Alkali-surfactant-polymer combination flooding (ASP flooding) is one of the main chemical EOR techniques for the significant increase of crude oil recovery in PetroChina. In this paper, the progress in field tests of ASP flooding, effects analysis and related problems in application are introduced and discussed. The development trend of ASP flooding is suggested. Field tests of ASP flooding in PetroChina have been performed since 1994, including six pilot tests in both sandstone and conglomerate reservoirs and three industrial tests, and the incremental oil recoveries of such tests were more than 19–20%. It is found that three factors are responsible for successful ASP flooding field tests : (1) Good performance of oil displacement agents. (2) Good profile control and oil displacement ability. (3) Reasonable well pattern and well spacing. Side effects encountered in field tests are as follows: (1) scaling and corrosion damaged the lifting system and shorten the average pump-checking cycle accordingly. (2) Strong emulsification resulted in many liquid treatment problems such as the excess of solid particle content over the standard of water circulation and high cost of water treatment. (3)The liquid production decreased greatly. The development trends in chemical combination flooding technique are proposed based on results of ASP flooding field tests. The strong alkali ASP flooding should be replaced by weak alkali ASP flooding or even alkali-free SP combination flooding. The application reservoir will cover from sandstone to conglomerate and carbonate, from low salinity and low temperature reservoirs to high salinity and high temperature ones, etc. The corresponding key techniques such as development of new chemical agents and advanced produced liquid treatment system should be considered in future tests and application of chemical combination flooding.

Most of the high permeability reservoirs in Daqing oil field have been conducted by water flooding and polymer flooding. The average oil recoverable recovery has reached to 53% after polymer flooding. Currently, the further development of such reservoirs has become a big challenge due to both serious heterogeneity reservoirs and highly dispersed residual oil. Foam flooding, as a candidate EOR technique integrating both properties of gas injection technique and chemical flooding, has been proposed. In this study, systematic laboratory experiments on foam flooding EOR technique for Daqing reservoirs after polymer flooding have been performed. Several operating parameters have important influences on the recovery efficiency.① Both the foamability and stability are the key factors to ensure high performance of recovery. The foam formulas were optimized with good performance of foamability and stability. ② Injecting mode is another important factor. Three main injection modes, including co-injection of gas and solution, alternative injection of gas and solution, and direct injection of foam were compared. The direct injection of foam is the most effective mode and the alternative injection of gas and solution is the poorest. ③ The gas liquid ratio can also affect the flooding efficiencies greatly. The optimized gas liquid ratio was proposed as 3:1-4:1 for direct injection mode at the reservoirs condition. EOR effect evaluation of foam flooding after polymer flooding has been conducted upon threelayer positive rhythm sandpack cores flooding tests. Results indicate that foam flooding can contribute 12-22% OOIP recovery even if the recovery after polymer flooding is nearly 55%. The obviously increasing of injection pressure during the foam flooding indicates that nitrogen foam flooding has excellent profile control ability. Foam flooding can block thief zones for highly heterogeneous reservoirs. It may become a promise EOR method for Daqing reservoirs after polymer flooding. IntroductionWithin the past decades, polymer flooding as the major EOR technique has been conducted successfully across Daqing oil field in China [1-3]. The recovery efficiency by polymer flooding is 10% higher than that of water flooding for main reservoirs in Daqing Oil Field. And average oil recoverable recovery has reached to 53% after polymer flooding.Logging data of drilling wells indicate that swept thickness of the reservoir increased 21.4% from 68.6% of water flooding to 90% of polymer flooding, and oil saturation reduced 11.9% from 52.8% to 40.9% [4]. As demonstrated in Fig. 1. the residual oil distribution after polymer flooding was highly heterogenous. Therefore, the further development of such reservoirs has become a big challenge due to high water cut, poor sweep efficiency, severe heterogeneity and highly dispersed residual oil [5][6][7]. Foam flooding, as a candidate EOR technique integrating both properties of gas injection technique and chemical flooding, has been proposed. Significant advances of foam flooding have been achieved in...

For mature oil fields, foam flooding is an attractive chemical EOR technique and many pilot tests have been carried out in China. The performance of foam flooding pilot tests and its affect factors on oil recovery was discussed in this paper. The development trend and key technologies of foam flooding technique are pointed out. Eighteen foam flooding pilot tests have been carried out in China from 1994 to 2010. Good performance have achieved in sixteen pilot tests. Through effects analysis of the pilot tests, three main aspects are concluded for affecting the performance of foam flooding tests. First, the characteristics of target reservoirs influence effects of foam flooding tests. The performance of foam flooding in higher oil viscous reservoirs is better than that in light oil reservoirs. The reservoir temperature and formation water salinity also influences the effects of foam flooding. Secondly, the chemical formula of foam solution and the size of slug influence the performance of foam flooding. The stability of foam formula influences the effects of foam flooding greatly. With the same amount of surfactant solution, the effect of high concentration small-sized slug is better than that in low concentration large-sized slug. Last, the injection method and gas liquid ratio can directly influence the foam performance in the reservoir, gas and liquid mixing injecting model is better than surfactant solution-alternation-gas (SAG) injection, and reasonable gas liquid ratio is important for guarantee good effects of foam flood. At present, the trend of foam flooding in China is from nitrogen foam flooding and natural gas foam flooding to air foam flooding. The key technologies of foam flooding are the development of high stable foam formula with oil tolerance, salt and temperature resistance, good injection method and reasonable injection parameter etc.

Reservoirs with high temperature and high salinity are widely distributed in various countries, which contribute an important percentage of oil output in the world. Pilot tests show that chemical flooding technique is one of effective EOR (Enhanced Oil Recovery) ways to improve the oil recovery for mature oilfields. The key technology of chemical flooding is to develop high efficiency surfactants with low cost. In this paper, the betaine surfactant has been synthesized with cheap raw material of fatty acid, and its functional group of hydroxylpropyl sulfo hydrophilic group can improve the heat resistant and salt tolerant abilities of the surfactant. The surfactant was characterized by Infrared Spectra, Raman Spectra and Element Analyzer. The analytical data show that the surfactant is consistent with the designed molecular structure, hydroxylpropyl sulfobetaine. The interfacial tension between the sulfobetaine solution and crude oils achieve ultra-low values (less than 1.0×10-2 mN/m) with temperature range from 30 °C to 90 °C, or salinity range from 20000 mg/L to 120000 mg/L, when the surfactant concentrations are from 0.05 wt% to 0.3 wt%. The parameters of hydroxypropyl sulfobetaine show that it is a suitable candidate for the oil-displacing agent due to its good long-term stability (within 180 days), low critical micelle concentration (4.74×10-5 mol/L), low dynamic adsorptions (0.44–0.72 mg/g), good injectivity and mobility. Oil recoveries increased 20 % - 24 % (OOIP, Original Oil In Place) after water flooding, with both weak alkali ASP and alkali-free SP formulations combined the sulfobetaine. And the oil displacement efficiencies of weak alkali ASP or alkali-free SP flooding have reached to 73 % - 76 %. Excellent properties of the hydroxypropyl sulfobetaine indicate that it is a promising surfactant, which can be applied in reservoirs with high temperature and high salinity.

Lab study of chemical EOR for the carbonate reservoir was performed through core characterization, chemical formula screening, surfactant adsorption losses experiments and oil displacement core flooding tests of chemical flooding.The research results lay the foundation of future pilot tests for chemical combination flooding applying to carbonate reservoirs.Core characterization by scanning electron microscope and mercury injection capillary pressure experiment prove that there are plenty micropores and a few emposieu within rock, porosity of formation cores is relatively high but permeability is low, the reservoir lithology belonged to typical biostromal carbonate reservoir and the heterogeneity is severe. Chemical flooding formula was investigated by polymer and surfactant screening tests. Salt tolerant polymers including STARPAM and KYPAM showed good viscosifying performances than conventional polymer when prepared with formation water. Amphoteric surfactant AS-13 and anion-nonionic surfactant SPS1708 were selected and ultra-low interfacial tension between crude oil and formation water can be obtained in alkali-surfactant-polymer (ASP) and alkali free surfactant-polymer (SP) systems. Adsorption losses of surfactants on core sample showed that the dynamic adsorption losses of surfactant AS-13 and SPS1708 were 0.46mg/g and 0.37mg/g respectively. Core flooding tests of chemical flooding proved that more than 17~18% incremental oil recovery over water flooding could be obtained with ASP (0.6wt% Na 3 PO 4 + 0.3wt% surfactant + 1000ppm polymer) or SP (0.3wt% surfactant + 1000ppm polymer) flooding. The effect of both ASP and SP flooding was better than that of surfactant flooding.The experimental results are considered to be technical feasibility and confirm the effectiveness of chemical EOR methods especially the SP flooding for the biostromal carbonate reservoir, which may present further understanding for chemical EOR field application in carbonate reservoirs.