Water Weakening of Artificially Fractured Chalk, Fracture Modification and Mineral Precipitation during Water Injection—An Experimental Study

Tine Vigdel Bredal, Reidar Inge Korsnes, Udo Zimmermann, Mona Wetrhus Minde and Merete Vadla Madland
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Tine Vigdel Bredal: Department of Energy Resources, University of Stavanger, Ullandhaug, 4036 Stavanger, Norway
Reidar Inge Korsnes: Department of Energy Resources, University of Stavanger, Ullandhaug, 4036 Stavanger, Norway
Udo Zimmermann: Department of Energy Resources, University of Stavanger, Ullandhaug, 4036 Stavanger, Norway
Mona Wetrhus Minde: The National IOR Centre of Norway, University of Stavanger, Ullandhaug, 4036 Stavanger, Norway
Merete Vadla Madland: The National IOR Centre of Norway, University of Stavanger, Ullandhaug, 4036 Stavanger, Norway

Energies, 2022, vol. 15, issue 10, 1-23

Abstract: This experiment was designed to study the water-weakening effect of artificially fractured chalk caused by the injection of different compositions of brines under reservoir conditions replicating giant hydrocarbon reservoirs at the Norwegian Continental Shelf (NCS). NaCl, synthetic seawater (SSW), and MgCl 2, with same ionic strength, were used to flood triaxial cell tests for approximately two months. The chalk cores used in this experiment originate from the Mons basin, close to Obourg, Belgium (Saint Vast Formation, Upper Cretaceous). Three artificially fractured chalk cores had a drilled central hole parallel to the flooding direction to imitate fractured chalk with an aperture of 2.25 (±0.05) mm. Two additional unfractured cores from the same sample set were tested for comparison. The unfractured samples exposed a more rapid onset of the water-weakening effect than the artificially fractured samples, when surface active ions such as Ca 2 + , Mg 2 + and SO 4 2− were introduced. This instant increase was more prominent for SSW-flooded samples compared to MgCl 2 -flooded samples. The unfractured samples experienced axial strains of 1.12% and 1.49% caused by MgCl 2 and SSW, respectively. The artificially fractured cores injected by MgCl 2 and SSW exhibited a strain of 1.35% and 1.50%, while NaCl showed the least compaction, at 0.27%, as expected. Extrapolation of the creep curves suggested, however, that artificially fractured cores may show a weaker mechanical resilience than unfractured cores over time. The fracture aperture diameters were reduced by 84%, 76%, and 44% for the SSW, MgCl 2 , and NaCl tests, respectively. Permeable fractures are important for an effective oil production; however, constant modification through compaction, dissolution, and precipitation will complicate reservoir simulation models. An increased understanding of these processes can contribute to the smarter planning of fluid injection, which is a key factor for successful improved oil recovery. This is an approach to deciphering dynamic fracture behaviours.

Keywords: geo-mechanical compaction; water-weakening effect; artificial fracture; mineral dissolution; mineral precipitation; fracture modification; improved oil recovery (IOR) (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: 2022
References: View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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