PhD candidate at The National IOR Centre of Norway, Jaspreet Singh Sachdeva, defended his dissertation for the degree of PhD (philosophiae doctor) at the University of Stavanger Monday 20 April, 2020. That is, Jaspreet was actually at home in Bærum. The listeners followed the defence in their respective home offices.
The defence was in two parts, a trial lecture titled "Does chalk behave like rocks or soils, and when? A constitutive model review”. The actual defence had the title: «Impact of Wettability on Rock Mechanics and Oil Recovery».
Results of the PhD project
The main results of the research are summarised below:
- Aging leads to mixed wet state: 21 days aging time is required to attain a stable wettability for Kansas chalk type with the aging parameters defined in the study.
- Wettability affects elastic stiffness and plastic strength.
- Injection of reactive brines into chalk on volumetric creep rate: Induces chemical reactions leading to additional creep rates in both Kansas and Mons chalk types & comparable strain rate is attained at a creep stress of 1.5 times the yield stress at 130°C. These observations are insensitive to the initial wettability and hence oil and water saturations in the core.
- Geochemical effects are not affected by the presence of oil and the wetness of the core: Results from the water wet cores are applicable to reservoir systems. 6. No improved oil recovery observed due to compaction and/or non-equilibrium flow.
Implications for the industry
The implications of this research work on the petroleum industry are as follows: The experimental results on both Kansas and Mons outcrop chalks have shown that the compaction rates, during the injection of reactive brines, are independent of the initial wettability and hence the initial oil/water saturation in the cores. This has been further confirmed by the ion chromatography carried out on effluent samples. This shows that the oil present in the pore spaces do not obstruct and block the path of the brine injected during waterflooding to contact the grain-grain contacts. Hence, the results obtained from the wettability-altered cores are similar to those from water-wet cases. Therefore, it is concluded that the results from the water-wet cores obtained from the experimental studies carried out in the past three decades are applicable to the real reservoir systems. This is especially applicable to the chalk reservoirs that show close similarity to the Kansas chalk. It is further expected that deeply buried and more diagenetically overprinted chalks, such as Ekofisk and Valhall chalk reservoirs in the Norwegian Continental Shelf, are predicted to behave very similar to Kansas outcrop chalk.
The members of the Dissertation Committee were:
- Dr. Edvard Omdal, ConocoPhilips, Stavanger
- Professor Arne Graue, University of Bergen
- Helle F. Christensen, GEO, Copenhagen
- Professor Rune Time, University of Stavanger, Norway (administrator)
Anders Nermoen, NORCE and Merete Vadla Madland, Universitetet i Stavanger have been supervising Sachdeva.