If you were a geologist who was paid to measure the commercial viability of completing oil & gas drilling projects in certain areas, well logs would be your right-hand man. Why? Because well logs document all the data collected by sophisticated instruments below the earth’s surface. It’s only from this information that oil companies can gauge how much oil and gas is likely to exist in a specific area BEFORE sinking money into completing a costly drilling project.
When prospectors first identify a specific area they have strong reason to believe to be rich in oil and/or natural gas, a hole will be drilled initially. They will lower into this hole data-gathering instruments in order to collect vital information. From these instrument readings, engineers and drillers can glean info such as porosity*, water saturation, depths and thicknesses of formations, types of formations, temperature, radioactivity of the rock, presence of different types of fluids, estimated permeability**, pressures and how dramatically the formations slant. This information, taken into account collectively, helps oil companies determine whether or not a well is likely to be commercially viable. If the company determines the well is going to be commercially viable (in all likelihood), its team will determine how to move forward. If the company determines the well is not going to be commercially viable (in all likelihood), they abandon the project.
Now then, well logs have been documented since the early 1900s. In Texas, well logs are submitted to and held on record by the railroad commission, which has well records dating back to 1964. These logs are public information and open to be viewed by anyone, although they aren’t very useful to the untrained eye. Plus, the Texas Railroad Commission’s inventory is quite overwhelming, with more than 132 million pages of well information. Oye!
For oil and gas companies, this logged information is invaluable. As logging instruments have gained in sophistication and analysis technology has greatly advanced, oil companies can revisit wells with previously documented logs and reassess their commercial viability under new context (e.g. current price of oil, cost of production). A well previously deemed commercially unviable can be looked at now with sharper, more accurate instrumentation and then reanalyzed by experts.
Below, you see two logs with data recorded from the same well, at the same depth. The first was created with old technology. It shows a 4.5-foot payzone because the instruments took readings at infrequent intervals (every 5 or 10 feet), using equipment that–by today’s standards–would be described as subpar. The oil company that recorded this log determined the well to be commercially unviable at the time (i.e., there wasn’t enough presence of oil and gas showing to justify the cost of completing the project). The second log was created with newer technology. It shows a 10-foot payzone because the instruments took readings at more frequent intervals (every 1 foot), using equipment that–by today’s standards–is cutting-edge. The information presented in the recent well log shows this well could be commercially viable. A substantial payzone is shown and an oil company would have cleaner, more accurate information to use in their decision making.
The difference is in the technology … and being able to read the data presented by said technology.
*Porosity measures how porous the rock is. This is vital because it gives geologists information about a rock formation’s ability to hold fluid (oil). A highly porous rock in an area rich with oil is likely to hold oil in small pockets throughout the formation. An oil company then can break apart the rock and “free” the oil.
**Permeability measures resistance. How much resistance will a rock formation present if oil needs to flow through it? Formations with low permeability make it difficult for oil to flow, whereas formations with high permeability make it easier for oil to flow through (and for oil companies to extract).