Polymer Injection in a Heavy Oil Reservoir under Strong Bottom Water Drive
- Nasser Said Al Azri (Petroleum Development Oman) | Widad Al Ajmi (Petroleum Development Oman) | Ahmed Kazzaz (Petroleum Development Oman) | Sankaranarayanan Ramalingam (Petroleum Development Oman) | Abulaziz Morshidi (Petroleum Development Oman) | Alexander De Kruijf (Petroleum Development Oman) | Esam Abubaker Jamal (Petroleum Development Oman) | Iman Khamis Al Busaidi (Petroleum Development Oman) | Abdullah Al Mahrouqi (Petroleum Development Oman) | Badar AlKharusi (Petroleum Development Oman) | David Brooks (Shell Intl. E&P Co.)
- Document ID
- Society of Petroleum Engineers
- SPE EOR Conference at Oil & Gas West Asia, 11-13 April, Muscat, Oman
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 7.1.9 Project Economic Analysis, 5.1.2 Faults and Fracture Characterisation, 5.3.2 Multiphase Flow, 2.4.3 Sand/Solids Control, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 1.2.2 Geomechanics, 5.6.4 Drillstem/Well Testing, 5.4.6 Thermal Methods, 5.1.5 Geologic Modeling, 5.5.11 Formation Testing (e.g., Wireline, LWD), 5.7.2 Recovery Factors, 3.3 Well & Reservoir Surveillance and Monitoring, 1.1 Well Planning, 4.3.4 Scale, 4.2 Pipelines, Flowlines and Risers, 1.6 Drilling Operations, 7.1.10 Field Economic Analysis, 5.6.5 Tracers, 1.6.9 Coring, Fishing, 5.6.11 Reservoir monitoring with permanent sensors, 3.3.1 Production Logging, 5.4.1 Waterflooding, 1.8 Formation Damage, 3 Production and Well Operations, 4.1.5 Processing Equipment, 5.6.1 Open hole/cased hole log analysis
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Implementing Enhance Oil Recovery techniques in heavy oil reservoirs with strong bottom water drive has been a challenge in the oil industry. This paper describes an Enhanced Oil Recovery process in which polymer is injected into a clastic reservoir with a strong bottom aquifer drive bearing heavy-oil (250-500 cP). The high reservoir permeability (2-5 Darcy) enables stretching the viscosity limit of a standard polymer application.
The presence of a strong bottom aquifer maintains high reservoir pressure, which could provide a challenge to injectivity. The close proximity of injectors to the oil water contact reduces the efficiency of the polymer flood through water fingering, and polymer loss to the aquifer. To best understand details of the influence of aquifer on the recovery process, test different development scenarios and address key uncertainties, detailed simulation study was conducted. The simulation results showed that the optimum development concept which would help reduce impact of polymer loss to the aquifer would be to utilize the currently existing and future horizontal producers, augmented with additional infill horizontal injectors placed approximately mid-way in the oil column. Optimization of the development was performed using the simulation model where the polymer viscosity, slug size, and injector location were optimized for net present value.
Uncertainty analysis using the simulation model showed that factors such as poor injectivity, poor conformance control and high kv/kh ratio have negative impact on process efficiency. To address and mitigate these key risks and uncertainties a number of activities are underway. These activities include intensive laboratory tests, field injectivity test and a field trial where polymer is injected in newly drilled injectors. The paper discusses study to identify the optimum development concept, key uncertainties and associated risk reduction activities. Finally, this paper discusses the design and the surveillance aspects of the upcoming field trial.
Producing heavy oil reservoirs under primary depletion or water flood normally yields low ultimate recovery and leads to the application of EOR techniques. Thermal and chemical (mainly polymer) techniques are practiced in many parts of the world to unlock medium and heavy oil resources. However, in an environment where heavy oil is above a strong aquifer, additional challenges arise. The aquifer continuously provides pressure to the system, making injectivity (e.g. in case of polymer flood) and efficiency (e.g. in case of steam flood) a concern. Following the evaluation of three EOR techniques (Polymer Flood, Insitu Combustion and High Pressure Steam Injection) polymer was found to be the most economical and practical solution in this environment. This paper addresses the plans put together to address some of the key risks and uncertainties associated with applying polymer in a medium heavy oil reservoir supported by a strong bottom aquifer.
Polymer flooding is a chemical EOR technique applied in medium heavy oil reservoirs. The objective of the process is to improve the mobility contrast between the oil and the aqueous phase, and hence improve the displacement sweep efficiency. In moderately heterogeneous reservoirs, polymer flooding is also applied to improve the volumetric sweep efficiency. Typically a slug of polymer is injected (0.5-1 PV), chased by water. In some cases, optimization is also possible by grading the polymer, i.e. progressively decreasing the polymer concentration (and hence viscosity) in order to optimize the flood economics.
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