Shut-in a well to perform a PBU test for surveillance
Apart from baseline initial PBUs following a new production start-up, most of the production PBUs should be obtained from opportunistic shut-ins. However, in some cases, we need to plan for additional PBU tests for surveillance, and that might be a challenge with the management team…
Below is an attempt to make your life easier with some justification for a PBU test.
Plan PBU tests for surveillance
During the first to second week of production, a new well should be tested with one or two baseline initial PBUs to obtain the initial well and reservoir performance (KH, Skin, reservoir pressure, connectivity). These initial shut-in tests become the “reference” PBUs and will be used for comparison, in particular against opportunistic PBUs later in the well’s life.
The initial baseline PBUs need to be long enough to see past the wellbore storage and get access to the radial flow regime in the horizontal plane across the entire net reservoir thickness. Ideally, a design study should be performed with a well test program.
Monitor and predict well performance
In addition to reservoir pressure data, a PBU interpretation provides information on skin and the effective permeability.
In an oil well for example, the effective permeability to oil could be observed as decreasing due to gas breakout, which could be the main cause of a rapid rate decline.
In some cases, we could observe an increase in KH, due to repressurisation with water injection. With short opportunistic PBUs, it might be difficult to catch this and the team may need some planned longer shut-ins.
Planned PBUs could be used to try to understand whether the change in effective permeability is reversible. This should be a key issue in reservoir understanding, and should help to predict performance and optimize field management.
Prediction of water breakthrough
PBU tests could help to identify and monitor the water front. A shut-in will then provide indications to predict water breakthrough, with a couple of months in advance on some cases. This will help the subsurface team to get prepared and obtain rapid learning from the water breakthrough.
It is even more critical to perform frequent PBU tests before water breakthrough. With an increasing watercut, it might become difficult on some occasions to differentiate between possible causes of KH decrease.
Lack of good quality operational (opportunistic) shut-ins to adjust reservoir pressure, monitor well performance and recovery process, etc…
While it is generally possible to track well performance and reservoir pressure using PBUs from operational shut-ins, there might not be any good quality and interpretable PBU test for a certain period. In addition, there might not be any plan for shut-in for a period of months.
Although the production loss is taken seriously, a request needs to be made to shut the well in for surveillance. Otherwise, it would become increasingly difficult to address key reservoir issues without good quality PBU tests.
Well management during a period of rapid decline
A change in rate of decline might be caused by a changing wellbore damage (skin) or/and by pressure support problems. A planned PBU test at that moment will help to understand this performance deviation, which could result in the need for a well optimum treatment so as to maximize the well’s production life.
Assess the impact of a well intervention
To fully understand the impact of a well intervention, we need to perform a PBU before and after the operations. Thus, the PBU analyst will be able to detect the change for each skin component (mechanical skin, geometrical skin or turbulence), the change in effective permeability around the wellbore, in perforation height or horizontal length, in the fracture dimension or conductivity, etc…
HSE when drilling a nearby well
A planned PBU test may be needed to provide a better quality prediction of reservoir pressure during reservoir drilling of a nearby well. This will the subsurface team to take the decision whether neighboring wells should be shut in during that stage for HSE reasons.
Calibration of 4D-Seismic
Planned PBU tests should be contemplated when acquiring seismic data, so as to minimize uncertainty in reservoir pressure and avoid loss in value in the program. As the seismic interpretation will be influenced by reservoir pressure, it is critical to obtain good estimates from PBU tests to calibrate the seismic.
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Why testing wells ?
- Confirmation of discovery and productivity
- Clean-up and rate measurement
- Large volume fluid sample
- Well and reservoir performance
- (skin, KH, Pi, heterogeneity, boundaries)
- Reservoir connectivity & proven volume
- Flow behaviour around wellbore
- Large scale of investigation (100-1000s ft)
- Use of opportunistic shut-ins
- Track permeability, skin, reservoir pressure
- Monitor performance over time
- Understand performance deviation
- Assess well intervention
- Quality control rate measurement
No other alternative to:
obtain large fluid sample
evaluate permeability over large distances (~100s-1000s feet),
assess well damage (skin)
investigate connectivity over large volume
Why using our services?
Extensive experience from Exploration to Production, in all types of wells and reservoirs worldwide, in particular North Sea (UK and Norwegian sectors), GoM, Brasil, Azerbaijan, Algeria, Angola, Canada, Egypt, Oman, Jordan, Indonesia, etc…
We have expertise in deconvolution.
Deconvolution is a great asset for your team. It helps to improve the understanding of the pressure data, refine initial pressure and add reservoir insights. While deconvolution is not new, it is often misused in the industry.
We are also dedicated to coaching you with deconvolution.
We care and are dedicated to you!
We can act as your team well test expert, provide a 2nd review or simply reduce your expert’s workload.
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