Abstract: A method for underground treatment of subsurface materials comprises providing an injection pattern and a recovery pattern, the injection pattern and the recovery pattern located proximate to a subsurface treatment zone and at least one of the injection pattern and the recovery pattern comprising a plurality of lateral bores extending from a main bore. A treatment solution is injected through the injection pattern and recovered through the recovery pattern.

Abstract: The present invention is directed to the use of electromagnetic radiation, acoustic energy, and surfactant injection to recover hydrocarbon-containing materials from a hydrocarbon-bearing formation.

Abstract: In a WAG flood oil is displaced from a subterranean formation by injecting water alternately with gas into a single injection completion per pattern. The ratio of water to gas injected is the WAG ratio. In this invention, two separate injection completions are used in each pattern, with one placed directly above the other. A very low WAG ratio is used for injection into the bottom extremity of the formation. A very high WAG ratio is injected into the upper interval, at as high a rate as can safely be used without fracturing the formation. In the preferred embodiment, two horizontal well bores serve as the two completion intervals. Proper design of this method gives a vertical sweep efficiency of the gas that is several-fold greater than the best of previous WAG flood designs, especially in thin formations.

Abstract: A method and system for recovery of hydrocarbons from a hydrocarbon-bearing formation. A gaseous component of the produced hydrocarbon-containing fluid is separated from the fluid. The gaseous component is combusted with air in a power plant. Mixing and compressing of the gaseous component and air are realized to produce a flammable and pressurized gas-air mixture prior to combustion. An exhaust gas resulting from combustion is injected into the formation.

Abstract: A system comprising a carbon disulfide formulation storage; a mechanism for releasing at least a portion of the carbon disulfide formulation into a formation; and a mechanism for creating a pulse in the carbon disulfide formulation in the formation.

Abstract: Compositions containing surfactant compounds according to formula (I) ROCH2CH(OH)CR1R2ZCR1R2CH(OH)CH2OR,??(I) wherein Z is S, SO, or SO2, can have a range of equilibrium and/or dynamic surface tensions and a range of foaming performance attributes, depending upon the particular values of Z, R, R1, and R2. The compounds of formula (I) may be prepared by a process that includes reaction of a sulfide source such as a metal sulfide or bisulfide with an alkyl glycidyl ether. The compounds may be useful in any of a broad range of applications requiring the use of a surfactant.

Abstract: A method of treating a hydrocarbon containing formation is described. The method may include providing a hydrocarbon recovery composition to the hydrocarbon containing formation. Hydrocarbons in the hydrocarbon containing formation may interact with the hydrocarbon recovery composition. The hydrocarbon recovery composition may include an aliphatic anionic surfactant and an aliphatic nonionic additive. In some embodiments, an aliphatic anionic surfactant may be branched. In other embodiments, an aliphatic nonionic additive may be branched.

Abstract: An apparatus uses at least one injection pump (9) positioned in proximity to an undersea petroleum well (10) to provide hydraulic fluid for hydraulic pumping equipment positioned in the bottom of the well, in order to cause a flow of produced oil. The injection pump (9) is able to suction hydraulic fluid from a tank of hydraulic fluid (8) positioned on the deck of a service unit (40). Alternatively, injection pump (9) is able to utilize water from the sea as a hydraulic fluid. Alternatively, the injection pump (9) may be integral with a Christmas tree manifold (6) or may be installed in an auxiliary well (90) in order that it's external portion does not enter into contact with seawater.

Abstract: A circulation loss combination for water-based drilling fluid system(s) comprising: a first amount of alkali metal silicate; a second amount of water insoluble particulate; and, a quantity of water soluble activating agent effective to reduce the pH of the water-based drilling fluid system to a value sufficiently low to form an effective circulation loss structure at a desired period of time after addition to the water-based drilling fluid system.

Abstract: A method and a plant for simultaneous production of a gas for injection into an oil field and production of methanol, dimethyl ether and/or other oxygenated hydrocarbons or production of higher hydrocarbons from natural gas is disclosed. An air separation unit (ATR) for production of pure nitrogen for injection and pure oxygen for production of synthesis gas (“syngas”) by authermal reformation of a natural gas is an essential part of the method and plant.

Abstract: A method and apparatus for producing gas from a hydrate formation includes the use of at least one wellbore which penetrates the hydrate formation and further extends into an aquifer below the hydrate formation. The aquifer provides relatively warm water which may be produced up and into the hydrate formation thereby causing the release of gas from the hydrate. Suitable flow control and monitoring equipment may be included to control the flow of water produced from the aquifer and gas produced from the hydrate formation.

Abstract: A method utilizes the energy of water that flows out from a high-pressure reservoir. Water and hydrocarbons are separated in a down-hole separator and are brought separately to the seabed. In a first aspect the energy of the water is utilized to inject the water into an underground formation with a lower pressure. In a second aspect the energy is utilized to drive a turbine which in turn is driving a pump for pressurizing hydrocarbons. The invention utilizes a method and an arrangement to control the separator by control valves on the well head for each phase.

Abstract: A method of treating a hydrocarbon containing formation is described. The method may include providing a hydrocarbon recovery composition to the hydrocarbon containing formation. Hydrocarbons in the hydrocarbon containing formation may interact with the hydrocarbon recovery composition. The hydrocarbon recovery composition may include an aliphatic anionic surfactant and an aliphatic nonionic additive. In some embodiments, an aliphatic anionic surfactant may be branched. In other embodiments, an aliphatic nonionic additive may be branched.

Abstract: A process for the recovery of oil from a subsurface reservoir in combination with the production of liquid hydrocarbons from a hydrocarbonaceous stream involving: (i) separating an oxygen/nitrogen mixture into a stream enriched in oxygen and an oxygen depleted stream; (ii) partial oxidation of the hydrocarbonaceous feed at elevated temperature and pressure using enriched oxygen produced in step (i) to produce synthesis gas; (iii) converting synthesis gas obtained in step (ii) into liquid hydrocarbons; and (iv) recovering oil from a subsurface reservoir using at least part of the oxygen depleted gas stream produced in step (i).

Abstract: A method for recovering oil (24) from a natural oil reservoir (18) includes the steps of separating air to produce an oxygen rich stream (40) and a nitrogen rich stream (34), providing a natural gas stream (12) and feeding at least part of the oxygen rich stream (40) and the natural gas stream (12) into a gas to liquid or GTL conversion installation (42) to produce hydrocarbon products (44) and heat. The heat produced in the gas to liquid conversion installation is used to produce energy (20) to pressurize (16) the nitrogen in the nitrogen rich stream (34) to produce a pressurized nitrogen rich stream (22). The pressurized nitrogen rich stream (22) is passed into a natural oil reservoir (18) to enhance the recovery of oil (24) from the reservoir.

Abstract: A method for controlling pressure of a dual well system includes drilling a substantially vertical well bore from a surface to a subterranean zone and drilling an articulated well bore from the surface to the subterranean zone using a drill string. The articulated well bore is horizontally offset from the substantially vertical well bore at the surface and intersects the substantially vertical well bore. The method includes drilling a drainage bore into the subterranean zone. The method includes pumping a drilling fluid through the drill string when drilling the drainage bore. The method includes pumping a pressure fluid down the substantially vertical well bore when drilling the drainage bore. The pressure fluid mixes with the drilling fluid to form a fluid mixture returning up the articulated well bore which forms a frictional pressure that resists fluid flow from the subterranean zone.

Abstract: A process for enhanced oil recovery from an extraction operation comprises the steps of selection of an appropriate hydrocarbon bearing stratum; providing at least one production well and one injection well; and injecting into the target stratum a slurry formed from sand, viscous liquids or oily sludge, which is delivered at or near formation fracture pressures. Monitoring of bottom hole pressure is carried out, to permit delivery of the slurried wastes in a series of injection episodes, in which the length of the episodes and interinjection periods is determined by maintaining the bottom hole pressure within a preselected range. The position and spread of the slurried wastes within the target stratum may be monitored through the use of additional monitoring steps.

Abstract: A method and apparatus for exploiting oilfields involving the installation of a well network in the form of an open or non-open ring that is generally non-circular. Horizontal well sections (3) are drilled from vertical injection (1) or producing (2) wells that already exist, to interlink them. The vertical wells that are located in the same line are used as injection wells, thereby promoting oil sweeping in the reservoir (R) towards the ring-shaped producing wells (P1) or (P2). In another embodiment, vertical service wells are drilled for monitoring the characteristics of the reservoir (R). From these wells, horizontal wells are drilled in a ring-shaped form to obtain concentric well rings from the periphery to the central region of the reservoir (R). The outermost horizontal well is used as injection well and the innermost annular horizontal wells are used as producing wells.

Abstract: A method of treating a hydrocarbon containing formation is described. The method may include providing a hydrocarbon recovery composition to the hydrocarbon containing formation. Hydrocarbons in the hydrocarbon containing formation may interact with the hydrocarbon recovery composition. The hydrocarbon recovery composition may include an aliphatic anionic surfactant and an aliphatic nonionic additive. In some embodiments, an aliphatic anionic surfactant may be branched. In other embodiments, an aliphatic nonionic additive may be branched.

Abstract: The invention concerns an aqueous viscoelastic fluid for use in the recovery of hydrocarbons. According to the invention this fluid comprises a first viscoelastic surfactant and a second surfactant able to decompose under downhole conditions to release a compound itself able to reduce the viscosity of the aqueous viscoelastic fluid.

Abstract: The present invention provides the use of surface-modified nanoparticles in fluids used to recover hydrocarbon from underground formations. The use of surface-modified nanoparticles in such fluids provides foams that are stable under pressure yet have a shorter foam lifetime than typical surfactant-stabilized foams after the pressure is released or lowered.

Abstract: The present invention relates to petroleum recovery operations, and more particularly, to the use of pulse technology to enhance the effectiveness of waterflooding operations. The systems of the present invention generally comprise an injection means for continually injecting a fluid into the subterranean formation, and a pressure pulsing means for periodically applying a pressure pulse having a given amplitude and frequency to the fluid while the fluid is being injected into the subterranean formation.

Abstract: A method for treating a relatively permeable formation containing heavy hydrocarbons in situ may include providing heat from one or more heat sources to a portion of the formation. The heat may be allowed to transfer from the heat sources to a selected section of the formation. The transferred heat may reduce the viscosity of at least some hydrocarbons within the selected section. A gas may be provided to the selected section of the formation. The gas may produce a flow of hydrocarbons within the selected section. A mixture of hydrocarbons may be produced from the selected section.

Abstract: A coal formation may be treated using an in situ thermal process. A mixture of hydrocarbons, H2, and/or other formation fluids may be produced from the formation. Heat may be applied to the formation to raise a temperature of a portion of the formation to a pyrolysis temperature. The mixture may be produced from the formation through a plurality of production wells. A selected number of heat sources may be positioned in the formation for each production well.

Abstract: It has been discovered that carbonate powders and bicarbonate powders are useful to increase the pH and corrosion resistance of high-density brines, such as zinc bromide brines, without significantly reducing their densities. The carbonates and/or bicarbonates should be water-soluble and may be sodium, potassium, magnesium and/or ammonium carbonates and/or bicarbonates and the like. The carbonates and/or bicarbonates are easily added in powder or other finely divided solid form.

Abstract: A method for predicting the secondary porosity system (SPS) porosity, and thereby permeability, of a coal bed involves determining an initial condition in the coal bed, including an initial SPS pressure and an initial sorbed gas composition, determining a pressure strain effect due to increasing the SPS pressure to a value greater than the initial SPS pressure, and determining a sorption strain effect due to changes in the sorbed gas composition resulting from decreasing the methane content and increasing the content of a stronger adsorbing fluid (SAG) relative to the initial sorbed gas composition. Preferably, the method uses data from test injections of water and/or a weaker adsorbing fluid (WAG) and a SAG. The data is used in the inventors' model to compute a SPS porosity and an absolute permeability at a reference SPS pressure and a reference sorbed gas composition. Preferably, the reference pressure is atmospheric pressure.

Abstract: A multilateral injection/production/storage completion system. In a described embodiment, a method of completing a well having a first wellbore intersecting each of second, third and fourth wellbores includes the steps of: injecting a first fluid into a first zone intersected by the second wellbore; receiving a second fluid into the third wellbore in response to the first fluid injecting step; flowing the second fluid from the third wellbore to the fourth wellbore; storing the second fluid in a second zone intersected by the fourth wellbore; and then producing the second fluid from the second zone to a remote location.

Abstract: A method of stimulating coalbed methane production by injecting gas into a producer and subsequently placing the producer back on production is described. A decrease in water production may also result. The increase in gas production and decrease in water production may result from: (1) the displacement of water from the producer by gas; (2) the establishment of a mobile gas saturation at an extended distance into the coalbed, extending outward from the producer; and (3) the reduction in coalbed methane partial pressure between the coal matrix and the coal's cleat system.

Abstract: The invention relates to oil and natural gas production and can be used for recovering hydrocarbons from hydrocarbon-bearing formations, for example, from oil-bearing formations, or, for example, from gas-condensate reservoirs. A method for recovery of hydrocarbons from a hydrocarbon-bearing formation, comprises: recovering a hydrocarbon-containing fluid through at least one production well, separating at least a part of a gaseous mixture from the fluid, injecting a gas through injection well. The separated gaseous mixture (all or a part of it) is combusted with air, which is used as oxidant, in a power plant, and, exhaust gases resulting from said combustion, which comprise nitrogen and carbon dioxide, are discharged from the power plant. Said air and the separated gaseous mixture are mixed and a gas-air mixture resulting from said mixing is compressed prior to said combustion, or the gas-air mixture is ignited during said compression.

Abstract: Methods for optimization of oil well production with deference to reservoir and financial uncertainty include the application of portfolio management theory to associate levels of risk with Net Present Values (NPV) of the amount of oil expected to be extracted from the reservoir. Using the methods of the invention, production parameters such as pumping rates can be chosen to maximize NPV without exceeding a given level of risk, or, for a given level of risk, the minimum guaranteed NPV can be predicted to a 90% probability. An iterative process of generating efficient frontiers for objective functions such as NPV is provided.

Abstract: The present invention relates to a device for creating a reaction zone in an aquifer, for circulating and purifying ground and raw water, in particular for tap water use, which aquifer comprises satellite wells and at least one extraction well wherein each satellite well comprises at least two, essentially vertical water conducting sections separated from each other in substantially vertical longitudinal direction, and having at least two geohydrologic zones, whereby said zones are arranged to alternating emit water to the surrounding, and receive water coming from the outside surrounding, respectively, whereby adjacent wells are arranged for opposite flows so that substantially horizontal flows are obtained in a water leading layer, in which layer the wells have been placed between adjacent wells, and whereby the water of at least one section is arranged to be pumped in one direction from below and upward, and at least in one vertical section, form above and downward, respectively, and to be lead out through

Abstract: A method of producing fluids from a subterranean formation through a single well in a network of separate well-bores, comprising the steps of: forming a well having a horizontal section located within the formation; completing and equipping such well to produce fluids from the formation; producing fluids from the formation through such well; forming at least one additional well having a horizontal section located within the formation such that such well is in fluid communication with the first well, without intersecting with the horizontal section of the first well, and using such additional well as an conduit within the formation to allow and cause fluids contained in the formation which drain or flow into the horizontal section of such additional well-bore, to flow to and be produced through the first well-bore.

Abstract: Improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that intersects a horizontal cavity well. The drainage patterns provide access to a large subterranean area from the surface while the vertical cavity well allows entrained water, hydrocarbons, and other deposits to be efficiently removed and/or produced.

Abstract: An improved method for management of by-products from subterranean zones, comprising drilling a first well system into a subterranean zone, wherein the first well system comprises a first drainage pattern. By-product and gas from a first volume of the subterranean zone is removed via the first well system. A second well system is drilled into the subterranean zone, wherein the second well system comprises a second drainage pattern, and by-product is moved from a second volume of the subterranean zone to the first volume of the subterranean zone. Gas is then produced from the second volume of the subterranean zone. Subsequent drainage patterns repeat the process.

Abstract: A process and equipment for extracting and disposing of sour reservoir components initially contained in natural hydrocarbons. The stream of natural hydrocarbons extracted from a reservoir is initially subjected to an optional gas/liquid separation. The gaseous hydrocarbons are then scrubbed with a liquid absorbent to dissolve sour reservoir components such as hydrogen sulphide and carbon dioxide and thereby form a solution. The liquid absorbent may be water that is preferably sufficiently free of oxygen and solids to be of a quality suitable for re-injection. The solution is pumped back into a well. The well may be the reservoir that produced the hydrocarbons, or adjacent geological formations, with the re-injected sour water being employed for production stimulation. Alternatively, the well may be a depleted reservoir. The scrubber may be a multiple-stage packed column or tray column that preferably allows for condensate skimming.

Abstract: A description is given of a system for exploiting oilfields, be these either already developed or to be developed.

Abstract: A method of increasing the productivity of oil, gas and hydrogeological wells has the steps of performing a slot unloading, providing a cyclical treatment of a near well zone with a formation-treating substance, with a use of cutting slots, determining a region to be treated, selecting a corresponding volume of a treating technological composition, and introducing the volume into a formation to be treated, and subdividing the method into a two stages including a first stage performed by a partial slot unloading of a near well zone so as to remove a main part of support stresses, and a second stage of removing a remaining part of support stresses by a cyclical treatment of the well with a formation-treating substance with control by the density of the rock to be treated and performing a corresponding correction.

Abstract: The present invention generally provides a method and apparatus for injecting a compressible fluid at a controlled flow rate into a geological formation at multiple zones of interest. In one aspect, the invention provides a tubing string with a pocket and a nozzle at each isolated zone. The nozzle permits a predetermined, controlled flow rate to be maintained at higher annulus to tubing pressure ratios. The nozzle includes a diffuser portion to recover lost steam pressure associated with critical flow as the steam exits the nozzle and enters a formation via perforations in wellbore casing. In another aspect, the invention ensures steam is injected into a formation in a predetermined proportion of water and vapor by providing a plurality of apertures between a tubing wall and a pocket. The apertures provide distribution of steam that maintains a relative mixture of water and vapor.

Abstract: The present invention relates to an oil production method for producing oil from an oil-containing reservoir with using horizontal wells, by drilling a gas injection well and a production well to be locate at an appropriate distance between them, depending upon at least a ratio between an averaged vertical permeability and an averaged horizontal permeability in the oil-containing reservoir producing the oil therefrom.

Abstract: The invention relates to an environmentally friendly method for generating energy from natural gas. Through the combustion of the natural gas with a mixture comprising substantially oxygen and CO2, a number of advantages are achieved with regard to the emission of CO2 and NOx. According to the invention, the CO2-rich product gas is injected into a natural gas reservoir from which natural gas has been extracted. By the underground replacement of natural gas by CO2, a pressure drop in the natural gas reservoir can be controlled, so that subsidence is prevented. Additionally, in this manner, the emission of CO2 is reduced or even wholly prevented.

Abstract: The present invention provides a process of preparing of a gas composition suitable for the injection in an oil-containing field to increase the degree of recovery and simultaneously reduce the discharge of CO2 to the atmosphere. However, injection of a gas composition containing large amounts of oxygen will result in a degraded submarine formation which is not desirable. The present invention relates to a process for the production of a gas composition comprising N2, CO2, minor parts of NOx, VOC (volatile organic compounds) and about 0-2.0 mole % O2 from an oxygen containing exhaust gas, wherein a stream of an exhaust gas from the combustion of air and natural gas in a gas turbine containing 18% by weight O2 or less, is combusted with natural gas, whereupon the desired gas composition is discharged as a flue gas. Further, a process of recovering oil from submarine formations is also described, where said gas composition is compressed and injected into a submarine formation.

Abstract: A method and apparatus detects the presence of a fluorescent tracer dye, a change in capacitance, or a change in fiber optic electrical properties to determine whether or not a TCP gun has fired. The method and apparatus detects the number of charges fired to determine whether or not all TCP guns have fired and also determines the contributions of injection wells to producing wells by introducing fluorescent tracers into injection wells and detecting the presence of the fluorescent tracers at production wells. The invention places fluorescent dye particles in a gravel pack to sense when a gravel pack is deteriorating by detecting the tracer dye particles in the well flow.

Abstract: An improved method for management of by-products from subterranean zones, comprising drilling a first well system into a subterranean zone, wherein the first well system comprises a first drainage pattern. By-product and gas from a first volume of the subterranean zone is removed via the first well system. A second well system is drilled into the subterranean zone, wherein the second well system comprises a second drainage pattern, and by-product is moved from a second volume of the subterranean zone to the first volume of the subterranean zone. Gas is then produced from the second volume of the subterranean zone. Subsequent drainage patterns repeat the process.

Abstract: Disclosed is a method of producing a pressurized stream of substantially inert gas. The method comprises collecting the exhaust gases from an internal combustion engine, directing the exhaust gases into the intake of a compressor for compressing to a desired pressure, and recirculating a portion of the compressed exhaust gases back to the intake of the compressor such that the pressure of the exhaust gases within said compressor intake is maintained above atmospheric pressure. Also disclosed is an apparatus for producing a pressurized stream of substantially inert gas utilizing the described method.

Abstract: A process is disclosed for stimulating the activity of microbial consortia in a subterranean formation to convert hydrocarbons to methane, which can be produced. Fluid and rock of the formation are analyzed. The presence of microbial consortia is determined and a characterization made (preferably genetic) of at least one microorganism of the consortia, at least one being a methanogenic microorganism. The characterization is compared with at least one known characterization derived from a known microorganism having one or more known physiological and ecological characteristics. This information, together with the information obtained from the analysis of the fluid and rock, is used to determine an ecological environment that promotes in situ microbial degradation of formation hydrocarbons and promotes microbial generation of methane by at least one methanogenic microorganism of the consortia. This information is then used as the basis for modifying the formation environment to produce methane.

Abstract: The present invention is a method for re-gassifying Liquefied Natural Gas (LNG) in a subterranean formation/cavity, storing the resulting gaseous hydrocarbon in the same or connected strata, then subsequent conventional production and delivery of the gas to end users. LNG is injected into a permeable subterranean reservoir through surface and wellbore equipment suitable for operations at cryogenic temperatures. The liquid hydrocarbon vaporizes in the permeable rock/cavity near the injection wellbore as it gains thermal energy from the surrounding strata. The resulting gas is held within the reservoir for subsequent production and/or immediately produced by producing wells in the same or contiguous formations. The invention eliminates the need for onshore LNG receiving/storage terminals.

Abstract: A control system and method for determining optimal fluid injection pressure is based upon a model of a growing hydrofracture due to waterflood injection pressure. This model is used to develop a control system optimizing the injection pressure by using a prescribed injection goal coupled with the historical times, pressures, and volume of injected fluid at a single well. In this control method, the historical data is used to derive two major flow components: the transitional component, where cumulative injection volume is scaled as the square root of time, and a steady-state breakthrough component, which scales linearly with respect to time. These components provide diagnostic information and allow for the prevention of rapid fracture growth and associated massive water break through that is an important part of a successful waterflood, thereby extending the life of both injection and associated production wells in waterflood secondary oil recovery operations.

Abstract: A method of remediating a site of earth and groundwater contamination includes the steps of drilling at least one injection well, and preferably a plurality of injection wells, into the groundwater in a contaminated area. At least one, and preferably a plurality of extraction wells, are drilled into the earth above the groundwater, the vadose zone, in the contaminated area. The surface of the earth above the contaminated area is sealed, such as by a layer of concrete, asphalt, or plastic sheeting. Air and nutrients are injected into the contaminated area through the injection wells. The air is injected on a substantially continuous basis while the nutrients are injected on a batch basis. Air and vapor is extracted on a substantially continuous basis from the contaminated area by the extraction wells, which may be either vertically or horizontally positioned.

Abstract: A method of stimulating coalbed methane production by injecting gas into a producer and subsequently placing die producer back on production is described. A decrease in water production may also result The increase in gas production and decrease in water production may result from: (1) die displacement of water from die producer by gas; (2) die establishment of a mobile gas saturation at an extended distance into the coalbed, extending outward from the producer; and (3) the reduction in coalbed methane partial pressure between the coal matrix and die coal's cleat system.

Abstract: A method of remediating a site of earth and groundwater contamination includes the steps of drilling at least one injection well, and preferably a plurality of injection wells, into the groundwater in a contaminated area. At least one, and preferably a plurality of extraction wells, are drilled into the earth above the groundwater, the vadose zone, in the contaminated area. The surface of the earth above the contaminated area is sealed, such as by a layer of concrete, asphalt, or plastic sheeting. Air and nutrients are injected into the contaminated area through the injection wells. The air is injected on a substantially continuous basis while the nutrients are injected on a batch basis. Air and vapor is extracted on a substantially continuous basis from the contaminated area by the extraction wells, which may be either vertically or horizontally positioned.