Retrievable vs. Permanent Installations

When deciding how to deploy downhole passive seismic arrays, one important factor to consider is whether the array will be retrievable or whether it will be cemented in place.  There are benefits to each method and a variety of options exist for operators to choose from.

Retrievable Arrays

Retrievable arrays are often preferred by operators for short-duration monitoring programs, or in instances where the wellbore housing the monitoring array needs to be accessible at a later date.  A number of options are available for retrievable arrays.

Wireline Deployment

Retrievable wireline deployment for microseismicShort duration monitoring programs lasting days to weeks (such as hydraulic fracture monitoring) typically use wireline deployments.  Arrays of microseismic sensors (15 Hz geophones) are installed in monitoring wells using either fiber optic or 7 conductor wireline cable.  Sensors are coupled to the well casing using high performance magnets or clamp arms.  Tractors may be used to position sensor arrays in horizontal wells, while gravity is used to position sensor arrays in vertical wells.  Wireline deployment is well established in the oil and gas industry, however can become expensive for longer durations.

Innovative wireline deployment methods include ESG's Whip-array®, which links two separate sensor arrays for simultaneous deployment in the horizontal leg and vertical section of a well.  The Whip-array provides improved detection ranges and event location accuracy, and offers opportunities for advanced multi-array microseismic monitoring.

SuperCable™

Retrievable supercable deployment for microseismicESG's SuperCable™ deployment is a unique option for longer-duration retrievable monitoring. Built on ESG’s experience in downhole microseismic monitoring solutions, ESG’s innovative SuperCable™ deployment strategy provides longer-term retrievable borehole acquisition at lower cost than traditional wireline-based acquisition equipment. The method deploys arrays of 15 Hz geophones with opportunities to customize arrays to incorporate other sensor types if required.

For short duration projects such as hydraulic fracture stimulations, wireline deployment is the accepted method for temporary downhole microseismic monitoring.  Unfortunately, conventional wireline tools are typically not designed for extended deployment periods and as a result, the equipment becomes too costly over longer durations.  For long-term reservoir monitoring, many operators choose to deploy permanent systems.  The SuperCable™ represents an innovative monitoring solution that offers the flexibility of temporary wireline deployment, with the performance and cost benefit of long-term monitoring systems. 

The SuperCable employs either a skid- or container mounted winch assembly, or the use of a wireline truck along with a crane.  ESG’s robust sensors are coupled to the side of the well using custom magnets. The magnets used to couple the sensors to the well provide better vector fidelity than bow springs and are comparable in performance to cemented permanent solutions. The array can also be removed and re-deployed in another well on-site in the future.

Bowspring or Magnetic Coupling

Retrievable bowspring deployment for microseismicESG designs and manufactures its own downhole sensor arrays with retrievable bowspring or magnetic coupling.  Bowspring arrays are custom designed to be deployed on most sizes of production tubing, such as coiled tubing, while magnetic arrays are an option for cased wells with good cement fidelity.  Sensors are positioned within the bowspring frame, which is then compressed as it is deployed in a well.  The bowspring exerts outward force on the inside of the well casing to provide good coupling for the sensors.  Sensor pods consisting of 4.5 or 15 Hz geophones and/or force balanced accelerometers (FBAs) are custom-built to meet client specifications.

Permanent Arrays

Permanent arrays are often preferred for long-term monitoring programs (spanning years rather than weeks) and offer the benefit of excellent sensor coupling to the wellbore.  Cementing sensor arrays in place is also a cost-effective solution for operators over long durations, when compared to wireline-based deployments.  ESG designs and manufactures its own downhole arrays for permanent installation.  Sensor pods consisting of 4.5 or 15 Hz geophones and/or force balanced accelerometers (FBAs) are custom-built to meet client specifications on analog cable for deployment in vertical or deviated wells on rigid tubing. 

 

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