In order to properly plan a well program and to drill a well, both safety and economically, knowledge and understanding of formation pressures and fracture gradients is essential. Formation pressure analysis is, therefore, an integral part of any drilling operation. It is one of the most important services provided by ML services, but is almost one of the, technically, most demanding.
Quantitative Pressure Analysis
- Calculation of Bulk Density
from drilled cuttings
from sonic transit times
from density logs
- Calculation of Overburden Gradient
- Calculation of Formation (Pore) Pressure using Dexp method
- Determinate Normal Compaction trend (NCT)
- Shift Normal Compaction trend
- Calculation of Fracture Pressure Gradient
Hubbert and Willis method
NIS Naftagas ML services use the following parameters to indicate overpressured regions while drilling:
- Dexp – any leftward deviation of subsequent normal trend line (shale line) indicate relative undercompaction, this is turn indicates overpressure or increase porosity.
- Temperature – Theory states that a zone of low heat flow (thermal shadow) occurs prior to the overpressured zone i.e. zone of abnormally high heat flow.
- Cuttings – splintery cuttings can be indicator of possible overpressured region.
- Gas – changes in amount of gas are fundamental in detecting of abnormal pressured zones.
- Connection and Trip gas – are typical of well imbalance and are a valuable aid to evaluating differential pressure and therefore formation pressure.
- Background gas – increasing of BG indicate drilling in negative ΔP conditions or approaching imbalance.
- Composition of the gas – occurrence or increased incidence of the heavier gas components is commonly observed when drilling into a transition zone.
- Lost / Gain, Leak of Test, Formation Integrity Test, MDT tool, SIDPP, SICP etc.
Post drilling data used to Pore Pressure calculation:
- Sonic Transit Times
- Repeat Formation Test (RFT)
- Hydrodynamic measurements in well