System and method for monitoring strain & pressure

Abstract

A method for monitoring a well treatment, comprising the steps of installing at least one distributed acoustic strain sensor in at least one monitoring well, said monitoring well being a known distance from the treatment well, initiating a well treatment on the first well, monitoring the formation surrounding the monitoring well using the distributed acoustic strain sensor, and using the distributed acoustic strain sensor, detecting a change in strain at a first location in the monitoring well, using the change in strain to make determinations about the well treatment. The sensor may comprise a fiber optic cable. The change in strain may be used as an indicator that the effect of the well treatment has extended beyond a predetermined preferred treatment zone, the treatment may be a fracture treatment, and the well treatment may be controlled or ceased based on the determinations made in step e).

Description

RELATED APPLICATIONS[0001]The present case claims priority to U.S. provisional application Ser. No. 61 / 425,603, filed on 21 Dec. 2010, which is incorporated herein by reference in its entirety.TECHNICAL FIELD OF THE INVENTION[0002]The present disclosure relates generally to a system and a method for measuring strain and / or pressure in an underground formation.BACKGROUND OF THE INVENTION[0003]In oilfield operations there is a often need to measure changes in formation strain or pressure that occur as a result of well interventions such as hydraulic fracturing and fluid injection. These operations generally create high pressures in the formation, often leading to breakdown (fracturing) of the rock matrix, and will strain the formation in a volume surrounding the intervention. Measurement of this formation strain can be diagnostic of the effectiveness of the intervention and can lead to modification of the intervention parameters that can give significant economic benefit if the measur...

AI Technical Summary

Benefits of technology

[0010]The change in strain detected in step d) can be used as an indication that the effect of the well treatment has extended to or beyond the limit of a predetermined preferred treatment zone and the well treatment may be controlled or ceased based on the determinations made in step e). The present method can also be used to determine information about the formation between the first well and the monitoring well.

Problems solved by technology

These operations generally create high pressures in the formation, often leading to breakdown (fracturing) of the rock matrix, and will strain the formation in a volume surrounding the intervention.

Notwithstanding the foregoing, there is currently no in-situ method for measuring, in a volume around the treatment well and at an acceptable cost and accuracy, formation strain during well interventions.

Surface and vertical seismic profile (VSP) measurements can be used, but these are not accurate and require calibration, as they yield formation velocity as the raw measurement, which in turn needs to be converted into strain.

In principle, formation strainmeters could be deployed in a permanent installation outside of casing but this can be prohibitively expensive, especially if multiple wells and depth stations are targeted.

Furthermore, it is sometimes desirable to detect formation strain and / or pressure in a treatment well, which is difficult if not impossible using traditional pressure or strain gauges.

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