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Well logging, also known as borehole logging is the practice of making a detailed record of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface or on physical measurements made by instruments lowered into the hole. Some types of geophysical well logs can be done during any phase of a well's history: drilling, completing, producing, or abandoning. Well logging is performed in boreholes drilled for the oil and gas, groundwater, mineral and geothermal exploration, as well as part of environmental and geotechnical studies.
Depth conversion is an important step of the seismic reflection method, which converts the acoustic wave travel time to actual depth, based on the acoustic velocity of subsurface medium.
In geophysics, vertical seismic profile (VSP) is a technique of seismic measurements used for correlation with surface seismic data. The defining characteristic of a VSP is that either the energy source, or the detectors are in a borehole. In the most common type of VSP, Hydrophones, or more often geophones or accelerometers, in the borehole record reflected seismic energy originating from a seismic source at the surface.
A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.
A tubing hanger is a component used in the completion of oil and gas production wells. It is set in the tree or the wellhead and suspends the production tubing and/or casing. Sometimes it provides porting to allow the communication of hydraulic, electric and other downhole functions, as well as chemical injection. It also serves to seal-in the annulus and production areas.
Production fluid is the fluid mixture of oil, gas and water in formation fluid that flows to the surface of an oil well from a reservoir. Its consistency and composition varies.
Logging while drilling (LWD) is a technique of conveying well logging tools into the well borehole downhole as part of the bottom hole assembly (BHA).
Geosteering is the optimal placement of a wellbore based on the results of realtime downhole geological and geophysical logging measurements rather than three-dimensional targets in space. The objective is usually to keep a directional wellbore within a hydrocarbon pay zone defined in terms of its resistivity, density or even biostratigraphy. In mature areas, geosteering may be used to keep a wellbore in a particular section of a reservoir to minimize gas or water breakthrough and maximize economic production from the well. In the process of drilling a borehole, geosteering is the act of adjusting the borehole position on the fly to reach one or more geological targets. These changes are based on geological information gathered while drilling. Originally only a projected target would be aimed for with crude directional tools. Now the advent of rotary steerable tools and an ever-increasing arsenal of geophysical tools enables well placement with ever-increasing accuracy. Typically a basic tool configuration will have directional and inclination sensors, along with a gamma ray tool. Other options are neutron density, look ahead seismic, downhole pressure readings et al. Due to the vast volume of data generated, especially by imaging tools, the data transmitted to surface is a carefully selected fraction of what is available. Data is collected in memory for a data dump when back on surface with the tool.
Petrophysics is the study of physical and chemical rock properties and their interactions with fluids.
A water cut meter measures the water content (cut) of crude oil and hydrocarbons as they flow through a pipeline. While the title "Water cut" has been traditionally used, the API released a technical report using the title/term OWD or On-Line Water Determination, however as these were trademarked by a manufacturer they have been superseded in current dialogue by the term WCA or Water Content Analyser. The API is in processes of developing a standard in conjunction with the EI, the ISO committee has not yet developed an international standard for these devices though the EI has a published standard based upon the original content of the original API technical report. There are however standards in place for fiscal automatic sampling of crude oil that are used for determination of quality and water content namely API 8.2, EI 476 and ISO 3171.
Differential sticking is a problem that occurs when drilling a well with a greater well bore pressure than formation pressure, as is usually the case. The drill pipe is pressed against the wellbore wall so that part of its circumference will see only reservoir pressure, while the rest will continue to be pushed by wellbore pressure. As a result, the pipe becomes stuck to the wall, and can require millions of pounds of force to remove, which may prove impossible. In many cases the drilling fluid (mud) weight is reduced, thus relieving the pressure difference and releasing the stuck pipe string. Should this option be unavailable, as in sour gas wells, a specialty fishing company is called to retrieve the stuck pipe or 'fish'. Many options exist once a fishing company is on site: oil or nitrogen may be pumped down the well, or the fish may be 'washed over' using a carbide shoe on a string of washpipe. Jarring is not usually attempted with differential sticking due to the massive amount of pressure that holds the pipe in place.
A caliper log is a well logging tool that provides a continuous measurement of the size and shape of a borehole along its depth and is commonly used in hydrocarbon exploration. The measurements that are recorded can be an important indicator of wash-outs, cave ins or shale swelling in the borehole, which can affect the results of other well logs.
The aniline point of an oil is defined as the minimum temperature at which equal volumes of aniline and lubricant oil are miscible, i.e. form a single phase upon mixing.
In petroleum geology, a trap is a geological structure affecting the reservoir rock and caprock of a petroleum system allowing the accumulation of hydrocarbons in a reservoir. Traps can be of two types: stratigraphic or structural. Structural traps are the most important type of trap as they represent the majority of the world's discovered petroleum resources.
True vertical depth is the measurement of a straight line perpendicularly downwards from a horizontal plane.
Estimated pore pressure, as used in the oil industry and mud logging, is an approximation of the amount of force that is being exerted into the borehole by fluids or gases within the formation that has been penetrated.
The Conductor Pipe is a large diameter pipe that is set into the ground to provide the initial stable structural foundation for a borehole or oil well. The Conductor pipe is the first string of casing and is the largest diameter casing to be installed in a well. It can also be referred to as a drive pipe because it is often driven into the ground with a pile driver.
A cement bond log documents the evaluation of the integrity of cement work performed on an oil well. In the process of drilling and completing a well, cement is injected through the wellbore and rises up the annulus between the steel casing and the formation.
Squeeze job, or squeeze cementing is a term often used in the oilfield to describe the process of injecting cement slurry into a zone, generally for pressure-isolation purposes.
Formation fluid refers to the naturally occurring liquids and gases contained in geologic formations. Fluids introduced during the drilling process are called drilling fluids. Fluids in an oil or gas reservoir are called reservoir fluids. The fluids flowing from the wellhead of an oil or gas well are called production fluids.
References
- Upward Continuation in Schlumberger's Oilfield Glossary
- Downward Continuation in Schlumberger's Oilfield Glossary
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