Mechanisms of Injectivity Decline in Lower Jurassic Sandstones During Reinjection of Cooled Formation Brine: A Case Study from the Polish Lowlands

Łukasz Kłyż (), Krzysztof Nowak, Renata Cicha-Szot and Grzegorz Leśniak
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Łukasz Kłyż: Oil and Gas Institute—National Research Institute, 25A Lubicz Str., 31-503 Krakow, Poland
Krzysztof Nowak: Oil and Gas Institute—National Research Institute, 25A Lubicz Str., 31-503 Krakow, Poland
Renata Cicha-Szot: Oil and Gas Institute—National Research Institute, 25A Lubicz Str., 31-503 Krakow, Poland
Grzegorz Leśniak: Oil and Gas Institute—National Research Institute, 25A Lubicz Str., 31-503 Krakow, Poland

Energies, 2025, vol. 18, issue 21, 1-20

Abstract: The decline in the injectivity of injection wells is a serious problem in geothermal systems. In this article, we analyse the mechanisms responsible for the reduction in permeability in Lower Jurassic sandstones during the injection of cooled formation brine. Flow experiments were conducted on rock cores using three types of brines with varying degrees of contamination. The studies included microscopic analysis, scanning electron microscopy (SEM) and mercury intrusion capillary pressure (MICP) before and after the experiments. The results showed that the main factor in the decrease in permeability is the formation of a filter cake from secondary iron minerals on the front surface of the core. Filter cake formation was observed in all samples, with ferrous sediment penetrating to a maximum depth of 1.5 cm from the core front. In addition, the mobilisation of clay particles was observed, which accumulate in pore constrictions, causing additional flow restriction. Mercury porosimetry revealed significant increases in hysteresis values in the front zone (from 16.5 to 42%), indicating complex pore connectivity changes without substantial porosity reduction. The rate of injectivity decline correlates strongly with the fluid flow velocity. The results of the study provide a scientific basis for optimising reinjection processes in geothermal systems and developing strategies to prevent formation damage.

Keywords: injectivity decline; pore clogging; reinjection; geothermal doublet; fines mobilisation; formation damage (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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