1. New perspectives on ionic control of produced water and low sulphate seawater: Wettability insights from MFT
Average water-wet fraction presented by Dan Chalk (DnK) aged with Ekofisk Formation Water and various Smart brines at a constant temperature of 115ºC. The error bars represent the standard deviation of the experimental data in percent. Adapted from Godinho, 2017.
E. DOS SANTOS GODINHO1, A. SOHAL 1, K. STEFFENSEN 1, G. THYNE 1 and E. G. SØGAARD1
1) Department of Chemistry and Bioscience, Aalborg University, Esbjerg, Denmark
Introduction
The oil price downturn and its slow and fragile recovery have induced the necessity of new and cost-efficient enhanced oil recovery (EOR) methods that will favour the oil recovery optimization from the existing fields.
Reservoir water flooding is frequently applied at a secondary recovery stage for pressure maintenance, after primary recovery to overcome reservoir subsidence problems. However, this process is normally inefficient leaving 45% of the original oil in place unrecovered (Thomas, 2008).
Modified flotation technique (MFT) is a fast and reliable technique to estimate the wettability of reservoir rocks. This method can be of use to determine the wettability state if the reservoir is subjected to interaction with different brines (s.l.).
Results
Chalk Wettability: chemical composition dependency
Advanced Waterflooding
Component [mass %]
Dan Chalk 1
Dan Chalk 2
CaO
95.3
92.20
MgO -
0.85
Al2O3
0.44
0.52
SiO2
3.30
5.19
P2O5
0.35
0.32
K2O
0.13
0.12
SrO
0.43
0.36
Fe2O3
SO3
0.06 Cl
0.01
0.02
Total
100.02
99.95
Injection fluid: Ekofisk Formation Water (20%) + Advanced brine (80%)
Objective
To search the optimal injection fluid composition to be used in ionically modified water flooding. In this work the goal is to seek further use for produced water, which has been mixed with low sulphate seawater and synthetic seawater  Increase the reservoir water wetness.
Table 1 Dan Chalk 1 and Dan Chalk 2 chemical composition provided by XRF analysis (Godinho, 2017; Steffensen, 2018).
Figure 3 Average water-wet fraction presented by Dan Chalk (DnK) aged with Ekofisk Formation Water (EFW) and smart brines (mixture of produced water (PW) and low sulphate seawater (LSSW) at a constant temperature of 115°C. The error bars represent the standard deviation of the experimental data in percent. Adapted from Godinho (2017).
Figure 2 Flotation Wettability Index (FWI) or Wetting Index presented by Dan Chalk 1 (DnK) and Dan Chalk 2 (UnK) if subjected to the same experimental conditions. Constant Temperature of 115°C. Adapted from Godinho (2017).
Conclusions
Microvariations and chalk heterogeneities can lead up to 15% difference in wettability estimations;
The injection fluid composition shall be designed accounting for the singularities of the each crude oil-brine (s.l.)-rock system;
Potential determining ions (PDIs), especially Ca2+ and Mg2+ , and Potential scale forming ions (PSFIs) have shown to play an important role regarding the wettability modification of Dan chalk and Unknown Chalk.
References
Donaldson, E.C. and Alam, W. [2008] Wettability. Gulf Publishing Company, 336pp, ISBN:
Godinho, E.S. [2017] Effectiveness of Produced Water in Advanced Waterflooding. Unpublished Semester Report in Enhanced Oil Recovery. Aalborg University.
Sohal, M.A.N., Godinho, E., Thyne, G., Steffensen, K. and Søgaard, E. G. [2017] Effect of temperature and potential ions on North Sea chalk wettability. DHRTC conference 2017, Kolding, Denmark.
Sohal, M. A. N. [2016] Wettability Modification in Chalk: Systematic Evaluation of Salinity, Brine Composition and Temperature Effects. PhD Thesis. Aalborg University. DOI: /vbn.phd.engsci
Steffensen, K. B. [2018] Optimization of Injection Fluids with Scope of Reservoir Wettability. Unpublished Master Thesis. Aalborg University.
Thomas, S. [2008] Enhanced Oil Recovery – An Overview. Oil & Gas Science and Technology – Rev. IFP 2008, 63 (1), 9-19.
Zhang, P., Tweheyo, M.T., Austad, T. [2006] Wettability Alteration and Improved Oil Recovery in Chalk: The Effect of Calcium in the Presence of Sulfate. Energy & Fuels, 20,
Method
CONTACT INFORMATION
Erica Godinho: Erik Søgaard:
Figure 1 Modified Flotation Technique (MFT) schematic and process based on Sohal, (2016). The MFT diagram depicts all the stages encompassed by the method. Blue drop shape represents the addition of synthetic Ekofisk Formation water and the brown drop shape represents the addition of crude oil. Oven temperature is 115˚C. Adapted from Godinho, (2017).