There are many types of wells visible in the satellite images: oil wells, gas wells, water or gas injection wells, observation wells, etc. How does one distinguish them?
At high enough image resolution, there are some consistent differences, as shown in the following image of two adjacent wells in Ghawar:
Both wells are characterized by a broad rectangular area, roughly 100-150 meters on a side, graded in the sand. There is usually a black spot off to the side; this corresponds to remnants of the reserve pit used to contain drilling mud. Pipelines extending from the wells are clearly visible, although there are curious differences. The pipeline for the left well is a smooth curve extending from the general area of the well, whereas the one for the right pipeline extends directly from the wellhead and has 90 degree kinks of about 10 meters every 500 meters or so.
These are clearly different well types, and by following the pipelines to their destination, these can be identified unambiguously as a gas well (left) and an oil well (right). Gas wells (non-associated) feed into manifolds and then to gas plants, whereas oil wells feed into Gas Oil Separation Plants (GOSPs). Shown at right is the infrastructure for the Haradh gas field. The Haradh Gas Plant, completed in 2004, is located in the lower right corner. Manifolds are indicated by green placemarks, and wells by black/green circles. Pipelines also bring gas from the Tinat and Waqr fields.
Haradh Gas Plant
There are different flavors of oil wells as well, such as conventional vertical wells, deviated or horizontal wells, and Maximum Reservoir Contact (MRC) wells (which are horizontal wells with multiple arms extending from a single wellbore). For completed wells, however, there is no consistent difference between their appearance. One might that expect considerably less equipment and drilling equipment needs to be used for a simple vertical well, and it is observed that older wells have smaller drilling pads.
Newer oil well (left) vs. old oil well (right)
Water injection well identification is more challenging, as these often start out as oil wells and are later converted as they "water out". Shown at left is a water injection well for the Haradh III increment. It is a horizontal well, completed in 2004.
The wells shown above are all from the Ghawar area. Wells in other "vintage" areas, such as Abqaiq, have the same appearance. In contrast, wells in Shaybah look very different. These wells (horizontal and MRC) are often drilled together in orderly arrays, with the individual laterals extending from underneath sabkhas (salt flats) to underneath the sand dunes. Placing wellheads on top of the sand dunes was apparently not a good idea. There are two wells in the picture at left.
Another old field, Qatif, was recently (2004) rejuvenated with horizontal wells. For this project, Saudi Aramco took the Shaybah approach even further. The Qatif field underlies an area that has considerable population and agriculture. In addition, the oil has high concentrations of hydrogen sulfide gas. For safety reasons during drilling, multiple wells were grouped together on platforms. One extreme example is shown to the right. The red placemarks indicate individual wellheads.
Moving to something completely different, we have the example of Hawtah, a field south of Riyadh. Hawtah employs wells with electric pumps at the bottom of the wellbore. A building or some other infrastructure is visible at each well site.
Well at Hawtah. Note additional feature in upper left part of graded area.
Finally, for something even more literally removed, here is an oil well in eastern New Mexico, USA. You can make out the "nodding donkey" at the wellhead.