I am doing a project in the university and I have been asked to do dry hole analysis for some wells in which all data given are seismic and logging data
Please, see the following websites:
http://www.mhnederlof.nl/hindsight.html
http://www.searchanddiscovery.com/pdfz/documents/2006/06124tearpock2/images/tearpock2.pdf.html
Dear Mohamed,
You will only classify a well as "dry well" after drilling through a target zone without obtaining significant amount of hydrocarbon (gas, oil or condensate) while drilling & analysis of wireline logging. if there is trace hydrocarbon shows the well can be regarded as dry well, in my opinion. Even, when drilling there won't be much gas coming to surface & this may depend on the drilling fluid mud weight, if high it will push back hydrocarbon into the formation. The only way to test the reservoir is through wireline logging, the resistivity data may indicate hydrocarbon presence however it is best to correlate all other data to be certain about your conclusions.
In terms of seismic, I am not too sure but you can evaluate the TWT velocity through the reservoir section. If the reservoir has hydrocarbon the velocity anomaly will be different from a barren reservoir. You can use this information to to map the hydrocarbon bearing horizon in the strata.
Good luck
Thank you all to your answers. I have been looking to any kind of information regarding this topic and I found that the main reasons of getting a dry hole can be due absence of HC charge, absence of reservoir, incompetent seal and invalid structure test. I am wondering how to check the seal and structure competency in a 2D seismic data.
Dear Mohamed:
Shadrach Noku gave an excellent answer. I would only add that the term "dry hole" is a colloquial term that developed decades ago in the North American petroleum industry, and it connotes a non-productive well. Each non-productive well is unique, has unique reasons for not having hydrocarbons. The possible reasons for a dry hole that you list are generally the most common. I would add the lack of a stratigraphic trap to that list, as in some cases, the prospect may have not involved a structural trap. As for checking seal and structural competency with 2D seismic data, there is no easy answer because the lack of seal or closure on a structural trap could easily be in the third dimension, which your 2D seismic does not image. There is, unfortunately, no easy answer for such a problem.
Proposal of any well for drilling is backed up by geological model built on the basis of seismic input, wirline logging input from the nearby well and pressure production data of the wells surrounding the region (in case of development well). But the input for exploratory well is chiefly from seismic and wirle line logging data. Based on the seismic and wireline logging data some geological model is prepared and wells are proposed on the basis of geological model to tap HC. But if after drilling the well became dry it implies that the geological model has to be improved. Dry hole analysis includes why there is no HC . This analysis will help in rectifying/fine tune the geological model and prevent further drilling of dry holes.
Absence of HC can be due to many reason namely absence of seal/cap rock, absence of structural closure, imperfect cap rock etc. Structural closure and be spotted in the seismic section but for identifying the character of cap rock can only be done precisely with the help of logs. GR-SP, density, sonic log can indicate if the cap rock is fractured or not. The extension of the same could be checked in the seismic if the horizons are marked accurately.
"Dry hole" is a colloquial rearm used in North America oil and gas, and widely used throughout the industry globally. Its usage varies by operator and over time, but the simplest meaning is that the well was unsuccessful, e.g did not produce commercial quantities of oil and gas. But, what failure means varies depend on the economics of the well at the time the well was drilled. At one extreme it may mean that no hydrocarbons were encountered at all, and at the other that no commercial hydrocarbons were produced. Dry Hole analysis generally refers to a technical review of why the well failed to produce commercial hydrocarbons. Most analysis focus on each of the major risk elements: reservoir, seal (top or lateral), hydrocarbon charge, and trap/structure. But, the analysis may extend to completion method, and other factors relating to drilling and completing the well. These operating issues are particularly important to dry hole analysis in low permeability ("shale, or "tight reservoir") plays. There are lots of "dry" holes that have tested oil and gas. And, plenty of dry holes that were re-entered and completed when commodity prices improved. And "dry" holes that eventually produced oil and gas with different drilling and completion practices. Just keep in mind that there is a economic component to the analysis.
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