For those working in other parts of the Energy industry, ‘Cased Hole Logging’ and ‘Cased Hole Data Analysis’ are probably terms you have heard in passing but perhaps not be aware of exactly what it is.
So, what is it and what is its purpose? To explain that let’s take a step back to see where this specialty sits in the wider picture.
Most people in the Oil & Gas industry will be familiar with the terms ‘Subsurface’ or ‘Geoscience’ which cover the analysis of any data recorded beneath ground level, either within a well or the surrounding area. Sitting within the Subsurface/Geoscience domain we also have ‘Petrophysics’ which specifically covers the interpretation of ‘Well Log Data’ recorded from inside the well, usually by LWD or Wireline logging Tools.
But even within the Petrophysics domain we have specialist areas. Those working in Petrophysics will often say the log data they are working on is either ‘Open Hole’ or ‘Cased Hole’. These terms are describing the stage or state that the well is in when the data was recorded.
‘Open Hole’ is a term used to describe the well immediately after it has been drilled. This is the opportunity for wireline logging tools to record data to evaluate the formation and/or the reservoir. During this time a combination of weighted fluids and pressure control keeps the structure of the well stable. But soon after, (usually within a matter of weeks) the well will be completed, which usually involves running Casing and Tubing (terms for specialized pipes used in the Oil & Gas industry) into the well. The Casing is usually cemented into place to provide stability to the well, then perforations (deliberately created holes using explosives) are made to the casing over the reservoir zones before the well is produced. Once the pipe has been run in-hole, the well is no longer considered ‘Open Hole’ and is instead called ‘Cased Hole’.
Once the environment has changed from Open Hole to Cased Hole, most of the logging technology used at the Open Hole stage is no longer fit for purpose because we now have steel pipe and cement between the tool and the reservoir causing erroneous data readings. However, by this point the objectives of logging have also changed. We are no longer in the discovery mode of identifying where the reservoir is and where hydrocarbons exist, that is usually known by this stage. We are now more interested in the condition of the well, its production performance and how fluid contacts may have changed in the reservoir over time.
The graphic below illustrates the difference in environments between Open Hole and Cased Hole and shows how objectives usually differ when we record log data in each.
Also note there is only one window of opportunity to record Open Hole data during a well’s lifetime – that’s the time between the well being drilled and completed (usually a matter of weeks). On the other hand, Cased Hole logging can be carried out any time after completion right up to the end of the well’s life, assuming intervention of the well is operationally and commercially viable.
Once in a Cased Hole environment we now need a whole new range of technologies to achieve our objectives, these are known as Cased Hole logging tools. The below graphic shows technologies available on the market for specific Cased Hole objectives. This uses generic names for the technology - each logging vendor will have specific names for their version of the technology.
Of course, this Cased Hole specific technology will record a completely different set of data to its Open Hole equivalent and raw data alone is not enough to answer the objectives. To achieve these, we must carry out Cased Hole Log Analysis or Interpretation that involves specific equations and methodologies developed over the years, and this is where Cased Hole analysis software comes in.
In years gone by the analysis would need to use separate software packages for each specific technology for each objective. Luckily, Geoactive now provides a comprehensive suite of software modules covering all Cased Hole objectives alongside Open Hole analysis, all using our Interactive Petrophysics (IP) software platform.
In summary, Cased Hole log data refers to a niche area within the wider subsurface data domain. It is recorded in a very particular environment using specialist technology and requires specialist knowledge and software to extract answers from.
If you’re interested to find out more about IP’s comprehensive suite of software modules applicable to both Open and Cased Hole objectives, reach out to Ross directly or click the link to find out more.