The OGS geophysical-drilling testing site (PITOP) was set up with the purpose of providing a framework facility for studying and testing geophysical methods, technologies and borehole/surface tools in realistic conditions (Fig. 1).
Located in the foothills of Eastern Alps, 110 km NW from OGS headquarters in Trieste, this facility mainly consists of a scaled-down version of a drilling yard in which four wells were drilled in Quaternary alluvial sediments lying on Miocene conglomerates.
The inter-well distances are 40-50 m. All the wells, of variable depths (300, 385, 420 and 150 m) and dimensions (6”, 12”, 8”1/2 and 5” diameters), with cased and open-hole depth sections, are fully accessible.
Two of the wells are instrumented by permanent sensors (3-C geophones and DAS fibre optic sensors) cemented outside the casing. Two of the existing wells are potentially available for further drilling phases, and all wells are available for downhole instrumentation testing.
The site is geophysically and geologically characterized by master logs, well logs, vertical seismic profiles, crosswell and surface seismic data.
Permanent Laboratories equipped with instrumentation for data recording, in-field quality control (QC), real-time signal processing and conditioning, including remote satellite data transmission and acquisition control, are available at the well site.
Auxiliary seismic sources and sensors (including permanent ground force sensors at shallow depth) are available both on the surface and downhole. The test site is also instrumented with permanent downhole (150 m well) and surface seismometers for natural seismicity monitoring.
Permanent borehole tools
Well instrumented by an array of 3C borehole geophones cemented outside the casing between 40 and 240 m depth, usable for multi-offset VSP and cross-well measurements.
Portable borehole tools
Portable seismic sources and receivers:
· Bolt borehole air gun (max 500 m depth), 3” and slim borehole sparker source (max cable length 1.3 km) usable for cross-well and reverse VSP (RVSP) applications.
· Wireline VSP (Fig. 2B,C,D), max depth 2 km standard cable, Avalon system, 3C borehole geophone, normal 3” size and 1”11/16 slim tools.
· Hydrophone chains, 24 array of hydrophones usable with 10 and 5 m spacing (configuration with max depth 300 m).
· Downhole and surface broadband seismometers for natural seismicity monitoring.
(see figure 2)
Ground force and load cells / source emission control
· Permanent ground-force calibration facility: Buried (Kulite) soil stress sensors and accelerometers installed in a shallow permanent configuration to measure near-field and emission from surface seismic sources to recover and remove the far field source signature in the borehole array.
· Portable load cells (Seismic Source Load cells) used to measure ground force below surface vibrator sources, to measure near-field of surface seismic sources to recover and remove the far field source signature in the borehole array.
(see figure 3)
Additional surface tools
Receivers and recording systems:
· Single geophones, 6- and 12-geophones groups, max 400 traces.
· Summit DMT, Seismic Source DaqLink recording units, high-frequency National 90 channels.
Vibrators and other seismic sources
· MiniVib IVI 2500, operating in vertical (P) and horizontal vibration modes.
· Large seismic vibrator: Prakla Vibroseis 28 klbs.
· Accelerated dropping mass.
Air gun in pits can be available on demand.
(see figure 4)
While drilling technology
To be considered in particular with percussive-action drilling. It is envisaged that this offered drilling monitoring technology can be potentially and advantageously used and refined in conjunction with other active and/or passive borehole monitoring methods and technologies, and includes the following tools (Fig. 5):
· On-rig pilot-line set up;
· Management system for automated control by mud-logging data;
· Quality control of field data, automated acquisition and data pre-processing;
· Modelling of drill-string and borehole signals, and RVSP data processing;
· Down-hole tools data transfer interface setting and management;
· 2D (3D tbd) RVSP, crosswell configuration SWD survey.
(see figure 5)
Lubricator (max 10 bars)
Lubricator tool for use of tools in wells with over pressures at well head (max 10 bar). Portable, after site specific adaption for installation.
The site has the unique characteristic to be drillable, to realize tests useful to improve monitoring well technologies, and usable at the same time for geophysical and instrumental monitoring, also with easy access to the surrounding area.
OGS currently uses this borehole facility for special testing of instrumentation and methodologies. The OGS experience includes field tests for calibration of fibre optic sensors usable for monitoring of CO2 plume migration.
OGS has used and can potentially uses this test site in cooperation with research institutes and/or industry in the framework of specific projects.
Borehole and recording instrumentation used for the purposes of the ENOS (Onshore CCS in Europe) and Geothermal acquisition projects were preliminarily tested at PITOP site.
Geophysical and technical support for project preparation, planning and execution. Support for in-field quality control (QC) and subsequent data analysis and processing.