On the base of molecular structure design, we have synthesized hydrophobically associating water-soluble polymers. The solution properties of hydrophobically associating water-soluble polymer as a function of electrolytes concentration temperature and shear rate have been investigated. The enhance in oil recovery obtained in core flow experiment with the polymers solution is higher. This polymer is developed for use under hostile reservoir conditions. Introduction Water-soluble polymers are broadly used in the field of polymer flooding, combinational chemical flooding and well-drilling mud. In the most EOR field applications, one of the most important effects of these polymers is to increase the viscosity of the water solution. They can remarkably enlarge the sweep volume and enhance the sweep effective, thus highly increase the produce of petroleum. In Daqing Oil Field China, the produce of petroleum is 12% higher when polymer flooding is used instead of water flooding, The oil increment for every ton of polymer injected is 120 tons and more than 7 million tons have been produced by polymer flooding in 1998(1). The partially hydrolytized polyacrylamide (HPAM) is among these polymers and is widely used in polymer flooding and combinational chemical flooding in China. The electrostatic resistance among the (coo- groups makes the molecular chains of HPAM extend and this extension can effectively enlarge the fluid mechanical volume of the polymer and then increase the viscosity. However, In salting solution, the existence of sal ions weakens the electrostatic resistance and makes the chains coil up, which results in an obvious decrease of the fluid mechanical volume and the viscosity. Furthermore, HPAM is easy to be attacked by thermal oxidation degradation when the temperature of oil reservoir is above 60°C and completely lose its viscosity. As the consequences, a high concentration of the polymer is required in actual applications and HPAM is not suitable for oil reservoir with high temperature and high saltness. All these disadvantages seriously retard the propagation of combin-ational chemical flooding in China. The synthesized hydrophobically associating polymer in our study has a structure of hydrophilic molecular main chains with a few hydrophobic groups. In the polymer water solution, the hydrophobic groups gather together as pushed by water. It results in physical association both among and within polymer molecular chains. This association can increase the fluid mechanical volume, therefore it has a strong effect on increasing the viscosity of the water solution. Adding small molecular electrolytes into water solution can then increase the polarizability of the water solution and then reinforce the hydrophobic association. The salt-resistance thus improved. Furthermore, the hydrophobic effect can be regarded as a process of entropy increase, which means that as temperature increases, the hydrophobic effect also increase. The hydrophobic association is favored when temperature increase in certain conditions. It means that water-soluble hydropho-bically associating polymers should have higher temperature-resistance than ordinary water-soluble polymers (2). Some of the results of our study will be shown here. Experiments and Materials Acrylamide sodium carbonate and sodium chloride are chemically pure. Alkyl cation hydrophobic monomer with propenyl groups was prepared by our own. The length of alkyl group in hydrophobic monomer varies according to different application requirement.
This paper wn _ for preasntation at II!@ SPE Internatlond Sympo81um on Oilfkild Ch6mWW in &n Antonb, TX, U.S.A., 1+17 Pehuy IWS.
Amphoteric polymer and MMH drilling fluid systems have been widely applied in oil fields in recent years with good benefits. The applications have shown the advantages and disadvantages of the two drilling fluid systems. Based on the analysis and research of molecular structure and mechanism of the two kinds of additives in drilling fluid, the molecular structures of new polymers, metal complex - amphoteric polymers PMHA, JMHA, are designed and researched. The new products have properties of both amphoteric polymer and MMH, that is, high inhibition, high thixotropic, stable drilling fluid rheological, excellent filtrate control ability and the ability of protecting production formation from damage. Applications in Zhongyuan, Jiangsu and Liaohe oilfields showed that it increased drilling rate, decreased the trouble under well bore and the enlargement rate of well diameter. The metal complex-amphoteric polymer products have good compatibility with other additives. The drilling fluid system formulated by these products has stable rheological properties with low cost. Now the drilling fluid system has been successfully applied in vertical, directional, deep and slim hole wells in China's oil fields. Taking advantage of the metal complex - amphoteric polymers, we have formulated drilling mud systems, such as the fresh water mud, high-density mud with high salinity, slim hole drilling fluid and completion fluid. P. 525
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