12. W-E Cross-section with focal mechanisms and fault pattern is depicted.