How ‘Measurement While Drilling’ Communication is just like the internet.
You may have read in the finance pages that fracking and technology made it possible for America and other countries to find and extract oil in places and ways that were previously impossible. And while some may have positive or negative views of the fracking industry and the final by-product – petroleum products, many may wonder what exactly is this technology they talk about? Part of it involves the ability to point the drillstring in an exact direction and know which way it is going at all times…pretty much. I hedge my description here not due to instrument or operator error, but lag times in deciphering a vast amount of data being sent from miles away thru a drilling operation and all that entails…too much to go into for this brief blog. Lets call it ‘near real time’ data acquisition.
Directional or Horizontal drilling techniques have revolutionized the oil industry. It was first invented by H. John Eastman of Eastman Kodak fame, and you would literally drop a small piece of film with a compass rose down the hole to figure out where you were. This first gained credibility in 1933 when a relief well was drilled to stem a blowout in the town of Conroe, TX. The ability to point the bit in a certain direction and at a certain angle (Directional Drilling), have made it possible for oil companies to maximize output of oil and gas reservoirs, by maximizing the surface area of the exposed reservoir. In addition, near bit measurements of certain rock properties make it possible to assure that the bit stays in the zone of interest to the maximum and most
efficient extent possible.
How do ‘tools’ work, and how is this information obtained? These two questions go hand-in-hand, but this paper looks mainly at the latter. Turns out, there are many similarities between how this info is obtained and how the internet works.
How MWD works
In Measurement While drilling or MWD, data is picked up from the tool in the hole(gamma, directional etc) and transmitted from the tool via a series of mud pulses which are received at a transducer on the standpipe. These mud pulses are detected as a change in pressure. An analogy would be the average garden hose. When you put your thumb over the end of the hose to constrict flow, the pressure in the hose increases all the way back to the spigot.
These changes in pressure or pulses are detected at the standpipe transducer and converted to electrical impulses from 4 to 20 mA (milliamps). These electrical impulses are forwarded to other instruments which eventually convert to graphical representation
These quiggles are then converted to data such as Inclination, Azimuth and value of the gamma readings at the point of the sensor downhole.
The internet (as you may not realize) is really just a series of electrical pulses, on or off and converted to 1’s or 0’s or binary. This browser window that you are probably reading this on, sends info down the ‘stack’ of layers which make up the 7 layer OSI model (again, beyond the scope of this blog) until it is converted into those 1’s and 0’s that are received at the physical ‘wire’ (although that may encompass fibre optics) thru a series of routers that may end up on the other side of the earth. These binary bits are then received at their destination and sent back up the ‘stack’ to be decoded until they finally display what you’ve requested in the browser again. Get it?
Binary pulses make it possible. So just as mud pulses are sent up an oil well to the rig and finally to an engineer to tell where they are beneath the earth, so is this info that are reading sent from a computer somewhere to your browser.
MWD tool diagram