Engineering considerations in mud logging in operational activities in drilling an oil well

10 months ago

Introduction

Mud logging is an activity that goes beyond being able to generate a detailed record of the information that is intrinsic in the drilling mud as it comes back from the bottom to the surface, since mud logging has a broad vision as that service that performs a detailed record of the drilling parameters without losing sight of the monitoring of the lithology that comes associated with the drilling mud with the rock cuttings cut by the drill bit in the well bore as it goes deeper.

Who performs the mud log monitoring?

In the experience obtained in the field I realized that this mud logging service is not done by the company that owns the drilling, but on the contrary, the mud logging is done by an outsourced company, however I who worked in the state oil company of my country Venezuela always involved me with the activities that such mud logging companies performed as a lithological evaluation, type of fluids contained in the well, ROP curve, description of the master log, lithological analysis of the strata every 10 feet drilled.

The reason why I got involved in these activities, even though it is an activity that is not performed by the owners (PDVSA), is because I consider that this activity should be supervised with the knowledge of the case, since without knowledge it is impossible to properly monitor the supervision that must be performed to such outsourced companies in mud logging operations.

Expanding a little on the activities performed by outsourced mud logging companies, we can also find gas detection, since if the drilling of the well is an exploratory well it is very likely that there are gas upwellings from the formation to the well, for this it is important that the mud logging company places a mobile laboratory near the drilling platform, in order to allow it to carry more closely the detection of formation gas.

Influence of engineering on the mud logging service provided

The mud logging service must consider an interpretation of the drilling parameters that depend on the mud log, for this it is important that the technicians share information from the mud log with the drilling engineers in a reliable way, all with the intention that they can determine the position of oil and natural gas with respect to the depth where they may be contained, also that they can study the lithology of the bottom of the well and thus to make decisions that involve among many things for example a change of drill bit, if for example the mud logging technician notifies the drilling engineer that formation gas is entering the drilling mud, the most convenient thing is that if you have an engineering vision, the drilling engineer sends to measure the density of the drilling mud, because if the density falls below the values according to the design of the drilling program, then you have to add some densifier to increase the density of the drilling mud.

The most important thing for the mud logging technician is the elaboration of the mud log where the lithology changes are specified for each 10 feet deep interval, this allows the whole logging team including the geologists to be able to study these lithology changes according to the drilling needs of a particular well, The ability to sample drill cuttings flowing from the bottom of the hole to the surface when the drilling mud is circulating allows engineers to have a tool available to correlate future lithology of other wells to be drilled.

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What is the extent of mud logging?

Mud logging includes observation and microscopic examination of drill cuttings (formation rock chips) and evaluation of gaseous hydrocarbons and their components, basic chemical and mechanical parameters of the drilling fluid or drilling mud (such as chlorides and temperature), as well as collection of other information. on drilling parameters. The data is then plotted on a graphical log called a mud log.

Within what is the mud log a thorough observation of the drill cuttings can be made by observation with a microscope, as the rocks downhole are cut in the form of chips and it can only be determined what type of rocks those chips belong to if they are observed through a microscope, also the mud log can have a scope that goes as far as the evaluation of chemical and mechanical parameters that can help a better understanding of the components that the drilling mud may have incorporated from the bottom of the well.

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Outsourced mud logging companies also have monitors where many of the drilling parameters such as ROP, rpm, mud pump flow rate, torque, weight on bit, pump pressure, mud volumes, among others, can be viewed.

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One of the highlights of the scope of the mud logging service is that it allows monitoring a very important parameter in well control such as the calculation of the "d" (corrected) exponent, which is a very important aid for the control of well pressures and thus avoid a possible blowout at the surface.

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The way a geologist looking at a formation cuttings sample is as follows:

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It can be seen how there is variability in the different types of rocks, which for a mud logger and his geological knowledge helps to make a lithological study of the formations that are passing through while the well is being drilled.

As a conclusion, it can be said that mud logging is an extremely fundamental activity in the drilling of a well, since mud logging extends to other drilling parameters that are fundamental at the moment of needing to reach an analysis about some operational problem related to the drilling of the oil well.