In the

petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larges ...

, a well test is the execution of a set of planned

data acquisition Data acquisition is the process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems, abbreviated by the acro ...

activities. The acquired data is analyzed to broaden the knowledge and increase the understanding of the hydrocarbon properties therein and characteristics of the underground

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

where the

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

s are trapped. The test will also provide information about the state of the particular

well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

used to collect data. The overall objective is identifying the reservoir's capacity to produce hydrocarbons, such as

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

and

condensate Condensate may refer to: * The liquid phase produced by the condensation of steam or any other gas * The product of a chemical condensation reaction, other than water * Natural-gas condensate, in the natural gas industry * ''Condensate'' (album) ...

. Data gathered during the test period includes

volumetric flow rate In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol (sometimes ). I ...

and

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

observed in the selected well. Outcomes of a well test, for instance flow rate data and

gas oil ratio When oil is produced to surface temperature and pressure it is usual for some natural gas to come out of solution. The gas/oil ratio (GOR) is the ratio of the volume of gas ("scf") that comes out of solution to the volume of oil — at standard ...

data, may support the well allocation process for an ongoing production phase, while other data about the reservoir capabilities will support reservoir management. Well Testing Equipment

Scope and definitions

There are many flavours of well tests and various ways to categorize test types by its objectives, however two main categories only by objectives, these are productivity tests and descriptive tests. According to ''The Lease Pumper’s Handbook'' of Oklahoma Commission on Marginally Producing Oil and Gas Wells, there are four basic well test types: potential tests, daily tests, productivity tests, and gas oil ratio tests, the latter three in the broader productivity test category. Test objectives will change throughout the different phases of a reservoir or oil field, from the exploration phase of wildcat and appraisal wells, through the field development phase and finally through the production phase, which may also have variations from the initial period of production to improved recovery by the end of the field lifecycle time.

Exploration phase

Professionals working with

reservoir modelling In the oil and gas industry, reservoir modeling involves the construction of a computer model of a petroleum reservoir, for the purposes of improving estimation of reserves and making decisions regarding the development of the field, predicting f ...

may get information about the rock permeability from

core sample A core sample is a cylindrical section of (usually) a naturally-occurring substance. Most core samples are obtained by drilling with special drills into the substance, such as sediment or rock, with a hollow steel tube, called a core drill. The h ...

s. Other sources of information to the model are well log data and seismic data, but such data are complementary only, and for example, seismic data is insufficient to interpret whether a

structural trap 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 trap ...

has been sealed. Information from well tests will supplement the amount of information with flow rate data, pressure data, and other, which is needed to build a rich reservoir model. The main objective in the exploration phase is to assess the size of a reservoir and state with a given certainty whether it has the properties for commercial exploitation and shall contribute to accounting for available reserves. Well testing taking place before permanent

well completion Well completion is the process of making a Oil well, well ready for production (or injection) after drilling operations. This principally involves preparing the bottom of the hole to the required specifications, running in the production tubing and ...

is referred to as

drill stem test A drill stem test (DST) is a procedure for isolating and testing the pressure, permeability and productive capacity of a geological formation during the drilling of a well. The test is an important measurement of pressure behaviour at the drill st ...

ing or formation testing - depending on the technology used.

Field development phase

The reservoir model is further developed to support the field development planning and to advise for the optimal location for extra production wells to be drilled. Descriptive well tests are designed and performed in the new wells.

Field production phase

Flow test

This test has also been called daily test and may have various other namings. Often, and especially at offshore fields, a number of wells produce to a common separator, and flows from several separators or facilities may be headed into a commingled flow in pipeline that transports oil or gas for sale (export). The total flow rate of all wells in total are measured, but the contributions of the individual wells are unknown. It is important to know the individual contributions to account hydrocarbon material balance and for well monitoring and reservoir management. To obtain individual well flow rates, it is common to use a smaller test separator. This is an isolated and down-scaled processing system in parallel with the normal flows. Regularly, for example once a month per well, the flow from one and only one selected well is led into the test separator for determining well flow rate for the selected well. The separator divides the flow from the well into the streams of individual products which typically are oil, gas and water, but may include

natural-gas condensate Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natur ...

. Contamination may also be removed and fluid samples collected. This helps to allocate individual flow rate contributions, but the method has uncertainties. Flow rate, water cut, GOR and other parameters for the test system can deviate from production separators. This is generally taken into account by the allocation of products back to individual wells based on the field total, and by using data from the individual well tests. Another method to obtain individual well flow rates takes the

state observer In control theory, a state observer or state estimator is a system that provides an estimate of the internal state of a given real system, from measurements of the input and output of the real system. It is typically computer-implemented, and pr ...

approach, where the states to be estimated as the unknown flow rates from individual wells. This approach allows the incorporation of other modes of measurements such as spin-cuts (manual water cut readings) and

dynamometer A dynamometer or "dyno" for short, is a device for simultaneously measuring the torque and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its instantaneous power may be calculated, and usually displayed by the ...

card based inferred rates. The reconciliation of these measurements with the flow tests, along with a systematic mechanism to account for measurement noise, leads to improved per well rate estimation accuracy.

Multiphase flow meter A multiphase flow meter is a device used to measure the individual phase flow rates of constituent phases in a given flow (for example in oil and gas industry) where oil, water and gas mixtures are initially co-mingled together during the oil pr ...

s have to some degree reduced the need for flow tests and test separators. Multiphase flow meters are not suitable for all applications where clean-ups are required post workover. In the absence of accurate, robust and low-cost multi-phase flow meters, large oil fields with thousands of wells continue to rely on well tests as the primary source of information for production surveillance.

References

* {{reflist, 2, refs= *{{Cite journal , volume = 16 , issue = 4 , pages = 52–63 , authors = I. Atkinson, B. Theuveny , title = A New Horizon in Multiphase Flow Measurement , journal = Oilfield Review (A Schlumberger Magazine) , accessdate = 2013-05-23 , date = Spring 2005 , url = http://www.slb.com/~/media/Files/resources/oilfield_review/ors04/win04/composite.pdf , display-authors=etal *{{Cite web , title = Continuous well-flow estimates improve production allocation , accessdate = 2013-05-23 , authors = Ron Cramer, Dave Schotanus, Kolin Ibrahim, and Nick Colbeck , date = 21 Dec 2009 , url = http://www.ogj.com/articles/print/volume-107/issue-47/drilling-__production/continuous-well-flow.html *{{Cite journal , volume = 9 , issue = 1 , pages = 1–12 , title = Enhanced production surveillance using probabilistic dynamic models , authors = Ashutosh Tewari, Stijn De Waele, Niranjan Subrahmanya , journal = International Journal of Prognostics and Health Management , date = May 2018 , url = https://www.phmsociety.org/node/2470 *Aghar, H et al (2007) *{{Cite book , publisher = Oklahoma Commission on Marginally Producing Oil and Gas Wells , last = Langston , first = Leslie Vernon , title = The lease pumper's handbook , location = Norman, Okla. , url = http://www.ok.gov/marginalwells/documents/C-14.B-Standard%20Tests.pdf , date = 2003 *{{Cite journal , doi = 10.1088/0957-0233/24/1/012003 , issn = 0957-0233 , volume = 24 , issue = 1 , pages = 012003 , last = Thorn , first = R. , author2=G. A. Johansen , author3=B. T. Hjertaker , title = Three-phase flow measurement in the petroleum industry , journal = Measurement Science and Technology , date = 2013-01-01 , bibcode = 2013MeScT..24a2003T , s2cid = 120658473 Petroleum production