Microseismic monitoring is a powerful regulatory and production optimization tool in use for oil field operations such as Enhanced Oil Recovery (EOR), carbon sequestration or natural gas storage. During such injection operations, maintaining the integrity of the reservoir is essential.
Through our RESMAP® services, ESG has pioneered the use of passive seismic (microseismic) monitoring in long-term reservoir operations, to provide feedback on the reservoir integrity. Using in-house manufactured downhole sensors and data acquisition equipment, ESG has installed permanent and temporary microseismic monitoring systems to provide life-of-field (LOF) monitoring for EOR operations and underground storage projects around the world.
While microseismic monitoring of hydraulic fracturing is commonly performed using temporary wireline-based downhole sensor arrays, for EOR and long-term reservoir operations it is considerably more cost-effective to utilize a permanent Life-of-Field (LOF) approach to monitoring. Combining permanent downhole arrays with near-surface networks ensures a broad spectrum of signals is accurately captured, ranging from small microseismic events to larger magnitude induced seismicity.
Microseismic sensor arrays consist of geophones or accelerometers and may be deployed in offset monitoring wells and/or on the surface to detect seismic energy associated with rock failures or reservoir deformation during injections. These custom built sensor arrays ‘listen’ to the microseismic activity taking place in the reservoir. The microseismic events associated with injections are captured using ESG’s Paladin® data acquisition systems. These low power devices are suitable for remote monitoring stations and can be powered by solar panels.
Data is relayed via Ethernet, DSL, fiber or radio telemetry to a central site computer station where ESG’s proprietary Hyperion Seismic Software begins automatic processing and event triggering. Microseismic data is then transmitted via satellite to ESG’s offices for advanced processing and analysis. Images of the microseismic events are displayed in an interactive 3D format and are uploaded back to client sites for quick and simple interpretation.
Microseismic monitoring systems can be used to verify that injected fluid and hydrocarbons remain contained within reservoirs and do not escape through pre-existing fluid flow pathways or fault structures within the reservoir.
As pressure increases in a reservoir as a result of injection, the reservoir can expand and deform, exerting stress on overlying cap rock. Micro-fractures may develop in the cap rock or faults and fracture networks may be reactivated, acting as conduits for fluid migration. When this happens, seismicity may be observed to track upwards from the cap rock boundary. Microseismic monitoring can identify the propagation of fractures within the caprock layer and provide an early warning if the integrity of the caprock has been compromised, allowing operators to reduce reservoir pressures.
The high temperatures and reservoir cyclic compaction/dilation of steaming operations often subject well casings to severe tensile stresses, weakening their structure and resulting in failures such as cement cracking or casing shear.
Microseismic monitoring systems can be installed to specifically monitor well casings. Alerting systems provide instant warning if near-wellbore events bear the specific frequency characteristics of a casing shear event. Operators can respond appropriately to minimize downtime and limit damage.
Many uncertainties exist with respect to how fluids such as steam or water travel vertically and laterally within a reservoir. Due to changing reservoir stresses during steam injection operations, tiny fractures may be induced along the edges of the steam front.
Operators can benefit from the ability of microseismic monitoring to visualize the position and movements of a steam chamber within a reservoir, while learning how the steam is developing within the reservoir over time. Increased knowledge of where the steam chamber is located enables operators to better control and optimize the operation.
ESG has actively monitored a variety of underground storage projects involving the injection of waste water from oil and gas operations as well as subsurface storage of human biowaste and carbon sequestration.
Subsurface injection of water after it has been used in hydraulic fracturing or waterflooding is a common disposal method. Fluid is typically injected into depleated reservoirs, aquifers or salt caverns for long-term storage. Microseismic monitoring during waste injection can be acomplished using borehole or near-surface arrays to ensure that induced seismicity thresholds or limits set for Class II injection wells are not exceeded. Near-surface instrumentation may also be used to implement traffic-light systems to regulate induced seismicity.
Similar to CO2 sequestration, clients want to ensure containment of biowaste in the underground formation such as depleted oil and gas formations or salt caverns. A temporary, downhole microseismic monitoring solution was designed and implemented to ensure caprock integrity and observe the location of any events which may signify the vertical movement of gas or fluids from the formation.
The deep underground injection of biowaste helps to address the issue of CO2 emissions from municipal sewage sludge. Typical disposal methods of biowaste include land applications, composting or landfill disposal, where they degrade and release carbon dioxide into the atmosphere. Sequestering biowaste underground provides an ideal environment for the anaerobic breakdown of the material, resulting in the conversion of the organic material into carbon dioxide (dissolvable in the formation fluid) and the accumulation of methane gas. The methane gas can then be collected for use as an energy source.
In Carbon Capture and Sequestration (CCS) operations, carbon dioxide is captured from a power plant or industry source before being compressed. Compressed CO2 requires a much smaller storage volume. The carbon dioxide is then injected into deep geological formations with a sufficient overlying caprock layer to contain the gas within the formation. Deep saline formations are good candidates for CO2 sequestration, as well the use of CO2 in enhanced oil recovery requires the injection of CO2 into existing oil wells to help increase the production oil.
As a member of the Midwest Regional Carbon Sequestration Partnership (MRCSP) along with other industry, research and government collaborations, ESG works to develop high-value monitoring solutions to help organizations reduce their carbon emissions. ESG has provided microseismic monitoring services for carbon sequestration activities throughout North America. ESG’s temporary or permanent downhole sensor arrays (dual 3-component geophones) are installed and used to detect and map any microseismic events associated with carbon injections.
ESG differentiates itself from other companies who offer microseismic analysis based on our advanced understanding of microseismicity, and our ability to continuously develop new high-end data processing techniques.
Our focus on research and development means that we can develop new ways to interpret and understand microseismicity in reservoir applications. These advanced processing capabilities allow ESG to conduct a more in-depth analysis of the detected events and subsequently provide our clients with a better understanding of how to optimize their operations.
The corner stone of ESG’s advanced analysis capabilities for long-term reservoir monitoring applications is Seismic Moment Tensor Inversion. With this technique, ESG can use its patent-pending workflow to describe the mechanism of failure induced at the event source and distinguish whether the failure was due to tensile opening/closing or shear slip.
From this information, ESG is able to identify dominant fracture planes and construct a three-dimensional discrete fracture network (DFN) that defines the size, orientation and complexity of fracture generation, to evaluate trends and describe reservoir processes. Observation of failures with respect to pre-existing fracture and fault networks and the stress behavior in the reservoir can indicate whether fractures are fluid-induced or due to stress-transfer effects, and may provide insight into out-of-zone growth or seismicity near caprock barriers.
To date, ESG has installed over 500 permanent microseismic monitoring systems around the world for mining, oil and gas and geotechnical applications.
Specifically, ESG has deployed permanent life-of-field microseismic monitoring arrays for long-term reservoir monitoring applications, (some of which have been in operation for over a decade) in the heavy oil sands of northern Alberta, the diatomaceous oil fields in California and oil fields in the Middle East. ESG has also deployed RESMAP® systems for carbon sequestration, gas storage, geothermal and waste injection sites around the world.