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

Dry hole - A boring that does not contain commercially viable hydrocarbons. 
Flat spot - Possibly an oil-water, gas-water or gas-oil contact on a seismic section; flat due to 
gravity. 
Hydrocarbon in place - amount of hydrocarbon likely to be contained in the prospect. This is 
calculated using the volumetric equation - GRV x N/G x Porosity x Sh / FVF
GRV - Gross rock volume - amount of rock in the trap above the hydrocarbon water contact 
N/G - net/gross ratio - proportion of the GRV formed by the reservoir rock ( range is 0 to 1) 
FVF - formation volume factor - oil shrinks and gas expands when brought to the surface. 
The FVF converts volumes at reservoir conditions (high pressure and high temperature) to 
storage and sale conditions 
Prospect - a lead which has been more fully evaluated. 
Recoverable hydrocarbons - amount of hydrocarbon likely to be recovered during 
production. This is typically 10-50% in an oil field and 50-80% in a gas field. 
2.5 Drilling 
In the early years of petroleum industry, wells were not drilled but were punched with cable 
tools. On a cable tool rig, a heavy bit with a chiseled edge was suspended on a line of rope or 
wire cable. The hole was made through the constant raising, lowering and pounding of the bit 
into the earth. By the late 1920s, most operations used rotary drilling equipment, which was 
more efficient, drilling deeper and faster. 

---

 
8 | 
P a g e
To a large extent, drilling still involves turning a drill bit at the end of lengths of steel pipe. 
Each piece of pipe is about 9 m long and is added, a length at a time, by threading onto the next 
piece of pipe. The bit, drill collars (which add weight to the bit) and lengths of pipe are called 
the drilling "string." The whole string is turned by a rotating platform, the rotary table. The 
revolving bit cuts and grinds through rock formations, lubricated and cooled by drilling fluid 
commonly called drilling "mud," a mixture of water or oil, clay and chemicals. 
A deep-rated drilling rig, which might be used to drill holes 5,000 m deep, is composed of 
much heavier, larger and stronger equipment than one used to drill shallow wells. 
For offshore drilling, rigs generally are permanently mounted on barges or platforms so that 
they can be towed from well site to well site. Some offshore drilling rigs are mounted on 
specially designed ships which move under their own power. 
Fig (3) 

---