Oil and Gas Sector: Why use TRE data?

Environmental risk mitigation

Responsible extraction and storage of oil, gas and CO2 is at the core of oil company policy. Oil fields are not always conveniently placed in non-urbanized areas hence appropriate precautions must be taken in order to protect areas surrounding the worked fields.
TRE’s monitoring products allow our clients to regularly monitor production areas, proving maximum possible risk mitigation.  Worked field deformation rates are constantly measured remotely allowing compliance with the regulations and standards set by local authority agreements.  Early indicators of possible policy-breaching situations (e.g. gas-storage field pressure reaching limit, oil extraction rate too high, etc.) are used to avoid potentially damaging and legal implications.

Asset protection

Detecting millimetre ground-surface displacements not only gives an insight into the movement of fluid within the subsurface, but also allows strategic decisions to be made above ground, for example: injection/extraction pumping rates, borehole locations, etc.
By accurately and densely mapping the surface response to fluid movement in the subsurface, PSInSAR™ quantitative measurements can help the identification of strategic steam, water and CO2 injection zones - based on fluid flow models.
PSInSAR™ can detect vertical and east-west surface movements.  Early detection of potentially hazardous shear zones can avoid expensive damages, for example: well casing breakages or dog-legging, surface-based plant, above-ground buildings or structures and pipelines.

Reservoir permeability estimation

A breakthrough in PSInSAR™ technology now gives our clients the ability to determine the permeability of the subsurface.  Better understanding of fluid-flow dynamics in the subsurface allows informed decision making into the commercial viability of an oil field.

 
Figure: RTK analysis of two time series showing cross-correlation coefficient (R),
time-lag coefficient (T) and scale factor (K)

TRE has developed RTK analysis: an algorithm used to analyze the relationship between fluid extraction/injection volumes and the permeability of the subsurface.  Monitoring subtle changes on the ground surface allows interpretation of three key subsurface parameters.  These variables are:

• R - Cross-correlation map (similarity measurement) - high values highlight where, and if, ground displacement strongly resembles gas volumes stored in the reservoir.
• T -Time lag (propagation delay) – where R values are high it is possible to estimate a map showing the propagation delay (T) between injection/extraction rates and the ground deformation response.  Recent studies have shown that this map can be used successfully to obtain insights into reservoir permeability.
• K - Scale factor – where R values are not negligible, it is possible to identify the area affected by injection/extraction activities and, based on geo-mechanical models, estimate how the area will respond to higher injection/extraction rates.

Fault and fracture identification

An advantage of constantly and consistently monitoring ground deformation over actively worked oil and gas fields is the ability to produce regular temporal cross-section displacement maps. 
Gradient (second order) analysis identifies areas of increased and consistent vertical displacement values relative to the surrounding areas. Such events often occur along faults and fractures within the oil field.
The PSInSAR™ technique can be used to give strong indications into the location of faults and fractures within the subsurface.  The ability to identify active faults and fractures activated by the extraction/injection of fluids can give a unique insight into fluid flow movements and in understanding these movements our clients can have significant financial advantages.

Tracking injected fluid

Tracking fluid movement within the subsurface is an involved process using seismics, resistivity and other ground based surveys.  PSInSAR™ uses SAR mounted satellite platforms to monitor millimetre displacements in the subsurface.  Monitoring such changes on the surface and using complex modeling techniques for the subsurface, pressure variations within the field can be calculated.
As a direct result, the movement of injected fluids within the field can be tracked.  Maps of the ground surface response to subsurface fluid flow allow the computation of fluid flow models, which in turn shows the location and extent of the subsurface system.
An advantage of constantly monitoring such fluid injections is the early warning of unexpected fluid migration, leading to possible surface break-outs, damages to infrastructures, eruptions or related environmental impacts.

Effective injection/extraction strategies

PSInSAR™ gives the possibility to regularly and accurately measure millimetre deformations on the subsurface.  These deformations in turn give us an insight into fluid flow within the subsurface, through the use of complimentary ground based data sets and PSInSAR™ algorithms.  
Understanding how the reservoir responds to the extraction and injection of fluids is fundamental to understanding its limits.  Apart from mitigating the risk of over pressuring due to injection or structural damage due to over extraction, our PSInSAR™ data gives our clients the possibility to optimize reservoir production through effective injection and extraction strategies.

Cost-effective

PSInSAR™ provides thousands of ground measurement points - each with time-series displacements and annual velocity data.  Compared to traditional ground-based surveys this is hundreds to thousands of times greater than alternative data collection methods, for example, GPS, leveling surveys, tiltmeters, etc.

Millimetre Accuracy

PSInSAR™ data is collected over regular intervals with high-frequency instruments and so millimetre ground displacements are detectable.  As the data is collected over large areas, it is possible to identify areas of ground that are subsiding from areas that are relatively stable.  This data is translated into millimetre displacements per year, compared to surrounding stable regions, and maps are produced highlighting subsiding regions.

High Spatial Density

Over large, flat areas (as is usual with oil and gas fields) a high number of ground reflectors is achievable.  For every reflector that produces a stable reflection signal throughout the entire satellite image dataset, displacement (and hence velocity) calculations can be made.  This means that for a typical oil field, a measurement point can be identified every 20m – hence, over an entire oil field, high spatial densities of up to 20 thousand points is not unusual.

Historical archives

PSInSAR™ data uses satellite image archives that are available dating back to 1991.  These historical data sets can be used to analyze and highlight past trends that have occurred over an oil field which could be informative for future production.

Integration with Alternative Survey Techniques

Integration of PSInSAR™ data with ground based surveying techniques is simple and effective. The high number of ground points identified using the PSInSAR™ technique allows accurate validation of traditional ground monitoring techniques, such as GPS, tiltmeter and leveling surveys. Exploiting the simultaneous visualization of homogenized datasets collected from two or more different surveying techniques permits the extraction of each technique’s key strengths. 
Management of the high number of ground displacement points identified using PSInSAR™ is made even easier with a customized GIS toolbar, designed by TRE.

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