Importance of mud logging in well drilling activities // Petroleum engineering
One of the most important logs in drilling wells is the mud log, since one of the functions of the drilling mud is to drag the cuttings made by the drill bit from the bottom of the well to the surface, which is why if we study all those cuttings with which the drilling fluid comes from the bottom of the well we can know the characteristics of the geological formations that we are going through while we are drilling.
All this helps us that when we have to drill another well in the same field and the same reservoir, then we can be prepared with all the information we collect from the mud logs of the neighboring wells.
Who performs mud logging in well drilling?
In my experience as a drilling operations engineer in the state industry PDVSA (Petroleos de Venezuela S.A.) I can tell you that the mud logging activities were performed by various outsourced companies, logically the national company with this service could obtain the benefits of having information on the lithology of the various geological formations that are traversed during drilling.
Logically these are services that are only used for the drilling of exploratory wells, since once a record of the subsoil formations is obtained, the drilling of the other wells in the same area will be drilled with the information previously obtained in the drilling of the exploratory well, hence the importance that the information collected is good and transparent.
Can mud logs only be used in petroleum well drilling?
Not only oil is the only natural resource found in the subsoil, but also water is found in the lithological formations of the subsoil, so it is very profitable to carry out a mud log in water wells or in wells where other minerals have to be extracted, since it is also necessary to use a drilling mud to drag the cuttings obtained from the subsoil to the surface.
Is the outsourced company only responsible for mud logging?
As the operators have to be collecting mud samples from the shale shaker to be able to analyze these samples, they run the risk of having an accident by contact with some poisonous gas coming from underground, so one of the other secondary activities apart from performing a mud log is that of gas detection at the surface.
In addition to the detection of any poisonous gas, the mud logging company will also quantify the amount of natural gas that each sample analyzed may contain.
The service provided goes beyond the mud logging service
While drilling the oil well, mud logging technicians perform the following activities:
[1] Determine the position of the oil with respect to depth: When you start drilling an oil well you must already have an estimate of what will be the depth where the producing reservoir is, so you must constantly be calculating the depth of the well and the length remaining to reach the area where the oil is located.
[2] Identify downhole lithology: When the technician takes a sample of the drilling mud, he washes the sample by passing it through sieves where only small rock cuttings are left, which are supposed to be cut by the drill bit in the subsoil, these cuttings are analyzed under a microscope by the technician to determine if at a certain depth they are passing through a rock interval that can be: shale, sandstone, limestone, among others.
[3] Monitor natural gas entering the drilling mud stream.: The monitoring of the natural gas entering the well is very important, since it is possible to take previsions with respect to the drilling mud density, since if a lot of natural gas is entering the well, it is most likely that the drilling mud density will decrease, if this is detected in advance, then densifying material can be added to the drilling mud and increase the density to the parameters according to the well design plan in the construction of the drilling well.
What other scopes can the mud logging service cover?
There are two primary activities performed by the mud logging service which are: evaluation and microscopic analysis of drill cuttings (formation rock chips) and evaluation of gaseous hydrocarbons and their components, however these activities can be extended to some drilling parameters such as: torque, RPM, GPM, SPM, ROP. Although many of the drilling parameter variables can be seen by the driller on the rig, it is important that there is an extension of the mud logging service to these parameters, as they can be contrasted with those seen at the wellhead.
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