Recent Advances of Alkali-Surfactant-Polymer ASP Flooding in China

Abstract

AbstractAlkali-surfactant-polymer (ASP) flooding is very promising chemical enhanced oil recovery (EOR) technique which has drawn lots of attention. Compared with surfactant-polymer (SP) flooding and polymer flooding, ASP flooding incremental oil recovery can be much higher. This has been verified by several field tests in China. Alkali distinguishes ASP flooding and SP flooding. Alkali plays an important role in ASP flooding. How to select the alkali in the ASP flooding involves ASP flooding mechanisms. Although it is generally a consensus that the ASP flooding adopts weak alkali Na2CO3, strong alkali NaOH was also used both in laboratory and many field tests in China. ASP flooding field tests in Daqing oilfields are notable for the largest number and the biggest size in the world. ASP flooding was first put into commercial application in Daqing. Hence, the lessons and learnings from Daqing field practices as well as laboratory studies can help to provide insights into ASP flooding mechanisms. The number of strong alkali ASP flooding (SASP) field pilot projects is three times that of weak alkali ASP flooding (WASP) in Daqing. This was mainly caused by the difficulty to find suitable surfactants that can reduce oil water IFT to ultra-low for Daqing high wax content and low acid value oil. Earlier surfactants can only attain ultra-low IFT in presence of NaOH. The performance of WASP field tests (B-2-X) using surfactant Daqing petroleum sulfonate (PS) was well above expectation, and some SASP blocks had too high rate of corrosion and scaling. This makes WASP feasible and more attractive than SASP. Due to the sharp fall of oil price, how to choose alkali in Daqing oilfield is of great importance for optimum economic benefit. In 2012 and 2013, the first SASP and the first WASP demonstration project were put into operation in Daqing oilfield. In 2014, Daqing oilfield started to promote ASP flooding in an industrialized manner. In 2015, Daqing oilfield's ASP Flooding production accounted for nine percent of the oilfield's total oil production. In 2016, Daqing oilfield's ASP Flooding oil production reached more than 4 million tons, accounting for more than ten percent of the total oil production. This paper investigated the mechanisms of ASP flooding with a focus on alkali effect. The interaction between different chemicals, polymers, alkalis, surfactants were also studied. Surfactants screening has also been reviewed. The surfactants screening process differences between China and the USA were discussed.