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Slides and talking points are provided courtesy of AAPG Visiting Geoscientist Fred W. Schroeder.
The notes for each slide are printed next to each thumbnail. Below each thumbnail are download links for the individual slide. Right-click on a link to save the file to your hard drive. To preview the full-size slide image, click on the thumbnail.
To download the entire presentation right-click and save the appropriate link.
Going Beyond Exploration
Lecture Files | There are no Exercise Files
Title slide – the Alpha wildcat discovers oil!
What happens next
Here is part of our exploration flow chart – up to making a discovery
reviewed our Alpha prospect to management
they approved the expenditure for a wildcat well
we got a rig on-site to drill Alpha
we waited expectantly for the well to reach our target depth
the well encountered a thick oil-bearing interval – success!
Just as a reminder… here is our pre-drill assessment
51% chance to exceed the economic minimum
The well found oil down to a depth of 4500 meters – very close to our prediction
The net-to-gross and porosity of the sand is slightly better than we predicted – great
Our preliminary estimate is 325 MBO – our assessment was that there was a 20% chance to find this much
So what is next?
Still within exploration, we would drill one or more confirmation (aka delineation) wells
Before management approves $2 billion to build & install a platform, they want more proof that Alpha can make some money
The exploration folks will work the details of where to drill – mainly to address the biggest uncertainties
6 months later, a rig is on location to drill a second well
The biggest uncertainty is how much oil is NE of the major fault
We find the OWC is again at 4500 m – the fluids are in communication at a geologic time scale
We also find the porosity is a little better at the delineation well – more good news
Based on 2 wells, we revise the EUR (estimated ultimate recovery) to 34b MBO
Now management is ready to move Alpha from the
Exploration phase to the field Development phase
Given the results of the discovery and one delineation well, Alpha is turned over to Development
In development, geoscientists are needed to answer questions such as:
Can we …………
Is the reservoir ……….
How many ………………
What sort ………….
How can we ………………
What uncertainties remains
To answer development questions, we need more detail on the reservoir, its properties, and the distribution of oil & gas
We want to understand where to place wells to get the most for the least cost
For exploration, we can live with a 'broad brush' picture of the reservoir
For development, we need considerably more detail
As shown on the right, we may drill some more wells during development – before placing a production platform
Why might they have drilled the western development well (#3)?
Confirm the oil-water contact
See if reservoir quality changed (better or worse) at the western edge of the field
Why might they have drilled the eastern development well (#4)?
The oil is isolated from the rest – probably have to develop as a separate compartment
Is there enough oil to merit producing it – or is it cost-prohibitive
See if reservoir quality changed (better or worse) at the eastern edge of the field
If some big surprise occurs when drilling the development wells, it may be possible to cancel the development without too much loss
Data quality that was adequate for exploration may not be adequate for development issues
The seismic data may need to be reprocessed – using more sophisticated, expensive, time-consuming methods
We may have to reshoot a new survey to get acceptable data quality
Data on the right is 'sharper' and has better vertical resolution (red & black bands are thinner -> more stratigraphic detail)
The development department has a platform built, installed, and start to produce oil at Alpha
The initial production rates (barrels/day) are about what they predicted
Now the field is turned over to the Production Department
In production, geoscientists are needed to answer questions such as:
How should we …………
Can we ……….
What about ……..
Is there ………….
Can we build …….
A very useful tool for production people is a reservoir simulation
A detailed geologic model of the reservoir is built – rock type/lithology, porosity, permeability, etc.
Then fluids are placed within each cell of the geologic model along with fluid properties
The reservoir simulator models how the fluids move through time
Until recently, the first simulation would be run after about 5 years of production time
The simulation would be calibrated by doing a history match - comparing the simulated production (red curve) with the actual production data (blue boxes)
If a reasonably good history match is obtained, the model is taken to be fairly accurate
Then we can simulate future production – 10, 20, 30 years into the future
We can do some 'what if' scenarios – e.g., if we placed 3 additional producers at these locations and 5 injectors at these locations, how much additional oil would we produce?
If the cost of these 8 wells is less than the value of the additional oil, we might do it
Obviously if the cost of the 8 additional wells would not be recovered, we would not do it – look for other 'profitable' scenarios
We can also look for portions of the reservoir that are not swept of oil (in the simulations) and target these locations with additional wells – if profitable
So geoscientists can have great value to an energy company
Do work that leads to added HC reserves – making new discoveries, getting more from producing zones, or finding additional zones to produce
They can get more reserves at lower costs
Investing in ……
Drilling in ………..
Correctly assessing ………
For example, say that:
I am on a team of 4 working production at the Alpha field
The initial plan was to drill 10 wells
Average cost for a well is $75 million
Through our team effort, we determine that we can get the same amount of oil with only 8 wells drilled in more optimum locations
The team of 4 saved the company $150 million (cost of 2 wells)
That would be enough to pay each person for 50+ years – they have certainly earned their keep!
Let's go forward 5 years after the start of production (drawing fluids out of the reservoir)
Our main objective is to maximize production while minimizing the costs
We would build a computer model of the subsurface – with rocks and fluids
We would simulate how each well would produce fluids over the 5 years of production
We use the actual well production to calibrate the model (simulation)
If we get the model to match actual production, we build confidence that the model is close to reality
Then we can model production into the future
With the model, we can test ideas such as "what if we add to producers at locations A, B and C and an injector at location Z?"
The subsurface (geologic model) is an integration of all geologic, geophysical, petrophysical and interpreted or conceptual information about the reservoir into a single 3D numerical description of that reservoir
Each cell in the model is assigned rock and fluid properties:
Rock type (lithology)
Cell size can vary depending on the field size, computing resources, etc.
But they are typically about 50 to 100 m in X and Y and about 1 m in depth (Z)
The first task is to get a history match – a model (simulation) that matches the history of field production
If this is done, then we start to model future production
We can see the impact of using EOR – enhanced oil recovery methods
Or of doing infill drilling
The main question is will the cost of EOR and/or infill drilling going to result in enough extra production that the extra costs are more than recovered by the extra oil or gas to sell