dbMap/Web – Depth-Volume Compute Method
The Depth-Volume method is a variation to the depth-area compute methods, and uses a depth-cumulative volume profile to compute the volume.
The Depth-Volume Method specifies a depth-cumulative volume relationship as a series of points, where the volume at each depth represents the cumulative volume above that depth.
For any iteration, GRV is determined from the depth-cumulative volume profile, using the volume corresponding to the Spill Point.
GRV Gas is determined as the volume at the Gas-Oil contact, for Gas-Oil targets, or at the Gas Water contact for Gas only targets, or the spill point, whichever is shallower. For Oil only targets, GRV Oil is determined as the volume at the Oil-Water contact or the Spill point, whichever is shallower. For Gas-Oil targets, GRV Oil is the volume at the Oil-Water contact or Spill point (whichever is shallower) minus the GRV Gas volume.
From this point on, the computation proceeds in the same way as the GRV method.
For the Depth-Volume method, volume values are always fully correlated with one another. So that if, for some iteration, the volume at a particular depth is the P90 for that volume distribution, the volumes for every other depth will also be the P90 for their distributions for that iteration. This is done because if the volumes at different depths were uncorrelated, the simulated reservoir in the computation would likely take on impossible shapes.
For each Depth-Volume pair, the depth must be a single value, but the volume can be specified as a probability distribution to represent uncertainty in the estimate.
These depth-volume 'pairs' are entered on the Depth-Volume tab, and the Contact and Spill Point depths on the Geology tab:
Contact Points
The depth-volume method includes input variables for the oil and gas contact points, which define the extent of the volume calculation. The gas volume is calculated as the volume below the reservoir top and above the gas contact, while the oil volume is the volume below the gas contact and above the oil contact.
The range of depth values must extend at least to the maximum contact point depth in order for the computation to run successfully. For this reason, it is preferable to use a bounded distribution like Triangular, or Stretched-Beta for the contact points to ensure that there are no outlying values outside the depth range.
The Oil Percentage variable cannot be edited, as it is computed from the relative volumes of oil and gas.
Spill Point
Reservoir spill point can be specified. It is the maximum extent of the gross rock volume (GRV). For each iteration, no depth below this will be considered.
Column Height
The column height feature is not available for the Depth-Volume method.
Profile Chart
A 'Profile Chart' is available for the Depth-Volume Method. It provides a means to check and confirm the representation of the depth-volume relationship is as expected.
The chart also shows the top of the structure: the point where the volume is zero. One must define an entry with a volume equal to zero for the calculation to work.