Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-07-12
2003-12-02
Popovics, Robert (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S194000
Reexamination Certificate
active
06656366
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for the reduction or elimination of the buildup of solids in a system or conduit, such as a conduit for the transport of typical hydrocarbon streams produced from oil or gas wells (mixture of crude oil, condensate, fresh water or brine, natural gas). The invention has special relevance to deep water subsea wells where phase separation and purification is difficult, but is not limited to only deep waters. More particularly, the present invention relates to a method for precipitating solids dissolved in the produced stream, in a treatment apparatus positioned upstream of the system or conduit, as well as precipitating other solids formed when mixed phases are at selected pressures and temperatures. An example of the latter is the creation of solid natural gas hydrates as a mixture of gas and water is cooled under pressure. Further, the present invention relates, but is not limited, to precipitation driven by cooling the stream in the treatment apparatus to or near the ambient temperature surrounding the system or conduit. Still further, the present invention relates to a treatment apparatus including a flow passage having a sufficient size and length to effect precipitation and/or deposition of created solids, and a removal device adapted to remove said solids in a fashion such that they can be transported in the subsequent conduit without flow interruptions.
BACKGROUND OF THE INVENTION
Typically, when crude oil is produced from a reservoir, it contains water, gas, and dissolved solids, such as wax, asphaltene, organic salts, and inorganic salts. Waxes, or high molecular weight paraffins, found in crude oil production systems generally include branched and straight, high carbon number (average carbon numbers of 18+, more particularly 40+) alkane hydrocarbon chains. An alkane is a hydrocarbon molecule having the general empirical formula C
n
H
2n+2
, where n, the carbon number, is a positive integer. Asphaltene is defined as the fraction of the crude oil insoluble in n-heptane, but soluble in toluene. Asphaltenes are complex polar macro-cyclic molecules that typically contain carbon, hydrogen, nitrogen, oxygen, and sulphur. The inorganic salts that may be present include any inorganic salt typically present in produced streams and which may precipitate to form salt deposits known as scale. Such inorganic salts include sulfates, for example BaSO
4
, CaSO
4
, and SrSO
4
, and carbonates, for example CaCO
3
, MgCO
3
, and FeCO
3
, in addition to the more common chlorides of sodium, calcium, and magnesium. The inorganic salts that may be present also include silicon oxides, such as SiO
2
, or more commonly various silicates. A salt generally is an ionic complex between a positively charged cation, for example Ca
2+
, and a negatively charged anion, for example SO
4
2−
. An organic salt is a salt that is a compound of carbon and therefore includes a carbon-containing cation.
Some of these dissolved solids may precipitate as a thermodynamic parameter, such as temperature or pressure, changes. For instance, the solubility of wax decreases with temperature reduction and with pressure reduction, especially if such results in liquid hydrocarbon shrinkage as the lighter components flash to the vapor phase. The “cloud point” of a fluid, also referred to as the “wax appearance temperature” is the temperature at which wax first appears in solid form as the fluid cools. Normally, this data is taken at atmospheric pressure; substantially higher pressures typically require cooler temperatures before precipitation is induced. Similarly, salt solubilities typically decrease with decreasing temperature and decreasing pressure. Asphaltenes form primarily due to a decrease in pressure. When the pressure drops to the bubble point pressure, the asphaltene molecules may precipitate in some systems, typically ones rich in paraffins and poor in resins and aromatics. Further, asphaltene solubility below the fluid bubble point decreases with rising temperature. Sometimes, asphaltene deposition may occur with wax deposition.
Further, some of these dissolved solids may precipitate as chemical composition parameters change, such as composition changes caused by mixing of two or more fluid streams. For example, hydrate, salt, and asphaltene precipitation can also be caused on mixing of two or more streams. For instance, hydrates may precipitate on mixture with fresh water, asphaltene precipitation can be induced by the addition of lower paraffins, multiple brine mixtures can lead to incompatibilities resulting in the precipitation of one or more of the salts.
As indicated previously, the precipitation of solids may also be induced by phase changes of one or more of the fluid components. For instance, water may form ice on sufficient cooling and water and certain light gases may form clathrate hydrates (for example, as described in
Natural Hydrates Of Natural Gases
, E. D. Sloan, Marcel Dekker, Inc. N.Y., 1997) at lower temperatures or higher pressures or a combination of the two effects. Specifically, the lighter gases include the lower hydrocarbon gases with less than 5 hydrocarbons as well as CO
2
, H
2
S, N
2
, and the like. When a flowing stream is cooled below the hydrate dissociation temperature, the temperature, calculated or measured, at a given pressure at which hydrates will dissociate into water and gas, then water present in the system will tend to combine with the light gases to form solid hydrates.
In extracting oil from a reservoir and transporting it, precipitation may. occur at any one of the stages along the flow, including in the formation near the well bore, within the well, and beyond the well, in a conduit or pipeline, especially if the pipelines are multi-phase, cold sub-sea lines. In the formation near the well and at the well bottom, the crude temperature is normally higher than the cloud point or hydrate dissociation temperature, avoiding wax and hydrate precipitation, however, salts and asphaltenes can and have precipitated due to pressure draw down. As the crude oil travels up the well, the temperature and pressure drop, which may cause additional solids precipitation. At the well head, the pressure may be reduced further by a choke to stay within flow line pressure limits (LPL's); the pressure drop across the choke will induce additional cooling (Joule-Thomson expansion) both of which may cause further precipitation of wax, salt, and hydrate. After the choke sub-sea well streams enter multi-phase flowlines for transport to shallow water, surface piercing structures where the streams are separated. The flow in deep water flowlines is further cooled by the cold waters (typically 40 F) surrounding the flowlines.
On the other hand, late in the life of the well, as the depleted field pressure declines, the wellhead pressure may need to be raised by multiphase pumps or other means in order to overcome the hydrostatic pressure resulting from the elevation increase to the host platform. The increased pressure may induce hydrate formation. Beyond the wellhead, with or without increased pressures by artificial compression, the produced fluid has to pass through the flow line or lines, such as tiebacks, to the host facility.
Deep water subsea flowlines are used to transport oil, gas, and aqueous fluids from subsea well(s) to a host facility where the fluids are separated and treated for sale. The flowlines may combine fluids from several wells or even several fields; that is, several different fluids may be mixed. In particular, extended tieback systems are useful for the development of small fields in deep waters, by tying back subsea trees or manifolds that are remote from processing facilities. These deep water flow lines are typically cold, near (rarely below) the freezing point of water.
When the cooling occurs in a flowing pipeline, well or similar conduit, the formation of waxy or paraffinic, hyd
Amin Rajnikant M.
Fleyfel Fouad
Fung Gee Seng
Kalpakci Bayram
O'Sullivan James F.
Conley & Rose, P.C.
Halliburton Energy Service,s Inc.
Popovics Robert
LandOfFree
Method for reducing solids buildup in hydrocarbon streams... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for reducing solids buildup in hydrocarbon streams..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for reducing solids buildup in hydrocarbon streams... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3135530