And the evolution of the stages involved in the oil and gas

 
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Fig 4 (Drilling ship)
 
2.6 Down hole Technologies 
During recent decades the technologies used to find and produce oil have gone through a 
revolution. In particular, horizontal drilling and the ability to drill several horizontal laterals 
from a single wellbore have transformed the drilling sector. Horizontal drilling is possible 
because of improvements in bit design, better down hole motors and bigger rigs. 
Geo-steering is one of a number of revolutionary down hole technologies developed since the 
1990s. In recent years, it has been given a lift by high-impact, measurement while drilling 
tools and techniques. More importantly, the industry can now isolate many completion zones 
(areas from which oil and gas are produced) in horizontal wellbores. This makes reservoir 
fracturing (and therefore production) possible from horizontal wells that reach out for several 
kilometers underground. 
It took rapid innovation in down hole tools to turn hydrocarbon-bearing shales and other 
low-
permeability rocks into producing reservoirs. Coil (“coiled”) tubing is the workhorse of 
underground technologies. A tool that began to make inroads into industry operations around 
1990, coil tubing has transformed many aspects of underground drilling and work-over 
operations. It refers to metal piping spooled on a large reel and used for down hole operations 

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in wells. Coiled tubing is often used to carry out operations previously done by wire lining, 
which involves lowering tools into a wellbore by an electrical cable. Wire line tools transmit 
data about the conditions of the wellbore to the surface. The main benefit of coil tubing over 
wire line is that you can pump chemicals through the coil. With coil tubing you are able to 
push tools and chemicals into the hole, whereas wire lining relies on gravity. 
The tool string at the bottom of the coil can range from something as simple as a jetting nozzle, 
for jobs involving pumping chemicals or cement through the coil, to a larger string of logging 
tools, depending on the operations. Coil tubing is also used for relatively inexpensive 
work-over operations. It is also used to perform open-hole drilling operations. 
As these technologies increased in sophistication and declined in relative cost, they led to a 
fundamental change in field economics. Producers are now investing more money 
underground than above ground.