The Effect of Wettability on Relative Permeability, Capillary Pressure, Electrical Resistivity and NMR

1. Benchmark Experiments on multiphase flow The Effect of Wettability on Relative Permeability, Capillary Pressure, Electrical Resistivity and NMR Saif AL-Sayari Prof. Martin Blunt

2. Experimental and network modelling studies have illustrated that, for a given sample, changes in wettability have a strong influence on relative permeability and oil recovery – in particular the work of Morrow and co-workers. • How do we characterise wettability at the pore scale? How can we relate this to macroscopic measurements? Can we use this information to predict relative permeability and oil recovery?.

3. Objective • Understanding the relationship between wettability and distribution of oil and water in pore space is a necessary step in the difficult problem of quantifying wettability and its effects on oil recovery. • Carry out a suite of experiments to obtain precise and accurate measurements of flow properties for a variety of rock samples with different wettabilities. • Compare with numerical predictions using pore-scale modelling.

4. Importance of this Project • Evaluation of the influence of contact angle and wettability on recovery are not very clearly discussed in the literature. These studies tend to focus on either experimental measurement of one property or simulation. • We propose to combine in one study the effects of wettability on multiphase flow parameters, looking at capillary pressure, relative permeability, electrical properties and NMR.

5. Approach • Perform experimental measurements on static and dynamic properties such as, Φ, k, FF, m, n, RI, kr, Pc and WI on a selected set of rock samples under different conditions, mimicking representative formations, to quantify the influence of wettability. • The data gathered will be used to validate and calibrate pore-scale modelling of the samples.

6. The main set of samples that will be studied, are: • SampleConditions • Sandpack Water-wet • Sandstone Oil-wet • Carbonates Mixed-wet • Fluids • Brine (5% NaCl and 1% KCl) • Oil (Isobar) Approach

7. Water-wet Mixed-wet Oil-wet Rock Oil Brine Wettability • The term “wetting” means liquid spreads or coats the solid surface and “non-wetting” means the liquid balls up and runs off the surface • Wettability controls the distribution of the fluids in the reservoir and therefore the oil recovered.

8. Wettability • Measurement of Wettability: • DirectIndirect • Contact angle Relative Perm. • USBM Capillary Press. • Amott index

9. Experimental work • Water-wet Samples • Conventional Core Analysis • Formation Factor • Nuclear Magnetic Resonance • Hg Injection Capillary Pressure • Pc by Porous Plate • Relative Permeability • Alteration of Wettability by aging in crude oil

10. Experimental work • Conventional Core analysis • Sandpacks: Synthetic sandpacks were chosen as the porous media because sandpacks are known to be quite homogeneous, and the wettability of the sandpacks can be controlled • Leavenseat LV 60

11. Experimental work • Conventional Core analysis • Sandpack samples

12. Experimental work • Conventional Core analysis • Fountainbleau Sandstone

13. Experimental work • Conventional Core analysis • Middle East Carbonates

14. Experimental work • Formation Factor with confining pressure • Sandpack Core 6 Core 7

15. Experimental work • Formation Factor with confining pressure • Fountainbleau Sandstone

16. Experimental work • NMR response • Sandpacks The peak around 20 ms relaxation time was due to presence of extremely small pores or bound water according to the CBVI (cutoff bulk volume of irreducible water) theory. The peak around 550 ms was generated by free water in the sandpack. Such a long T2 relaxation time corresponds to macropores in the sandpack.

17. Experimental work • Hg Injection Capillary Pressure • Fountainbleau Sandstone

18. Experimental work • Capillary pressure Porous Plate • When oil and water are placed together on a surface, a discontinuity in pressure exists across the interface separating them. This difference in pressure in known as Capillary Pressure • The rise and fall of fluid in capillary tubes is mainly due to the surface tension and wetting preferences

19. Experimental work • Capillary pressure by Porous Plate

20. Experimental work • Capillary pressure Porous Plate • The drainage of clean, water-saturated cores with oil or gas simulates the migration of oil or gas in a water-saturated reservoir • A step-wise pressure difference is established between the two phases in the core, and the saturation is determined by equilibrium at each step.

21. Experimental work • Relative Permeability Steady State method • Relative permeability data are essential for making engineering estimates of productivity, injectivity and ultimate recovery from reservoirs for evaluation and planning of production operations. These data are unquestionably one of the most important sets required in reservoir simulation studies.

22. Experimental work • Relative Permeability Steady State method • Two or three fluids are injected simultaneously at fixed rates until equilibrium is reached. The core saturation is measured at each equilibrium point and then a new ratio of injection rates is applied. Darcy’s law is used to obtain the effective permeability for each phase. Steady-state condition is determined to be established for each step of flow by continuous monitoring of the level of oil/brine interface in the burette and the pressure drop across the core

23. Experimental work • Aging with crude oil • Crude oil will be used to alter the wettability from strongly water-wet to mixed-wet and to oil-wet • Acid number measurements will be performed using the well known J. Buckley’s procedure Idealized triangular pore after primary drainage. The areas directly contacted by oil (bold line) have an altered wettability, whereas the corners that are full of water remain water-wet

24. Pore scale modelling • Characterizing wettability from a pore-scale point of view and then validate these predictions with experimental data. • NMR responses were simulated for the micro-CT images that were obtained by scanning two sandpacks (Leavenseat LV60 and Ottawa F42). The results were compared with experimental data and also with simulation results obtained from the network extracted from the Micro-CT images (Collaboration with Olumide Talabi). Ottawa F-42

25. Pore scale modelling • Comparing the NMR response measured experimentally with the NMR from pore-scale modelling and Micro-CT scanning (Collabration with Olumide Talabi). Leavenseat LV-60

26. Conclusion • Wettability affects all petrophysical properties of a reservoir since it controls fluid location, flow and distribution in a porous medium. • Knowledge of reservoir wettability is critical for many reasons ranging from oil migration from source rock to enhanced oil recovery. Therefore, proper understanding of reservoir wettability is crucial for determining the most efficient means of oil recovery. • Determination of reservoir wettability and its influence on petrophysical properties has been known to be a very challenging and complicated procedure despite the huge amount of work in this area. Many questions still remain unanswered. This fact is very well supported by the conflicting results of many researchers on the influence of wettability on petrophysical properties.

27. Benchmark Experiments on multiphase flow The Effect of Wettability on Relative Permeability, Capillary Pressure, Electrical Resistivity and NMR Saif AL-Sayari Prof. Martin Blunt