ASP Flooding: A Solution for Chemical Enhanced Oil Recovery in High Temperature, Low Salinity Reservoir

Hongyan, Cai (CNPC) | Jie, Cheng (China University of Geosciences) | Jian, Fan (RIPED) | Hexin, Luan (Xinjiang Oilfield Company) | Qing, Wang (RIPED) | Wenli, Luo (RIPED)

OnePetro 

Abstract

Presently, field application of Alkali-Surfactant-Polymer flooding (ASP) has achieved great technical success with incremental oil recovery more than 20%. The synergistic effects induced by the three components, alkali, surfactant, and polymer greatly activate remaining oil after water flooding.

With the depletion of oil resources, ASP technique expanded to reservoirs having harsh conditions, such as high temperature, high salinity, low permeability, and heavy oil. For such oilfields, severe conditions bring great technical challenges to chemical agents, making it more difficult to obtain a suitable formulation than that in a conventional reservoir.

The ASP flooding feasibility study was conducted for a massive reservoir with high reservoir temperature ranging from 80 °C to 85 °C and low salinity less than 3000 mg/L. Various evaluations, including polymer testing, surfactant screening and evaluation, long term thermal stability, phase behavior were conducted in the laboratory. Then, the performance of optimized ASP formulation was tested by two runs of core flooding.

Through detailed in-lab study, thermal tolerant polymer and surfactant were selected with satisfying performance. Sound emulsification was observed in phase behavior study of Alkali-Surfactant (AS). ASP flooding utilizing weak alkali Na2CO3 was recommended for such high temperature, low salinity (HTLS) reservoir. Results from core flooding tests demonstrated an incremental oil recovery range from 16.89% to 20.38%. ASP shows promising technical potential for such low salinity reservoir.

Introduction

After more than thirty years research and application, combined chemical flooding (CCF) has been proved as one of the most effective EOR techniques for the improvement of ultimate recovery in mature oilfields (Ji, et al., 2016; Liao, et al., 2017). In Daqing oilfield with moderate reservoir temperature and salinity, enlarged industrial mass application of Alkali-Surfactant-Polymer flooding (ASP) has achieved great success both technically and economically (Cheng et al, 2014). In the ASP formulation, alkali is beneficial to the reduction of interfacial tension (IFT), decreasing adsorption of surfactant on rock, and formation of in-situ surfactants through reactions between alkali and acidic components in crude oil. In ASP flooding, polymer viscosifies injection fluid and changes mobility ratio of water/oil. Surfactant remarkably decreases IFT with the help of alkali and mobilizes remaining oil after conventional water flooding (Shen, 2003). As for binary Surfactant-Polymer formulation (SP), surfactant must have higher interfacial activity compared with its counterpart in ASP due to elimination of alkali (Wang, et al., 2008; Qiao, 2012; Cai, et al., 2017). Even though ASP flooding has some side-effects caused by alkali, more availability of surfactant and higher enhanced oil recovery make ASP an important option in CEOR.