Why We Need Depth Conversion
Depth Conversion can sound tricky to get a grasp of however, it is much less daunting as it first may sound. Essentially depth is measured using seismic data which is acquired over a period of time and isn’t just measured on one day but several. Seismic data is collected by using a series of reflectors across the earth’s surface and measuring the time it takes for sound to travel from the source, to the reflectors and then received back to the source. This data is part of the basis of depth conversion.
You may be thinking, wells aren’t drilled using time, however, time is important when it comes to knowing how deep you can drill down. Seismic data is one part of depth conversion, the other part is velocity. Velocity can massively distort the depth, size and shape of possible reservoirs, so to determine the depth velocity also needs to be taken into consideration.
Velocity is essentially how hard or soft a rock is and depending on either will determine whether it is possible or not to drill down – if at all. The more porous a rock is the more sound it will absorb – the less porous the stronger the sound at the other end. This is why when measuring seismic data to determine depth, velocity plays a big part.
Velocity can be measured by using a geological hammer which is used to hit different types of rock. All rocks have their own identifying sound which will determine how hard or porous the rock is. If the rock “dings” the faster and harder the rock is, however, if the rock “squelches” the slower and more porous it is.
Once seismic and velocity data is found this can be input into specialist software which will be able to determine the depth in which it is safe to drill down for future oil extraction.
Determining depth before drilling down can save a lot of time and can actually save lives. It can be extremely dangerous to drill down into a surface that is too hard for the machinery and sometimes it can be impossible to do too!