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

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.

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.

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, wateflood recovery, electrical properties, NMR and relative permeability.

Approach Perform experimental measurements on static and dynamic properties such as, Φ, k, m, kr, Pc and wettability on a selected set of rock samples under different conditions mimicking representative formations. Quantification of the influence of wettability conditions on the dynamic and static properties. Use of the gathered data to perform detailed pore-scale modelling on the samples and comparison with conventional approach in reservoir simulation.

Approach Three main set of samples that will be studied, are: Sample Conditions Sandpack Water-wet Sandstone Oil-wet Carbonates Mixed-wet Fluids Brine (5% NaCl and 1% KCl) Oil (Multibar H)

Wettability Tendency of fluid to spread on a solid surface in the presence of other immiscible fluid. Wettability determination is important in reservoir characterization because it controls the distribution of the fluids in the reservoir and therefore the oil recovered. Water-wet Mixed-wet Oil-wet Rock Oil Brine

Wettability Measurement of Wettability: Direct Indirect Contact angle Relative Perm. USBM Capillary Press.

Phase 1 Sand pack – Water-wet Core Preparation Brine Preparation Conventional Core Analysis Special Core Analysis kr Pc Electrical Resistivity NMR

Relative Permeability Ability of the porous medium to conduct fluid flow when multiple fluid phases are present. Steady – State Method * Table and Graph (William Anderson, SPE, Conoco Inc.)

Relative Permeability - Procedure Clean Dry core 100% saturated with brine Measure ka for water Establish Swi by injecting 50 P.V. oil Establish Sor by injecting 50 P.V. brine Oil and Brine simultaneous circulation at given rates by two metering pumps (Having a stepwise decrease of the water fractional flow). Produced oil and brine are separated in graduated burette. 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

Capillary Pressure 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

Capillary Pressure Apparatus for Porous Plate Method:

Capillary Presure - Procedure Sw Swi Pc Water-wet Oil-wet Drainage Carmen-Kozney correlation to estimate pressure range. Put the core in the cell. Adjust the pressure and give the cell pressure difference. After three days, measure the volume and check if no more water is being produced. Calculate the water saturation corresponding to that pressure. 1 Increase the pressure in steps, and record the final equilibrium produced volume of the wetting phase at each step. Draw the Capillary Pressure vs. Sw

Electrical Resistivity When the rock is partially saturated with hydrocarbon, the resistivity of the rock is increased due to non-conductive properties of hydrocarbons. Wettability is an important factor for brine distribution, which contributes to the change of resistivity. Water-wet: brine is continuous, so the decrease of the cross-sectional area that can conduct flow will lead to the increase of resistivity. Oil-wet: brine is discontinuous, so the electrical resistivity will increase at a faster rate than in water-wet.

Electrical Resistivity Quadtech model 7600 RLC Frequency:10Hz-2MHz Pair of coaxial cables is used to connect the analyzer to two electrode conducting cell. Perform the frequency sweep.

NMR It is known that NMR resonance of fluids in the vicinity of solids can be quite different from that in bulk fluid. These effects are useful to the characterization of porous fluids and fluid distribution with NMR measurements.

NMR Oil Wet: Longer T2 peak value. Surface relaxitivity is smaller than WW. Water wet: T2 at Swi is wider than it is in OW.

Aging Procedure It is very important to establish a wettability condition as close as possible to that found in the reservoir

Aging procedure Fluid: Crude oil (Acid Number Measurements, J. Buckley) Technique: Core plug is saturated with brine Mount the core in the hasler cell Flood oil (at least 10 P.V.) to both ends of the core. Age the core in a crude oil at elevated temperature (for Sandpack 45 deg. C) Leave the core for 7 weeks. Flip and shake the core every ten days

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

Imperial College Analysis Using the 18 US Mesh defined as 1000 mm screen aperture Imperial College Analysis Sieve Size No. Sieve Opening ASTME II W1 W=3.0 kg t=1 hr W2 W=1.5 kg t=1 hr W3 W=1.5 kg t=1 hr W4 W=1.5 kg t=1 hr ΣW kg Ind Retained Cum Retained   mm g % 25 710 0.0 30 600 4 2 5 15 0.2 35 500 34 29 41 44 148 2.0 2.2 40 425 719 233 268 284 1504 20.0 22.2 45 355 1058 476 430 409 2373 31.6 53.8 50 300 732 428 371 358 1889 25.1 78.9 60 250 227 180 171 176 754 10.0 88.9 80 166 115 160 215 656 8.7 97.7 120 125 23 37 38 133 1.8 99.4 170 90 12 6 42 0.6 100.0 200 75 325 Total W 7.514 100.00 Saleh Al-Mansoori and Saif Alsayari

Sand Pack Core Plug

Conventional Analysis