Towards the e-field: Continuous Monitoring of Pore Fluid Phase Using Horizontal Wells
- Brian John Evans (Curtin University of Technology) | Bruce Hartley | Nasser Keshavar (Curtin University of Technology)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil and Gas Show and Conference, 15-18 March, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2009. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.2.1 Phase Behavior and PVT Measurements, 3 Production and Well Operations, 1.6 Drilling Operations, 7.2.3 Decision-making Processes, 2.4.3 Sand/Solids Control, 5.1.6 Near-Well and Vertical Seismic Profiles, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 3.3 Well & Reservoir Surveillance and Monitoring, 1.2.3 Rock properties, 1.14 Casing and Cementing
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The electric or e-field has been discussed at length in literature, in terms of the methodology of continuously remotely monitoring oil field production over a long term using vertical and horizontal wells, and transmitting data back to a monitoring centre. Conventional vertical well monitoring methods is adequate to monitor at points around an oil field but continuously monitoring where fluids are moving requires monitoring over an area using horizontal wells.
Recent research has shown that seismic methods can show subtle changes in pore fluid phase which enhances the potential for long term monitoring where pore pressure is reducing, where injected water or CO2 flood options have been chosen, and areas where gas is being replaced by water. If we can marry the use of slim-hole horizontal sensor cables with this recent demonstration of the detection of phase changes, then we have the tools for the first applied e-field scenario.
During 2007, laboratory tests injecting different amounts of CO2 into pore water showed that by monitoring the seismic transmission through a simulated rock, there was a change in seismic frequency response and transmission amplitude. Physical modeling has shown that a horizontal slim-hole well drilled to test the ability to put sensors in a horizontal well, can then be used for remote reservoir surveillance. A seismic source which walks around at the surface, produces data which is then processed to produce an indication that this method can be used as a first step for determining pore fluid properties over an area.
This paper presents the results of the experiments on pore fluid phase and discusses how the use of horizontal wells allows the ability to develop the e-field concept towards reality.
As the production of oil and gas depletes reserves in many cases leaving some 50 to 60% of reserves in-place, one of the most important issues during both production and operations to enhance production levels using stimulation methods, is that of understanding the location of missed pay zones. The industry is becoming accustomed to recording three dimensional (3-D) seismic reflection surveys to use the acoustic impedence contrast between the hydrocarbons in-place and the cap rock to produce data volumes of the reservoir which in turn provide areal images of reserves. When such 3-D surveys are repeated over time, after subtraction from the original 3-D data, the difference is known variously as the repeat 3-D difference volume or the time-lapse 4-D image volume. This can show missed pay zones, and provided that seismic reflection data quality is high having signal-to-noise ratios of around 12:1 (Smith, 2007), it becomes possible to sense changes in oil and gas location, and pressure effects which allow improved production management and step-out production wells to be drilled (Smith et al., 2007). Consequently, oil and gas monitoring for production management over time has been demonstrated as assisting the resource management decision processes.
Such 4-D seismic reflection survey difference slices through the reservoir provide excellent knowledge of oil in place, the location of gas sweet spots, pressure and information on the areal location of thief zones, and so on.
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