Technical Breakthrough in Production Engineering Ensures Economic Development of ASP Flooding in Daqing Oilfield

Abstract

Pilot tests commenced from 1980s in Daqing Oilfield have proved that ASP flooding could improve the recovery rate by 20% based on water flooding, while scaling issue in producers was the only factor which made it hard to reach that objective. Investigation in site indicated that more than 70 percent producers had scaling issues, and scaling types and degree in ASP producers varied dramatically in different wells and different period. In the peak of scaling period, the averaged running life was only a couple of months. A project focused on the harness of scaling issue in ASP producers was implemented from 2002. In the first stage, the study aimed at getting the scaling principle in ASP producers. A series of monitoring and analysis on producing fluid's ion concentration were implemented in different ASP producers. The scale deposited on tubing in different depths were picked out and analyzed. The scaling mechanism of ASP producing liquids in artificial lift systems were created which presented the varying principle of scaling ions as well as the characteristics of scale in ASP producers. A set of scaling principle prediction plates was also created with a success ratio being above 90%. In the second stage, a series of anti-scaling artificial lift techniques were developed including new anti-scaling pump, chemical scale removers and scale inhibitors, and other matching techniques. The new anti-scaling techniques were put into application from several wells up to near 1,000 wells. The operating rate has been improved by 4.13 percent as well as the operating cost decreased by 72.77%. The technical breakthrough in anti-scaling artificial lift systems improved the operating life of ASP producers considerably. It applied solid foundation for ASP flooding to become a beneficial method for mature oilfield development in commercial scale.

ASP Flooding: Theory and Practice Progress in China

“…The contact angle values are further decreased in presence of alkali resulting conversion of intermediate wet quartz to water-wet, which is the preferential need for the enhanced oil recovery [4]. The ASP flooding can alter the reservoir rock wettability from oil-wet to water-wet, as verified by coring before and after ASP flooding field test [13][14][15]. This helped explain why ASP flooding can improve both sweep efficiency and displacement efficiency.…”

“…According to capillary number theory and classical CDC, the equilibrium IFT of ASP system was required to be as low as 10 −2 mN/m even 10 −3 mN/m orders of magnitude and it would be best if it has a wide range of surfactant concentration [13][14][15]. In addition to developing more efficient and cost-effective surfactants, factors affecting the IFT are also concerned [13][14][15]47]. The polymer concentration has little impact on the oil-water IFT, and the IFT of polymer with different concentrations is at the same order of magnitude.…”

“…It was found through experiments that the active substance formed by nitrogen-containing heterocyclic compounds and alkali could produce synergistic effect with alkyl benzene sulfonate, reducing IFT. Such effect equals to that of acidic active component, solving the problems of low acid ASP flooding creatively in Daqing oilfield [13][14][15]. This progress is crucial for reservoirs that have low acid value crude.…”

“…In ASP flooding, the main purpose of adding alkali is to use cheap alkali to replace expensive surfactants so as to achieve its goal of reducing the IFT [13][14][15]. Alkali can reduce adsorption of the surfactant [5] and also adsorption of polymer because alkali reduces surfactant adsorption by increasing the rock surface's negative charge density, making it preferentially water-wet [24].…”

“…The pH value of different alkali can be seen from [57]. Alkali has a relatively large impact on the polymer [13][14][15], (Tang et al 2003). A high alkaline concentration will also reduce polymer viscosity; thus more polymer will be needed to reach a required viscosity [5].…”