Polyacrylamide as a displacement agent for tertiary oil recovery, has been in Daqing Oilfield, Shengli Oilfield, Dagang Oilfield, Changqing Oilfield, Xinjiang Oilfield, Henan Oilfield and put into use, of which Shengli Oilfield invests about 50,000 tons of dry powder every year, Daqing Oilfield invests more than 100,000 tons of polymer every year, and the oil increase of tertiary oil recovery in two oilfields reaches 1.7 million and 10 million tons respectively, providing a guarantee for the increase and stable production of the old oil fields in the east. It is currently the largest application field of polyacrylamide in China. Compared with other tertiary oil recovery technologies.
The polymer flooding technology is mature, low cost, low input-output ratio, and more suitable for the characteristics of domestic reservoirs. The following describes the development history of tertiary oil recovery, the mechanism of polymer flooding, the current situation and existing problems of polyacrylamide for oil displacement, and the development direction of polyacrylamide for oil displacement.
Development history of tertiary oil recovery
In 1986, our country completed the "Research on the Potential Evaluation and Development Strategy of Enhanced Oil Recovery in China's Onshore Water Injection Oilfields", formulated the policy that "Chemical flooding is the main direction of enhanced oil recovery technology research in the eastern oilfields of our country", and arranged the deployment of polymer flooding application test and multi-level chemical compound flooding pilot test.
Since 1996, polymer flooding technology has successively achieved industrialized production in our country's Daqing, Shengli, Dagang, Zhongyuan, Xinjiang and other oil fields. In 1996, it was 3.59 million tons, and in 2000, it exceeded 10 million tons for the first time. In 2008, it has exceeded 15 million tons, accounting for about 8% of our country's oil production that year.
In the 1960s, Shengli Oilfield began laboratory research on polymer flooding, conducted pilot field tests in 1992, expanded field tests in 1994, and industrialized application began in 1997. Application tests of polymer-surfactant-alkali composite flooding were carried out from the 1980s to 1997. In the 21st century, indoor research on polymer-surfactant binary composite flooding began, and pilot tests were carried out in 2003 (1). Expanded tests were carried out in 2006.
During the "Eleventh Five-Year Plan" period, according to the adjustment made to the original "Eleventh Five-Year Plan" for the "Eleventh Five-Year Plan" for the hard stability of oil and gas in Shengli Oilfield in January 2008, in order to ensure the effect of the third oil recovery and increase oil and slow down the decline in production, on the one hand, it is necessary to speed up the coverage of the remaining first and second types of reserves; on the other hand, it is necessary to take advantage of the favorable conditions of high oil prices to optimize the implementation of the plan, extend the polymer injection slug of the polymer injection unit, expand the scale of binary flooding and optimize the three types of reservoirs with relatively good reservoir conditions. The "Eleventh Five-Year Plan" third oil recovery covers 138 million tons of geological reserves and
At the same time, three pilot tests of new oil production areas should be carried out to make technical reserves for the "Twelfth Five-Year Plan". The EOR resource evaluation results show that the total resources suitable for chemical flooding in Shengli Oilfield account for 45.4% of the geological reserves of the water-injected units. Chemical flooding has a rich material basis and great potential. As of 2009, Shengli Oilfield has used geological reserves of 371 million tons, accounting for 33% of the geological reserves suitable for chemical flooding and 9.3% of the geological reserves in Shengli Oilfield.
Mechanism of polymer flooding
The mechanism of polymer oil displacement is mainly to use the viscosity of water-soluble polyacrylamide molecular chain to improve the fluidity ratio of the displacement fluid, increase the displacement efficiency and the affected volume, so as to achieve the purpose of enhanced oil recovery.
(1) Reducing the oil-water fluidity ratio can change the fractional flow curve. The oil saturation at the front of polymer flooding and the oil saturation at the time of breakthrough are significantly higher than those in water flooding, which indicates that polymer flooding can reduce the water content of the produced liquid, improve the oil recovery rate, and have a better displacement effect.
(2) Polymer flooding can improve the viscous finger-in phenomenon of water flooding in the heterogeneous plane by improving the fluidity ratio of water flooding, and improve the plane sweep efficiency; in the vertical heterogeneous formation, the polymer slug first enters the hyperpermeability layer, and uses the high viscosity characteristics to "block" the hyperpermeability layer, so that the subsequent water flooding turns into the low permeability layer. Increase the water absorption thickness and expand the vertical sweep efficiency.
(3) The polymer is retained by adsorption, mechanical capture, etc. when passing through the porous medium, which changes the penetration rate at the pores where the polymer is located. The part of the adsorbed polymer molecular chain facing the fluid has hydrophilicity, which can reduce the relative penetration rate of the water phase without reducing the relative penetration rate of the oil phase, that is, water blocking does not block oil; at the same time, polymer retention can increase the resistance coefficient and residual resistance coefficient, and the seepage resistance increases, causing the driving pressure difference to increase, which is conducive to driving the original oil layer that has not flowed and improving the oil layer's affected volume.
(4) Due to the viscous force of the polymer solution, it is difficult to move along the cracks in the pores and the water film, and it is propelled by piston in the pores to overcome the "Haines jump" phenomenon generated during the water flooding process and avoid the capture and retention of oil droplets in the pores
In addition, the polymer solution has the effect of improving the viscoelasticity of the oil-water interface, making the oil droplet or oil film easy to stretch and deform, easier to pass through the narrow throat, improving the microscopic oil displacement effect, and improving crude oil recovery