Abstract

This paper presents an enhanced oil recovery (EOR) evaluation for two heavy-oil fields in Africa. The objective of the evaluation is to identify the technically and economically viable EOR techniques for the fields. A total of thirteen established and emerging EOR techniques were evaluated in this study. The study included the first degree approximation of the oil recovery for the viable EOR techniques and the stand-alone project economics estimation.

The data required for the study include:

  1. fluids and rock properties;

  2. driving mechanism;

  3. production data;

  4. OOIP and recoverable reserves; and

  5. relative permeability curves.

Various EOR technique screening criteria, consisting of a list of reservoir parameters and their ranges which are likely to lead to a success, were applied to match the parameters of the study fields. The oil recovery predictions were estimated utilizing general reservoir parameters and developed correlations 1. The economic feasibility of the potential EOR techniques was then evaluated based on the stand-alone project economics that accounted for the revenue from the incremental oil and the associated operating and capital costs.

The evaluation results showed that the thermal EOR techniques: steam flooding and in-situ combustion are technically the most viable EOR techniques for the fields. It was then followed by the chemical EOR techniques. The performances of steam flooding and in-situ combustion are both very promising, with oil recovery of up to 49% OOIP. Comparing to the oil recovery of water flooding, a significant incremental oil recovery of 24% OOIP was obtained. However, the in-situ combustion process is able to accelerate the oil production, which significantly impacts the economic viability assessment, rendering the in-situ combustion process as the most technically, and economically feasible EOR process for the fields.

Based on the EOR evaluation, the oil recovery predictions and economic assessments of the thirteen EOR techniques, including the chemical, gas, thermal and microbial EOR techniques, served as a guideline to develop the long term corporate strategy regarding the EOR potential of the fields.

Introduction

Enhanced oil recovery (EOR) could increase technically and/or economically recoverable oil. In current reservoir management practice, various EOR options are considered much earlier in the productive life of a field.

Adopting the same reservoir management strategy, EOR technology was considered to increase the oil recovery factor in two heavy-oil fields (18–24oAPI) in African region. The predicted water flood oil recoveries of these fields are relatively low at about 17% to 25% STOIIP only. Thus, an EOR process instead of water flooding is worth to be considered at the beginning of these fields' lives.

Inevitably, economics always play the major role in "GO/NO GO" decision-making for expensive EOR projects. This screening study was carried out to rule out the less-likely candidates.

The objectives of this EOR screening study are to:

  • Identify suitable EOR processes for the study reservoirs by a quick GO/NO GO screening.

  • Estimate the expected recovery for the process (performance prediction using analytical methods) that passes the first screening criteria (GO/NO GO criteria).

  • Carry out preliminary stand alone project economics assessment on the best two processes for each reservoirs evaluated.

  • Select the most technically and economically suitable EOR process (for reservoirs screened to have more than one suitable process).

The screening study flow chart is shown in Figure 1.

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