R
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radial flow |
The flow of fluids into a wellbore from the surrounding drainage area. Also, could be descriptive of the flow from an injection well to the surrounding area. |
rate of penetration |
ROP. The measured distance that the drill bit or other drilling tool penetrates subsurface formations in a unit length of time. |
rathole |
Extra hole drilled at the end of the well (beyond the last zone of interest) to ensure that the zone of interest can be fully evaluated. The logging tool string may be as much as 120 ft [36.5 m] in length, so the rathole allows tools at the top of the logging string to reach and measure the deepest zone of interest. In addition, there is usually a small amount of extra hole drilled to allow for junk, hole fill-in and other conditions that may reduce the effective depth of the well prior to running logging tools. |
recovery factor |
The percentage of oil or gas in place in a reservoir that ultimately can be withdrawn by primary and/or secondary techniques. |
reinjection |
The process of pumping produced water or gas back into a porous and permeable formation by means of an injection well. |
relative permeability |
The ratio between the effective permeability to a given fluid at a partial saturation and the permeability at 100% saturation. The ratio of the amount of a specific fluid that will flow at a given saturation, in the presence of other fluids, to the amount that would flow at a saturation of 100%, other factors remaining the same. It ranges in value from zero at low saturation to 1.0 at 100% saturation of the specific fluid. Since different fluid phases inhibit the flow of each other, the sum of the relative permeabilities of all phases is always less than unity. |
repeat formation tester |
The repeat formation tester (RFT) is operated by an electrically driven hydraulic system so that it can be set and retracted as often as necessary to pressure test all zones of interest on one trip in the well. Two separate fluid tests can also be taken on one trip. Formation pressures are recorded at the surface in both digital and analog form. |
repeat section |
A log rerun over a short section of hole, generally 100m, to enable comparison of similarity with the main survey to show instrument stability and repeatability. |
reserves |
The unproduced but recoverable oil or gas in place, in a formation, that has been proved by production. |
reservoir |
A subsurface, porous, permeable rock body in which oil or gas or both can be trapped. Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. The three basic types of hydrocarbon reservoirs are oil, gas, and condensate. An oil reservoir generally contains three fluids: gas, oil, and water, with oil the dominant product. In the typical oil reservoir, these fluids occur in different phases as a result of the variation in their gravities. Gas, the lightest, occupies the upper part of the reservoir rocks; water, the lower part; and oil, the intermediate section. In addition to occurring as a cap or in solution, gas may accumulate independently of the oil. If so, the reservoir is called a gas reservoir. Associated with the gas, in most instances, are salt water and some oil. In a condensate reservoir, the hydrocarbons may exist as a gas, but, when brought to the surface, some of the heavier gases condense to a liquid or condensate. At the surface, the hydrocarbons from a condensate reservoir consist of gas and a high-gravity crude (i.e., the condensate). Condensate wells are sometimes called gas-condensate reservoirs. |
reservoir pressure |
The pressure found within a reservoir at a specific point in time. Sometimes reservoir pressure is thought of as original pressure or geopressure (prior to disturbance) but at other times is thought of as pressure existing after disturbance. Reservoir or formation pressure should be qualified as to time, condition, and place. |
reservoir temperature |
The field average temperature encountered in the reservoir. |
residual oil |
Oil remaining in the reservoir rock after the flushing or invasion process, or at the end of a specific recovery process or escape process. |
resistivity index |
The ratio of the resistivity of a formation bearing hydrocarbons to the resistivity it would have if 100% saturated with formation water. |
resistivity logs |
Any of a number of basic logs on which some aspect of formation resistivity has been recorded. |
returns |
The drilling fluid, cuttings, etc. which circulate up the hole to the surface. |
rig |
The machine used to drill a wellbore. In onshore operations, the rig includes virtually everything except living quarters. Major components of the rig include the mud tanks, the mud pumps, the derrick or mast, the drawworks, the rotary table or topdrive, the drillstring, the power generation equipment and auxiliary equipment. Offshore, the rig includes the same components as onshore, but not those of the vessel or drilling platform itself. The rig is sometimes referred to as the drilling package, particularly offshore. |
rig down |
To dismantle equipment after the completion of an operation. |
rig floor |
The area immediately around the rotary table and extending to each corner of the derrick or mast. The area immediately above the substructure on which the drawworks, rotary table, etc. rest. |
rig up |
To prepare equipment for an operation. |
riser |
A large-diameter pipe that connects the subsea BOP stack to a floating surface rig to take mud returns to the surface. Without the riser, the mud would simply spill out of the top of the stack onto the seafloor. The riser might be loosely considered a temporary extension of the wellbore to the surface. |
roughneck |
A low-ranking member of the drilling crew. The roughneck usually performs semiskilled and unskilled manual labour that requires continual hard work in difficult conditions for many hours. After roughnecks understand how the rig operates and demonstrates their work ethic, they may be promoted to other positions in the crew. |
roundtrip |
The action of pulling the drill pipe out of the hole and subsequently running the pipe back into the hole to the same depth. Roundtrips are made each time the drill bit is changed, for example. |
rugosity |
The quality of roughness or irregularity of a solid surface such as the borehole wall. |
run pipe |
To lower a string of casing into the hole. |
