Well Evaluation Innovation
From the earliest drilling operations, the need for operators to see the penetrated formation was paramount, in their minds. They needed to distinguish not only the rock properties but also their content and deliverability. The first electrical well-logging operation took place in 1927 after many years of successful experiments with surface resistivity measurements by Conrad and Marcel Schlumberger. The operation, in France, took more than 5 hours to record the resistivity over an interval of 140 m from a depth of 279 m. Henri Doll, one of the three wellsite engineers at the operation, wrote “We began making our measurements. Someone had to unplug the connector, someone else turned the winch. Someone had to run to the rig floor to look at the counter on the sleeve. I wrote down the measurements on a pad together with the depth…Then it was unplugged, rolled up one meter at a time.” (Schlumberger 2007)
Four years later the spontaneous potential of a formation could be measured, thus allowing permeable rock to be distinguished from nonpermeable rock. These measurements are far from the sophistication of today, but for me this demonstrates how seemingly simple innovations have made such a tremendous impact on our industry. The equipment currently used for logging wells and capturing and transmitting data is a far departure from the rudimentary operation that took place 85 years ago. The point is that the industry saw the need for the nascent technology, and its use all over the world allowed not only the measurements around a wellbore, but also provided results with which the geologists could match well correlations, map a field, and obtain the structure of the horizons.
Innovative ideas emerging in other industries began to have an impact on our well evaluation operations. The development of electronics in the 1930s led to a number of new developments in logging operations. The miniaturization of rugged circuit boards and components led to new tools that suffered less damage, which in turn reduced lost time during rig operations. The introduction of computers permitted the capture and interpretation of data. Transmission of data from wellsite to office has been enhanced by innovation in the telecommunications world, and remote logging operations have been enhanced by the use of satellite and other forms of telecommunication. Modern technology now permits multilocation access to live data from rig sites, thus permitting real-time management of situations that leads to speedy interpretation. When I worked on a wellsite in the late 1960s, logs were developed on site and physically moved by road, boat, or helicopter to the office-based engineers for evaluation; subsequently, further instruction was transmitted back to the wellsite by unreliable high-frequency radio. I can still recall the smell of ammonia used for printing those logs. I recently mentioned this to a few young engineers and the blank look on their face made me feel as if I was from the Stone Age, but that is what innovation has done in our industry.
The introduction of measurement-while-drilling and logging-while-drilling has enabled the evaluation of formations still ”fresh” and minimally contaminated by drilling fluids. These tools have also enabled the logging of horizontal wells and have been proven to improve the productivity of oil and gas wells.
As E&P companies have extended exploration and development to new frontiers, they have met new and varying challenges that have led to the need for advances in formation evaluation techniques. Some of these new challenges include complex lithologies, thin-beds and laminated formations, fractured basement reservoirs, anisotropy, subsalt plays, and unconventional reservoirs. These challenges were met with innovations and advances in formation evaluation, with numerous innovations and services offered by logging companies. One example I will discuss relates to low-resistivity pay, which is well known as one of the challenges in accurate estimation of hydrocarbon reserves in shaly sand environments. In most of these environments, the occurrences of sand-silt-shale laminations typically increase bound water volumes in rocks, and ultimately reduce the conductivity contrast across beds. Conventional resistivity measurements used in laminated shaly sand environments have over the years been bypassed, underestimated, or introduced huge uncertainties in the estimation of hydrocarbon reserves. Conventional resistivity tools are not sensitive to resistivity response tangential to bedding, which makes it impossible to accurately depict hydrocarbon-bearing formation resistivities. This challenge was overcome with the introduction of a triaxial multi-array induction tool that has the capability to measure and, through an inversion, output resistivities that are axial and tangential to bed boundaries, independent of well deviation angle. The tool has been employed in several shaly sand environments to identify reservoirs that could have been bypassed, determine true resistivities, and aid in accurately estimating hydrocarbon reserves. The result is identification of additional pay zones. In a world hungry for new sources of hydrocarbons, this is very much welcome.
When the Schlumberger brothers completed their first logging operation they had no concept of how this would revolutionalize the petroleum industry, which was still very young. Technology has progressed since the first log was made by hand, and now a whole bundle of logs can be run in one pass.
Yesterday’s tools may be obsolete, but the world is still endowed with innovative minds like the ones that laid the foundation that led to their development. SPE must continue to broadcast innovations through which we can find and develop more hydrocarbons. The world needs them.
- Schlumberger. 2007. 80 Years of Innovation. Sugar Land, Texas USA: Schlumberger Oilfield Services Marketing Communications