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A TYPE-CURVE APPROACH FOR ANALYZING SHALLOW STRAIN DURING WELL TESTS
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  • Lawrence C. Murdoch,
  • Leonid N. Germanovich,
  • Soheil Roudini,
  • Scott DeWolf,
  • Liwei Hua,
  • Robert Moak
Lawrence C. Murdoch
Clemson University

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Leonid N. Germanovich
Georgia Tech
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Soheil Roudini
Clemson University
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Scott DeWolf
Clemson University
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Liwei Hua
Clemson University
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Robert Moak
Clemson University
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Abstract

Strains occur at shallow depths in response to pressure changes during well tests in an underlying aquifer, and recent developments in instrumentation have made it feasible to measure essentially the full strain tensor. Simulations using poroelastic analyses indicate that shallow normal strains are approximately proportional to the logarithm of time when a well is injecting into or pumping from a uniform aquifer or reservoir. The drawdown is also a function of log time, as shown by the classic Cooper-Jacob type-curve analysis. The time when the semi-log straight line intercepts the zero-strain axis is similar to the time determined from the Cooper-Jacob pressure analysis, and it can be used to estimate hydraulic diffusivity, suggesting that horizontal strain data can be used directly to estimate aquifer properties. This approach is applied to data measured with shallow (30 m) borehole strainmeters during an injection test at a 530-m-deep sandstone aquifer/reservoir in Oklahoma. The results show intercept times for the shallow normal strain data are essentially the same as for deep pressure data from an equivalent radial distance. The slopes of the semi-log plots of the pressure and the strain increase at the same time, suggesting that they both respond to a lateral aquifer boundary. These results confirm the type-curve approach for interpreting strain data. Significantly, though, strain was measured at shallow depths while the pressure data was measured at 530 m depth. This suggests that strain data from shallow depths could be an effective way to improve the characterization of an underlying aquifer.