A Case Study on Compositional Reservoir Simulation for a large Tight Reservoir: A Detailed Road Map from Initialization and History Match to Prediction Simulation
- Mahmoud Ali Basioni (Abu Dhabi Co. Onshore Oil Opn.) | Ahmed Mohamed Dawoud (Abu Dhabi Co. Onshore Oil Opn.) | Mohamed Ahmed Ben Saad (Abu Dhabi Co. Onshore Oil Opn.) | Ahmed El Mahdi (Abu Dhabi Co. Onshore Oil Opn.)
- Document ID
- Society of Petroleum Engineers
- North Africa Technical Conference and Exhibition, 20-22 February, Cairo, Egypt
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.6.2 Core Analysis, 5.2.1 Phase Behavior and PVT Measurements, 5.4 Enhanced Recovery, 5.5.2 Core Analysis, 7.6.2 Data Integration, 4.3.4 Scale, 5.8.7 Carbonate Reservoir, 5.1.1 Exploration, Development, Structural Geology, 1.2.3 Rock properties, 4.1.2 Separation and Treating, 2 Well completion, 1.12.2 Logging While Drilling, 2.2.2 Perforating, 5.1.5 Geologic Modeling, 6.5.2 Water use, produced water discharge and disposal, 5.4.2 Gas Injection Methods, 5.2.2 Fluid Modeling, Equations of State, 4.1.5 Processing Equipment, 5.5.11 Formation Testing (e.g., Wireline, LWD), 5.5 Reservoir Simulation, 5.1.2 Faults and Fracture Characterisation, 5.5.8 History Matching, 5.3.4 Reduction of Residual Oil Saturation
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This paper illustrates a detailed workflow to build a compositional simulation model for a large gas-bearing with a sizable oil-rim carbonate reservoir in the Middle East. The workflow is emphasising on the importance of data gathering, validation, analysis and integration in building a sound simulation model from geological and dynamical perspective. One of the main achievements of this work was the concept behind matching the variable producing Gas-to-Oil ratio without jeoporadizing the match of other performance parameters. The key resolution to this problem is the careful setup of equilibration and fluid models.
The reservoir under study is a large gas-bearing with a sizable light oil rim reservoir. The vertical closure is about 4-5 times the reservoir thickness. The reservoir is about 40 ft thick with a porosity range of 7-18% and a very low permeability range of 0.1 - 5 mD.
Being the shallowest hydrocarbon-bearing zone in the field, the reservoir was penetrated by about 129 holes that targeted deeper horizons providing good structural control. The geological model was built based on all penetrating strings including eight cored wells. In addition to those wells, the reservoir has a good portfolio of dynamic data such as 8 MDT logs, 7 routine PVT data for both gas and oil, Rig-On-Site (ROS) tests from 13 appraisal and delineation wells. The good aerial and vertical spread of appraisal wells and their corresponding data acquisitions have provided good control points for initialization and history match processes.
Data integration provided a good understanding of fluid contacts and reservoir equilibration model. Model's porosity and permeability match logged and cored data. The log-derived saturation model which is based on porosity-classified rock types, matches logs saturations. There is an agreement between static and dynamic fluid-in-place results.
The reservoir is under a minor Early Production Scheme (EPS) since early 2006 with the objective of investigating well productivity and reservoir performance. Two wells are currently on-stream. One of the main challenges associated with this reservoir in addition to the very low permeability; is the clear variation in GOR production observed from ROS tests of appraisal wells and existing development wells. This variation is ranging between 200 - 1600 scf/stb at location close the ODT depth to 3000-8000 scf/stb when approaching the level of the gas-oil-contact, and finally shoots to a range of 10000 - 36000 scf/stb at shallower depths than the GOC.
Data Gathering, Validation, Analysis and Integration
Initial Reservoir Pressure and Fluids Contacts: RFT/MDT Pressure Data. Eight wells were selected to measure the initial formation pressure and pressure gradient using Repeat Formation Tester (RFT) and Modular Dynamic Tester (MDT) during the period of 1991 (starting with well-1) to the most recent well (well-8) at the end of 2009. Figure 1 shows a map view of all wells that were MDT/RFT tested. Figure 2 shows the pressure versus true vertical depth with respect to sub sea level.
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