Investigating the Effect of the Temperature and Pressure on Wettability

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Investigating the Effect of Temperature and Pressure on Wettability in Crude oil-Brine-Rock Systems Yongchao Zhang, Jianhui Zeng, Juncheng Qiao, Xiao Feng, and Yuyang Dong Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01404 • Publication Date (Web): 27 Aug 2018 Downloaded from http://pubs.acs.org on August 28, 2018

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Energy & Fuels

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Investigating the Effect of Temperature and Pressure on Wettability in Crude

2

oil-Brine-Rock Systems

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Yongchao Zhang†, ‡, ⁋, Jianhui Zeng*, †, ‡, Juncheng Qiao†, ‡, Xiao Feng†, ‡, and Yuyang Dong†, ‡

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†State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, PR China

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‡ College of Geosciences, China University of Petroleum, Beijing 102249, PR China

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⁋ Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK

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ABSTRACT Wettability is a key parameter that affects the petrophysical properties of reservoir

10

formations. The objective of the present work is to investigate the influence of temperature and

11

pressure on the wettability in crude oil-brine-rock (COBR) systems. By using a captive droplet

12

method, the contact angle results of seven minerals and two rock core samples over a range of

13

pressures and temperatures are reported. The data show that raising the pressure from 10 MPa to

14

70 MPa has no discernible effect on the contact angle regardless of mineral type. However, the

15

effect of temperature on the contact angle depends on the primary wettability types of the

16

minerals. For water-wet mineral surfaces, the temperature has a notable impact on the measured

17

contact angles, i.e., the contact angle decreases with increasing temperature; but for neutral-wet

18

or oil-wet samples, the influence of temperature on the measured contact angles is relatively

19

weak. To explain the behaviors of the wettability as a function of temperature, a mathematical

20

calculation is completed based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The

21

calculation results show good consistency with the experimental measurements.

22

Keywords: Physical experiment; temperature; pressure; wettability; contact angle; DLVO theory

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1. INTRODUCTION Wettability is defined as “the tendency of one fluid to adhere to a solid surface in the

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presence of other immiscible fluids” 1, 2. The knowledge of wettability is very important for

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many aspects in the petroleum industry, including estimation of oil reserves, prediction of

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production performance, and implementation of enhanced oil recovery (EOR) methods 3, 4.

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Under oil reservoir conditions, studies of wettability have focused on a crude oil-brine-rock

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(COBR) system. Changes in the wettability of the rock surface affect the microscopic

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distribution of formation liquid at the pore scale, which in turn affects the displacement process

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and relative permeability characteristics 5-7. It has been clearly shown that the wettability

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characteristics of reservoirs depend on several factors including oil composition, brine

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composition, pH, temperature and pressure 8-10.

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1.1 The effect of pressure and temperature on wettability Typically, it is assumed that the temperature may significantly affect the wettability

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performance on rock surfaces, and the pressure dependence of the wettability is relatively weak 2,

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11, 12

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studies show different viewpoints. Some researchers 13-15 reported experimentally that the

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wettability of a rock surface became more water-wet with increasing temperature. In contrast,

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other researchers 16-20 assumed the wettability would change towards oil-wet rather than water-

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wet with increasing temperature. In addition, some investigators believed that the changes in the

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wettability with temperature were not simply oil-wet-towards or water-wet-towards. For example,

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Wang and Gupta 12 and Rao 21 shared the same viewpoint that sandstones tended to become more

22

oil-wet with increasing temperature, while most carbonates tended to show water-wet behavior.

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Escrochi et al. 22 experimentally showed that the wettability of Berea sandstone was altered to be

. However, regarding the specific variation in the wettability with temperature, existing

2


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strongly oil-wet within a temperature window of 150 to 400 °C but was subsequently restored its

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original water-wetness with a further increase in temperature. In recent studies, Lu et al. 11 and

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Alotaibi et al. 23 reported that the observed changes in the wettability with temperature depended

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on several factors including the brine composition, salinity, and mineral composition of the

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system studied.

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In addition, controversy exists in the literature concerning the changes in the wettability

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with pressure. Most investigators believe that wettability is not sensitive to pressure conditions,

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and several studies have claimed a decreasing trend in the contact angles (a common method of

9

quantifying the wettability property) with increasing pressure 12, 18. This effect is also the reason

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why the pressure condition is also considered in our experimental design. In general, the literature review reveals that the mechanisms of wettability changes with

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temperature and pressure remain in question. Most previous studies have reported only the

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observed trends without sufficient explanations provided. There have been no previous studies

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addressing the roles of temperature and pressure on wettability in a systematic manner.

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1.2 DLVO Theory

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Several theories have been utilized for interpreting the wettability performance and its

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controlling factors, which includes the molecular kinetic theory 24, 25, hydrodynamic theory 26,

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and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory 27-29. The DLVO theory was

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developed to explain the interactions between colloidal particles and their aggregation behaviors.

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Some researchers have applied this theory to study the phase interactions and surface energies in

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a hydrocarbon-brine-rock system 30-34. Hirasaki 35 developed a calculation model based on the

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DLVO theory and the augmented Laplace-Young equation to determine the stable and 3


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metastable film-thickness profiles at three-phase contact regions. The interdependence of the

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spreading, contact angle and the capillary pressure was studied in Hirasaki’s research. Schembre

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et al. 36 experimentally studied the wettability alteration as a function of temperature. In their

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work, the DLVO theory was developed for calculations of fines stability and the wettability of

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silica surfaces. In Chaturvedi et al.’s research 37, the wettability of coal was investigated at scales

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that ranges from the microscopic to the core. The microscopic wettability was evaluated based

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on the DLVO theory. The estimates of the contact angles suggest a trend that goes through a

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maximum at a pH approximately 4. The core-scale wetness obtained from the imbibition

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experiments shows similar trends as those predicted at the pore scale. Sadeqi-Moqadam et al. 38

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predicted the contact angle, the work of adhesion, and the stability of a wetting film on rock

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surfaces using different calculation models based on the DLVO theory and the augmented

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Laplace-Young equation. In Sadeqi-Moqadam et al.’s work, different factors and their

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importance of improving the predicted results were thoroughly investigated. However, seen from

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the published literature, two problems relating to the DLVO calculations of wettability in the

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COBR system are still unsolved. (1) The obtained experimental results do not always favor the

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calculation predictions 25. (2) An integrated framework of the combined experiments and

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theoretical calculations has been rarely reported.

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The aim of the present work is to investigate the effects of temperature and pressure on the

19

wettability in COBR systems. To achieve this goal, a set of experiments and a DLVO calculation

20

are conducted systematically. The paper is organized as follows. In Section 2, we present our

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experimental materials and methods. Section 3 is devoted to a presentation of the experimental

22

results. In Section 4, an attempt is made using a mathematical model based on the DLVO theory

23

to explain the observed experimental results. Concluding remarks are presented in Section 5. 4


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2. MATERIALS AND METHODS

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2.1 Materials

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The oil sample was taken from the Chang 7 member of the Yanchang formation in the Ordos

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basin, a typical tight-oil reservoir in China. Before the experiments, a filtration procedure was

5

made to ensure that there was no sand nor other solid deposits remaining in the oil samples. The

6

properties of the oil sample are listed in Table 1. Seven different types of minerals and two rock

7

core samples were used as the rock substrates in the experiments. The two rock core samples are

8

a sandstone core and a carbonate core, whose mineralogy compositions are given in Table 2. The

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seven single minerals with high purity (more than 98 % based on X-ray diffraction analysis)

10

included calcite, dolomite, illite, chlorite, feldspar, smectite, and quartz. Synthetic brine was

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prepared as the aqueous phase based on the geochemical analysis of the produced water from

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Yanchang formation, whose property is shown in Table 3.

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Table 1

14

Table 2

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Table 3

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2.2 Contact Angle Measurements

17

Fig. 1

18

Fig. 2

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The experimental apparatus used in this work is DSA-100HP from KRÜSS GmbH,

20

Germany (Fig. 1). The DSA100HP combines a drop shape analyzer (DSA100) for contact angle

21

analysis with a high-quality measuring cell for high-pressure and high-temperature applications. 5


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A schematic diagram of the apparatus is shown in Fig. 2. The experimental apparatus consists of

2

a rock sample holder, a pressure and temperature sealed cell, pressure and temperature control

3

system (injection pumps, oil storage cylinder, water tanks, thermostat, and regulators), and data

4

acquisition and processing system (camera, light source, and computer). In Fig. 2, injection

5

pump 1 is used for oil injection during the test; and injection pump 2 is used for injecting brine

6

and controlling the confining pressure of the cell. The temperature of the measuring cell is

7

controlled by a thermostat connected to the cell. The experimental parameters are orthogonally

8

designed to ensure that the two specified parameters (pressure and temperature) can be estimated

9

independent of each other. The designed pressure measurements increase from 10 MPa to 70

10 11

MPa, and the temperature measurements increase from 35 °C to 110 °C. Specific experimental procedures for the contact angle measurements under different

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temperature and pressure conditions are given as follows.

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(1) To avoid unwanted remaining impurities influencing the measurements, the high-pressure

14

and high-temperature cell and oil-flow lines (lines used for oil injection) are cleaned with toluene

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first, then followed by methanol. The water-flow lines (lines used for brine injection) are flushed

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with ethanol first, followed by synthetic brine. At least 10 pore volumes of liquid are used for the

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cleaning or flushing procedures.

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(2) The seven mineral samples and two rock core samples from hydrocarbons are cleaned using

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Soxhlet extraction method 10. Afterward, the samples are heated in the oven at 120 °C for 72 h.

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(3) The samples are cut into substrates with the diameter of Φ 2.5 cm × 0.2 cm. One side of each

21

substrate is polished with aluminum oxide powders with a particle size of 0.25 µm to minimize

6


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the effect of surface roughness on the measurements. Polishing is terminated with brine rinsing

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and ultrasonic cleaning 39. The samples are heated in the oven at 120 °C for 72 h.

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(4) The mineral substrates are submerged in the oil sample for aging. The aging time and

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temperature are 7 days and 60 °C, respectively 40, 41. After aging, the substrates are cleaned with

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synthetic brine and are submerged into the synthetic brine for 48 h.

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(6) A substrate is placed on the sample holder. The cell is filled with synthetic brine using

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injection pump 2. An oil droplet is deposited on the polished surface of the substrate by

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controlling the injection needle vertically up or down. The volume of the oil droplet is 10 µL.

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The temperature and pressure condition of the cell is set at a designed value (35 °C and 10 MPa

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for the first measurement).

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(7) The pressure is raised from 10 MPa to 70 MPa in steps by injecting brine into the cell. For

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each pressure measurement, the system is left for at least three hours to ensure that the

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mineral/brine/oil interfaces reach equilibrium. Three hours later, the images of static contact

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angle are captured and recorded. The captured images are analyzed to obtain the contact angle

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values using ADVANCE software by fitting the oil drop profile to the Young-Laplace equation.

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(8) The substrate is held within the cell, and the measurement temperature is increased

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incrementally. Step (7) is repeated until all the tests were finished.

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(9) Steps (6) - (8) are repeated on the other samples.

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2.3 Limitations of the measurements

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For a better comparison with other works, the limitations of the experiments are addressed

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before analyses. First, all the measured contact angles are static contact angles. For the studies

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under reservoir conditions, the dynamic contact angle (advancing and receding contact angle) 7


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may be more reliable and representative 42. However, limited by the experimental apparatus,

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measurements of the dynamic contact angles under high-temperature (up to 110 °C) and high-

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pressure (up to 70 MPa) conditions are very difficult. The surface roughness and surface

4

contamination, respectively, have a dramatic impact on the measured contact angle values. To

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reduce the impact of the surface roughness on the results, different experimental polishing

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procedures have been utilized for substrate preparation in literature. These procedures include

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the use of carborundum powder 43, abrasive paper 44, alumina powder 39, etc. Drelich et al. 45

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experimentally studied the effect that different polishing approaches produce on the contact

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angle measurements. The necessity for the removal of alumina particles from the sample surface

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after alumina powder polishing was also recognized in Drelich et al.’s research. In our work, the

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samples were polished and cleaned according to the procedure of Drelich et al. before being used

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for contact angle measurement. To eliminate the effect of some systematic errors on the results,

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all the nine samples were polished and cleaned in the same manner. Furthermore, in the field of

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surface chemistry, surface cleaning is important to reduce the impact of surface contamination on

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wettability determination. Surface cleaning methods using different chemical reagents and

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techniques can be found in the literature 46-48. These cleaning procedures guarantee highly

17

accurate and reproducible results for contact angle measurements. However, the main aim of the

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contact angle measurements in our work is to study the wettability behaviors after oil aging as a

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function of temperature and pressure using different rock samples. Thus, a simple surface

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cleaning procedure of synthetic brine rinse and submersion was conducted after oil aging. This

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simple procedure was probably sufficient to clean the surface properly for our research.

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3. EXPERIMENTAL RESULTS

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Energy & Fuels

In this study, the dependence of the wettability on pressure and temperature is explained

2

according to the contact angle results from experiments. In the petroleum industry, contact

3

angles in a range of 0° to 75° are considered water-wet, angles of 75° to 105° are referred to as

4

neutral-wet and angles of 105° to 180° are considered oil-wet 9. Based on the measured results, it

5

can be calculated that the average contact angles of the samples, as shown in Fig. 3-i to 3-ix, are

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34.75°, 117.11°, 105.57°, 87.42°, 57.70°, 56.86°, 42.80°, 84.78°, and 33.46°, respectively.

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According to the petroleum industry standards, sandstone, illite, chlorite, feldspar and quartz can

8

be considered water-wet minerals; carbonate and calcite are oil-wet minerals; the remaining

9

dolomite, smectite are neutral-wet minerals.

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3.1 The effect of pressure on the surface wettability

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Fig. 3

12

Fig. 3 illustrates the effect of pressure on the measured contact angles. Figs. 3-i to 3-ix show

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the contact angle results for sandstone core sample, carbonate core sample, calcite, dolomite,

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illite, chlorite, feldspar, smectite, and quartz, respectively. From Fig. 3, contact angles of all the

15

samples show minor changes with the increase of pressure. The variations of contact angles

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within a pressure window of 10 MPa – 70 MPa are 2.0°, 2.0°, 3.0°, 1.0°, 2.5°, 1.5°, 3.0°, 1.5°,

17

and 1° from Fig. 3-i to 3-ix, respectively. Compared with reported experimental results in other

18

works 4, 49, it can be concluded that the surrounding pressure has no discernible effect on the

19

measured contact angles, regardless of mineral type.

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3.2 The effect of temperature on the surface wettability

21

Fig. 4

9


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Fig. 4 shows the effect of temperature on the measured contact angles. The results show that

2

temperature has a noticeable impact on the measured contact angles but with different

3

characteristics for different samples. In Figs. 4-i, 4-vii and 4-ix, the contact angles of sandstone,

4

feldspar, and quartz show obvious decreasing trends with the increase of temperature; and the

5

variations of contact angles are 11°, 8°, and 9°, respectively, in a temperature range of 35 °C -

6

110 °C. In Figs. 4-ii, 4-iv, 4-vi, 4-viii, the measured contact angles of the samples (carbonate,

7

dolomite, chlorite, and smectite) remain fairly constant with increasing temperature. Even though

8

an overall decreasing trend with temperature can be found for carbonate, the variation in the

9

contact angle against the carbonate surface is much less than the others. Therefore, the contact

10

angle variation in carbonate is considered constant here. In Fig. 4-iii and Fig. 4-v, the measured

11

contact angles of calcite and illite, respectively, decrease with temperature first. A further

12

increase in temperature induces the contact angles to restore their original values. The contact

13

angle variations of calcite and illite are 5° and 4°, respectively.

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In brief, the trends of the contact angles as a function of temperature are different for

15

different samples. However, when the wetting preferences are brought into consideration, a

16

general conclusion covering all the variational features can be reached. That is, for water-wet

17

minerals, the temperature has a notable impact on the measured contact angles, i.e., the contact

18

angle decreases with the increasing temperature; however, for neutral-wet or oil-wet samples, the

19

temperature dependence of the contact angles is relatively weak.

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4. DLVO CALCULATIONS AND DISCUSSION

21 22

To explain the observed trends of the measured contact angles with temperature, a calculation model was built based on DLVO theory.

10


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4.1 Calculation method based on the DLVO theory

2

Fig. 5

3

In the COBR system, the wetting behavior of the rock surface depends on the stability of the

4

thin brine film between the rock surface and oil drop 50 (Fig. 5). This relationship can be

5

described by the augmented Laplace-Young equation 51-53 written as

6

Pc = Π + 2 γ H

,

(1)

is the capillary pressure, Π is disjoining pressure in the thin film, γ is the interfacial

7

where

8

tension, and H is the meniscus curvature. Representing the thin film as a Gibbs diving surface, a

9

relationship between the contact angle and the disjoining pressure can be deduced as 54

Pc

cos θ = 1 +

10

1

γ

Pc

∫ h.d Π ,

(2)

0

11

where h is the separation distance between two surfaces. The disjoining pressure of the brine

12

film 55 is described as the force that tends to disjoin or separate the two interfaces. A negative

13

value of the disjoining pressure means attraction between the contact interfaces. Based on Eq. 2,

14

the correlations between the contact angles and its controlling factors (e.g., temperature) can be

15

explained by calculating the disjoining pressure.

16

The DLVO theory assumes that the disjoining pressure per unit area between two contact

∏( h) ) can be well estimated by three additive contributions, as in Eq. 3 29. The

17

interfaces (

18

contributions are identified as the London van der Waals force ( W V D W ), the electrical double

19

layer force ( W EDL ), and the structural forces ( WS ).

11


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∏( h) = W ( h) +W ( h) +W ( h)

1

VDW

EDL

(3)

S

2

The structural forces are usually assumed to be constant with a change in the temperature and

3

pressure conditions 31. Therefore, the variation in the calculated disjoining pressure with

4

temperature can be explained by only considering the van der Waals (VDW) and electrical

5

double layer forces (EDL) forces.

6

4.1.1 Van der Waals (VDW) forces

7

VDW forces are usually present due to the effect of polarization between different particles.

8

A widely used approximation method to estimate the VDW forces is the Lifshitz continuum

9

method 56, which is given by WVDW = −

10

H . 12π h 2

(4)

11

In Eq. 4, H is the Hamaker constant 35, 57, which defines the strength of the VDW force. Typical

12

values of H range from 10-21 - 10-19 J. In our studied case, the Hamaker constant in the COBR

13

system is calculated through

H =

14

 ε −εw 3 k BT  o 4  εo + εw

 , 

is the Boltzmann constant, T is the surrounding temperature in Kelvin,

15

where

16

dielectric permittivity of crude oil,

17

dielectric permittivity of rock.

18

4.1.2 Electrical double layer (EDL) forces

kB

  εs − εw ⋅   εs + εw

εw

(5)

εo

is the

is the dielectric permittivity of water/brine, and ε s is the

12


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Energy & Fuels

The EDL forces are caused by the development of the charges between an interacting

1 2

surface and the liquid bulk media 31; these forces play an essential role on the wettability

3

determination. The EDL forces can be derived from the solution of the Poisson- Boltzmann

4

equation (PBE). In one dimension, the PBE is given in a form of d 2 Ψ −e = dh 2 ε wε

5

 − zi eψ  K BT

∑ z ρ exp  i

i

 , 

(6)

e is the electron charge, ε is the permittivity of the

6

where Ψ is the electrostatic potential,

7

vacuum, and

8

However, Eq. 6 is a non-linear secondary-order differential equation and cannot be easily

9

analyzed. To obtain a linear solution for the EDL forces and obtain the correlations between

zi

and

ρi

are the valency and charge density of different ions, respectively.

10

EDL forces and temperature, the Debye- Hückel (D-H) approximation is used here to simplify

11

the 1-D PBE. Notably, the D-H approximation is valid for the condition of

12

ψ < 2 5m v

13

59

14

58

z i eψ

K BT < 1

or

. Deviations from the conditional limitations can cause errors in the calculation 38, 54,

. Another essential condition for solving the PBE is the boundary condition. Usually, the

15

solution of the PBE can be obtained using two types of boundary conditions: (i) linear constant

16

potential- constant potential boundary condition (PP condition) and (ii) linear constant charge-

17

constant charge boundary condition (CC condition) 38. The PP condition is represented by those

18

surfaces in which charges can freely transfer through their surfaces. Therefore, their potentials

19

are sustained at a constant level. In contrast, the CC condition assumes a constant charge at their

20

interfaces, where the charge transfer is restricted. For a COBR system, the CC condition seems

21

to be closer to reality for the contact interfaces of the phases 60. However, the general solution for 13


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1

the PBE based on CC condition is very complicated and not convenient for further analysis. For

2

instance, the following equation proposed by Gregory 61 is probably the simplest expression for

3

the CC condition. This equation is reasonably accurate for the condition of a 1:1 electrolyte 27.

  1    ze ζ + ζ kT 2  2  ze (ζ − ζ ) kT  2 e− kh  (   1 2 1 2)   ∏ EDL ( h ) = ρ kT 2 1 +  ekh 2 − e−kh 2   − ze(ζ + ζ ) kT 2 − 2 ,         1 +  kh 12 2− kh 2     e −e 

4

5

6

where

ζ 1 and ζ 2

(7)

are the ζ -potentials of the different media interfaces.

In recent research, Mahani et al. 30 used a DLVO model by using the PP condition to

7

estimate the interaction potential at the crude oil and carbonate rock interfaces. A good

8

consistency between their predicted results and experimental results was obtained in their work.

9

Based on their experience, in our work, the solution of the PBE was calculated using the PP

10

condition assumption, which is believed to be simple and realistic enough for the study of the

11

correlation between wettability and temperature. In a COBR system, an expression for the EDL

12

potential based on the PP condition and D-H approximation is given as

∏

13

EDL

(h) =

εε w k  2ζ sζ o − (ζ s2 + ζ 2 )e − kh  o

e −e kh

− kh

,

are the ζ -potentials of the rock/ brine and crude oil/ brine interfaces,

14

where

15

respectively. The inverse of k in Eq. 8 is known as the Debye length 27.

16

ζs

and

ζo

(8)

k −1 =

εεo KBT 2NAe2 I

,

14


(9)

Page 15 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

∑z

1

In Eq. 9, I = 0.5

2

the ion of the type in brine,

3

Avogadro’s number.

4

4.2 Calculation Results

5

2 i

pi , which represents the ionic strength. The parameter zi is the valence of

pi is its concentration expressed in mol/L, and N A is the

The published ζ -potential data as a function of temperature are very sparse in previous

6

studies. Based on the literature reviewed, the ζ -potential data versus temperature for three

7

minerals (quartz, calcite, and carbonate rock) are carefully selected. Most of these ζ -potential

8

values used for the calculation are from Rodríguez and Araujo’s 62 and Al Mahrouqi et al.’s

9

studies 63. Scattered values are selected from other related literature 11, 19, 30, 36, 59, 64. All these ζ -

10

potential values are measured at a NaCl electrolyte concentration of 0.01 M at a pH of 7.

11

However, due to the limitation of the Zetasizer instrument, all the measuring temperatures of the

12

obtained ζ -potential data are restrictedly below the maximum of 70 °C. Fig. 6 gives the

13

selected ζ -potential values of quartz, calcite, carbonate, and crude oil samples obtained from

14

the literature. It is shown that the ζ -potential of quartz and calcite decrease with an increase in

15

temperature; the ζ -potential of the carbonate and oil sample shows an increasing trend with

16

increasing temperature. However, it should be noticed that the experimental instrument, material,

17

and procedures used in the literature for these selected data were not exactly the same. Several

18

contradictory measured values for the minerals (e.g., kaolinite mineral) in the literature were not

19

used for the DLVO calculation because of their effect on accuracy. Literature data 65, 66 also

20

report varying trend of zeta potential as a function of temperature for other minerals and rock

21

samples.

15


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Fig. 6

2

Table 4

3

Based on Eqs. 4 – 5 and Eqs. 8 – 9, the disjoining pressure values for different samples are

4

calculated. Other essential parameters used in calculations are given in Table 4. Figs. 7 – 9 show

5

the calculated disjoining pressure isotherms for the quartz-brine-crude oil system, calcite-brine-

6

crude oil system, and carbonate-brine-crude oil system at three different temperatures. Using Eq.

7

9, it can be calculated that the separation distance for the three COBR systems is approximately

8

10 nm. The variation in the separation distance with temperature is negligible for the temperature

9

range studied. From Figs. 7 - 9, the calculated disjoining pressure values are negative for all

10

three cases, indicating the interfacial forces between the minerals and oil droplets are attractive.

11

With an increase in temperature, the disjoining pressure isotherm trends to the X-coordinate axis

12

(the separation distance coordinate axis) in Figs. 7 – 9, which means that the attraction between

13

the mineral and oil phases decreases with increasing temperature. Moreover, the variations in the

14

attraction decrease with the temperature at a separation distance of 10 nm are different for

15

various minerals. The variation for water-wet quartz is much larger than that of the other oil-wet

16

minerals (calcite and carbonate) when the temperature increased from 25 to 70 °C. This behavior

17

indicates that compared with the oil-wet calcite and carbonate samples, the wettability of quartz

18

is more likely to be altered toward water-wetness with an increase in temperature. The calculated

19

results in this section show good consistency with the observed experimental trends in Section 3.

20

Note that the contact angle measurements were conducted under temperature conditions of 35 –

21

110 °C. However, we cannot complete the calculations for temperature conditions above 70 °C

22

due to the absence of the ζ potential data. Therefore, the DLVO trends as a function of

23

temperature are partly extrapolated. 16


Page 16 of 38

Page 17 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

Fig. 7

2

Fig. 8

3

Fig. 9

4

4.3 Discussions

5

Recently, Mahani et al.30 published a research study addressing the influence of brine

6

salinity and temperature on the wettability alteration in carbonates using core sample

7

experiments and DLVO calculations. A comparison between Mahani et al.’s research and our

8

presented work is first presented in the following discussion. As reported in Mahani et al.’s work,

9

increasing temperature will increase the measured contact angles of the carbonate samples.

10

These experimental results seem to contradict our presented results. Actually, the reported

11

contact angle results in Mahani et al.’s work were measured using sea water and 25-times diluted

12

sea water. It can also be found in the authors results that the ζ potential values of the formation

13

water as a function of temperature show obvious different behaviors from the measurements

14

using sea water. Furthermore, the main aim of Mahani et al.’s research was to evaluate the

15

influence of the brine salinity and temperature on the carbonate wettability alteration. Only, three

16

carbonate samples including one dolomite and two limestone specimens are used for the

17

wettability alteration experiment. The contact angle results of the three samples show similar

18

behaviors with temperature. However, in our work, seven mineral samples and two rock core

19

samples with various wettability values are used for studying the contact angle trend as a

20

function of temperature. It is experimentally reported that minerals with different wettability

21

show different alteration behaviors as a function of temperature. The DLVO calculation is used

22

for explaining the observed experimental results. 17


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

The presented work was completed on the basis of a relationship between the ζ -potential

2

and the contact angle. However, there are complexities and limitations in utilizing such a

3

relationship. The reason is given briefly as follows. The contact angle in the COBR system is

4

controlled by the thickness of the thin brine film (Fig. 5), which is affected by the charges at the

5

rock-brine and crude oil-brine interfaces of the thin film 67. The charges at the interfaces of the

6

thin brine film, however, are difficult to measure experimentally. Instead, the ζ potential data

7

was utilized for representing the behavior of the thin brine film. But, the problem is that the ζ

8

potential values do not necessarily represent the charges at the interfaces of the thin brine film 11.

9

This is the first limitation of this work. Another limitation of this research is that the ζ potential

10

measurements are not conducted using the same samples as the contact angle measurements.

11

Thus, the DLVO calculations can be explanations rather than validations for the observed contact

12

angle trends. In terms of accuracy, only three minerals including quartz, calcite, and carbonate

13

with ζ potential data obtained from the literature are used for the DLVO calculations. The

14

selected three samples seem representative since both water-wet mineral and oil-wet samples are

15

taken into consideration. In our research, a next step would include using experimentally

16

measured ζ potential data to estimate the contact angle behaviors of various rock samples with

17

temperature and then compare these results with the observed experimental results. Some

18

important aspects including surface roughness and oil aging time will be considered in the future

19

work.

20

5. CONCLUSION

21 22

Based on the experimental and DLVO calculation results, the following conclusions can be drawn: 18


Page 18 of 38

Page 19 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Energy & Fuels

1. Raising the pressure from 10 MPa to 70 MPa has no discernible influence on the mineral surface wettability regardless of mineral type in the COBR system.

2 3

2. In the COBR system, the variation in the mineral surface wettability as a function of

4

temperature depends on the wettability types. For water-wet mineral surfaces, the

5

temperature has a noticeable impact on the contact angles, i.e., the contact angle

6

decreases with increasing temperature; however, for neutral-wet or oil-wet samples, the

7

temperature dependence of the measured contact angle is relatively weak.

8

3. A DLVO calculation considering the van der Waals, electrostatic forces is successfully

9

utilized for explaining the temperature dependence of wettability in COBR system.

10

4. The DLVO calculations show that the disjoining pressure of water-wet mineral and oil-

11

wet minerals increases with increasing temperature, but the variation in the disjoining

12

pressure with temperature for water-wet minerals is much larger than that for oil-wet

13

minerals. These results agree with the observed experimental results.

14 15

AUTHOR INFORMATION

16

Corresponding Author

17

*E-mail: [email protected]

18

ORCID

19

Yongchao Zhang: 0000-0002-0288-9398

20

Jianhui Zeng: 0000-0003-1000-2205

21

Notes

22

The authors declare no competing financial interest. 19


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

ACKNOWLEDGMENTS

2

This work was financially supported by the National Natural Science Foundation of China

3

(Grant No. 41330319). I would like to express my sincere thanks to Heriot-Watt University for

4

their help in the preparation of the manuscript.

5 6

20


Page 20 of 38

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61.

7

and Interface Science 1975, 51 (1), 44-51.

8

62.

9

reservoir minerals. Journal of colloid and interface science 2006, 300 (2), 788-794.

Behrens, S. H.; Christl, D. I.; Emmerzael, R.; Schurtenberger, P.; Borkovec, M.,

Gregory, J., Interaction of unequal double layers at constant charge. Journal of Colloid

Rodríguez, K.; Araujo, M., Temperature and pressure effects on zeta potential values of

10

63.

Al Mahrouqi, D.; Vinogradov, J.; Jackson, M. D., Temperature dependence of the zeta

11

potential in intact natural carbonates. Geophysical Research Letters 2016, 43 (22).

12

64.

13

of silicates. Colloids and Surfaces 1986, 21, 355-369.

14

65.

15

investigation of the effect of temperature, salinity and salt type on brine/mineral interfacial

16

properties. 2017, 59, 136-147.

17

66.

18

interfacial properties of low to high rank coal seams. Fuel 2017, 194, 211-221.

19

67.

20

salinity brine. Current Opinion in Colloid & Interface Science 2015, 20 (2), 105-114.

Ramachandran, R.; Somasundaran, P., Effect of temperature on the interfacial properties

Arif, M.; Jones, F.; Barifcani, A.; Iglauer, S. J. I. J. o. G. G. C., Electrochemical

Arif, M.; Jones, F.; Barifcani, A.; Iglauer, S., Influence of surface chemistry on

Myint, P. C.; Firoozabadi, A., Thin liquid films in improved oil recovery from low-

21 22

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Page 29 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Energy & Fuels

Table 1. Properties and compositions of the oil sample used in the experiments Properties/ compositions

Values

saturates content (wt %)

60.01

aromatics content (wt %)

22.97

resins content (wt %)

9.01

asphaltenes content (wt %)

2.84

density (g/ml)

0.95

viscosity at 25 °C (cP)

747.60


79.54


46.50

2 3

Table 2. Mineral compositions (in wt %) of the sandstone and carbonate core samples Mineral compositions

Sandstone

Carbonate

Quartz

48

trace

Feldspar

22

-

Calcite

6

80

Dolomite

3

18

Chlorite

5

-

Illite/smectite

10

-

Kaolinite

6

-

4 5 6

Table 3. Brine properties and compositions

（g/cm3） Salinity (mg/L) Density（

33634

1.051

Ionic concentration（（mg/L））

pH

6.729

Na+

Ca2+

Mg2+

Cl-

10419

1750

318

21147

7 29


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Page 30 of 38

1 2

Table 4. Parameters used for the disjoining pressure calculation Parameter

Unit

Value

KB

J/K

1.38×10-23

εw

F/m

ε

F/m

8.85×10-12

εo

F/m

2.00

εs

F/m

7.00

e

Coulomb

1.60×1019

NA

mol-1

6.02×1023

78.30 (298 K)

69.90 (323 K)

3 4 5

30


63.80 (343 K)

Page 31 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1 2

Fig. 1 Experimental apparatus DSA100HP from KRÜSS GmbH

3

4 5

Fig. 2 A schematic diagram of the wettability measurement apparatus

6 7 8 31


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Page 32 of 38

i: sandstone (av.CA=34.75°)

ii: carbonate (av.CA=117.11°)

iii: calcite (av.CA=105.57°)

iv: dolomite (av.CA=87.42°)

v: illite (av.CA=57.70°)

vi: chlorite (av.CA=56.86°)

vii: feldspar (av.CA=42.80°)

viii: smectite (av.CA=84.78°)

ix: quartz (av.CA=33.46°)

Fig. 3 The effect of pressure on the contact angles. The samples in Fig. 3-i to 3-ix represent sandstone, carbonate, calcite, dolomite, illite, chlorite, feldspar, smectite, and quartz, respectively. The term “av.CA” refers to the average contact angle the sample 1

32


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Energy & Fuels

i: sandstone (av.CA=34.75°)

ii: carbonate(av.CA=117.11°)

iii: calcite(av.CA=105.57°)

iv: dolomite(av.CA=87.42°)

v: illite (av.CA=57.70°)

vi: chlorite (av.CA=56.86°)

vii: feldspar (av.CA=42.80°)

viii: smectite (av.CA=84.78°)

ix: quartz (av.CA=33.46°)

Fig. 4 The effect of temperature on the contact angles. The samples in Fig. 4-i to 4-ix, represent sandstone, carbonate, calcite, dolomite, illite, chlorite, feldspar, smectite, and quartz, respectively. The term “av.CA” refers to the average contact angle the sample 1

33


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 5 Profile of the contact region in the COBR system 1 2 3 4 5 6 7 8

34


Page 34 of 38

Page 35 of 38

Temperature (°C)

Temperature (°C) 0

10

20

30

40

50

60

70

80

90

0

100

0

10

20

30

40

50

60

70

80

90

100

40 20

-20

0

ζ potiential (mV)

ζ potiential (mV)

-40 -60 -80 -100

-20 -40 -60 -80 -100 -120

-120

Calcite Estimated Calcite Oil Sample

-140

Quartz Estimated Quartz Oil Sample

-140 -160

-160

Quartz

Calcite

Temperature (°C) 0

10

20

30

40

50

60

70

80

90

100

0 -20 -40

ζ potiential (mV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-60 -80 -100 -120

Carbonate Estimated Carbonate Oil Sample

-140 -160

Carbonate Fig. 6 Estimated ζ potential values used in the calculations obtained from the literature. The asterisk symbols in the figures are the estimated data for our calculation; and the filled symbols depict the experimental data from the literature 1

35


Energy & Fuels

Separation Distance (h) (nm) 0

10

20

30

40

50

60

70

80

90

100

0.0E+00

The Disjoining Pressure (atm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 38

-2.0E-07

-4.0E-07

The attraction decreases with the increasing temperature

-6.0E-07

Quartz at 25 °C Quartz at 50 °C Quartz at 70 °C

-8.0E-07

-1.0E-06

-1.2E-06

Fig. 7 Calculated disjoining pressure results versus separation distance in quartz at different temperatures

36


Page 37 of 38


10

20

30

40

50

60

70

80

90

100

0.0E+00


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-2.0E-07

-4.0E-07


-6.0E-07

Calcite at 25 °C Calcite at 50 °C Calcite at 70 °C

-8.0E-07

-1.0E-06

-1.2E-06

Fig. 8 Calculated disjoining pressure results versus separation distance in calcite at different temperatures 1

37


Energy & Fuels


10

20

30

40

50

60

70

80

90

100

0.0E+00


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 38

-2.0E-07

-4.0E-07


-6.0E-07

Carbonate at 25 °C Carbonate at 50 °C Carbonate at 70 °C

-8.0E-07

-1.0E-06

-1.2E-06

Fig. 9 Calculated disjoining pressure results versus separation distance in carbonate at different temperatures 1

38


Investigating the Effect of the Temperature and Pressure on Wettability

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