Capillary Pressure data integration helps defining carbonates reservoir compartmentalization

Francisco Caycedo (Cayros Group)

This post is about an interesting example of how the capillary pressure data integrated with other information helped to understand the compartmentalization of a carbonate field that was under water injection.

One of the potential problems affecting the efficiency of water injection techniques is the areal variation of the rock quality. In this case study, a permeability barrier was preventing that one part of the field benefits from the waterflooding influence. No faulting or any other structural feature was observed in the seismic.


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.

Very important well control situation "kick & ballooning formation"

Hossam Nofal (Drilling Fluids Engineer & Accredited Well Control instructor, Egypt Oil & Energy)

One of the most important well control situations which can be misinterpreted by non-sufficient trained crew and could result in exacerbating the situation more and more. so, I will give a great concern to the main key points for identifying both of them.


Increased heavy gas reading Investigation

Bacem Ben Abdallah (Advanced Services Manager at Geolog International B.V.)

We encountered a very strange gas reading starting form the top of shallow Formation to TD. We record a higher heavy gas percentage, light gas ( C1, C2) become less than heavy which give the below figure :
C3>=iC4>=iC5>=nC4>=nC5> C2>C1 ?

We started Investigation From Gas Chromatograph Calibration has been check in, it was confirm to the standard gas calibration and to the original calibration and setting.
• We inject pure Methane in Gas line we got a good reading.
• We decide then with the client after many meeting to Change the gas Chromatograph for the next well
• To send Vaccutainer gas sample next well to take gas sample for further analysis. Give same result as chromatograph field reading.

With the calibration bottle C1 is around 10% and iC5 is 0.7% (ratio is 1 for 13), you Inject mixture gas in gas line you obtain at your chromatograph end a C1 of 1.4% and a iC5 of 0.3% (ratio is 1 for 2.5) how we explain this by gas equipments mal function or the presence of overpressure source rock transition zone?


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.


Pressure bleed-off from overpressured shale with time?

Jayanta Dutta (Senior Operations Geologist in Reliance Industries Ltd)

I would like to have a discussion on pressure bleed-off from a overpressured shale with time. If it happens then what are the processes governing this mechanism and how does it happen? Shale which having high temp, more than 80-90 deg C, (thermal stress dominated condition) shows mostly normal pressure. So, does thermal history play a major role for bleed-off or time with other physical processes play the main role? Also, share any example of thermally stressed high temperature overpressured shale?