Geophysics, and the process of Depth Conversion, is something which, like most sciences, is something which is constantly changing, and there are more and more ways to efficiently ascertain much-needed data about oil and gas reservoirs as time goes on - therefore improving the process as well as improving the results of the process.
In 2018, Depth Conversion is something which is robust and telling to all manner of uncertainties and risks associated with oil and gas reservoirs. We identify the most relevant ways in order to perform accurate and efficient time to depth conversions in this article below.
Initially, the first step in a time to depth conversion is to interpret a set of time horizons from a derived image volume. Image volume by itself is something which is derived from time migration, and time horizons, by their very nature, are then associated with layer boundaries. These layer boundaries can have velocity contrast and/or geological formations of interest.
Secondarily, RMS velocity functions are picked at analysis locations around the survey area. They are combined with the time horizons ascertained from the first step in order to expand them into horizon-consistent RMS velocity maps. A good interpreter will pick this data from gathers which are derived from prestack time migration.
Dix Conversion is a method which is then commonly used to convert the RMS Velocity maps in order to then derive interval velocity maps. This, in turn, allows for a far greater accuracy in the final depth conversion and should be considered quite integral to the process. After this, the interval velocity map will be compared to the later ascertained depth horizon and will form the initial model for the depth conversion.
The interpreter is then afforded a choice of vertical ray or image ray depth conversion of the time horizons which were ascertained earlier. The choice solely depends on the quality of the data which has been gleaned so far.
The beauty of the depth conversion process is that no two reservoirs are the same, and there is no set method. The interpreter is invited to use the method that he or she feels will fit the reservoir in general.
There are ways to take the arduousness out of this procedure, but still benefit from accurate depth conversions. Take Velit for instance - this plugin is available for both Petrel and IHS Kingdom Software suites, and work to interrogate the data ascertained by the best algorithm for the scenario in order to allow the interpreter a better workflow, as well as better time management through completing the tasks in a speedy and efficient manner thanks to the vast number of libraries included within the Velit Software.
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