The application of polyacrylamide in petroleum industry
1. Application of polyacrylamide in tertiary oil recovery
Polyacrylamide flocculant plays an important role in petroleum exploitation because of its properties of thickening, flocculation and rheological regulation of fluid. It is widely used in drilling, plugging, acidizing water, fracturing, well washing, completion, drag reduction, scale prevention and oil displacement. In general, polyacrylamide flocculants are used to improve oil recovery (EOR). In particular, many fields have entered secondary and tertiary production, and reservoir depths are generally more than 1,000 m, some of which are as deep as 7,000 m. The heterogeneity of the formation and the offshore field have put more stringent conditions on PAM for oil production. Deep and offshore production have also put new requirements on PAM for shear resistance. High temperature (above 100℃ to 200℃), calcium ion, magnesium ion, seawater degradation resistance.
Since 1980s, great progress has been made in basic research, preparation, application research and variety development of PAM.
Phillips Petroleum Co. Expert Mohammed M.A. And Peter H.D., the research results of PAM in high temperature and high salinity mineralized water show that:
(1) At low salinity (<20×10-6), the turbidity point of PAM solution was above 204℃ regardless of concentration, degree of hydrolysis and relative molecular weight. When the concentration of divalent cation increases slightly, the turbidity point decreases greatly, and the higher the degree of hydrolysis, the turbidity point decreases more obviously.
(3) The effect of calcium ion on reducing the turbidity point is greater than that of magnesium ion, Sr ion and Ba ion at the isomole level.
(4) When the concentration of divalent cation is greater than or equal to 100×10 Juan, the degree of hydrolysis is the key parameter to determine the turbidity point of polyacrylamide flocculant solution;
(5) Relative molecular mass and concentration also affect the turbidity point, but are secondary factors to the degree of hydrolysis.
(6) The turbidity point of the solution decreases after the hydrolysis of polyacrylamide flocculant. Hydrolysis is an equilibrium process, and the equilibrium value of hydrolysis varies with the temperature.
(7) When the temperature is less than 75℃, polyacrylamide flocculant is stable in any aqueous solution of salinity, over 75℃, with the rise of temperature, precipitate formation is accelerated, reducing the salinity of water can prolong the stability time, but the required salinity is often lower than the actual salinity of oilfield water.
2. Used as a water plugging adjustment agent
In the process of oilfield production, due to the heterogeneity of the formation, the problem of water flooding often occurs, and water plugging is needed. The essence of water plugging is to change the seepage state of water in the formation, so as to reduce the oil field water production, maintain the formation energy, and improve the ultimate oil recovery. Polyacrylamide flocculant chemical water plugging agent has the selectivity of oil and water permeability, the oil permeability can be reduced by more than 10%, and the water permeability can be reduced by more than 90%. Selective water plugging this feature is not other water plugging agent, usually according to the formation type to choose the appropriate molecular weight of polyacrylamide. Medium molecular weight ((500 ~) can be selected for reservoirs with good homogeneity and high average permeability. 700) x 10). Polyacrylamide flocculant; High molecular weight (1000×10) can be selected for fractured reservoirs with low bedrock permeability or reservoirs with large permeability changes. Above) of polyacrylamide. Polyacrylamide can not be crosslinked when used, but it can be crosslinked with aluminum salt, chromium salt, zirconium salt and other gel use, but also can add some resins to form mutual capacitive polymer network, so that it has higher temperature resistance. This method has been applied to water plugging of high water-cut carbonate bottom water reservoir in China and achieved obvious results. Polyacrylamide can also be used to adjust the water absorption profile in the formation and block large pores, and good results have been achieved in practice.
A lot of experiments have been done in the use of polyacrylamide flocculant in various oil fields in China. Polyacrylamide with average molecular weight of (300 ~ 350)×10 'and degree of hydrolysis of 10% ~ 15% has been used in oil Wells for water plugging. The hydrolysis degree was 30% and the relative molecular weight was 400×10. In geological drilling, the polyacrylamide flocculant plays a role in maintaining the stability of hole wall and preventing the leakage of borehole. The use of polyacrylamide flocculant with a degree of hydrolysis of 30% as drilling fluid treatment agent can reduce the penetration rate of drilling fluid, improve the drilling hole speed, shorten the mixing time of drilling fluid, thus reducing the number of drilling fluid mixing and increasing the clay slurry rate of 30% ~ 50%. Sometimes, partially cross-linked polyacrylamide is used in water shutoff. In order to improve the selectivity of plugging oil, the crosslinking degree should be as low as possible. The relative molecular weight of polyacrylamide flocculant is usually in (300 -- 500)×10. The relative molecular weight is selected according to the permeability of pore structure. When the permeability is greater than 1D, the molecular weight of polymer is 300×10. Left and right is appropriate. When the permeability is higher, ding (500 ~ 800)×10. Polyacrylamide. The degree of hydrolysis is also related to the properties of the plugging rock. Limestone has strong adsorption capacity and the degree of hydrolysis should be higher, about 20% ~ 30%, while sandstone has low adsorption capacity and the degree of hydrolysis is 5% ~ 20%.
3. Used as drilling fluid regulator and fracturing fluid additive
Partially hydrolyzed polyacrylamide (HPAM) is often used as a drilling fluid modifier, which is obtained from the hydrolysis of polyacrylamide. Its function is to adjust the rheological property of drilling fluid, carry cuttings, lubricate drill bit, reduce fluid loss and so on. The drilling fluid modulated with polyacrylamide has a low specific gravity, which can reduce the pressure and plugging of oil and gas zones, make it easy to find oil and gas zones, and is conducive to drilling. The drilling speed is 19% higher than conventional drilling fluid and about 45% higher than mechanical drilling speed. It also significantly reduces stuck drillers, reduces wear and tear on equipment, and prevents lost circulation and collapse.
Fracturing technology is an important stimulation measure for tight formation development. The fracturing fluid made of methylene polyacrylamide crosslinking is widely used because of its high viscosity, low friction resistance, good sand suspension ability, small filtration, good viscosity stability, less residue, wide supply, convenient preparation and low cost.
In fracturing and acidizing treatment, polyacrylamide flocculant is prepared into an aqueous solution with a concentration of 0.01% ~ 4% and pumped into the underground stratum to fracture the stratum. Polyacrylamide flocculant aqueous solution has the function of thickening and carrying sand and reducing the loss of fracturing fluid. Moreover, polyacrylamide has the effect of resistance reduction, so the pressure transfer loss can be reduced.
4. Oil well cement additives
The terpolymer prepared by AMPs, methacrylic acid and acrylamide is suitable for various saline drilling fluids and has a good high-temperature retardancy effect. United States: Halliburton's AMPS and acrylic copolymer, AMPS and N, N dimethyl acrylamide copolymer and carboxymethyl hydroxyethyl cellulose composite as admixtures for oil well cement can effectively reduce high temperature filtration loss of water drilling fluids.
5. Drilling fluid treatment agent
Graft copolymer of AMPs with acrylamide and starch, copolymer of AMPs with acrylamide and N, N methylene acrylamide, graft copolymer of AMPs with humic acid and acrylamide in fresh water drilling fluid, brine drilling fluid, saturated brine drilling fluid
The well fluid and seawater drilling fluid have good filtration loss reduction and temperature and salt resistance.
Contamination by clay dispersion and other factors tends to increase the viscosity of drilling fluids, and viscosity reducers are needed to control the rheological properties of drilling fluids. Ferric chrome lignosulfonate viscosity reducer (FCLS) is the most commonly used viscosity reducer for drilling fluids. The terpolymer of AMPs, acrylic acid and methacrylic acid was used as viscosity reducing agent of drilling fluid instead of FCLS, which retained the good salt resistance and temperature resistance of FcIJS, and overcame the toxicity of FcIJS. The research shows that terpolymer has stronger resistance to high-priced metal ions than binary copolymer.
6. Completion fluid and workover fluid additives
The copolymer of AMPS with acrylic acid and itaconic acid can be used as a viscosifier to prepare seawater and brine, increasing the viscosity of completion fluids by more than four times and providing good thermal stability, overcoming the disadvantages of traditional polymers in brine system viscosity reduction.
7. Oilfield water treatment agent
AMPs homopolymer and acrylic acid, acrylonitrile, acrylamide copolymer formed, can be used as a flocculant of oilfield sewage treatment and sludge dehydrating agent and scale inhibitors, antiscale F.G oodrich company launched by AMPs, ternary copolymer of acrylic acid and styrene sulfonate of calcium sulphate scale and calcium phosphate scale has good inhibition, The scale inhibition rate is above 97%. Literature shows that AMPs copolymer as water treatment agent has the characteristics of less dosage and better effect than existing polyacrylamide water treatment agent.