Power Generation Onshore is an item of the type where the main machine is a single large piece and itself forms a large module.  If we consider large scale then this item may be steam driven by a steam turbine and the machines themselves as modules are installed in a hall. The next lower of order are Gas Turbines of the type GE Frame 5's and 9's. These may have considerable power output and the driver and generator are again in themselves modules. Other associate modules are formed for the air intake system and exhaust. Some systems require back end divergent exhaust systems with large diverter valves which are also modules. For the lower range of size these items of equipment may be incorporated into a single module. Whatever the power required it is usual to combine a series of Gas Turbine Generators to achieve the total power output, this approach gives more reliability, allows flexibility in meeting the power requirements and backup in times of failure. An example of this is Khuffe Study in the Offshore example where 2 machines were used. Those machines (drivers) were common with the machine sited in a Sonatrach Gas Condensate pipeline station on shore in the desert. The one difference is the the inlet filters for offshore are mainly used to remove saline  moisture into the engine whereas the onshore filter must deal with sand and dust  in the intake.  The examples show some examples of systems. The first is the larger system where the Module is usually the Gas Turbine and Generater, the other parts are lage and voluminous and may be modularised but can also be built up on site. The sizes of these machines go up to approach 1000 MWatts. Smaller size machines may still have the Module being the Gas Turbine and its E.power Generater or oyher machine such as a pump but all the components may be incorporated into a Module. The degree of Modulation is best determined by study, in most situations all can be incorporated into one module but the practicallity of this  needs to be determined eg can it be transported? 
In a similar manner to Gas Turbines diesels are sometimes used, usually for the smaller power and in groups to achieve total power requirements, As the Diesel driver say for Uisige Gorm or West Navion were in Offshore modules  they again can occur in a similar style of module onshore bur suitable for land application e.g; sand and dust inlet filters .
Drilling Onshore does not have the complications as illustrated in the offshore applications . The drill enters the ground usually with no water interface. The  BOP is at the well head above ground. The 2nd thing to note is that the demands for length of drill pipe are usually far less  and the pressure to use double pipe is less. Most land drills are smaller than the modules demanded for offshore. The other requirement is that they demand transportability to the location of drilling. In the US even though road systems are more substantial particularly in terms of space, it has even historically been the requirement to have drilling rig's transportable as a single module. The drilling spread itself such as mud tanks, mud pumps etc have also been modularised to be transported and to easily hook up into a drilling spread. Fracking has seen this  as a requirement to be able to move rigs to many land locations, the rig module being a one piece motorize unit or  with an attached trailer. Beside the Drilling Rig all the other parfanalia of Mud, Water, gas treatment etc as illustrated in Section 1f Demand isoften made up of modules of a standard design replicated to meet the gross demand. The major scene changer (both on and offshore) is the use of Directional Drilling. The mobile rig can no be driven to a location and a substantial area around the drilling can be explored/confirmed. Having established the presence of a reserve  its extremities can the be explored by further directional dilling
Mobile Drilling Spread on Trailer
Mobile Drilling Spread on Trailer
Directional Drill showing Changes of Direction to Extremities of Field
Directional Drill showing Changes of Direction to Extremities of Field
MODULEitus
a general understanding of Modules 
Index, Section  5, Modules Onshore
General
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Level 1
Level 2
Combined Cycle Power Gen
Combined Cycle Power Gen
. The Diagram illustrates the extent of these.
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