Dear Agasthiya Raj

you should measure the contact angle of different areas on your sample and report the average of them. it's usual that a sample has different contact angles in different areas.

Dear Agasthiya Raj,

The reproducibility is needed for your experiment. Try to take a lots of data then get the average of it. If the standar deviation still high, there are high possibility that either the methodology or experimental setup is not perfect.

Contact angles can also change over time. Be sure to let the value stabilize.

Thanks to all

. The substrate should be sanded with fine sandpaper, treat it with air, rinse with deionized water, and dry it in an oven.

. Give at least two hours for the system to get stabilized when the droplet is initiated.

From experimental point of view, first you need to smooth the surface of your thin sections, second you have to saturated them with formation water, the velocity of droplet release is another factor. the angle of your needle is important too. The place where your setup is should be stable. Stability of angles is function of time, temperature, salinity, composition of oil, type of salts that are existing in your brine samples. Additionally the right and left hand side of droplet could have different angles,. When you give the time (like 2 hours as Hasan Alsaedi said), although your angles are stables that could results in evaporation of water, hence salinity level of your brine is changing, I think gupta et al performed their angles up to 140 hours, (How they avoid evaporation? I really do not know) Additionally, the mineralogy of thinsection might not be the same. Moreover, you have to make an average as Yalda Majooni said. Hope it helps. And do not worry, you are not the first person who get confused with his contact angles in his lab. All of us had experienced that. :) Alireza.

Measuring the contact angle, various things could factor in to the final result so I will name them from the scratch. Firstly, the way you prepare your surface is so important. If the the rock surface is not well-polished and if it contains unmodified edges or rippling it emplifies the effect of hysteresis.

At the second stage, the time you spend on aging oil and solution to subsequently mimic the initial wettability and the alteration is important. The aging period for rocks are rediculosly different.

Thirdly, sometimes everything is good but you forgot to clean your surface or dry it carefully after aging.

Fourthly, the dirt may sometimes causes the rock to not to disclose its real condition.

At the final stage, consider this fact that contact angle measurement is a case seni

senstive experiment.