Preparation and Salt-Resistant Water Shutoff Performance of Cationic Hydrophobically Associating Polymer Gel PADL
A novel cationic hydrophobically associating polymer gel (PADL) was synthesized and characterized, demonstrating superior injectability, thermal stability, and salt-resistant water shutoff performance in high-salinity fractured reservoirs due to its dense 3D porous network and synergistic electrostatic and hydrophobic interactions.
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Oil fields around the world are reaching a difficult stage in their lives. After years of pumping, the rock formations that once held vast amounts of oil have become tired and complex. In many of these mature fields, water has begun to take over. As water floods through the underground rock, it finds the easiest paths, often rushing through natural cracks and fractures while bypassing the oil trapped in the tighter, more stubborn rock. This phenomenon, known as "channeling," causes wells to produce mostly water instead of oil, leaving valuable resources behind. To fix this, engineers need a way to block these water-filled cracks without damaging the rock or clogging the oil pathways. The challenge is finding a material that is strong enough to stop the water, flexible enough to fit into tiny, irregular cracks, and tough enough to survive in the harsh, salty environment deep underground.
Researchers at Southwest Petroleum University and the Xinjiang Oilfield have developed a new solution to this problem: a special type of gel designed to plug these water channels. They created a substance called PADL, a thick, jelly-like material made from a mixture of different chemical building blocks. The goal was to build a gel that could be pumped deep into the ground as a liquid, wait for the right moment to turn solid, and then hold firm against the pressure of the flowing water, even when that water is extremely salty.
The team started by mixing several ingredients together in a beaker. The main ingredient was a common chemical called acrylamide, which forms the soft, water-loving backbone of the gel. To this, they added a special salt-resistant component that carries a positive electrical charge, and another ingredient with long, oily chains that like to stick to each other. They also included a metal-based substance that acts like a glue, linking the molecules together into a strong network. When these ingredients were heated, they reacted to form a gel that looks like a dense, three-dimensional sponge with tiny holes ranging from two to ten micrometers across. This structure is crucial because it allows the gel to be flexible and strong at the same time.
One of the biggest hurdles for gels in oil fields is salt. Deep underground, the water is often filled with dissolved minerals like calcium and magnesium, which can cause ordinary gels to shrink, collapse, or lose their strength. The researchers found that their new gel behaves differently. Instead of shrinking in salty water, the gel actually became stronger. This happens because the positively charged parts of the gel push against each other just enough to keep the structure open, while the salty water forces the oily parts of the gel to huddle together even tighter, creating a more robust network. The metal "glue" holding it all together is also resistant to being pulled apart by the salt ions. As a result, the gel maintained its strength and elasticity even in water with a salt concentration as high as 84,739 milligrams per liter, which is more than twice the salinity of the ocean.
To test how well this gel works in real-world conditions, the team poured it into rock samples that had cracks of different sizes, ranging from very thin slits to wider gaps. Before the gel hardened, it flowed easily into even the smallest cracks, showing that it could reach deep into the reservoir. Once it set, the gel formed a solid plug that could withstand immense pressure. In the narrowest cracks, the gel held back water with a pressure of up to 3.2 megapascals, a force strong enough to stop the flow completely. Perhaps most importantly, the gel showed a smart ability to choose where to plug. When tested in rock with both high-permeability and low-permeability areas, the gel flowed preferentially into the high-permeability water channels and blocked them, while leaving the oil-rich, low-permeability zones largely untouched. It also showed very little tendency to clog the oil itself, meaning it could stop the water without hurting the oil production.
The gel proved to be stable over time as well. When kept at the temperature of the target oil field for six months, it remained firm and did not break down. This combination of properties—easy to inject, strong once set, resistant to salt, and selective in what it blocks—suggests that this new material could be a powerful tool for oil producers. It offers a way to shut off unwanted water in difficult, salty, fractured reservoirs, potentially allowing more oil to be recovered from fields that were previously considered too problematic to produce efficiently. The researchers describe this as a promising step toward better managing water in mature oil fields, providing a material that adapts to the harsh underground environment rather than fighting against it.
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