from the bottom of its legs to the top of the 
drilling mast, can drill as many as 18 directional 
wells. Figure 37 is a photograph of this platform. 
Some companies believe permanent fixed plat- 
forms can be installed in depths of more than 600 
feet. Generally, various well and production con- 
trol equipment is located on the platform. 
In some cases the subsurface reservoir is close 
enough to shore that the wellhead and producing 
equipment can be located on land; in other cases 
man-made islands have been built to support these 
facilities. Obviously, these approaches are confined 
to fairly shallow waters. 
Figure 37. World's largest fixed platform located 
in 340 feet of water in Gulf of Mexico off the 
mouth of the Mississippi River. (Shell Oil photo) 
2. Development Drilling 
After oil is found through exploratory drilling 
(usually with a mobile platform), the exploitation 
cycle is begun. First is development drilling, 
almost all done from a fixed surface platform 
using land technology. Associated activities and 
problems involving separation and subsequent 
storage and transportation of the hydrocarbons 
generally dictate use of a surface platform as a 
base of operations. 
VI-168 
Sometimes a contractor will be engaged differ- 
ent from the one involved in exploratory drilling, 
because of the changed nature of the drilling in the 
development phase. Usually several holes are 
drilled before the platform is established to pin- 
point the oil pool in quantity and quality. The 
initial well usually is drilled vertically, but subse- 
quent wells usually are drilled slanting out from 
the platform to cover a wider area. Depending 
upon depth and other considerations, reservoirs 
more than a mile horizontally from the platform 
can be reached in this manner. Such wells usually 
are completed conventionally with the wellheads 
above water on a platform. 
With such a platform, it also is possible to 
connect more distant wells to production-handling 
equipment on the platform. Such wells cannot be 
drilled from the platform itself and require a 
floating rig. Some may be completed using existing 
underwater completion techniques. (Underwater 
completion is discussed in a subsequent section.) 
3. Installation of Producing Equipment 
After development drilling, the rigs are re- 
moved, and producing equipment is installed. 
Since crude oil usually is accompanied by large 
volumes of entrained and dissolved gases (and 
eventually water), a major purpose of the platform 
operation is to separate these materials. If there is 
too much gas or water mixed with the oil, it 
cannot be pumped ashore efficiently or econom- 
ically. Provisions are made on the platform for: 
—Measuring accurately and controlling flow rate 
from oil or gas wells. 
—Cleaning the flow lines to remove sand and 
paraffin deposits. 
—Injecting chemicals for control of corrosion, 
scale, or hydrates in the well and the flow lines. 
—Separating entrained gases and water from the 
raw product. (Oil, gas, water, and natural gas 
liquids seldom occur as pure products in the field.) 
—Accessibility for periodic maintenance. 
—Storage before subsequent transportation. 
—Facilities for supplementary recovery operations. 
