Well logging is a practice used by geologists to analyze and record various types of data pertaining to rock formations around boreholes after or during drilling. The practice dates back to the early 20th century and was initially founded by Conrad Schlumberger to establish the absence or presence of underground iron ores.
Sending electricity underground as an experiment proved more beneficial than expected. The process also helped reveal formation boundaries and subsurface structures. This means it could tell where ore-bearing rocks were, but also details about gas and oil-bearing formations. This marked the beginning of the practice of well logging, which has now become an essential part of production and exploratory drilling.
Often known as borehole and mud logging, the practice aids in answering many questions concerning the well’s commercial viability. In a nutshell, it helps establish whether there’s enough gas or oil in the well to merit beginning extraction and completing production.
What Exactly Does Well Logging Record?
Mud logging units help define many characteristics and properties, such as the type of formation around a borehole, its thickness, permeability, and porosity. Since not all sedimentary formations are equal and neither do all bear gas or oil, drillers use this information to identify how deep they need to drill to access the reservoir rock.
When it comes to permeability and porosity, the latter impacts how much gas or oil a rock formation holds. Highly porous rocks often indicate reservoir rocks. Meanwhile, permeability signifies the capacity of porous rocks to transport water, fluid, or crude oil. Large pores, therefore, mean higher permeability.
Well logging also helps determine information about the temperature, fluid pressure, and amount of water in the formation. The borehole’s temperature is crucial for the cementing and casing phase because different temperatures typically require different cement types.
Water is commonly found in underground gas and oil. Sometimes they share the same reservoir, while other times water reservoirs can be close to the gas and oil reservoirs. Well pressure is another critical consideration in drilling, especially in terms of safety. Well logs also help determine the different types and properties of crude oil and natural gas to be encountered during drilling.
Common Types of Methods Used for Well Logging
#1- Wireline Logging
This refers to the Schlumberger method that’s still widely used to this day. It involves lowering the mud logging unit using a wireline—an electric cable—into the borehole to record generated data.
The tool has advanced over time, featuring many sensors that detect and send data back to the surface that engineers can use to establish the well’s viability.
Also known as electrical logs, wireline logging helps measure certain characteristics and properties of rock formations and the well’s conditions which are then combined to bring out a complete picture.
#2- Logging-While-Drilling (LWD)
LWD is applied during the drilling process. A logging tool equipped with sensors is attached to the drill string to measure and record the borehole conditions and properties of formations in directional drilling.
Since directional boreholes aren’t vertical, wireline logging isn’t possible in the scenario. Logging-While-Drilling also helps measure the properties of surrounding formations with the mud entering or affecting them.
#3- Mud Logging
This technique involves an analysis of rock cuttings and drilling mud to identify the minerals in the formation while determining whether there are gas and oil resources present in it.
Performed at the drilling site, mud logging for oil exploration involves using drilling mud samples that return from the bottom of boreholes during drilling prior to it going back underground to lubricate the drill bit. During the process, rock cuttings samples are also obtained when the mud brings them up to the surface.
Mud loggers use the samples released by the formation undergoing drilling to establish whether traces of gas or crude oil were found in the drilling mud. The mud loggers determine the mineralogical properties of formations from the rock cuttings.
Besides helping the evaluation process for the gas and oil-bearing potential of the rock, it also helps determine the behaviors drillers can expect when drilling the well in terms of permeability, porosity, and other aspects.
Monitoring the quantity and quality of the drilling, along with the penetration rate of the drill bit, further provides important information regarding the drilling speed. It also enables making more precise calculations about drilling times.
The key to efficient well logging, however, lies in the skills and geology tools and equipment used by the onsite teams. Technological advancements have helped us develop extremely precise well logging tools for measuring all properties of the fluids and rocks at any drill site.
To make things even more efficient, CNPS is offering a wide range of solutions that have helped O&G companies optimize yields and improve safety and results in exploration and extraction operations.
Besides mud logging equipment and geological field supplies, we also provide alloy OCTG, GRP, RTP, GRE, and FRP piping systems, GRE casing solutions, and other cutting-edge products to the oil and gas, industrial, water, and marine & offshore sectors worldwide.
You can set up a consultation with experts at CNPS to streamline the most suitable ISO and API-compliant geological supplies for your operations. We’ve made all the information available online, but our representatives are also easily reachable via a quick call.