The ASP flooding technology is about to enter the promotion stage of industrialization in Daqing sandstone reservoir. Some test sites were quite successful. Comparing with water flooding, the oil recovery of ASP flooding technology could increase by more than 20% [1Carrero, E.N.; Queipo, N.V.; Pintos, S.; Zerpa, L.E. Global sensitivity analysis of alkali-surfactant-polymer enhanced oil recovery processes. J. Petrol. Sci. Eng., 2007, 58(01), 30-42.
[http://dx.doi.org/10.1016/j.petrol.2006.11.007] -3Aalaie, J.; Vasheghani-Farahani, E. Swelling behavior of sulfonated polyacrylamide nanocomposite hydrogels in electrolyte solutions: comparison of theoretical and experimental results. Iran Polym. J. Eng. Edu., 2012, 21(03), 175-183.
[http://dx.doi.org/10.1007/s13726-012-0016-3] ]. For the reservoirs with high heterogeneity and thick main reservoir, the injected chemical liquid in the late ASP flooding seriously flow along the high permeable layer [4Wang, K.L.; Ding, Y.J.; Yan, Y.T.; Sun, L.B. Physical simulation of oil displacement effect by using ASP composite profile control agent. J. of Daqing Petrol. Inst., 2005, 29(01), 30-36.], leading to the futile circulation of chemical agents. The deep profile control technology could be applied in ASP flooding, which could significantly reduce the futile cycle of the ASP liquid in the high permeable layer, and increase the oil displacement efficiency of ASP flooding [5Zhang, K.; Qin, J.S.; Chen, X.L. Double action of Cr³⁺ gel on modifying profile and removing CaCO₃ in ASP flooding. Petrol. Sci. Technol., 2010, 28(05), 445-457.
[http://dx.doi.org/10.1080/10916460902744562] -9Liu, J.X.; Sui, C.B.; Lu, X.G.; Wang, R.J.; Wang, L.; Li, Q.; Wang, S.X. Mechanism analysis and evaluation of compatibility between profile control agent and “Surfactant/Polymer” system. Oilfield Chem., 2012, 28(01), 65-67.]. Presently, profile agents, such as HPAM/Cr³⁺, HPAM/Al³⁺ and HPAM/organic phenol, have poor stability due to the higher pH value, molecular shape could be easily changed in high pH, leading to the low gel strength in the reservoir [10Paul Willhite, G.; Zhu, H.J.; Natarajan, D.; McCool, C.S.; Green, D.W. Mechanisms causing disproportionate permeability reduction in porous media treated with chromium Acetate/HPAM Gels. SPE J., 2012, 07(01), 100-108.
[http://dx.doi.org/10.2118/77185-PA] -12Lou, Z.B.; Li, D.S.; Fan, A.X.; Du, Z.X.; Song, X.B. Experimental evaluation and field application of pre-cross linked polymer particle flooding in eastern Wenliu block 25 of Zhongyuan oilfield. J. Southwest Petrol. Uni. (Sci. & Techn. Edition), 2012, 34(5), 125-130.]. Despite the polymeric particles have good alkali resistant, they could not well match the oil layer. At present, there is no successful experience to use for reference in alkali profile control system. Therefore, it is of great significance to research the alkali-resistant profile agent for improving oil recovery under condition of high pH value and the development effectiveness of ASP flooding [13Zhou, Y.L.; Jiang, H.Q.; Wang, C.; Sang, G.Q.; Liu, L. Experimental study on microscopic percolation mechanism of polymer microsphere profile control and flooding by nuclear magnetic resonance. J. Xi’an Shiyou Univ., 2013, 28(01), 70-75. [Natural Science Edition].-16Rao, P.; Wang, J.; Pu, C.S.; Ma, Z.Y.; Liu, P.P. Application of the compound indepth profile modification in Gasi oilfield E31 reservoir. Oilfield Chem., 2011, 28(4), 390-393.].

In this paper, based on the actual reservoir and development situation in ASP flooding testing area, Daqing x oilfield, the alkali-resistant profile agent was developed, using polymer as the main agent, and organic and inorganic chemical crosslinking agent, together with stabilizer. The performance evaluation, core liquidity experiment and displacement experiment for the prepared profile agents were carried out, and the profile control agent application has been given in field test.

In this paper, the alkali-resistant gel-type profile agent was studied by blending the polymer solution, metal crosslinking agent, and organic crosslinking agent to prepare profile agents. Under the action of the crosslinking agents, the constitutional units of polymer could be crosslinked, forming the spatial lattice structures with the resin filler from the organic crosslinking agent, which has high strength and alkali resistance.

Through optimizing polymer concentration and molecular weight, organic crosslinking agent type and concentration, metallic crosslinking agent type and concentration, stabilizer concentration, the alkali-resistant profile agent formulation has been determined. Taking the optimization of polymer concentration for example, the experimental result is shown in Fig.(1), the formative gel picture of different polymer concentrations is shown in Fig. (2).

Fig.(1) The gel viscosity of different polymer concentrations.

Fig.(2) The formative gel picture of different polymer concentrations.

With the increasing polymer concentration, the viscosity of gel system is increased, gelation time is shorten. This is because under certain conditions, the hydraulic radius of polymer molecule is curtained. As concentration of polymer increasing, the chance of the collision and winding of polymer molecules is large, the polymer molecules react with crosslinking agent is much, which increasing the force among the polymer molecules, and the viscosity of gel system increased.

According to experimental result, the composition of the alkali-resistant profile agent was as follows: partially hydrolyzed polyacrylamide: Mw=25000000, 1800~2000 mg/L; metallic crosslinking agent: 0.15% chromium acetate; organic crosslinking agents: 0.1% phenol and 0.08% methyl aldehyde; 0.2% NaCl. The gelation time of profile agent was 4~5 days and the viscosity of the gel was 2320~3510 mPa•s, the stabilization time was more than 60d, it can meet the deep profile requirements in the process of ASP flooding.

The average permeability of X block is 343×10^-3 μm². It started to ASP flooding in March 2014, the injection rate is 0.2PV/a. The effect of some production well was bad, this type wells mainly focused on the water injection well of the basic well pattern. Inefficient and invalid cycle of injection liquid was serious, the relative imbibition of high permeable layer was up to 69.2%. X block is divided into 1# test area and 2# test area. The alkali resistance profile control agent was injected in 1# test area in September 2015, and the injection pore volume is 0.035PV, the water cut classification is shown in Table 4, the water cut curves of two test area are shown in Fig. (5).

Table 4

Water cut classification in 1# test area.

Fig.(5) Contrastion of water cut in 1#test area and 2#test area.

As is shown, after injecting alkali resistance profile control agent, the well number which water cut were less than 80% was from 19 up to 22, the number of wells which water cut were more than 90% was from 8 reduced to 1. The water cut of 1# test area is decreased greatly, the water cut is 4% less than 2# test area. So far, the recovery percent of 1# test area is 2.86% more than 2# test area.

The composition of the alkali-resistant profile agent was as follows: polyacrylamide: Mw=25000000, 1800~2000 mg/L; metallic crosslinking agent: 0.15% chromium acetate; organic crosslinking agents: 0.1% phenol and 0.08% methyl aldehyde; 0.2% NaCl. The profile agent had little effect on the interfacial tension of ASP system, the gelation time could be tuned by adjusting the concentration of delayed coagulant. From the results of core liquidity experiment, the alkali-resistant profile could be seen that the residual resistance factor of the profile agent is greater than 50 in pH=12. The results of oil displacement experiment show that the recovery ratio of ASP flooding with alkali-resistant profile agent enhanced by about 4% comparing with that of the ASP flooding. The development effect of x oilfield field shows that, this alkali-resistant profile agent can be applied in the process of ASP flooding, and it can achieve considerable effect, it can enhance oil recovery by 3%.