ABSTRACT

Chemical Enhanced Oil Recovery (EOR) processes are being considered for large field applications with recent high price of crude oil. However, applications are generally directed towards onshore environment, with temperature less than 85oC, using fresh water as the injection water. Malaysian oil fields are located offshore, with high reservoir temperatures of more than 100oC and use sea water as injection water. This paper reports on laboratory results that were part of an R&D project investigating the feasibility of increasing oil recovery through chemical EOR processes for oil fields in Malaysia.

Chemical EOR processes investigated include surfactant, surfactant-polymer, alkaline-surfactant, and alkaline-surfactant-polymer. A unique 2-stage softening prepared seawater for the two processes using alkali. Thermal aging studies at 119oC were used to screen chemicals for stability and degradation. Interfacial tension and phase behavior tests of stable chemicals were used to select formulations. Linear corefloods and thermal degradation tests were used to select polymers. Oil recovery studies used field proportioned injected chemical volumes in radial corefloods.

Dilute surfactant processes without alkali recovered little incremental oil. This was attributed to heavy consumption loss of surfactant. Average incremental oil recovery in coreflood studies by alkali-surfactant flooding was 14.6% OOIP and by alkaline-surfactant-polymer flooding was 28.6% OOIP respectively. This proved that there is potential for chemical EOR application in Malaysia.

INTRODUCTION

Despite the very harsh environment for chemical EOR processes in Malaysia, PETRONAS has undertaken an R&D project whose scope of work includes:

  • Phase 1: screening of suitable reservoirs and chemical processes,

  • Phase 2a: detailed chemical laboratory design,

  • Phase 2b: reservoir modeling to estimate process performance,

  • Phase 3: economic evaluation and

  • Phase 4: conceptual pilot design.

This paper focuses on the laboratory aspects of the study (Phase 2a) of the Angsi I-68 reservoir that was selected in Phase 1. It includes the overall chemical EOR processes evaluations and design, and observed incremental oil production from coreflood experiments at laboratory scale.

Chemical EOR Considerations

Chemical EOR processes in offshore environments are constrained much more by "footprint" or available space on platforms than are their onshore counterparts. Therefore, the simpler the process utilized the better. An ideal process would be to simply add a liquid surfactant to the seawater currently being injected. The objective would be to mobilize waterflood residual oil trapped by capillary forces by reducing interfacial tension. A single liquid surfactant would require only storage, metering, and blending into the injection stream. Any other chemicals added would have the same requirements, which may be complicated if, for instance, the chemical were a solid rather than a liquid. However, an objective of the R&D program was to investigate a range of Chemical EOR processes that may be technically viable. These included surfactant (S), surfactant-polymer (SP), alkaline-surfactant (AS), and alkaline-surfactant-polymer (ASP).

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