In the oil and gas industry, the term wireline usually refers to the use of cable to collect subsurface geophysical and petrochemical data. The subsurface information describes and allows for analysis of subsurface geology, reservoir properties and production characteristics. There are four basic types of wireline: multi-conductor, single conductor, slickline and braided line.
Wireline logs were first developed in 1927 and are used to measure formation properties in a well through electrical lines of wire. Various wireline tools are specially designed instruments lowered into a well bore on the end of the wireline cable. Operation may require additional equipment and methods of controlling pressure.
Description In the oil and gas industry, the term wireline usually refers to the use of cable, or wireline, to collect subsurface geophysical and petrochemical data. The subsurface information describes and allows for analysis of subsurface geology, reservoir properties and production characteristics. Wirelines are electric cables that transmit data about the well. Consisting of single strands or multi-strands, the wireline is used for both well intervention and formation evaluation operations. Wirelines are useful in gathering data about the well in logging activities, as well as in workover jobs that require data transmittal.
Wireline can also refer to the delivery of well construction services such as pipe recovery, perforating, plug setting and well cleaning, and fishing.
Types There are four basic types of wireline: multi-conductor, single conductor, slickline, and braided line. Other types of wireline include sheathed slickline and fibre-optic lines.
Multi-conductor Lines consist of external armor wires wound around a core of typically four or seven conductors. The conductors are bound together in a central core, protected by the outer armor wires. These conductors are used to transmit power to the downhole instrumentation and transmit data (and commands) to and from the surface. Multi-conductor cables are used primarily in open- (and cased-) hole applications. Typically they have diameters from to with suggested working loads from . (Note that wireline diameters and performance characteristics are typically expressed in imperial units.) Multi-conductor cables can be sheathed in smooth polymer coverings but are more commonly open wound cables.
Single-conductor Cables are similar in construction to multi-conductor cables but have only one conductor. The diameters are usually much smaller, ranging from to and with suggested working loads of 800 to 7,735 lbf. Because of their size, these cables can be used in pressurized wells making them particularly suited for cased hole logging activities under pressure. They are typically used for well construction activities such as pipe recovery, perforating and plug setting as well as production logging and reservoir production characterization such as production logging, noise logging, pulsed neutron, production fluid sampling and production flow monitoring.
Braided Line has mechanical characteristics similar to mono-conductor wireline, and is used for well construction and maintenance tasks such as heavy duty fishing and well bore cleaning work. 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.
Slicklines
Slickline is a smooth single strand of wireline with diameters ranging form 0.082" to 0.160". Slickline has no conductor (although there are specialized polymer coated slicklines and tubing encapsulated (TEC) slicklines). They are used for light well construction and well maintenance activities as well as memory reliant subsurface data gathering. Slickline work includes mechanical services such a gauge emplacement and recovery, subsurface valve manipulation, well bore cleaning and fishing.
Used to place and recover wellbore equipment, such as plugs, gauges and valves, slicklines are single-strand non-electric cables lowered into oil and gas wells from the surface. Slicklines can also be used to adjust valves and sleeves located downhole, as well as repair tubing within the wellbore. Wrapped around a drum on the back of a truck, the slickline is raised and lowered in the well by reeling in and out the wire hydraulically.
Wireline logs
First developed by Conrad and Marcel Schlumberger in 1927, wireline logs measure formation properties in a well through electrical lines of wire. Different from measurement while drilling (MWD) and mud logs, wireline logs are constant downhole measurements sent through the electrical wireline used to help geologists, drillers and engineers make real-time decisions about the reservoir and drilling operations. Wireline instruments can measure a host of petrophysical properties that form the basis of geological and petrophysical analysis of the subsurface. Measurements include self-potential, natural gamma ray, acoustic travel time, formation density, neutron porosity, resistivity and conductivity, nuclear magnetic resonance, borehole imaging, well bore geometry, formation dip and orientation, fluid characteristics such as density and viscosity and formation sampling.
The logging tool, also called a sonde, is located at the end of the wireline. The measurements are made by initially lowering sonde using the wireline to the prescribed depth and then recorded while raising it out of the well. The sonde responses are recorded continuously on the way up creating a so-called "log" of the instrument responses. The tension on the line assures that the depth measurement can be corrected for elastic stretch of the wireline. This elastic stretch correction will change as a function of cable length, tension at surface (called surface tension, Surf.Ten) and at the tool end of the wireline (called cablehead tension, CHT) and the elastic stretch coefficient of the cable. None of these are constants, so the correction has to be adjusted continuously between when starting the logging operation to recovery to the reference point (usually surface, or zero depth point, ZDP).
Workover operations
When producing wells require remedial work to sustain, restore or enhance production, this is called workover. Many times, workover operations require production shut-in, but not always.
Slickline firing head system In workover operations, a well-servicing unit is used to winch items in and out of the wellbore. The line used to raise and lower equipment can be braided steel wireline or a single steel slickline. Workover operations conducted can include well clean-up, setting plugs, production logging and perforation through explosives.
Wireline tools
Wireline tools are specially designed instruments lowered into a wellbore on the end of the wireline cable. They are individually designed to provide any number of particular services, such as evaluation of the rock properties, the location of casing collars, formation pressures, information regarding the pore size or fluid identification and sample recovery. Modern wireline tools can be extremely complicated, and are often engineered to withstand very harsh conditions such as those found in many modern oil, gas, and geothermal wells. Pressures in gas wells can exceed 30,000 psi, while temperatures can exceed 500 deg Fahrenheit in some geothermal wells. Corrosive or carcinogenic gases such as hydrogen sulfide can also occur downhole.
To reduce the amount of time running in the well, several wireline tools are often joined together and run simultaneously in a tool string that can be hundreds of feet long and weigh more than 5000 lbs.
Natural gamma ray tools Natural gamma ray tools are designed to measure gamma radiation in the Earth caused by the disintegration of naturally occurring potassium, uranium, and thorium. Unlike nuclear tools, these natural gamma ray tools emit no radiation. The tools have a radiation sensor, which is usually a scintillation crystal that emits a light pulse proportional to the strength of the gamma ray striking it. This light pulse is then converted to a current pulse by means of a photomultiplier tube (PMT). From the photomultiplier 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
Nuclear tools measure formation properties through the interaction of reservoir molecules with radiation emitted from the logging tool. The two most common properties measured by nuclear tools are formation porosity and rock density:
Formation porosity is determined by installing a radiation source capable of emitting fast neutrons into the downhole environment. Any pore spaces in the rock are filled with fluid containing hydrogen atoms, which slow the neutrons down to an epithermal or thermal state. This atomic interaction creates gamma rays which are then measured in the tool through dedicated detectors, and interpreted through a calibration to a porosity. A higher number of gamma rays collected at the tool sensor would indicate a larger number of interactions with hydrogen atoms, and thus a larger porosity.
Most open hole nuclear tools utilize double-encapsulated chemical sources.
Density tools use gamma ray radiation to determine the lithology and density of the rock in the downhole environment. Modern density tools utilize a Cs-137 radioactive source to generate gamma rays which interact with the rock strata. Since higher density materials absorb gamma rays much better than lower density materials, a gamma ray detector in the wire line tool is able to accurately determine formation density by measuring the number and associated energy level of returning gamma rays that have interacted with the rock matrix. Density tools usually incorporate an extendable caliper arm, which is used both to press the radioactive source and detectors against the side of the bore and also to measure the exact width of the bore in order to remove the effect of varying bore diameter on the readings.
Some modern nuclear tools use an electronically powered source controlled from the surface to generate neutrons. By emitting neutrons of varying energies, the logging engineer is able to determine formation lithology in fractional percentages.
Resistivity tools In any matrix which has some porosity, the pore spaces will be filled with a fluid of oil, gas (either hydrocarbon or otherwise) or formation water (sometimes referred to as connate water). This fluid will saturate the rock and change its electrical properties. A wireline resistivity tool direct injects current (lateralog-type tools for conductive water-based muds) or induces (induction-type tools for resistive or oil-based muds) an electric current into the surrounding rock and determines the resistivity via Ohm's law. The resistivity of the formation is used primarily to identify pay zones containing highly resistive hydrocarbons as opposed to those containing water, which is generally more conductive. It is also useful for determining the location of the oil-water contact in a reservoir. Most wireline tools are able to measure the resistivity at several depths of investigation into the bore hole wall, allowing log analysts to accurately predict the level of fluid invasion from the drilling mud, and thus determine a qualitative measurement of permeability.