The objective of this work is to investigate, develop, and demonstrate the direct link between wellbore casing strain / deformation measurements, and sealed well pressure responses. The paper presents new laboratory experiments for casing deformation that tie directly to wellbore deformation during hydraulic fracturing and to subsequent pressure increases caused by intersections of fractures with horizontal wellbores. We show that wellbore strain measurements can be combined with surface wellbore pressure measurements to diagnose fracture intersection and estimate geometry and growth rates.

A casing strain experiment was set up to measure wellbore deformation caused by loads that are encountered during fracture intersection. Multiple strain gauges were installed on a joint of 5.5" P110 casing radially and longitudinally, as well as azimuthally around the pipe. A load frame was utilized to stress the casing at various points along the pipe to develop relationships between load, strain, and deformation. Analytical models were deployed to compute the expected casing strain for thick-wall pipes and were compared to our laboratory measurements. Numerical modeling was performed to simulate the casing strain response and the induced pressure change at the surface as hydraulic fractures approach and intersect the wellbore.

The results of the laboratory measurements of azimuthal casing strain agree well with fully coupled 3D numerical modeling. Sealed wellbore pressure responses calculated from the magnitude of these deformations agree well with the actual field responses. This work now allows us to relate the sealed well response to a quantifiable fracture geometry and region of deformation along the casing. Strain profiles from deformation are developed and allow a direct coupling of volume change in the wellbore due to fracture arrivals. We display the various fracture properties required to generate the observed field responses (0.1-10 psi order of magnitude). Additionally, Sealed Wellbore Pressure Monitoring (SWPM) field data is reported, interpreted and explained with the help of our experimental data and numerical simulations.

This work deploys first of its kind measurements to enhance the interpretation of a sealed well pressure response during fracturing. The additional knowledge of wellbore strain and deformation together with surface pressure responses is a major leap forward in further understanding the full utility of downhole strain and casing ovality responses as a diagnostic. This work sets the stage for using physical wellbore deformation as a key, low-cost fracture diagnostic method and opens up a new category of diagnostic technologies for the industry based on integrating surface pressure and downhole strain measurements.

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