Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
2002-10-31
2004-09-14
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S744000, C210S747300, C210S788000, C210S800000, C210S808000, C210S103000, C210S104000, C210S109000, C210S116000, C210S138000, C210S143000, C210S170050, C210S188000, C210S512100, C210S533000, C494S001000, C494S002000, C494S010000, C494S037000, C209S715000, C209S725000, C166S053000, C166S267000, C096S156000, C096S157000, C096S209000, C096S408000
Reexamination Certificate
active
06790367
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to both a method and an apparatus for separating and measuring solids from a multi-phase stream of well fluids.
BACKGROUND OF THE INVENTION
When drilling a well or borehole into the earth and through underground formations a common concern in virtually every application is the collection, separation, disposal, and in some cases the measurement, of the well fluids expelled from the well during the drilling process. Regardless of whether an overbalanced, balanced or under balanced drilling technique is utilized, pressurized drilling fluid returns are expelled from the well and must be treated in order to separate the components, recycle particular materials, and process or otherwise dispose of the remaining fluids and their constituent parts. Depending upon the nature of the drilling process being utilized and the geology through which the wellbore is drilled, the drilling fluid returns may include a wide variety of solid, liquid and/or gas components. Where the well is an oil or gas well, drilling fluid returns typically include oil, water, rock particulants (sand), natural gas, and various other hydrocarbon compounds. The encountering of high pressure underground formations, in combination with the fact that in most drilling operations high pressure drilling fluids are pumped from the surface down into the borehole to help fluidize cuttings and drive them upwardly out of the well, results in the drilling fluid returns extracted from a well often being at a relatively high pressure. For environmental and economic reasons the multi-phase returns must usually be separated and processed before their components can be recycled and put to further use or disposed. Since the returns are in many cases at elevated pressures or contain noxious or hazardous materials, their processing necessitates the use of dedicated and specialized equipment.
Multi-phase well fluids are also typically generated during the fracing and testing of oil and gas wells, and are commonly encountered in producing wells. As in the case of the drilling of a wellbore into the earth, multi-phase returns generated in producing oil and gas wells, and those generated during the fracing or testing of a well, are typically processed with specialized equipment to separate their component parts, avoid the release of hazardous materials into the air or the environment, and in some cases to measure the volumetric rate of production of solid phase returns.
Current techniques and equipment that have been developed to process multi-phase well fluids typically employ the use of one or more separation vessels that are primarily designed to separate the solid, liquid and gas components of the returns. In some instances the treatment of the returns is carried out in two or more separate and distinct stages. For example, an initial separator may be utilized wherein a portion of the solid component (ie sand) is separated from the well returns. The gas, liquid and any solids that may be carried over into the gas and liquid phases are then transported to a subsequent separation stage for further processing. When a high pressure separator is used a significant amount of the sand is removed thereby helping to minimize erosional effects that may otherwise occur if the solid particulate material were allowed to flow through the piping, valves and other components of the separation system. In addition, since the sand is separated at full wellhead pressure, the relative size of the equipment necessary can be kept to a minimum as the process is conducted prior to any gas expansion that will occur at a downstream low pressure stage.
While such prior existing separation methods and devices have been relatively effective, they all suffer similar inherent limitations when it comes to the disposal or removal of sand separated out of the returns. Prior systems also do not readily provide for the volumetric measurement of the sand component expelled from the well. Traditionally sand that has been extracted from multi-phase well fluids by means of a separation vessel has been removed from the vessel through the manual operation of a dump valve or similar apparatus. As sand accumulates within the separation vessel an operator would typically activate a dump valve to allow the sand to be removed for further processing or disposal. In order to lengthen the interval between the time that an individual would be required to dump the accumulated sand, others have increased the size of their separation vessels providing a greater volume within which sand can accumulate. However, doing so runs contrary to one of the reasons for utilizing an initial well-head pressure separation stage; namely, the ability to minimize the size of the necessary equipment. As a result, others have suggested that the dump valve be controlled by a timer that is set to open the valve after a pre-determined interval. In such instances a “guesstimate” of the volume of solids produced over time is prepared and the timer controlling the dump valve set to correspond to an anticipated solid production level. Unfortunately, this less than scientific method creates significant problems when the valve is open for too long and gas carry under occurs (particularly if there is hydrogen sulfide present). Similarly, problems will be encountered where there are no solids present that require the opening of the dump valve, in which case there will be an unrestricted passage of multi-phase well fluids through the dump valve resulting in increased disposal costs. Further, where the time interval that the dump valve is left open is too short, an excessive amount of solids may build up within the separation vessel, potentially resulting in a solid carry over into the separation stage. An increased volume of solids in a subsequent separation stage can significantly increase the erosion of downstream piping and components.
The “timed” method of opening and closing a dump valve suffers from the further limitation of making it difficult to measure the volume of solids produced from the well. To determine a solids production rate a separate tank (having some form of gauge or other measurement device) into which the solids can be placed and thereafter measured is most often used. Aside from having a low degree of accuracy, the use of such equipment increases the overall physical size of the separation system. If the well contains hydrogen sulfide or other toxic gases, it will be necessary to utilize a vacuum truck to remove the solids from the separation vessel thereby even further increasing the difficulty in measuring the volume of solids produced. As a result, such prior existing methods provide only a general estimate of the volume of solids production, at best.
Rather than directly measuring solids production, others have suggested monitoring for the presence of solids within multi-phase well fluid returns through the use of an erosion/corrosion probe. Such a unit is typically placed in a fitting within the returns line so that it intrudes into the stream of untreated well fluids flowing from the well to the separation system. The probe will then be exposed to the erosion generated by solids passing through the pipeline. A small voltage is passed through the probe such that as the probe erodes there is a reduction in its resistance that may be measured and used to calculate an equivalent reduction in probe diameter, and hence determine the presence of solids in the well returns. Unfortunately while such systems can be used to predict the presence of solids within well fluids, and to some degree an increase or decrease in the amount of solids present, they are incapable of quantifying the volume of solid production from the well. Other similar systems that are based upon acoustic probes generally only identify the presence of solids and their range of accuracy is normally limited at low solid concentrations.
SUMMARY OF THE INVENTION
The invention therefore provides a method and an apparatus for separating and measuring solids from multi-phase well fluids tha
Schmigel Kevin
Speed David
Stefureak Peter
Merek & Blackmon & Voorhees, LLC
Northland Energy Corporation
Reifsnyder David A.
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