Natural oil reservoirs are most likely to be found in a range of different sedimentary rocks including

• Carbonates
• Clay
• Quartz
• Chert

Exploration of subsurface geology is what contributes to the discovery of new areas rich in oil more than anything else. This data is determined and dependent on many measurements including:

• Distributions of organic carbon
• Gas yields in the analysis of cuttings
• Observed state of kerogen in the area
• Distributions of heavy hydrocarbons
• Vitrinite reflections
• Wireline log correlation
• Lithology and oil-compatible rock types

1. A source of oil and gas (often old, organic matter)
2. A porous and permeable reservoir rock
3. A barrier to fluid flow that allows for quantities to accumulate (a trap)

Porosity refers to the natural sorting of the various sizes of grains of a formation rock that determine the amount of space that exists for oil to reside in, while permeability is a denotation of the degree of ease with which fluids flow through the interconnected pore spaces of a rock

• Porosity(p), being the open volume between the grains of a rock formation, is usually regarded good if p>15%, fair if 10%<p<15%, and poor to trace when p<10%
• Permeability is typically deemed good if there is little to no gas found in cuttings because most or all of the gas would’ve escaped from the cutting of a permeable formation

It is just important to know that traps, which are necessary for accumulations to form, can come about from several different geological factors. The main types of traps are:

• Anticlinal traps
• Fault traps
• Stratigraphic traps
• Lenticular traps

Their distribution depends on a few key factors:

• Source rock
• Reservoir rock
• Porosity
• Permeability relative to reservoir fluids
• Relative densities of the fluids with the oil
• Hydrodynamics of the reservoir
• Migration variables like lithology or temperature

The choice of which rig type to use depends on the area that a reservoir is found in.

• Land rigs are used for land wells (water depth = 0)
• Barges are used for shallow waters (depth ~ 0-50 ft)
• Jack-Ups are used for slightly deeper water (depth ~ 50-350 ft)
• Fixed-Platforms are used for even deeper areas (depth ~ 350-1000 ft)
• Semi-Submersibles can go extremely deep (depth ~ 1000-1500 ft)
• Drill ships can theoretically drill at any depth (depth ~ limitless)

• The derrick
• The drawworks with its drilling line
• The crown block and the travelling block
• The drilling fluid circulation system, which includes the standpipe, the rotary hose, the drilling fluid pits, and the pumps

While drilling is progressing, the drillpipe is suspended and rotated by the hook and rotary systems. Drilling mud is perpetually circulating through the drillpipe to get from end to end of the drill and serve its purposes. These components all work together to achieve the three main functions of all rotary rigs:

• Hoisting
• Rotating
• Circulating

• Heavy-weight drillpipe: placed below the length of pipe on a drillstring and meant to, among other things, help with stability and rigidity while being strong
• Crossover sub: deals with changes between different types and sizes of drillpipes and collars
• Stabilizers: short subs with ‘fins’ located between the collars that are intended to maintain a straight hole by keeping the collars centralized, and in certain drills are used to change the directional vectors of the overall drilling path
• Collars: used to create the axial force needed to advance the drill bit and help by both adding weight to the drill bit and acting as a shock absorber to minimize the forces of impact caused by drilling
• Drill bit: the most important part of the drill; the cutting structure is made up of diamond dust/crystals bonded to a tungsten carbide stud, which is either pressed or molded into the body of the bit itself, and the crystal structure is self-sharpening

The drilling process itself includes:

• Continuously adding drillpipe
• Making connections
• Analyzing the log readings to determine if adjustments need to be made
• Tripping in and out of the hole whenever changes need to be made on the bit

• Control subsurface pressures and prevent caving (density)
• Remove cuttings from the borehole (viscosity)
• Suspend cuttings when circulation stops (gel strength)
• Cool and lubricate the bit and drillstring (additive content)
• Wall the borehole with an impermeable filter cake (water loss)
• Release the cuttings at the surface
• Help support the weight of the drillstring/casing
• Ensure maximum possible information about the formation through analysis of cuttings

• It must remain in an ideal range to prevent blowouts, and, on the other hand, formation fractures
• It is a function of the mud density, the true vertical depth, and a conversion constant dependent on the units of pressure used

The cuttings, mud solids, and other particles that mud picks up during circulation must be removed before the mud can recirculate. Also, treatment chemicals and clays must be added to the mud to maintain the required properties of the mud. These functions are performed by the:

• Shale shaker
• Settling pit
• Desander and desilter
• Centrifuge
• Degasser
• Mixing hopper
• Suction pit

It is important to consider the type of well you are going to drill because it can give you an idea of how difficult of a well you will have to complete and whether you should use an open or closed hole completion. This procedure is done after the initial drilling phase and takes steps to:

• Make the wellbore as efficient as possible in producing hydrocarbons
• Isolate the producing zone and bypass the damaged zone
• Counteract debris contamination of the wellbore
• Reduce the overall effects of the drilling process

Not only the directional of the well being drilled must be considered, but every important factor that can be analyzed about the formation must be considered

• Most of the well analysis data runs through the logging units stationed at the rig
• The most common units built today are Advanced Logging and Formation Analysis units and DrillByte units

• Coring (bottomhole or sidewall)
• Wireline logging
• Measurement while drilling
• Formation tests

With all of this information considered, the engineers and geologists operating the rig can decide the best procedures for casing the rig and for maintaining a steady course for the drill. Important functions of casing are:

• Preventing caving of the borehole
• Providing a means of containing formation pressures
• Providing a means of attaching surface equipment
• Confining production to the wellbore
• Preventing inter-formation flow, thus permitting the production of a specific zone
• Permitting the installation of lift equipment for producing the well
• Creating a borehole of known diameter for future operations

Key functions of a successfully directed drill:

• Reaching the desired formation
• Preventing blowouts, twistoffs, or any other mechanical problem that would halt drilling or require fishing operations to be done
• Maintaining desired levels of torque, pressure, and temperature on the drillstring
• Maintaining optimal hook positions and hook loads for the relative formation