Comparison of Strong-Alkali and Weak-Alkali ASP-Flooding Field Tests in Daqing Oil Field

Abstract

Summary Alkali/surfactant/polymer (ASP) flooding is one of the most-promising enhanced-oil-recovery (EOR) technologies. Strong alkali (NaOH) was used in early field tests mainly because of its stronger emulsification ability and wider surfactant range, which can meet the requirements of ultralow interfacial tension (IFT). However, subsequent field tests indicated that the advantages of a strong alkali did not outweigh the disadvantages caused by serious scaling and production-capacity loss. Although a critical comparison of strong alkali ASP (SASP) and weak alkali ASP (WASP) on the basis of field tests is quite difficult and complex, considering the small differences in reservoir characteristics, injected fluid, and operational changes, the two completed field tests in Daqing provided us with valuable and important information. The petrophysical features of the two field tests were similar. The well spacings and well patterns of the two field tests were critically the same, and the same screening standards and design ideas were followed. The incremental recoveries of WASP and SASP were nearly the same, while WASP had a higher peak oil production than SASP after the injection took effect. WASP was proved to have less liquid-producing-capacity loss than SASP. The emulsification effects of WASP were weaker than those of SASP, which also lowered the difficulty and cost of the treatment of the emulsified fluid. The chromatographic separation was different in the two pilot tests, in which WASP had alleviated chromatographic separation. Breakthrough of the polymer occurred before the alkali followed by the surfactant, and this occurred at 0.06 pore volumes (PV) for SASP but was delayed until 0.13 PV for the WASP flooding. The scaling of SASP was much-more severe than that of WASP, leading to a much-higher treatment cost. The economic performances of the two tests, which are of vital importance in a low-oil-price era, were quite different, and WASP had much-better performance than SASP. The input/output ratios of WASP in B-2-X and SASP in B-1-DD were 1:3.7 and 1:2.3, respectively. The returns on investment (ROIs) of WASP in B-2-X and SASP in B-1-DD were 19.1 and 12.9%, respectively, whereas the financial internal rates of return (FIRRs) after tax were 22.3 and 18.0%, respectively. The average FIRR of local oil-industry projects is 12%. Field tests indicated that WASP is both technically and economically better than SASP under the conditions in the Daqing oil field.

Research progress of viscoelastic surfactants for enhanced oil recovery

“…Due to the limitations of conventional single chemical flooding technology, the concept of chemical combined flooding is proposed, and the most representative one is alkalinesurfactant-polymer (ASP) flooding (Abdurrahman, 2017;Guo et al, 2018;Khalilinezhad et al, 2016;Yang et al, 2019). Regarding the ASP flooding mechanism, researchers have conducted many in-depth studies in recent years.…”

“…provides a guarantee for the long-term stable production (Zhang et al, 2016;Zhu, 2015). According to reports, China's chemical flooding related technologies accounted for more than 55% of EOR produced oil in China (Gao, 2014;Guo et al, 2018).…”

Optimal Design of Alkaline–Surfactant–Polymer Flooding under Low Salinity Environment

“…The experiments were divided into the following tests: the phase behavior test to find the best-performing formulation of the ASP elements, the filtration ratio (FR) test to examine the polymer transport stability, and the coreflooding test to estimate the actual flow performances of the ASP formula determined. The alkali was selected to be sodium carbonate (Na 2 CO 3 ; Daejung Chemicals, Goryeong, Korea), of which its effectiveness has been validated [4,14,15]. The polymer was hydrolyzed polyacrylamide (HPAM), Alcoflood 955 polymer with a molecular weight around 4.5 million Dalton (Ciba Specialty, Basel, Switzerland).…”

“…Alkaline-surfactant-polymer (ASP) flooding intends to integrate a synergy of chemical mixtures, e.g., alkalis, surfactants, co-solvents, and polymers, in order to recover residual oil [1][2][3][4][5]: alkalis and surfactants mobilize residual oil and reduce the interfacial tension between the displacing phase and the oil; polymer slug enhances mobility ratios and volumetric sweep efficiencies. Successful ASP flooding can be achieved by designing an optimal ASP formula that is closely related to phase types, i.e., microemulsion, such as Winsor types I (II-), II (II+), and III, which formation salinity influences significantly.…”

Dialkyl Sulfobetaine Surfactants Derived from Guerbet Alcohol Polyoxypropylene–Polyoxyethylene Ethers for SP Flooding of High Temperature and High Salinity Reservoirs

“…The ASP project in Daqing oilfield, China, probably with the biggest scale in the world, produces over 4 million tons of oil annually (Olajire, 2014). However, field tests have indicated that using caustic alkali in ASP flooding can cause some detrimental effects (Guo et al, 2018; Wang et al, 2004; Zhu et al, 2012a). The calcium (Ca 2+ ) and magnesium (Mg 2+ ) ions contained in connate water may react with the alkali to form insoluble precipitates (Goswami et al, 2018; Li et al, 2016b), leading to permeability reduction as well as scaling build‐up on surface of pipes and downhole equipment, especially in high salinity reservoirs (Sheng, 2014).…”