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GEO

EXPRO VO

L. 7, NO

. 4 – 2010

Ocean Bottom Node Seismic

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Technology, Experienceand Performance

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GEOSCIENCE & TECHNOLOGY EXPLAINED

G E O L O G Y G E O P H Y S I C S R E S E R V O I R M A N A G E M E N T

Country Profi le: Senegal

geoexpro.com

VOL. 7, NO. 4 – 2010

WESTERN NEWFOUNDLAND: An Open Air Museum

GHAWAR, SAUDI ARABIA:The King of Giant Fields

TECHNOLOGY EXPLAINED:Depth Imaging; Microseismics;

Dip analysis

58 geo expro september 2010

The Application of Microseismics in the Oil and Gas IndustryUntil now, microseismic monitoring as a commercial business has been limited mainly to short term monitoring of hydraulic fracture operations and long-term monitoring of steam injections. However, microseismics have other applications within the oil industry.

Real-time microseismic processing workflow and decision making.

TOP I C T E C H N O L O G Y

geo expro september 2010 59

Microseismicity can be recorded with sensors deployed a number of different ways.

10-FE-0105 ED-Wireline-Microseismic-GEO ExPROOctober 2010 issue

Table 1. Overview and analysis of deployment options for microseismic sensing system.

APPROVAL SHEET

Deployment Pros Cons Applications

Surface geophones Q��No drilling costQ��More freedom to spatially

optimize arrayQ��Traditional configuration for

surface seismic reflectionQ��Potentially monitor large area

Q��Increased noise at surfaceQ��Signal attenuated by caprockQ��Signal further attenuated by

weathering layer

Q��Monitor large magnitude microseismic events

Q��Earthquake monitoring

Shallow well Q��Simple drillingQ��More freedom to optimize

the arrayQ��Potentially monitor large area

Q��Less noise than surface but more than deep wells

Q��Signal attenuated in caprock

Q��Monitor large magnitude microseismic events

Q��Earthquake monitoring

Cemented observation well Q��Quiet locationQ��Good sensor couplingQ��Permanent deployment

Q��Drilling expensiveQ��No option to repairQ��Limited option to use well for

other purposes

Q��Existing wells ready for abandonment

Wireline observation well Q��Quiet locationQ��Data quality controlled by sensor

and well completionQ��May need to suspend a well for

temporary monitoring

Q��Temporary deploymentQ��Limited access based on well

availabilityQ��Preparation costs

Q��Hydraulic frac monitoringQ��Short term reservoir monitoring

Outside casing Q��Well can be used for production/injection

Q��Good sensor coupling

Q��Requires careful installation and preparation

Q��No option to repairQ��Noise will change with well

operationsQ��Size of wellbore and upper

casings will increase

Q��Long term life-of-field monitoring applications from hydraulic fracturing to reservoir monitoring

Tubing deployed in dedicated monitor well

Q��Good sensor couplingQ��Can be retrieved

Q��Limited access based on well availability

Q��Preparation costs

Q��Longer term for reservoir monitoring

Tubing deployed in flowing well (annular space between casing and tubing)

Q��Well can be used for production/injection

Q��Can be retrieved

Q��Well completion may constrain location

Q��Noise will change with well operations

Q��Longer term life-of-field monitoring applications from hydraulic fracs to reservoir monitoring

voir. 1e induced seismicity may be used to map seismically active faults, fractures, 2uid fronts and 2uid paths. In this article we give an overview of micro-seismic usage and the enhancement in tech-nology and work2ows, including the future integration of microseismicity with other real time measurements from the well and inter-well space, which will further improve the usage of microseismicity.

microseismic basics Induced microseismicity can be a conse-quence of oil3eld operations from either production or injection. Microseismic events are induced in the reservoir rock matrix due to pore pressure changes and geomechanical stress 3eld relaxation as reservoir 2uids are produced or injected. Stress change slippage, which is predominantly in shear, can occur along zones of weakness like new or pre-ex-isting fractures and faults, and emit microseis-micity. In hydraulic fracture monitoring the direct aim is to fracture the rock, which can be monitored through microseismic emissions. To provide useful and meaningful reservoir information it is necessary to detect and ac-curately locate a population of microseismic events. Since there are many more small events than large ones, the resolution of mi-

Recent developments and improvements have signi3cantly increased the usage of microseis-mics as a reservoir monitoring tool. In par-ticular, they are used in reservoir injection and integrity monitoring (for example, in hydrau-lic fracture operations, injection of drilling cutting waste, gas storage, injection of CO2 and H2S and steam injection operations) and in production monitoring (oil production, gas production, compaction and fault activation). Microseismic monitoring provides a direct method for monitoring stress changes and geomechanical deformation within a reser-

croseismic monitoring is related to the size of the detected event population. It is important to detect as many events as possible, which makes the placement of the sensors and use of a monitoring system with a low noise 2oor important. Microseismic events can be located in space and time and their distribution patterns interpreted in terms of geomechanical defor-mation associated with injected or produced reservoir 2uids. Applications include moni-toring of 2uid fronts, 2uid barriers or leakage paths due to faulting or breached cap rock. 1is information can be used to improve res-ervoir management and allow better planning of future wells.

microseismic monitoring system Successful microseismic monitoring projects require the use of sensors that are well-coupled to the rock and decoupled from man-made noise sources. Such sensors need to form part of a system that is designed to record low energy signals at close distances and thereby deliver both quality and quantity in terms of microseismic signal. In addition to these mi-croseismic requirements, any installed system also needs to meet the speci3cations required of all oil3eld equipment.


kim gunn maver, shawn maxwell, nick koutsabeloulis, and robert greenaway, schlumberger


Live processing in real time during a hydraulic fracture treatment in the Barnett Shale. Each stage is represented by different colored estimated stim-ulated volumes.

The Omega-Lok clamping system: (left) Tetrahedral geophone mounted in the clamp and used for microseismic data acquisition is on the left. (right) The clamp mounted on tubing before it is deployed.

The final processed microseismic events located in relation to the well trajectory. Red dots were the first phase of the well stimulation, green dots the second phase of the stimulation and finally the yellow dots were the third and final phase.

1e right deployment solution depends on monitoring objectives, well availability, prox-imity to microseismic events, timing, oil3eld access and cost. With the recent develop-ments in microseismic sensing systems for live wells, technical solutions are available for nearly all microseismic project scenarios. Microseismics have three main applica-tions within the energy industry: short-term hydraulic fracture monitoring, long-term res-ervoir monitoring, and environmental moni-toring. 1e last is not associated with oil3eld activity, although it may in2uence oil3eld op-erations, and is therefore not discussed here.

hydraulic fracture monitoringHydraulic fracture monitoring is when mi-croseismicity is induced as a consequence of the fracturing of the reservoir formation. 1is is now a common technique, especially in unconventional reservoirs, which are often naturally fractured and require speci3c stimu-lation techniques to economically produce. One particular example is the Barnett Shale in Texas, where the combination of horizontal drilling, large volume water fracs and micro-seismic imaging of the fracture network has transformed the Barnett Shale from an eco-nomically marginal play to one of the largest natural gas 3elds in the United States by imaging the far-3eld fracture geometry. Mi-croseismic fracture images have been funda-mental in terms of current understanding of the importance of complex fracture networks in unconventional reservoirs. Hydraulic fracturing operations are typi-cally of short duration and ideally suited to a wireline deployment in an oAset well. With the sensor array restricted to one or possibly

two or more observation wells, a system with good vector 3delity is required to provide accurate microseismic locations. 1e sensor spacing and position in the well are critical to optimize the location accuracy. 1e example shows the result of a case study where engineers used real-time microseismic to decide on the timing and eAectiveness of a 3ber diversion technique. Like most wells in the Barnett Shale, production from this par-ticular well had signi3cantly declined since it was originally fraced. Microseismic data from the original well completion showed that the heel portion of the well was not stimulated. 1e objective of the re-fracing was an attempt to extend the fracture network, and in particular to attempt to better stimulate the heel. During the initial stages of the stimulation, the micro-seismicity was primarily clustering in the same

areas as from the original stimulation. Based on this observation, progressively more aggressive 3ber diversion stages were incorporated, which ultimately steered the stimulation towards the heel and increased the eAective stimulated volume. As a result, production increased.

long-term reservoir monitoringWhere microseismicity may be induced as a consequence of oil3eld operations from production or injection or with geothermal projects involving simultaneously injecting and producing water it can be utilized for long-term reservoir monitoring. To ensure close proximity to the reservoir to improve sensitivity during the record-ing of microseismicity, a dedicated moni-toring well has to be available or a live well


Closing the loops - From dynamic to static modelling

November 2nd-3rd, 2010 | Norwegian Petroleum Directorate

www.geologi.no/pg2010

Registration:For information and registration, see the conference web page: www.geologi.no/pg2010

Reduced conference fee when registration is made before October 1st, 2010. Special student fee. Abstract submission without conference registration will not be accepted.

Conference organizer:Geological Society of Norway (NGF)www.geologi.no

Contact information:[email protected] / Tel.: +47 73 90 44 68

Programme available from September 15th

AD-II_210x280_Layout 1 25.08.10 11.02 Side 1


Microseismic event

Water Injection—Reservoir “Seal” Failure

Temperature

Dept

h

Pres

sure

Time

Producer

Injector

Shut in

Injector pressureProducer pressure

GeothermalDTS temperature

Temperature

Dept

h

GeothermalDTS temperatureFlowrate

has to be shut-in, due to the noisy live well environment, so shut-in costs or monitoring well availability may limit the application of microseismics for reservoir monitoring. 1 is limitation can be overcome by recording mi-croseismic events with tools properly installed inside live and highly deviated wells with no production/injection stops during recording. Such a tool must be insensitive to the 2 ow noise of the well to detect the microseismic

signals of very low energy. 1 e Omega-Lok clamping system, which is part of PS3-FW, has these attributes. It is a system of sensors, which are decoupled from the tubing and therefore providing background noise levels largely independent of 2 ow rate. During a test of the tubing clamping device with tetrahedral geophones, microseismicity was recorded during a three-step acid stimula-tion. A single well was used for the monitoring,

which at the reservoir depth of around 15,000ft was highly deviated. A 2-level Omega-Lok system clamping the sensors to the casing was used to record microseismicity during periods of 2 ow in the tubing. Good quality microseis-mic events were detected and localized, indi-cating the sensor coupling to the casing was eA ective and the noise 2 oor low providing reliable results and interpretable microseismic events.

Located microseismic events for the Karachaganak Field. The microseismic sensing system is deployed in well K125.

Extract of a 3D Geomechanical Earth Model from the VISAGE software showing comparison between detected microseismic events (coloured spheres) and estimated moment magnitude of induced shear deformation.

In connection with water injection to stimulate production, microseismicity may be used to detect a failure in the reservoir seal and explain the PT and DTS measurements.


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