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. 

Qualitative Pore Pressure Evaluation – 12 Things Every Wellsite Geologist Should Know!

Peter Gibson (Operations & Wellsite Geologist)

With increased focus on real time pore pressure evaluation it has become commonplace to utilise Pore Pressure Engineers to provide a “real time” quantitative pore pressure solution using LWD as the primary input. Whilst these LWD based pore pressure models are generally very good, it is vital to realise they have their limitations, particularly where offset well data is sparse or where the geology changes rapidly.  

The LWD sensors that provide the input to pore pressure models can be located 5 to 10’s of metres behind the bit. In addition, the LWD pore pressure models take time to interpret and they rely on establishing trends and deviations from trends and therefore the “real time” quantitative LWD pore pressure solution is often tens of metres behind the bit. Because of these limitations, it is imperative that the Wellsite Geologist is cognisant of the primary indicators of pore pressure and incorporates these pore pressure indictors with the Pore Pressure Engineers quantitative interpretation to provide an integrated pore pressure solution. 

This article discusses a number of tools that are available to the Wellsite Geologist and Pore Pressure Engineer to provide a qualitative assessment of pore pressure. I doubt that my list is all-encompassing and you are encouraged to add to the list. Be aware of false positives, any one of the primary pore pressure indicators used in isolation has the potential to provide a false indication of pore pressure. It is therefore essential to utilise all the qualitative and quantitative indicators of pore pressure to arrive at the best possible pore pressure solution. 

The use of qualitative pore pressure indicators are an important part of any pore pressure evaluation plan. They provide essential barriers in the well control bow-tie and require ownership by several disciplines at the wellsite. 

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.

Discover a Career in Geomechanics

Hamed Soroush (Shell International Exploration and Production)

By definition, rock mechanics is the theoretical and applied science of the mechanical behavior of rocks in the force fields of their physical environment. In practice, so-called “rock engineering” is concerned with the application of principles of engineering mechanics to the design and construction of structures of any type either on or in the rock, such as tunnels, mine shafts, underground excavations, open pit mines, road cuts, dams, skyscrapers, waste repositories, and oil or gas wells.

Though initially developed for mining and civil engineering purposes, geomechanics found its way into the oil and gas industry in the ’80s in order to improve hydraulic fracturing and drilling operations. In the contemporary petroleum industry, geomechanics is defined as the discipline that integrates rock mechanics, geophysics, petrophysics, and geology to quantify the response of the Earth to any changes in state of stress, pore pressure, and formation temperature.

Pore pressure using mud logs

Oluwakunle Ogunsakin

How do i analyse scanned mud logs and which software do i use to calculate Dxc pore pressure, fracture pressure on a tight schedule deadline?

What are the most common mistakes we make in pore pressure prediction?

Mark Tingay (Senior Geomechanics Specialist at Chevron)

The group members have a wide range of backgrounds and experiences - and I'm sure many of us have seen some pretty odd things done in pore pressure prediction!

What are some common mistakes that you have seen in pore pressure prediction? If you were training someone new to pore pressure prediction, what are the things you'd caution them against doing? What are your key dos and don'ts for pore pressure prediction?

Please try to avoid things that are just 'personal opinions', such as preferences you might have for a particular type of velocity analysis, software, or prediction model (e.g. Eaton, Bowers, Holbrook).

In pore pressure prediction using Poisson ratio, is it possible to use estimated shear wave velocity utilized by wire line logs and then use Vs & Vp to do PPP?

Morteza Azadpour (Ph.D. Student at Amirkabir University of Technology)

As you know pore pressure prediction using Poisson ratio needs Vs & Vp . In old wells that we don’t have shear wave velocity log; we can estimate shear wave velocity utilizing wire line logs (NPHI, RHOB, GR, LLD, DT). Now, by this method we have Vs and Vp. Is it possible to use Vp (sonic log) and this estimated Vs to do Pore Pressure Prediction using Poisson ratio method? What are the influential problems?

Pore pressure prediction using 2D seismic data, is it possible?

Saad Akber (Drilling Engineer at Halliburton)

I want to know about the pore pressure prediction through seismic data, in our region 2D seismic is much more common than 3D specially in the exploratory areas. And it is in these areas it is where you need this information the most for well designing, however it has been learnt that most 2D seismic data sets are not able to give the required info due to the poor quality. What are the quality control factors, and is there a way to calculate the close to actual pore pressure and fracture pressure gradients using 2D data. I will be grateful if it is discussed for my guidance here.