Standard Deliverables
- Petrophysical report
- summary of work completed
- important input parameters defined
- calculation methods reviewed
- PDF depth plot image for each well displaying input (raw) data
- PDF depth plot image for each well displaying output (answer) data
- bad hole intervals identified
- volume shale
- total organic carbon (for organic rich reservoirs)
- effective porosity (corrected for clay bound water and organic matter)
- water saturation
- bulk volume hydrocarbon and bulk volume water
- permeability index
- mineral bulk volumes
- net pay flag
- LAS file for each well containing quality checked and corrected raw data, including depth shifted core data
- LAS file for each well containing output (answer) data
- bad hole flag
- volume shale
- effective porosity (corrected for clay bound water and organic matter)
- water saturation
- bulk volume hydrocarbon and bulk volume water
- permeability index
- mineral bulk volumes
- net pay flag
- Net pay summary table based on cutoffs
- net pay thickness
- average volume shale, effective porosity, water saturation and permeability over net pay intervals
- average pore volume over net pay intervals
- average hydrocarbon pore volume over net pay intervals
- average flow capacity over net pay intervals
- Meeting and discussion of results with client’s Geologist or Engineer
Additional Deliverables
Facies Model
A facies model is used to distinguish the different flow units within a reservoir, with distinct statistical distributions for porosity, permeability, saturation, and mineralogy. To assign facies type, Aptian may use a custom discriminator set or a probabilistic clustering procedure.
Deliverables include the addition of the Facies track to the answer depth plot, along with the Facies data in LAS format.
Log Blocking
Blocked logs are based on minimum, maximum or average values between defined layers. The goal of log blocking is to remove shoulder effects from the logs, by assigning values which represent log readings from only the target layer. Blocked logs are then used as input for calculations.
Deliverables include depth plots and LAS files which include these data.
Mechanical Rock Properties
Mechanical rock properties are provided as an additional deliverable. Using the complete petrophysical analysis results described above, reconstructed sonic and density logs are generated. This step removes bad hole and light hydrocarbon effects from the logs so that accurate water-filled rock mechanical properties can be calculated. This process is also used to create missing log curves where needed.
Calculated mechanical properties include vertical Biot’s constant, bulk, shear, and Young’s moduli, and Poisson’s ratio. These results are displayed, along with the lithology track, on a separate mechanical depth plot.
This extra deliverable is recommended for all intervals which will require hydraulic stimulation to become productive. Use of the raw sonic and density logs instead of the reconstructed logs should be strongly discouraged because bad hole intervals and light hydrocarbon effects can be quite large, and will lead to calculation of erroneous stimulation parameters.
The following deliverables are provided for mechanical rock properties:
- PDF depth plot image for each well displaying reconstructed sonic and density logs, and mechanical rock properties
- bulk modulus
- shear modulus
- vertical Biot’s factor
- dynamic Young’s modulus
- static Young’s modulus
- Poisson’s ratio
- LAS file for each well containing reconstructed sonic and density logs, and mechanical rock properties
- bulk modulus
- shear modulus
- vertical Biot’s factor
- dynamic Young’s modulus
- static Young’s modulus
- Poisson’s ratio
Overburden Stress
Overburden stress is an important input to the closure stress equation. The best way to calculate overburden stress is to integrate the bulk density log, at the increment of the LAS file, from shallowest log reading to the target interval depth. However, before the bulk density log can be used, it must be corrected for abnormally low data caused by bad hole, coal, etc. (above the interval which now has reconstructed bulk density data). The other issue is that the bulk density log will not have readings to surface. To remedy, a depth function is used to assign bulk density values from surface to the shallowest log reading and to remove low bulk density values. Once these steps have been completed, the corrected bulk density log is used to calculate overburden stress.
Adding this output to the mechanical properties delivery will enable completion engineers to easily compute and calibrate closure stress. For this reason, Aptian recommends adding the overburden stress to the mechanical properties output set.
The following deliverables are provided for the overburden stress output:
- The overburden stress curve is added to the mechanical properties depth plot
- displayed as a stress and gradient
- The overburden stress data are added to the mechanical properties LAS file
- as a stress and gradient
Closure Stress
Aptian recommends closure stress calculation and calibration should, if possible, be carried out by an experienced completion Engineer. The completion Engineer will have direct access to field data which must be used for calibration of pore pressure and closure pressure.
However, Aptian does routinely calculate closure stress for clients. Calculation of closure stress is an optional addition to the mechanical properties set of deliverables. Closure stress requires overburden stress to first be calculated by integrating a corrected bulk density log. Once an accurate overburden stress is determined, the total stress equation is used, along with mechanical properties and pore pressure, to calculate closure stress. Finally, closure stress is calibrated to field measured data with a strain or stress correction factor.
The following deliverables are provided for the closure stress output:
- The closure stress curve is added to the mechanical properties depth plot
- displayed as a stress and gradient
- The closlure stress data are added to the mechanical properties LAS file
- as a stress and gradient
