Real-Time Pore Pressure Evaluation - What's Your Plan?

Peter Gibson (Operations & Wellsite Geologist)

Operations & Wellsite Geologist with 28 years experience seeking new opportunities worldwide. Are you about to drill a HP or HPHT well?  How do you plan to evaluate pore pressure in real time to ensure that the well is drilled safely and within budget?  In the planning phase, many operators will engage one or more pore pressure specialists to generate pre-drill pore pressure models using a combination of offset well data, seismic data, basin modelling and burial history analysis to assess the likely range of pore and fracture pressure profiles.  During the execution phase, one or more Pore Pressure Engineers will be utilised to evaluate pore pressure in real time using LWD and surface logging data as input.  Few companies however will construct a detailed and comprehensive Pore Pressure Evaluation Plan. 

Wellbore Stability

Chris Henderson (Directional Driller)

Wellbore Stability may be defined as the prevention of brittle failure or plastic deformation of the rock surrounding the wellbore due to mechanical stress or a chemical imbalance therein.

Before we start drilling, the mechanical stresses in the formation are less than the strength of the rock. The chemical action is also balanced, or occurring at a rate relative to geologic time (millions of years). Rocks under this balanced or near-balanced state can be considered as stable.

After drilling, the rock surrounding the wellbore undergoes changes in tension, compression, and shear loads as the rock forming the volume of the hole is removed. Chemical reactions also occur with exposure over time to the drilling fluid.

Under these conditions, the rock surrounding the wellbore can become unstable, begin to deform, fracture, and cave into the wellbore or dissolve into the drilling fluid.

Excessive rock stress can further collapse the hole resulting in a stuck pipe situation.

Hole squeezing from mobile formations (ie – Halites) can produce tight hole problems and stuck pipe.

Cavings from failing and caving formation makes hole cleaning more difficult and increases mud and cementing costs accordingly.

Understanding the conditions that cause hole stability problems can produce:

• More effective planning.
• Earlier and easier detection of warning signs.
• Contingency plans to avoid the progression of the problem.