Patent Application
20150096760
The present invention relates generally to methods and means for safely and efficiently exploiting hydrocarbon reserves, and in a particular though non-limiting embodiment to a modular exploration and production system including an extended well testing service vessel suitable for testing, separating and otherwise assisting in the exploration and production of oil, gas and natural gas reserves.
Innumerable systems and methods have been employed in efforts to find and recover hydrocarbon reserves around the world. At first, such efforts were limited to land operations involving simple but effective drilling methods that satisfactorily recovered reserves from large, productive fields. As the number of known producing fields dwindled, however, it became necessary to search in ever more remote locales, and to move offshore, in the search for new resources. Eventually, sophisticated drilling systems and advanced signal processing techniques enabled oil and gas companies to search virtually anywhere in the world for recoverable hydrocarbons.
Initially, deepwater exploration and production efforts consisted of expensive, large-scale drilling operations supported by tanker storage and transportation systems, due primarily to the fact that most offshore drilling sites are associated with difficult and hazardous sea conditions, and thus large-scale operations provided the most stable and cost-effective manner in which to search for and recover hydrocarbon reserves.
A major drawback to the large-scale paradigm, however, is that explorers and producers have little financial incentive to work smaller reserves, since potential financial recovery is generally offset by the lengthy delay between exploration and production (approximately 3 to 7 years) and the large capital investment required for conventional platforms and related drilling and production equipment. Moreover, complex regulatory controls and industry-wide risk aversion have led to standardization, leaving operators with few opportunities to significantly alter the prevailing paradigm. As a result, offshore drilling operations have traditionally been burdened with long delays between investment and profit, excessive cost overruns, and slow, inflexible recovery strategies dictated by the operational environment.
More recently, deepwater sites have been found in which much of the danger and instability present in such operations is avoided. For example, off the coast of West Africa, Indonesia and Brazil, potential drilling sites have been identified where surrounding seas and weather conditions are relatively mild and calm in comparison to other, more volatile sites such as the Gulf of Mexico and the North Sea. These recently discovered sites tend to have favorable producing characteristics, yield positive exploration success rates, and admit to production using simple drilling techniques similar to those employed in dry land or nearshore operations.
However, since lognormal distributions of recoverable reserves tend to be spread over a large number of small fields, each of which yield less than would normally be required in order to justify the expense of a conventional large-scale operation, these regions have to date been underexplored and underproduced relative to their potential. Consequently, many potentially productive smaller fields have already been discovered, but remain underdeveloped due to economic considerations.
An ongoing concern during such field exploitations relates to environmentally appropriate disposal of fluids produced during operations, particularly during the completion, repair, stimulation, early production, and production measurement stages; the same problem naturally arises during well service when carrying out off-line production and maintenance of existing facilities.
Controlling reception of resulting products has therefore been a challenge, since by their very nature such products are highly contaminating because they consist primarily of crude oil; gas; oily waters and production waters; chemicals (acids, aromatics, brines, etc.) used in connection with the stimulation and service of wells; and solids, including sands, drilling mud, well cuttings and drilling waste.
One of the ways that well service and disposal of effluents has been traditionally carried out is by marine companies that mobilize modules with portable equipment on support or supply vessels. When the vessels reach a platform, installation or well to be serviced, the modules are hoisted up and interconnected.
In some cases the platform or installation does not have space for storing fluids or simple test separators. In most cases there are no production lines through which the products can be sent for subsequent treatment. Consequently the effluents must be sent to a burner where the products are burned off, thereby resulting in environmental damage and inadvertent incineration of products with high commercial value such as crude oil and natural gas.
Another way in which well service needs have previously been met is by means of barges, frequently assisted by tug boats and other support vessels to maintain the barge in position, into which the unprocessed fluids are discharged in order to be transported to land for confinement or secondary utilization.
One of the most troublesome circumstances involves exploratory wells, which frequently use semi-submersible movable platforms or drilling ships, which usually do not have production lines or suitable storage capacity. In such cases the products are incinerated using burners installed for that purpose. Frequently, diesel fluids and compressed air are mixed to facilitate combustion, although in many cases the product is still not completely incinerated. Thus, the ecological damage to the environment is greater due to the residues that spill into the sea, as well as gases (primarily CO2) that are emitted into the air. Such solutions are therefore extremely inefficient, costly and highly contaminating.
In order to illustrate the principle of the traditional well service systems and what happens with the effluents, Prior Art
The mixture then goes to a conventional separation equipment unit (4) from which gas, oily water and crude are obtained; the gas (5) is sent directly to a burner emitting CO2 and other contaminating particles resulting from incineration; oily water (6) is poured back into the sea without being separated or processed, thereby carrying with it a large amount of hydrocarbons; crude oil (7) is sent to a distribution and pumping system (8); and if the installation, platform or ship does not have space for storing the crude, it can be sent through a line (9) to an incineration system (11) as described above. In most cases diesel and/or compressed air (10) are added to achieve combustion.
If the installation, platform, well or ship has storage space, the crude oil will be sent through a line (12) and stored in tanks (13) for subsequent disposal on land or another support vessel. Many of the foregoing activities are obviously wasteful, ecologically destructive and financially inefficient, and therefore inconsistent with the relatively lower profit margins expected from exploitation of marginal or declining fields.
There is, therefore, a longstanding need for a safe, efficient, environmentally friendly system that admits to careful and meaningful testing of product produced from marginal and declining fields that are compatible with self-tensioning riser systems having adjustable buoyancy chambers capable of maintaining approximately constant vertical tension on an associated drilling or production string, in which the height of a wellhead can be adjusted during exploration and production. There is also a need for an offshore exploration and production system that flexibly admits to field use in connection with both deepwater and shallow target horizons without necessarily being configured to conform to any particular operational depth, that can be coupled with a scalable, comprehensive well test service vessel designed and equipped to maximize return on operation investment in a safe and reliable, environmentally friendly manner.
An offshore exploration and production system including an extended well test service vessel is provided, the system including at least: a modular exploration and production system disposed in communication with an offshore well, the modular exploration and production system further comprising one or more adjustable buoyancy chambers and a lower connecting member disposed between the offshore well and the one or more adjustable buoyancy chambers; and an extended well test service vessel including at least: means for positioning said vessel into proximate communication with modular exploration and production system; interconnecting the vessel and the modular exploration and production system with means for loading and discharging hydrocarbons obtained from the well; separating the hydrocarbons into a plurality of constituent products; and discharging the products separated from the hydrocarbons into a storage means.
A method of using an extended well test service vessel in coordination with a modular exploration and production system is also provided, the method including at least: positioning the vessel into proximate communication with the modular exploration and production system; interconnecting the vessel and the modular exploration and production system with means for loading and discharging hydrocarbons obtained from an associated offshore well; separating the hydrocarbons into a plurality of constituent products; and discharging the products separated from the hydrocarbons into a storage means.
Referring now to the specific, non-limiting embodiment of the invention depicted in
In the example embodiment depicted in
In other embodiments, lower connecting member 5 further comprises one or more receiving members disposed to receive an attachment member disposed on well isolation member 4. In an alternative embodiment, lower connecting member 5 comprises an attachment member for attaching said lower connecting member 5 to a receiving member disposed on well isolation member 4. Methods and means of securely fastening lower connecting member 5 to well isolation member 4 are known to those of ordinary skill in the art, and may comprise one or more of a wide variety of fastening techniques, e.g., hydraulic couplers, various nut and bolt assemblies, welded joints, pressure fittings (either with or without gaskets), swaging, etc., without departing from the scope or spirit of the present invention.
Likewise, lower connecting member 5 may comprise any known connecting means appropriate for the specific application contemplated by operators. For example, in various embodiments, lower connecting member 5 comprises one or more of segments of riser, riser pipe, and/or pipe casing. In some embodiments, lower connecting member 5 comprises a concentric arrangement, for example, a fluid transport member having a smaller outer diameter than the inner diameter of a pipe casing in which the fluid transport member is housed.
In further embodiments, lower connecting member 5 is disposed in communication with one or more lateral stabilizers 6, which, when deployed in conjunction a plurality of tension lines 7, effectively controls horizontal offset of the system. By utilizing the buoyant forces of adjustable buoyancy chamber 9, lower connecting member 5 is drawn taut and held in a stable position.
In an alternative embodiment, one or more stabilizers 6 control horizontal offset of lower connecting member 5, and the height or depth of an associated well terminal member 14 is adjusted by varying the length of upper connecting member 12. In some embodiments, the vertical tension of lower connecting member 5 is held approximately constant while the height or depth of well terminal member 14 is adjusted. In further embodiments, the height or depth of well terminal member 14 is held approximately constant, while the vertical tension imparted by adjustable buoyancy chamber 9 on lower connecting member 5 is adjusted. In still further embodiments, the height or depth of well terminal member 14 and the vertical tension applied to lower connecting member 5 are held approximately constant, while lateral adjustments are performed using lateral stabilizer 6 and one or more of tension lines 7.
In certain embodiments, one or more lateral tension lines 7 are individually adjustable, whereas in other embodiments, the tension lines 7 are collectively adjustable. In further embodiments, one or more tension lines 7 are both individually and collectively adjustable. In still further embodiments, the one or more lateral stabilizers 6 are disposed in communication with a tension measuring means, so that a fixed or predetermined amount of lateral tension can be applied to lower connecting member 5 in order to better control system offset. In some embodiments, the tension lines 7 are anchored to the sea floor by means of an anchoring member 8, for example, a suction type anchor, or alternatively, a mechanical or conventional deadweight type anchor.
In a presently preferred embodiment, adjustable buoyancy chamber 9 is approximately annular in shape, so that lower connecting member 5 can be passed through a void longitudinally disposed in a central portion of the device. In further embodiments, adjustable buoyancy chamber 9 further comprises a plurality of inner chambers. In still further embodiments, each of the chambers is independently operable, and different amounts of air or gas (or another fluid) are disposed in the chambers to provide greater adjustable buoyancy control. In one example embodiment, adjustable buoyancy chamber 9 further comprises a fluid ballast that can be ejected from the chamber, thereby achieving greater chamber buoyancy and lending additional vertical tension to lower connecting member 5. Those of ordinary skill in the art will appreciate that many appropriate fluid ballast can be used to increase or retard buoyancy; for example, compressed air is an appropriate fluid that is both inexpensive and readily available.
In some embodiments, adjustable buoyancy chamber 9 further comprises a ballast input valve 15a, so that a fluid ballast can be injected into the chamber from an external source, for example, through an umbilical line run to the surface or a remote operated vehicle, so that an operator can deliver a supply of compressed gas to the chamber via the umbilical, thereby adjusting buoyancy characteristics as desired. In other embodiments, the fluid input valve is disposed in communication with one or more pumps or compressors, so that the fluid ballast is delivered to the chamber under greater pressure, thereby effecting the desired change in buoyancy more quickly and reliably.
In other embodiments, adjustable buoyancy chamber 9 further comprises a ballast output valve 15b, so that ballast can be discharged from the chamber. In instances where air or another light fluid is injected into the chamber while water or another heavy liquid is discharged, the chamber will become more buoyant and increase vertical tension on lower connecting member 5. Conversely, if water or another heavy liquid is injected into the chamber while air is bled out, the chamber will lose buoyancy, thereby lessening vertical tension on lower connecting member 5.
In alternative embodiments, the ballast output valve is disposed in communication with one or more pumps or compressors, so that ballast is ejected from the chamber in a more reliable and controlled manner. In some embodiments, the ballast output valve is disposed in communication with an umbilical, so that ballast ejected from the chamber can be recovered or recycled at the surface. In any event, a principal advantage of the present invention is that adjustments to the chamber's buoyancy and tensioning properties, and the ability to control the height of the well terminal member 14, can be performed at any time during either exploration or production, due to the various ballast input and output control means disposed about the body of the chamber.
In further embodiments, adjustable buoyancy chamber 9 is further disposed in communication with one or more tension lines 10 provided to anchor the adjustable buoyancy chamber to the sea floor. As before, tension lines 10 are anchored to the sea floor using known anchoring technology, for example, suction anchors or dead weight type anchors, etc. The one or more tension lines 10 can also provide additional lateral stability for the system, especially during operations in which more than one well is being worked. In one embodiment, the one or more tension lines 10 are run from the adjustable buoyancy chamber 9 to the surface, and then moored to other buoys or a surface vessel, etc., so that even greater lateral tension and system stability are achieved. In further embodiments, the tension lines 10 are individually adjustable, whereas in other embodiments, the tension lines 10 are collectively controlled. In still further embodiments, the one or more tension lines 10 are both individually and collectively adjustable.
In one example embodiment, adjustable buoyancy chamber 9 is disposed in communication with a vertical tension receiving member 11. In another embodiment, the vertical tension receiving member 11 is equipped with a tension measuring means (e.g., a load cell 16, strain gauge, etc.), so that vertical tension applied to lower connecting member 5 is imparted in a more controlled and efficient manner. In another embodiment, the buoyant force applied to tension receiving member 11 is adjusted by varying the lengths of tension lines 10, while the buoyancy of adjustable buoyancy chamber 9 is held approximately constant. In a further embodiment, the buoyancy of adjustable buoyancy chamber 9 is controlled by means of one or more individually selectable ballast exhaust ports disposed about the body of the chamber, which vent excess ballast fluid to the surrounding sea. In still further embodiments, the open or closed state of the ballast exhaust ports are individually controlled using port controllers known to those of ordinary skill in the art (e.g., plugs, seacocks, etc.).
In a presently preferred embodiment, the system is disposed so that a well terminal member 14 installed above buoyancy chamber 9 is submerged to a depth at which maintenance and testing can be carried out by SCUBA divers using lightweight, flexible diving equipment, for example, at a depth of about 100 to 300 feet beneath the surface. In some embodiments, the well terminal member 14 is submerged only to the minimum depth necessary to provide topside access to the hulls of various surface vessels servicing the well, meaning that well terminal member 14 could also be disposed at a much shallower depth, for example, a depth of about 50 to 100 feet. In alternative embodiments, well terminal member 14 is disposed at depths of less than 50 feet, or greater than 300 feet, depending upon the actual conditions surrounding operations. In still further embodiments, well terminal member 14 is disposed either at the surface or above the surface of the water, and a blowout preventer or a production tree is installed by workers operating aboard a service platform or surface vessel. This “damp tree” or “wet tree” model avoids the need to assemble long subsurface riser stacks, as would generally be required during deepwater operations. Moreover, disposing the well terminal member at or near the surface also permits testing and maintenance to be carried out by SCUBA divers or surface crews, without the need for expensive and time-consuming remote operated vehicle operations.
In some embodiments, well terminal member 14 further comprises either a blowout preventer or a production tree. In a presently preferred embodiment, however, well terminal member 14 further comprises a combined blowout preventer and production tree assembly configured so as to facilitate simplified well intervention operations.
In some embodiments, lower connecting member 5 terminates within the void formed in a center portion of the annular chamber 9, at which point an upper connecting member 12 becomes the means by which fluids are transported up to the wellhead. In other embodiments, lower connecting member 5 does not terminate within the void formed in a center portion of the annular chamber, but instead runs through the void and is subsequently employed as an upper connecting member 12 disposed between the chamber and the wellhead. In other embodiments, a vertical tension receiving member 11 is disposed between the buoyancy chamber 9 and upper connecting member 12, so that the chamber's buoyant forces are transferred to the vertical tension receiving means 11, thereby applying vertical tension to the drilling or production string extended below the chamber.
In further embodiments, upper connecting member 12 further comprises a well isolation member 13, e.g., one or more ball valves or blowout preventers, used to halt fluid flow in the event that well terminal member 14 is either removed or disabled, for example, during testing and maintenance operations. Those of ordinary skill in the art will appreciate that the precise types and exact locations of isolation valves 13 employed in the system are variable and flexible, the only real requirement being that the valves are capable of allowing or preventing fluid flow from the well 1 during periods in which testing or maintenance, or even an emergency safety condition, are present.
For example, well terminal member 14 can be equipped with a production tree so that a production hose disposed on a surface vessel can be attached to the system and production can commence. Alternatively, well terminal member 14 can terminate in a blowout preventer, so that the well will not blow out during drilling operations. In other embodiments, well terminal member 14 terminates in a combined production tree and blowout preventer assembly to facilitate simplified well intervention operations.
Turning now to the specific though non-limiting embodiments of the invention depicted in
In the example embodiment depicted in
In some embodiments, the system is moored to the sea floor using one or more mooring lines 31 connected to a first vertical tension receiving means 32a, while buoyancy chamber 30 is raised or lowered by either spooling-out or reeling-in lengths of one or more tension lines 37 disposed between a second vertical tension receiving means 32b and a chamber height adjustment means 33. As adjustable buoyancy chamber 30 rises, vertical tension is applied to vertical tension receiving member 34, which in turn lifts well terminal member 36 up toward the surface.
As seen in the example embodiment depicted in
A particularly effective solution for efficiently recovering hydrocarbons from a field includes integration of a modular exploration and production system comprising one or more wells disposed in communication with one or more self-standing riser systems together with a well test service vessel selectively and variably designed and equipped to fulfill the field's entire range of operational needs. Optimally, the well test service vessel will facilitate reception, separation, storage, offloading and reinjection of products received from a well in a safe, efficient and environmentally friendly manner, without requiring the size and full outfitting of a floating production and storage offtake vessel.
By designing and equipping with a goal of minimizing CO2 emissions discharged from a well (functionality not generally associated with well test service vessels), damage to the environment is minimized, and recovery of high-quality products ensures superior economic value. Such attention to well and production testing achieves operational costs attractive to large oil companies, and development of even marginal, remote and declining fields becomes commercially profitable.
In an extended combination of such technologies, a single well test service vessel is used in conjunction with a field of neighboring self-standing riser systems to serially test well and production processes, thereby resulting in project-scaled synergies between drilling, production and testing assets that lead to cleaner, more cost-effective recovery of higher quality yields. By combining a wide variety of newly developed systems and previously existing synergistic technologies, a flexible, scalable, commercially viable operating system that can be quickly deployed to produce cash flow and investment profits for investors and operators is achieved.
In the specific though non-limiting embodiment of a well test service vessel appropriate for such utilization depicted in
In one embodiment, a connection (2) between the vessel and the well is made by high-pressure flexible piping through which the mixture from the well flows. The flow can then be received through a system of control valves or choke valves (3). Once the mixture is received on the vessel, it is then sent through a line (4) to a system for processing, separation and measuring. In one embodiment, the separation and measuring comprises a plurality of phases, and results in the capture of a plurality of related products such as crude oil, natural gas, solids, chemical and solid wastes and sundry contaminants.
In a further embodiment, the oily water (6) is sent to a system that measures the content of contaminant particles (primarily hydrocarbons). If the content has a percentage that is lower than required by international or other appropriate governing standards, the water can be poured into the sea (7). If on the other hand the percentage of contaminants exceeds acceptable standards, the content is stored in tanks on the vessel for subsequent disposal (8), either by discharging at treatment terminals or injection into industrial waste wells.
Similarly, gas (9) is measured, quantified and analyzed for its properties, and then measured and treated (10) as necessary. In one embodiment, the gas is conditioned and tested for its characteristics or properties, and if considered appropriate, can be used to supply the mechanical or electrical power generation systems that the operation of the vessel requires, i.e., it will be utilized to generate electric energy (11). If the gas does not fulfill the required characteristics for the electricity generation system, it will be sent to the burner for incineration (12). In the event its pressure is greater than that of the well or production line, it can be transferred (13) to the production line or to an associated well. This latter approach also admits to compression of the gas for secondary commercial use.
In other embodiments, solid residues and chemical wastes are stored in containers or the like that are sent to onshore facilities for subsequent treatment and/or confinement according to governing environmental standards. From an environmental perspective it is ideal that no solid residue be dumped into the sea or incinerated.
In further embodiments, the crude oil or petroleum (14) is measured and characterized (15) and can be sent to the tanks on board the vessel for temporary storage (16) and subsequent discharge, or it can be reintegrated in hydrocarbon pipelines if available (17), or discharged into a support vessel, or a marine or onshore terminal.
In such manner, the principles of environmental conservation are achieved, since other than the exceptional cases in which the gas is incinerated, no other product is incinerated, unlike traditional systems in which virtually all of the products are incinerated.
In order to better describe the test vessel, a brief recitation of core functionality is appropriate. In short, the vessel should be capable of carrying out one or more of: (1) receiving product from a drilling, exploration and/or production platform or installation through interconnected piping between the installation and the vessel, and sending process flow from the well to a processing plant installed on a deck of the vessel; (2) separating gas, crude oil, water, reaction or waste products and solids into primary phases using multiphase separators; (3) conditioning products for final disposal using equipment installed on the vessel; such conditioning can include measuring, testing, chemical neutralization, dehydration, injection of inhibitors, filtering, compression of the products, etc.; (4) storing liquids in tanks disposed on the vessel, or in the case of stabilized or dehydrated crude oil transferring to the line for export to a marine or onshore terminal, or to a support vessel; in the case of oily water or production water, storage space should be provided for storing such waters prior to injection into wells or other facilities intended for receiving industrial wastes; (5) storing the solid wastes in portable containers for subsequent disposal in confinements in accordance with appropriate governing codes (whether corrosive, reactive, explosive, toxic, infectious and biological); (6) avoiding incineration of crude oil and associated products; (7) avoiding the dumping of partially incinerated liquids into the sea; (8) recovering products with commercial value such as crude oil and gas; (9) utilizing residual gas from the processing plant to be injected into export lines, waste wells or production wells to increase the pressure at the mantle, or to generate electric energy for the service of the vessel; and (10) recovering and processing products spilled into the sea by other vessels, marine installations and third-party equipment.
In one embodiment, when an associated well is serviced, one or more of the following basic constituent products are to be expected in the yield: (1) crude oil; (2) natural gas (sour or sweet), which may contain contaminants such as N2, CO2 and H2S, amongst others; (3) oily water, such as drilling or formation water resulting from separation of a mixture generally carrying the oily residues, solids, chemicals and drilling mud among other products; in the case of marine wells, there may also be a large quantity of salts and minerals; (4) solids, such as well drilling or maintenance cuttings, drilling mud, sand and clay; (5) liquid contaminants, such as diesel fluids, acids, aromatic hydrocarbons to stimulate flow, as well as gases such as N2 and CO2 among others; a mixture that vents from the well once it has reacted, is received as spent acids.
In another embodiment, the separation process is accomplished by means of one or more multiphase separators and flow control valves. The separators are designed to receive the mixture and separate all of the principal components. In such manner the mixture flows through various stages until the desired levels of separation are obtained. Those of skill in the pertinent arts will appreciate that the exact number of separators and type equipment installed on the vessel will vary by operational need, depending on the final parameters required (percentage of water, salinity and oil, and percentage of solids).
In a further specific example embodiment, once the separation and conditioning of the products is achieved, each of the five principal components is disposed of in the following manner:
(1) Crude Oil
(a) Transfer crude oil to an installation. The characteristics and volumes of the crude are measured, and it is then stored in tanks on the vessel for subsequent reintegration or exportation to a product pipeline to some offshore installation or platform. The transfer of crude can be achieved by transfer pumps and/or export pumps or the like. The crude can be conditioned by filtering and/or dehydration prior to export or transfer. The filtering apparatus can be equipped with cyclone, electrostatic or centrifugal separators with thermal treatment to eliminate the residues of water and solids. The conditioning can be accomplished by one or more of gas treatment units, centrifugal and/or coalescent equipment, among others. The conditioning can also be achieved with the retention of the crude emulsified with water inside the tanks of the vessel, i.e., the water is deposited at the bottom.
(b) Transfer to an auxiliary vessel. If the crude has not been reintegrated into a production line, it can be transferred to an auxiliary vessel, e.g., a tanker or a barge prepared and classified for the transport of hydrocarbons.
(c) Discharge at a marine or onshore terminal. If the crude has been stored in the tanks of the vessel, it can be sailed to a port terminal or other installation where the crude oil is discharged. The vessel's own discharge pumps can then be used to discharge the crude at the onshore terminals.
(2) Gas
(a) Export to a production line. If conditions occur or are generated in which the separation pressure is greater than the export pressure, including the compression of the gas, the gas can be sent to a hydrocarbons production or export line. These pressure conditions can occur naturally during the process of separating the components, or by gas compressors installed on the vessel to increase the export pressure.
(b) Utilization of the gas to generate electricity. Gas resulting from separation of the mixture is sent to a conditioning and treatment system in order to be utilized as fuel for the electricity generating systems of the vessel. This electricity is used for the vessel's propulsion systems, or consumed by the auxiliary systems of the vessel itself, such as lighting, power for service pumps, compression, navigation equipment, etc.
(c) Incineration. If the gas cannot be transferred to the production line and cannot be compressed for injection into the mantle of the subsoil or used for generating electricity, it can be directed to the burner line for incineration; consistent with the enhanced environmental aspects of the vessel as a whole, it is presently contemplated that such cases will be exceptional.
(3) Oily Water
(a) Neutralizing and storing water. Water separated during processing is generally received contaminated with oily residues, as well as solid residues, salts, minerals and chemicals. If it is determined that there is a certain level of acidity in the water, chemicals are added to neutralize it. In one embodiment the neutralized oily water is stored in the tanks of the vessel and will be disposed of as follows:
(b) Injecting into receptor well. There are receptor wells for receiving contaminated products, in which case all liquid residues, oily and/or acid or contaminated waters are injected in the subsoil at the bottom of the sea. The vessel has pumps of suitable capacity for discharging the products into wells dedicated for this purpose. Before injection, the fluids are filtered to prevent large size solids from damaging the formation of the industrial waste well. In this embodiment, there should be filters that are suitable in size and number, with appropriate strainer screens to avoid the injection of solids.
(c) Discharging into the sea. If no receptor well is available, the water must be treated and filtered to eliminate the content of grease, oil and residues, and be conditioned to an appropriate acidity or pH, for example according to acidity or pH standards of MARPOL [an International Convention for the Prevention of Pollution from Ships] before being dumped.
(d) Transfer to an auxiliary vessel. If the oily water or production water has not been able to be injected into an industrial waste well or cannot be conditioned to the acidity or pH conditions required by MARPOL, it can be transferred to an auxiliary marine unit such as a tanker or barge certified for the transport of this type of fluids.
(e) Discharge at a marine or onshore terminal. The vessel is capable of sailing to a port terminal or other facility where the oily water or production water is discharged to confinements or specialized treatment.
(4) Solid Products
(a) Storage in portable containers. In one embodiment, all solid residues such as sand, drilling mud and clays are stored in portable containers and are classified according to the CRETIB Code (Corrosive, Reactive, Explosive, Toxic, Infectious and Biological) or other governing law, and are shipped to corresponding authorized confinements.
(b) Storage in solids tank. Another alternative to CRETIB tanks is the fitting out of a solids receiving tank on the vessel, which allows the storage and transfer of solids to another marine support unit, or port or onshore terminal.
(5) Contaminating Liquids
(a) As appropriate. Contaminating liquids that may occur in servicing a well, such as aromatic acids, diesel, etc., can be stored in tanks on board the vessel. Depending on their composition, they will be treated as crude oil if the liquids are hydrocarbons, or otherwise as oily or production water.
Broadly speaking, the technical objective of the vessel is to receive the mixture from the well and then carry out the separation and disposal of the principal products, which must be stored and/or discharged for final disposal. The ship's activities are therefore broken down into at least five discrete steps in order to better describe a non-exhaustive inventory of appropriate components of the vessel. In one particular though non-limiting embodiment, those five steps are:
Step 1: Positioning of the ship.
Step 2: Interconnection for loading and discharging.
Step 3: Separation of the products.
Step 4: Storing the products.
Step 5: Discharging the products.
Step 1: Positioning of the Ship.
In one embodiment, the ship is moved using a propulsion system based on propellers or thrusters, and installed so as to allow free 360° or azimuth movement, and in any direction. The thrusters can vary in type and arrangement, and can be located at any position along the length and width of the vessel, or any combination thereof.
The configuration of thrusters will be dictated by the desired positioning class. For this category of vessel, it is desirable (though not necessarily required) there be a combination of thrusters that allow it to provide service according to Class 2 Dynamic Positioning (DP-2), in other words, redundant propulsion and positioning systems. The requirements for complying with DP-2 Classification are indicated by the relevant classification society.
For example, the dynamic positioning system comprises various components, among the most important of which are transverse, longitudinal and/or directional azimuth thrusters located at the stern and/or bow, or any combination thereof. In general, there will be no fewer than four combined thrusters that make it possible to maintain position even should one fail (a redundant system).
It is similarly desirable that all of the electrical panel systems, reference and control equipment be duplicated in order to ensure redundancy should one of the components fails. Typically, a DP-2 dynamic positioning system regulates the operation of the propulsion systems by means of external reference systems, whether satellite support, radar systems, radio, hydro-acoustic or weights and cables at the bottom of the sea, etc., to maintain the vessel in the selected position and course. The equipment and components comprising the parts of the system should likewise comply with the requirements of the relevant classification society.
Unlike conventional systems of propulsion and mooring by anchors, this type of computer-controlled equipment and machinery allows the vessel to have greater mobility and speed in positioning itself in the vicinity of the well.
Step 2: Interconnection for Loading and Discharging.
Once the vessel is positioned in the vicinity of the installation where the service will be provided, the connection/disconnection point must be located, which in general could be one of two types: (a) a surface connection, located above the well or sea level, sometimes known as a “dry head;” or (b) an underwater connection, located below sea level, sometimes known as a “damp head” or a “wet head.”
At the installation being serviced, a flow and pressure choke package can be installed comprised of a plurality of regulator valves. In one embodiment, this package has a system of flow shutoff valves in case of emergency or loss of control of the well. In a further embodiment, said system is connected electrically and by instrumentation to the emergency shutdown systems, and has a head for recording data including pressure, speed, temperature of the fluids and/or products, as well as records for sampling of production, and, if necessary, points for injection of chemicals.
The flexible piping installed on the vessel is connected such that it is capable of receiving and discharging the products. The vessel can have one or more flexible pipes, depending on the need to provide two or more services simultaneously (e.g., importing and exporting). In one embodiment, the flexible pipes are run through special openings or chutes to protect them from friction and wear that may occur with the yawing of the vessel. Said openings or systems are installed in line with the flexible pipes of the vessel.
Another option for running the hoses is through an opening in the hull known as a moon pool. In this case the hoses are run through the interior of the moon pool toward the well connection. This type of connection is especially convenient for underwater or wet head type connections.
Both the quick-connect pipe and the flexible piping are designed to withstand high pressures expected from the well. Nevertheless, in order to protect the installation and the vessel itself, the systems of flexible pipes are equipped with a quick connect system known as QCDC (quick connect/disconnect), and emergency valves. In general terms, a QCDC is a dual valve device that prevents the spill or escape of products in the event of accidental disconnection; as those of ordinary skill in the art will recognize, bi-directional valves are generally useful for this purpose.
According to another embodiment there is also a system for supplying auxiliary services and service fluids between the vessel and the installation being serviced; this system of transmitting services is known as the umbilical system, and water, compressed air, inert gas, electricity, instrumentation and control signals, chemicals for injection, among other things, can be sent through a composite connector composed of hoses and electrical cables and instrumentation from the vessel to the well connection.
Sometimes the package of choke or control valves cannot be installed on the installation due to a lack of space. In this event there is an alternative choke package on the vessel with the same capacities and characteristics as the portable package. In one embodiment this package is permanently installed on one of the processing decks of the vessel.
Step 3: Separation of the Products.
In this step the mixture or stream from the platform is imported to the vessel by the interconnection system described above, and is processed in the array of separation and conditioning equipment. The purpose of this step is to achieve the separation of the mixture in such a way that end products of oily water, solid residues, gas, chemical residues and crude oil can be obtained.
The combination of separators, conditioning equipment, pumps, pipes, valves, sensors, systems, etc., is called sometimes called the processing plant. The location of these separation and conditioning components is on a deck of the vessel called the “processing deck,” generally located above the main deck of the vessel. In one specific though non-limiting embodiment, the deck is disposed at least 10 feet (3 m) over the cargo tanks, so that the separation and conditioning equipment are not installed directly on the main deck of the vessel. The deck can be provided with skirting to contain spills and water to prevent products from falling onto other decks, structures or into the sea in case of an emergency spill or leak in any of the processing plant components. The processing plant deck has an open drainage system for evacuating possible spills and leaks. Moreover, rainwater passes through this fluid collection and measurement system, which can detect contaminant particles as well as determine the possibility of dumping it into the sea or treating it as oily water and injecting it into industrial waste wells.
A non-exhaustive recitation of equipment suitable for comprising the processing plant includes one or more of: multiphase separators; chemical and conditioner injection packages; devices for measuring temperature, pressure and flow for each of the streams, whether mixed or separated; flotation units; gas scrubbing units; cyclones or centrifugal separators; oil treatment units; electrostatic treatment units; systems for acquiring and recording processing information in real-time, e.g., a computerized system comprising sensors that measure flow, temperature, pressure, viscosity, etc., which are installed throughout the processing plant and collect information regarding the processing in real-time; systems for conditioning and using gas for generating power; and means for transferring other products obtained in the separation step (e.g., crude oil, gas, solids, oily water, etc.) to an associated storage and treatment system.
Step 4: Storage of Products.
As a result of processing the mixture through the vessel's processing plant, other products are obtained, e.g., crude oil, gas, oily water, solids, chemical waste, etc. The products so obtained are transferred and distributed for disposal or storage through a system called a processing head. The processing head is an array of interconnected pipes and valves used to distribute products and residues. The head is typically comprised of gate valves and control valves and associated accessories and piping, and is located between the main deck and the processing deck, thereby interconnecting the processing plant with the vessel's storage tanks.
The crude oil is generally sent to the vessel's cargo tanks. This step can be achieved by means of transfer pumps installed in each of the multiphase separators. Those of skill in the art will recognize that stored crude must first be stabilized; in other words, it must not contain high levels of gas in emulsion because the vessel's tanks should not be subject to relatively high pressures because it could generate a risk of explosion originating from pent-up internal pressure.
Once stored in the tanks, and for the purpose of discharging or transferring, the vessel's tanks are provided with discharge pumps installed in the bottom of the tank, or with suction in the lowest part to allow transfer of the stabilized crude oil between the tanks for purposes of stability of the vessel, thereby recirculating it through heat exchangers to make it possible to maintain viscosity under appropriate conditions and avoid the solidification of the products, in particular in low API gravity or high viscosity oils; or, for transfer to another support vessel or pumping with higher power equipment, to send the oil to export pipelines if they are available at the installation, and to inject it into a receptor or industrial waste well. The storage of oily water can comprise dedicated tanks, or it can be stored in tanks intended for the storage of crude oil. Solids and chemical residues on the other hand can easily be stored in one or more dedicated tanks located on the main deck.
The cargo tanks are generally considered one of the most hazardous spaces of a vessel, because in addition to storing the separation products, they can have gas in emulsion that will be released over time, thereby generating pressure inside the tanks. Consequently, devices and auxiliary systems are required to control and eliminate explosive and/or hazardous conditions of the storage tanks. The basic principle for eliminating the risk is by the displacement of the O2 oxygen that the tanks and pipes of the vessel's processing plant may contain. It should therefore contain an inertization system, which consists of the generation and supply of N2 nitrogen, steam, CO2 or any other approved inert gas in the tanks, thereby displacing the O2 oxygen during the maneuvers of loading or discharging the tanks where the crude oil and/or oily water is stored, as well as in the lines and pipelines of the products. In this manner explosive conditions are avoided.
In further embodiments the vessel is capable of receiving low API gravity crude oil (whether heavy or high viscosity crudes). Therefore, a heating system should be installed in each of the tanks in order to maintain the crude oil at an appropriate temperature, thereby reducing the viscosity and allowing it to flow and move.
With regard to the residues or solid products that are obtained from the separation, which are comprised primarily of drilling cuttings, drilling mud, sand and clays, these are temporarily stored in solid residue tanks, which are generally located on the main deck, in an arrangement that allows transfer by solid product pumps to send these residues to special containers for storage and sending to confinements. These containers should be classified in accordance with any relevant governing codes, and the dimensions and capacity of the containers should be designed so that they can be manipulated by the vessel's crane.
Step 5: Discharging of Products.
There are various ways to discharge crude oil, for example, discharging the oil onto a barge or other large support ship. In this event, the discharging or transfer will typically be carried out using one or more of the lines of the head distributor, where one of the lines can be equipped with a pipe bypass prepared with appropriate shut off valves at one or both sides (e.g., port and starboard). The discharging of the tanks can be performed by means of discharge pumps disposed within each of the vessel's tanks. The discharging should optimally be carried out at low pressure.
Another means for discharging crude is by discharge to an installation that has discharge lines leading to land or to another installation. This discharge method is typically carried out using the distributor or head by submersible pumps. In this manner the fluids can be sent to export pumps located at the level of the main deck. The fluid can then be re-pressured and sent to the installation or pipeline by means of flexible export piping.
Yet another discharge method comprises injection into another pre-existing well. In the relatively rare instance in which injection of crude oil into an oil well is required, it is typically done using an injection pump. In such cases the injection pump should be capable of producing a pressure greater than that of the mantle in the subsoil into which the crude oil of the will be injected.
Like the crude oil, oily water can be transferred to a barge or ship, discharged to a well or installation and injected into an operational well or industrial waste well. The required equipment is essentially the same as what was described for the transfer of crude oil.
In contrast, the discharge of solids is relatively simple. Since all solid waste is ultimately stored in containers classified according to their governing codes, discharge handling is typically clearly defined. Then, when the containers become full, they can be transferred by crane to support ships or onshore terminals for subsequent transfer to authorized centers for waste confinement and/or treatment.
The foregoing specification is provided for illustrative purposes only, and is not intended to describe all possible aspects of the present invention. Moreover, while the invention has been shown and described in detail with respect to several exemplary embodiments, those of ordinary skill in the pertinent arts will appreciate that minor changes to the description, and various other modifications, omissions and additions may also be made without departing from either the spirit or scope thereof.
