Application of polyacrylamide in oilfield operations

Polyacrylamide is a polymer compound, known as a “universal additive” and a “miracle product” due to its active acyl groups on its main chain and its water solubility. In the petroleum development process, polyacrylamide is widely used in oilfield operations such as drilling, well completion, cementing, fracturing, and enhanced oil recovery, and has multiple functions including thickening, reducing filtration loss, rheological regulation, gelling, diversion, and profile adjustment.

1. Application of polyacrylamide in drilling fluids

Partially hydrolyzed polyacrylamide (HPAM) is a commonly used polymer in drilling fluids. It effectively controls the rheological changes of drilling fluids and adequately lubricates the drill bit, preventing water loss and fluid depletion. After effective adjustment and treatment, HPAM can significantly reduce the density of drilling fluids and decrease the content of solids, thus enabling efficient and convenient applications in drilling for reducing filtration loss, flocculation, shale inhibition, dilution, and plugging lost circulation. The most commonly used HPAM types in drilling fluids are partially hydrolyzed polyacrylamide or its potassium salts, with the potassium salt of partially hydrolyzed polyacrylamide performing better as an additive than the partially hydrolyzed polyacrylamide itself.

2. Application of polyacrylamide in water shut-off and profile control

Polyacrylamide (PAM) is a water-blocking agent used in oilfield production to effectively address water seepage problems caused by formation structure. Using PAM water-blocking agents can reduce produced water and formation energy loss, while simultaneously improving oil recovery. This agent can selectively block water permeation and is widely used in oilfield production both domestically and internationally, reducing water permeability by over 90%. The polymer gel system prepared from PAM emulsion synthesized by Liu Zhiliang et al. has advantages such as rapid dissolution, convenient operation, and environmental friendliness. They have also developed a gel system suitable for offshore profile control, which allows for controlled gelation time in marine environments, forming a high-strength gel that effectively seals permeable layers.

3. Application of polyacrylamide in enhancing oil recovery

Many oilfields in China face a common challenge: complex geological formations and rapidly increasing water content in the extracted crude oil. Therefore, effectively extracting the crude oil remaining in the formation is an urgent problem to solve. Among various oil recovery methods, polymer flooding performs best, with polyacrylamide being the most commonly used polymer. Polyacrylamide has a high molecular weight and good hydrophilicity, which can change the flow rate ratio and improve the sweep efficiency during oilfield production, thereby significantly improving oil recovery.

4. Application of polyacrylamide in fracturing fluid

Petroleum, often called the “lifeblood of industry,” firmly holds the key to economic life. In recent years, human demand for petroleum resources has been continuously increasing. However, since the 1980s, human demand for petroleum has far exceeded the currently known reserves of oil reservoirs. In recent years, my country’s crude oil consumption has been increasing significantly every year, gradually making it a major crude oil consumer. Petroleum resources are non-renewable, and the supply-demand imbalance is severe, posing enormous challenges to my country’s oil and gas exploration and development.
The era of naturally erupting oil from geological formations using natural energy has ended, and most of my country’s oil and gas fields have entered the secondary and tertiary oil recovery stages. Many domestic and international oil companies are continuously developing commercially viable oil and gas fields and reservoirs to meet global oil demand. Because of the abundance of low-permeability oil and gas reservoirs and their rich resources, these companies are now focusing on developing low-permeability, ultra-low-permeability, and heavy oil and gas fields, as well as marginal oil and gas fields with small reserves. Currently, developing low-permeability and ultra-low-permeability oil and gas reservoirs presents numerous challenges, including high costs, low economic returns, and significant development difficulties. Therefore, the current technological goal is to effectively develop these low-permeability and ultra-low-permeability oil and gas reservoirs, increasing production while simultaneously reducing oilfield development costs.
Hydraulic fracturing is a core technology for enhancing the production of low-permeability oil and gas reservoirs. This technology has been developed and improved over 60 years and is now widely used in the exploration and development of many oil and gas fields. Hydraulic fracturing is a reservoir stimulation and production enhancement technology, also known as reservoir fracturing or fracturing. Its main purpose is to break up the reservoir by transmitting pressure through fluid, thereby increasing the production of the oil well. Originating in 1940, this technology has now become one of the important processes for enhancing the production and injection of oil, gas, and water wells.
In hydraulic fracturing, fracturing fluid is used to transmit pressure. Using a high-pressure pump unit at the bottom of the well, a liquid with a certain viscosity is injected into the well at a rate far exceeding the formation’s absorption capacity, creating high pressure near the target layer at the bottom of the well. When this pressure exceeds the fracturing pressure of the rock near the bottom of the well, it forces numerous fractures into the oil-bearing formation. Fracturing fluid containing proppant is then injected into these fractures, propelling them forward. As the pressure decreases, the proppant (usually ceramic pellets or quartz sand) remains in the fractures, forming a sand-filled fracture. This fracture has a certain width and height, which can improve the conductivity of the oil and gas reservoir and increase the production of a single well.
In recent years, my country’s oil exploration has continued to advance into deeper formations, with drilling depths exceeding 6,000 meters and reservoir temperatures reaching 180°C or higher. Therefore, the temperature and shear resistance of fracturing fluids have become particularly important, as only in these conditions can they achieve optimal performance and maintain proppant-carrying capacity in ultra-high temperature reservoirs.
Traditional organoboron crosslinked fracturing fluids exhibit significant performance degradation at temperatures of 180°C and above. Currently used guar gum thickeners degrade rapidly at 180°C, making it difficult to maintain sufficient effectiveness. Common solutions include increasing the amount of pre-flush fluid, selecting fracturing fluids with transition metal crosslinking, and increasing the amount of thickener. However, these methods can contaminate the formation and damage the reservoir, thus reducing the effectiveness of fracturing stimulation. Furthermore, with the accelerated development of shale oil and gas resources, the demand for guar gum is increasing, and its price is rising continuously, putting significant pressure on fracturing costs and affecting reservoir stimulation effectiveness and production.
To address these issues, numerous experts and scholars both domestically and internationally have conducted extensive and in-depth research on polyacrylamide-based polymer fracturing fluids. Studies have found that polyacrylamide-based fracturing fluids possess excellent water solubility and are free of acetal bonds, thus exhibiting high temperature resistance. Furthermore, compared to plant-based gums, these polymers have a lower content of water-insoluble substances. To achieve optimal results in the development of tight oil and gas reservoirs, advanced foreign technologies were adopted, focusing on the development of core drag-reducing agents. Highly efficient drainage aids and anti-swelling agents were developed, and through continuous optimization and improvement, a slickwater fracturing fluid system was formed, characterized by low friction, low viscosity, low damage, low cost, continuous mixing, and recyclability. These technical characteristics make this fluid system highly suitable for the development of tight oil and gas fields.