Like Cures Like Microbial Enhanced Oil Recovery in Biodegraded Crude

Abstract

Field A is an onshore oil field in Thailand. This area contains biodegraded medium-heavy crude reservoir; 19°API oil gravity and 144 cp viscosity. Therefore, the field suffers from a low recovery factor due to high crude viscosity. On one hand, bacteria have exerted an adverse effect on production, on the other hand, it means that the condition of the reservoir is suitable for implementing Microbial Enhanced Oil Recovery (MEOR). The MEOR is a technology that utilizes microorganisms (mainly bacteria), to enhance oil production, especially for medium-heavy oil. By feeding nutrients to bacteria, several metabolites were produced that would be useful for oil recovery. This technique is well known for its low investment cost, hence, high return. The technical screening confirmed that the reservoir and fluid properties are suitable for MEOR. Consequently, sixteen core samples and three water samples were collected for indigenous bacteria analysis. Although the laboratory indicated there are countless bacterial strains in the reservoir, the nitrate-reducing biosurfactant-producing bacteria group was identified. This bacteria group belongs to the Bacillus genus which produced biosurfactant and reduced crude viscosity by long-chain hydrocarbon degradation. Therefore, the treatment design aimed to promote the growth of favorable bacteria and inhibit undesirable ones. Consequently, a combination of KNO3 and KH2PO4 solutions and a specialized injection scheme was tailored for this campaign. The pilot consisted of two candidates those were well W1 (76% water cut), and well W2 (100% water cut). The campaign was categorized into three phases, namely, 1.) baseline phase, 2.) injection and soaking phase, and 3.) production phase. Firstly, the baseline production trends of candidates were established. Secondly, KNO3 and KH2PO4 solutions were injected for one month then the wells were shut-in for another month. Lastly, the pilot wells were allowed to produce for six months to evaluate the results. The dead oil viscosity of well W1 was reduced from 144 cp to 72 cp which led to a 6.44 MSTB EUR gain or 1.3% RF improvement. On the other hand, the productivity of well W2, the well with 100% water cut, was not improved. This was expected due to insufficient in-situ oil saturation for a bacteria carbon source. Considering the operational aspect, there was no corrosion issue or artificial lift gas-lock problem during the pilot.