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Diagnosing apparent hydraulic memory in pressurized slug tests with a lagging theory framework.

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Bibliographic Details
Title:	Diagnosing apparent hydraulic memory in pressurized slug tests with a lagging theory framework.
Authors:	Lin, Ying-Fan¹ (AUTHOR) yflin1110@cycu.edu.tw, Cheng, Li-Chen¹ (AUTHOR)
Source:	Advances in Water Resources. Sep2026, Vol. 215, pN.PAG-N.PAG. 1p.
Subjects:	Hydraulic models, Analytical solutions, Aquifers, Parameter estimation, Multilevel models
Abstract:	Pressurized slug tests often contain recovery structures that classical instantaneous flow models do not fully represent. These structures can also reflect wellbore storage, release procedure, pressure amplitude, support scale, and model nonuniqueness. This study develops an observation to memory transformation framework for diagnosing apparent hydraulic memory rather than treating fitted delay times as unique aquifer constants. A new radial analytical solution embeds lagging theory within the classical state factor form and introduces separate response times for flux memory and hydraulic gradient memory. The solution reduces to the classical response when lag effects vanish. We evaluated the framework with tabulated Minnelusa aquifer slug test records from three wells near Spearfish, South Dakota. The analysis combined classical and lagging theory formulations, deterministic fitting, Bayesian posterior sampling, residual diagnostics at the response scale, validation by pressure blocks, posterior principal component analysis, and a hierarchical model for pressure dependent repeated tests in one well. The lagging theory formulation reduced structured residuals, and posterior diagnostics showed that inferred delay times behave as apparent response descriptors tied to test conditions. Repeated partial release tests at one well supported a comparatively stable shared apparent memory interpretation, whereas repeated pressure amplitude tests at another well produced pressure dependent apparent memory. In the well tested at multiple pressures, the median flux memory response time increased from 2.50 s at 5 psi to 61.7 s at 30 psi, and the apparent memory length increased from 54 m to 264 m. Validation by pressure blocks improved the mean error for the withheld pressure from 0.134 for the classical formulation and 0.128 for the shared lagging formulation to 0.093 for the pressure trend formulation. Pressurized slug tests can therefore screen for systematic nonclassical recovery behavior and classify apparent delay behavior; material interpretation requires independent constraints on wellbore response, support scale, and pressure dependent behavior around the well. • A radial lagging theory solution extends classical state factor analysis of slug tests. • Transformation diagnostics separate improved curve fit from identifiable memory. • Block validation and hierarchical shrinkage classify pressure dependent apparent memory. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	Pressurized slug tests often contain recovery structures that classical instantaneous flow models do not fully represent. These structures can also reflect wellbore storage, release procedure, pressure amplitude, support scale, and model nonuniqueness. This study develops an observation to memory transformation framework for diagnosing apparent hydraulic memory rather than treating fitted delay times as unique aquifer constants. A new radial analytical solution embeds lagging theory within the classical state factor form and introduces separate response times for flux memory and hydraulic gradient memory. The solution reduces to the classical response when lag effects vanish. We evaluated the framework with tabulated Minnelusa aquifer slug test records from three wells near Spearfish, South Dakota. The analysis combined classical and lagging theory formulations, deterministic fitting, Bayesian posterior sampling, residual diagnostics at the response scale, validation by pressure blocks, posterior principal component analysis, and a hierarchical model for pressure dependent repeated tests in one well. The lagging theory formulation reduced structured residuals, and posterior diagnostics showed that inferred delay times behave as apparent response descriptors tied to test conditions. Repeated partial release tests at one well supported a comparatively stable shared apparent memory interpretation, whereas repeated pressure amplitude tests at another well produced pressure dependent apparent memory. In the well tested at multiple pressures, the median flux memory response time increased from 2.50 s at 5 psi to 61.7 s at 30 psi, and the apparent memory length increased from 54 m to 264 m. Validation by pressure blocks improved the mean error for the withheld pressure from 0.134 for the classical formulation and 0.128 for the shared lagging formulation to 0.093 for the pressure trend formulation. Pressurized slug tests can therefore screen for systematic nonclassical recovery behavior and classify apparent delay behavior; material interpretation requires independent constraints on wellbore response, support scale, and pressure dependent behavior around the well. • A radial lagging theory solution extends classical state factor analysis of slug tests. • Transformation diagnostics separate improved curve fit from identifiable memory. • Block validation and hierarchical shrinkage classify pressure dependent apparent memory. [ABSTRACT FROM AUTHOR]
ISSN:	03091708
DOI:	10.1016/j.advwatres.2026.105381