Progress and Effects of ASP Flooding

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 151285, ’Recent Progress and Effects Analysis of ASP-Flooding Field Tests,’ by Youyi Zhu, SPE, Qingfeng Hou, Weidong Liu, SPE, Desheng Ma, SPE, and Guangzhi Liao, SPE, State Key Laboratory of Enhanced Oil Recovery, Research Institute of Petroleum Exploration and Development, Beijing, prepared for the 2012 SPE Improved Oil Recovery Symposium, Tulsa, 14-18 April. The paper has not been peer reviewed. Alkali/surfactant/polymer (ASP) flooding is one of the main chemical-enhanced-oil-recovery techniques for increasing crude-oil recovery used by PetroChina. Field tests have been performed in China since 1994, including six pilot tests in sandstone and in conglomerate reservoirs and three industrial tests. Incremental oil recoveries of those tests were greater than 19–20%. Three factors were found to be responsible for successful ASP flooding. Good performance of the oil-displacement agents Good profile control and oil-displacement ability Reasonable well pattern and well spacing Side effects included scaling and corrosion damage to the lifting system that shortened the average pump-checking cycle, strong emulsification that resulted in many liquid-treatment problems, and greatly decreased liquid production. Introduction Since 1994, five ASP-flooding pilot tests have been carried out in different regions of the Daqing oil field. Oil recoveries have been enhanced by 20% compared with waterflooding. Weak-alkali ASP-flooding pilot tests were carried out in conglomerate reservoirs in the northern part of the second middle zone of the Karamay oil field, with oil recoveries improved by more than 20%. Table 1 summarizes these tests. Four expanded ASP-flooding field tests have been carried out in the Daqing oil field since 2000 using industrial surfactants made from heavy alkyl benzene sulfonate (HABS) and petroleum sulfonate. The application was ex-tended from a Type-I layer (higher average permeability—approximately 800×10−3 Μm2—and a thicker oil layer) to a Type-II layer (lower average permeability—approximately 500×10−3 Μm2—and medium oil-layer thickness). ASP flooding has been moved from strong-alkali-type (NaOH) to weak-alkali-type (Na2CO3) fluids. With the progress of ASP-flooding tests, ASP flooding has been applied on a large scale in the Daqing oil field since 2007. Commercial application has been implemented in the East-II Block of Xin 1-2 Region, the South 6 Region, the East-I Block, and the East-II Block of Xin 6 Region. The total reserves of these regions are 28.61×106 m3. Analysis of Field Tests ASP flooding exhibited good enhanced oil recovery in field tests. Chemical Agents. Chemical agents used in the ASP flooding were good quality and had stable performance. The ultralow oil/water interfacial tension (approximately 10−3 to 10−4 mN/m) was achieved when 0.05–0.3 wt% surfactant was mixed with 0.4–1.2 wt% alkali. The adsorption loss of surfactant to the rock was less than 1 mg/g of sand. According to sample data from the injecting well, the pass rate of HABS surfactant for ASP flooding was 99.5%. High-molecular-weight polymer, a salt-resistant polymer with a concentration of 1500 mg/L, was mixed with Daqing-oilfield formation water. The system showed good shear resistance and long-term stability, with a viscosity greater than 40 mPa•s. The viscosity ratio of chemical fluid to crude oil was ensured to be greater than 4.0. High-purity liquid alkali produced by an ionic-membrane process was used and worked well with the surfactant, yielding reduced scale deposit in the injection zone.