Braided line can contain an inner core of insulated wires which provide power to equipment located at the end of the cable, normally referred to as electric line, and provides a pathway for electrical telemetry for communication between the surface and equipment at the end of the cable.
Wireline is also a term used to describe Plain Old Telephone Service (POTS). Generally it is a wired telephone, traditionally using copper wire for transmission, as opposed to a wireless telephone, which uses radio frequencies to carry data. It has come into use more frequently to distinguish the type of telephone service one has. See also Landline
Open hole operations, or reservoir evaluation, involves the deployment of tools into a freshly drilled well. As the toolstring traverses the wellbore, the individual tools gather information about the surrounding formations. A typical open hole log will have information about the density, porosity, permeability, lithology, presence of hydrocarbons, and oil and water saturation.
Cased hole operations, or production optimization, focuses of the optimization of the completed oil well through mechanical services and logging technologies. At this point in the well's life, the well is encased in steel pipe, cemented into the well bore and may or may not be producing. A typical cased hole log may show cement quality, production information, formation data. Mechanical services uses jet perforating guns, setting tools, and dump bailors to optimize the flow of hydrocarbons.
Conrad and Marcel Schlumberger are considered the inventors of electric well logging. Conrad developed the Schlumberger array which was a technique for prospecting for metal ore deposits, and the brothers adopted that surface technique to subsurface applications. On September 5, 1927, a crew working for the Schlumberger brothers, lowered an electric sonde or tool down a well in Pechelbronn, Alsace France creating the first well log. In modern terms, the first log was a resistivity log that could be described as 3.5 meter upside-down lateral log .
In 1931, Henri G. Doll and G. Dechatre, working for Schlumberger, discovered that the galvanometer wiggled even when no current was being passed through the logging cables. This led to the discovery of the spontaneous potential (SP) which was as important as the ability to measure resistivity. The SP effect was produced naturally by the borehole mud at the boundaries of permeable beds. By simultaneously recording SP and resistivity, loggers could distinguish between permeable oil-bearing beds and impermeable nonproducing beds .
In 1940, Schlumberger invented the spontaneous potential dipmeter, which greatly improved the vertical resolution of the open hole logs. This tool allowed the calculation of the dip and direction of the dip of a layer. The basic dipmeter was later enhanced by the resistivity dipmeter (1947) and the continuous resistivity dipmeter (1952).
Oil-based mud (OBM) was first used in Rangely Field, Colorado in 1948. Normal electric logs require a conductive or water-based mud, but OBMs are nonconductive. The solution to this problem was the induction log, developed in the late 1940s.
The introduction of the transistor and integrated circuits in the 1960s made electric logs vastly more reliable. Computerization allowed much faster log processing, and dramatically expanded log data-gathering capacity. The 1970s brought more logs and computers. These included combo type logs where resistivity logs and porosity logs were recorded in one pass in the borehole.
The two types of porosity logs (acoustic logs and nuclear logs) date originally from the 1940s. Sonic logs grew out of technology developed during World War II. Nuclear logging has largely replaced acoustic logging, but acoustic or sonic logs are still run on some combination logging tools.
Nuclear logging was initially developed to measure the natural gamma radiation emitted by underground formations. However, the industry quickly moved to logs that actively bombard rocks with nuclear particles. The gamma ray log was introduced by Well Surveys Inc. in 1939, and the WSI neutron log came in 1941. These logs were important because they could be used in cased wells (wells with production casing). WSI quickly became part of Lane-Wells. During World War II, the US Government gave a near wartime monopoly on open-hole logging to Schlumberger, and a monopoly on cased-hole logging to Lane-Wells. Nuclear logs continued to evolve after the war.
The nuclear magnetic resonance log was developed in 1958 by Borg Warner. Initially the NMR log was a scientific success but an engineering failure. However, the development of a continuous NMR logging tool by Numar (now a subsidiary of Halliburton is a promising new technology.
Many modern oil and gas wells are drilled directionally. At first, loggers had to run their tools somehow attached to the drill pipe if the well was not vertical. Modern techniques now permit continuous information at the surface. This is known as logging while drilling (LWD) or measurement-while-drilling (MWD). MWD logs use mud pulse technology to transmit data from the tools on the bottom of the drillstring to the processors at the surface.
A wireline tool string can be dozens of feet long with multiple separate tools installed to perform multiple operations at once.
Natural gamma ray tools employ a radioactive sensor, which is usually a scintillation crystal that emits a light pulse proportional to the strength of the gamma ray pulse incident on it. This light pulse is then converted to a current pulse by means of a photo multiplier tube PMT. From the photo multiplier tube, the current pulse goes to the tool's electronics for further processing and ultimately to the surface system for recording. The strength of the received gamma rays is dependent on the source emitting gamma rays, the density of the formation, and the distance between the source and the tool detector. The log recorded by this tool is used to identify lithology, estimate shale content, and depth correlation of future logs.
Nuclear tools measure formation properties through the interaction of reservoir molecules with radiation emitted from the logging tool. Most open hole nuclear tools utilize double-encapsulated chemical sources.
Gamma rays emitted from the source pass into the formation. Depending on the density of the surrounding formation, some of the gamma rays will be absorbed into the rock while others are reflected back to the tool. The ratio of returning gamma rays to absorbed gamma rays is useful in determining formation density.
The hydrogen content of the formation, from oil or water, slows down the emitted neutrons until they reach a thermal or epithermal state. At the slower thermal and epithermal states, the tool is able to detect the neutrons. These counts therefore yield a count of slow neutrons, which is a clear indicator of the hydrogen content of the well.
Sonic tools generate sound wave and measure the time it takes to reach the detectors. This is used to measure the effective porosity. Sound waves travel slower in formations in which the pores are not interconnected.
The NMR measurement made by both a laboratory instrument and a logging tool follow the same principles very closely. An important feature of the NMR measurement is the time needed to acquire it. In the laboratory, time presents no difficulty. In a log, there is a trade-off between the time needed for polarization and acquisition, logging speed and frequency of sampling. The longer the polarization and acquisition, the more complete the measurement. However, the longer times require either lower logging speed or less frequent samples.
A cement bond tool, or CBT, is an acoustic tool used to measure the quality of the cement behind the casing. Using a CBT, the bond between the casing and cement as well as the bond between cement and formation can be determined. Using CBT data, a company can troubleshoot problems with the cement sheath if necessary. This tool must be centralized in the well to function properly.
Two of the largest problems found in cement by CBT's are channelling and micro-annulus. A micro annulus is the formation of microscopic cracks in the cement sheath. Channelling is where large, contiguous voids in the cement sheath form, typically caused by poor centralization of the casing. Both of these situations can, if necessary, be fixed by remedial electric line work.
A CBT gains its measurements by rapidly pulsing out compressional waves across the well bore and into the pipe, cement, and formation. The compressional pulse originates in a transmitter at the top of the tool, which, when powered up on surface sounds like a rapid clicking sound. The tool typically has two receivers, one three feet away from the receiver, and another at five feet from the transmitter. These receivers record the arrival time of the compressional waves. The information from these receivers are logged as traveltimes for the three and five foot receivers and as a micro-seismogram.
Recent advances in logging technologies have allowed the receivers to measure 360 degrees of cement integrity and can be represented on a log as a radial cement map and as 6-8 individual sector arrival times.
Casing collar locator tools, or CCL's, are among the simplest and most essential in cased hole electric line. CCL's are typically used for depth correlation and can be an indicator of line overspeed when logging in heavy fluids.
A CCL operates on Faraday's Law of Induction. Two magnets are separated by a coil of copper wire. As the CCL passes by a casing joint, or collar, the difference in metal thickness across the two magnets induces a current spike in the coil. This current spike is sent uphole and logged as what's called a collar kick on the cased hole log.
A cased hole gamma perforator is used to perform mechanical services, such as shooting perforations, setting downhole tubing/casing elements, dumping remedial cement, tracer surveys, etc. Typically, a gamma perforator will have some sort of explosively initiated device attached to it, such as a perforating gun, a setting tool, or a dump bailor. In certain instances, the gamma perforator is used to merely spot objects in the well, as in tubing conveyed perforating operations and tracer surveys.
Gamma perforators operate in much the same way as an open hole natural gamma ray tool. Gamma rays given off from naturally occurring radioactive elements bombard the tool. The tool processes the gamma ray counts and sends the data uphole where it is put onto a log. The information is then used to ensure that the depth shown on the log is correct. After that, power can be applied through the tool to set off explosive charges for things like perforating, setting plugs or packers, dumping cement, etc.
Setting tools are used to set downhole completion elements. Setting tools are typically large steel tools onto which a downhole completion can be screwed onto. One of the most common setting tools is manufactured by Baker Hughes.
Setting tools are explosively driven devices. A shooting CCL or a gamma perforator is used to apply power to detonate a low explosive in the setting tool. The gas pressure created by the deflagrating low explosive exerts a large force a piston holding back oil. The pneumatic pressure of the piston pushes the oil, which hydraulically separates the setting tool from the plug or packer. The downhole completion is now set in place.
Not only for completions, Setting tools can also run bridge plugs. Which are most commonly used to abandon a well. A certain amount of oil well cement must be then placed on top of the plug. A bondlog is also protocol, the cement must be bonded with the casing to abandon a well, if its not there must be squeze guns shot. So they can pump cement down the casing and through the squeze perforations and to the outside of the casing.
Electric line weakpoints are also located in the cable head. If the tool is to become stuck in the well, the weak point is where the tool would first separate from the wireline. If the wireline were severed anywhere else along the line, the tool becomes immensely more difficult to fish.
A measuring head records tension, depth, and speed. Current models use optical encoders to derive the revolutions of a wheel with a known circumference, which in turn is used to figure speed and depth. A wheel with a pressure sensor is used to figure tension.
For oilfield work, the wireline resides on the surface, wound around a large (3 to 10 feet in diameter) spool. Operators may use a portable spool (on the back of a special truck) or a permanent part of the drilling rig. A motor and drive train turn the spool and raise and lower the equipment into and out of the well – the winch.