Oil well logging is the process of documenting information (a well log) about the attributes of the geologic formations that were penetrated when a borehole was drilled. The practice yields tremendous benefit to the operator of the well, because of the valuable data it yields.
The process of well logging has come a long way since its inception in the early 1900s. Today, oil well logging uses state-of-the-art technology to help geologists and other professionals to be strategic in their decision making.
The Well Logging Purpose and Process
In petroleum exploration, formation evaluation is essential. Formation evaluation employs multiple methods in determining a well’s potential to produce oil. Formation evaluation is the process of deciding if the well is a good candidate for completion and stimulation activities. Through formation evaluation, the team targets the zones that offer greatest promise. Well logging, while it is not the only tool in the oilman’s arsenal, is a key technology through which he can assess the resource’s size, depth, substance, and performance.
The Process
To understand the process overall, it’s important to remember the purpose of logging and the type of information one is able to obtain through it. At its most elemental level, well logging is simply a graphical portrayal of downhole conditions to aid in the evaluation of a specific well. Through the process of making detailed records of the each well, one can chart its formations, traits, and fluid properties. This information establishes whether or not there is high enough quantity (and quality) of hydrocarbons to merit completing a well.
How is well logging done?
The electric logging process involves the lowering of measurement probes via cables into a well. From there, relevant data transmits electrically through the cables back to the surface. Data is then transmitted digitally and continuously and is (later) read by a team of trained specialists.
Key Data Collected
Most well logs search for the same key elements. Some of the detailed information obtained includes:
- Rock composition: information on strata types (limestone, shale, sandstone)
- Rock characteristics: porosity, permeability, and the presence of liquids
- Rock integrity: an analysis of structural weaknesses to highlight potential risk of instability
- Borehole dimensional properties: size, shape, borehole trajectory
- Liquid presence: properties of the fluids (if any) present in the borehole
For a more detailed, indepth look at what a full log records, click here.
Well Logging History
Well logging, sometimes referred to as “wireline logging,” began in 1927. Two French brothers, Conrad and Marcel Schlumberger, both geophysicists and petroleum engineers, ran what some consider the very first wireline log at the Pechelbronn Oil Company in France. The elder brother, Conrad, arrived at the concept of continuous well logging during his work as a university professor. Throughout his university work, Conrad couldn’t help but think how advantageous it would be if one could measure the conductivity of an ore bed. Entering into discussions with Marcel, the two picked up the challenge, and a scientific revolution ensued.
The brothers began conducting experiments that yielded impressive results. Electric logs, from the start, were a resounding success. Their breakthrough brought major and universally adopted changes in mining and petroleum production.
Timeline of Well Logging
Invented by Schlumberger
First well log created in France
Henri George Doll discovers Spontaneous Potential
Gamma Ray log is introduced
The earliest well logging was primitive, by today’s standards, but it was revolutionary nonetheless. Photo credit: ross-crain.com
The Spontaneous Potential Dipmeter
WSI neutron log
Bloch and Purcell discover Nuclear Magnetic Resonance
Felix Bloch (left) and Edward Purcell (right) were co-winners of the 1952 Nobel Prize for their discoveries in MRI. Photo credit: computerhistory.org
Basic dipmeter is enhanced by the Resistivity Dipmeter
Basic dipmeter is enhanced again by the Continuous Resistivity Dipmeter
Chevron and Schlumberger develop the Nuclear Magnetic Resonance log. A scientific success, but ultimately an engineering failure.
Sonic Logging
Introduction of transistor and integrated circuits, which makes electric logs vastly more reliable (computers brought into play)
Schlumberger patent is filed by Nicolaas Bloembergen
Schlumberger (the company) made its name in well logging. This early stock certificate shows images of the brothers in the corners. Marcel is in the upper left and Conrad in the upper right. Photo credit: Scripophily.net
Combo logs and logging while drilling are introduced, wherein resistivity and porosity are both recorded in one pass
Forward- Engineering developments by NUMAR, a Haliburton subsidiary, allows for Continuous NMR logging
Today
Today, geophysicists, geologists, scientists engineers, and oilmen around the world know the names Conrad Schlumberger and Marcel Schlumberger. Their contribution to geophysics resulted in the establishment of the Conrad Schlumberger Award, given annually to a chosen member of the “Association of Geoscientists and Engineers” who has made a notable contribution to the scientific and technical worlds. One past winner, Nigel Allister Anstey, made exceptional contributions to seismic exploration.
Tomorrow
Well logging has advanced further since its inception than even its creators could have imagined. Logging remains the answer for zone assessments. Throughout the history of well logging, practitioners repeatedly found methods to overcome limitations.
Some basic limitations do still exist, though. The main challenge is to decrease the Non Productive Time (NPT) involved in conventional logging. The solution? Robotic Logging Technology.
Robotic logging promises successful logging in all kinds of wells, in all kinds of weather, and within all trajectories. Its promise lies in its processing ability. By controlling a wireless logging tool from the surface, a team can realize advantages over conventional techniques, especially in terms of speed and the reduction of non proactive time.
The Well Log Legacy
The consumption of petroleum resources grounds our global infrastructure and economy. The importance of oil and gas necessitates work in environments ranging from desert climates in the Middle East to stormy offshore locations in the North Sea to arctic climates in Alaska and Siberia – not to mention the deepwater environments in the Gulf of Mexico. From exploration to abandonment, no matter the location, petroleum, and the discovery of it achieved through drilling, is essential for a balanced, thriving global economy.
Things have looked a little different since the pandemic of 2020. The demand for oil returned in 2021, though, as lockdowns abated. End of year data analysis puts the United States at the top of the global oil production list, with a production of 18,875,000 bpd.
Where To Next?
Logging, and petroleum extraction in general, would not be what it is (or where it is) today without the development of key technology. So where are we going? The past few years have been a breathless ride in the world of tech. From developments in AI to virtual and augmented reality, smartphones, the internet, and the rise of IoT, it’s clear we are headed towards even more technological advancement in the years to come.
The Future
When it comes to the future of oil and gas, “smart exploration and development” is the key. This requires the combination of not just developing technology but also developed thinking. As projects increase in ambition, smarter equals faster. So where to next? Anywhere. Wherever we go, it will all be aided, of course, by oil produced from logged well bores.