This invention relates generally to fossil fuel drilling and more specifically to problems associated with bacteria and other microorganisms that thrive in drilling fluids used in the fossil fuel drilling industry.
Drilling fluids have long been used in the oil and gas drilling industry when tapping underground reservoirs of oil, brine, gas, and water. The term “drilling fluid” as used in this disclosure is intended to encompass all types of fluids used in drilling operations including, for example, fracking fluid used in modern fracking operations, friction reducers, and drilling muds to name a few. Thus “drilling fluids” should be construed to mean any and all types of fluids that may be pumped into a bore hole during drilling operations. Drilling fluids are conventionally circulated down a bore hole through a drill pipe and bit and are returned through the earthen bore hole to the surface. These fluids serve a variety of purposes including, for instance, lubrication and cooling of the drill pipe and bit, transportation of cuttings to the surface, sealing and holding in place the traversed walls of the bore hole, establishing a hydrostatic head of pressure preventing the escape of high pressure fluids from the traversed formations, helping to liberate oil and gas from shale formations in fracking, and performing numerous other functions.
Drilling fluids have improved in efficacy over the years and modern drilling fluids usually include a complex mixture of many chemicals and other substances such as weighing materials, primarily barite (barium sulfate) or hematite to increase density; dispersants including iron lignosulfonates to break up solid clusters; flocculants, primarily acrylic polymers, to cause suspended particles in the fluid to group together for easier removal; surfactants like fatty acids and soaps to defoam and emulsify the fluid; and fluid loss reducers such as organic polymers to limit the loss of drilling fluid into under-pressurized or high permeability rock and earth formations. In addition to these and other additives, drilling fluids usually include one or more biocides such as organic amines, chlorophenols, or formaldehydes to kill bacteria, microbes, and perhaps other biological microorganisms that find their way into and thrive in the drilling fluid. In this disclosure, the terms bacteria, microbes, and microorganisms may be used interchangeably to refer to any microscopic living organisms in drilling fluid.
It is important to control the bacterial content of the drilling fluids for a number of reasons including the fact that bacteria and microorganisms can sour the fluid making it unsuitable for re-use. Further, certain bacteria common in drilling operations that ultimately find their way into drilling fluids are so called sulphate-reducing bacteria (SRB). These bacteria produce the toxic gas hydrogen sulphide, which can cause numerous problems. For example, hydrogen sulphide is corrosive and often causes significant drillstring and casing damage.
It has been suggested that SRBs and other biological organisms are either introduced to the formation by drilling or water injection or that they might be indigenous and activated by the drilling process. In either event, it is important to minimize the number of or eliminate SRB's and other microorganisms in drilling fluid. Previously, this has been accomplished as mentioned above through the addition of biocides to the drilling fluid. While this can be somewhat successful, it poses an environmental problem since many biocides are considered toxic substances that must be removed and treated before being released into the environment. Plus, chemical biocides for controlling microorganisms are themselves expensive and adversely affect the cost of a drilling operation.
A need exists for an efficient and effective process for eliminating or at least controlling biological microorganisms in drilling fluids in a way that does not require the addition of biocides and chemicals to the fluids and produces no environmentally unfriendly byproducts during use. It is to the provision of such a process that the present invention is primarily directed.
Briefly described, a system and method for exterminating bacteria and other microorganisms in drilling fluid are disclosed. The system includes a reservoir such as a holding tank for the drilling fluid and a controlled cavitation reactor. A pump draws drilling fluid from the reservoir and delivers the fluid to the inlet of the controlled cavitation reactor. The reactor has a cylindrical housing defining an internal cylindrical rotor. The rotor is rotatably mounted within the housing and has cavitation bores extending through its peripheral surface. A space between the peripheral surface of the rotor and the inner surface of the housing defines a cavitation zone. Within the controlled cavitation reactor, the drilling fluid passes through the cavitation zone with the rotor spinning at a relatively high rate of rotation.
In the cavitation zone, the drilling fluid is subjected to highly energetic shock waves and intense pressure variations created by continuous cavitation events in the fluid within the bores of the rotor. The cavitation activity, and thus the intensity of the shock waves and pressure variations, is controlled by the flow rate of the fluid and the rotation rate of the rotor. The goal is that the shock waves and pressure variations be sufficiently energetic to tear apart the tissue of bacteria and other living microorganisms within the drilling fluid.
After the drilling fluid is treated, it moves out of the controlled cavitation reactor and is delivered back to the drilling fluid reservoir or pumped to an oil or gas well for immediate use. The drilling fluid may be cycled through the controlled cavitation reactor as many times as needed to achieve an arbitrarily low bacteria content in the fluid, thus preventing souring of the fluid, greatly reducing corrosion of drilling equipment, and allowing the drilling fluid to be reused. Side benefits may include enhanced emulsification of the fluid, agglomeration of suspended particles for removal, and generally more homogeneity of the drilling fluid slurry.
Accordingly, a system and method are now provided for reducing bacteria and other microorganisms in drilling fluid that addresses the problems and shortcomings of traditional chemical treatments. These and other features, objects, and advantages of the system and methodology of this disclosure will be better appreciated upon review of the detailed description set forth below taken in conjunction with the accompanying drawing figures, which are briefly described as follows.
Controlled cavitation reactors for treating certain fluid flows are known. U.S. Pat. Nos. 8,465,642; 8,430,968; 7,507,014; 7,360,755; and 6,627,784, all owned by the assignee of the present patent disclosure, discuss variations of these controlled cavitation reactors. These patents are hereby incorporated fully by reference. To the extent that the patents may describe in detail the configurations and functions of controlled cavitation reactors, these configurations and functions will not be described in great detail again here. Also incorporated by reference is the disclosure of a copending (at the time of filing) patent application owned by the assignee of the present application and entitled Abrasion Resistant Controlled Cavitation Reactor.
Referring now in more detail to
A pump 19 is arranged in line with the slurry pipe 17 and is configured when activated to draw drilling fluid from the holding tank through the slurry pipe 17 and pump the fluid downstream of the pump. A flow meter 21 preferably is configured to monitor the flow rate of drilling fluid through the slurry pipe 17. In this way, the pump 19 can be controlled manually or with a computerized controller to establish a desired flow rate of drilling fluid through the system. A shut-off valve 22 may be incorporated in the slurry pipe 17 if desired.
The drilling fluid is delivered at a predetermined flow rate to a controlled cavitation reactor system 51. The controlled cavitation reactor system 51 includes a generally cylindrical housing 52 defined by a proximal end plate 53, a distal end plate 54, and a cylindrical peripheral wall 56. The end plates and the peripheral wall define a cylindrical interior cavity in the housing bounded by the inner surfaces of the end plates 53 and 54 and the inner surface of the peripheral wall 56. A cylindrical rotor 59 (
The peripheral surface of the rotor 59 is spaced from the inner surface of the peripheral wall 56 of the housing to define a cavitation zone 61 between the two. Cavitation bores are formed through the peripheral surface of the rotor. In the illustrated embodiment, the sides of the rotor and the end plates of the housing bound a proximal void zone 71 and a distal void zone 69. An inlet port 62 for receiving drilling fluid communicates with the housing within the proximal void zone 71. The inlet port preferably is arranged to introduce drilling fluid into the housing in a direction or along a path substantially tangential to the inner surface of the peripheral wall of the housing. An outlet port 63 communicates with the distal void zone 69, and is diametrically opposite to the inlet port 62 in this exemplary embodiment. The outlet port preferably is arranged to receive drilling fluid from the distal void zone in a direction or along a path substantially tangential to the inner surface of the peripheral wall of the housing.
In operation, the rotor 59 is rotated by the drive motor 64 in a counterclockwise direction when viewed from the distal end plate. Drilling fluid is introduced through the inlet port, urged under pressure through the cavitation zone, and is extracted through the outlet port. The tangential orientation of the inlet and outlet ports results in movement of drilling fluid into the reactor 52, through the cavitation zone 60, and out of the reactor 52 without making drastic changes in direction during the journey. This unique reactor configuration greatly reduces erosion of interior components of the controlled cavitation reactor caused by abrasive fluids. Abrasion resistance is desirable when treating drilling fluids since some drilling fluids can be abrasive in nature, containing small particles of sand, metal, and other materials. The method of this invention can be carried out by other controlled cavitation reactor designs without tangential inlets and outlets or with a different arrangement of tangential inlets and outlets, such as those disclosed in the incorporated patents. Accordingly, the scope of the methodology disclosed herein is not limited by the configuration of a particular controlled cavitation reactor or the placement and configuration of its inlet and outlet ports.
While in the cavitation zone 61, high energy cavitation events are continuously created in the fluid within the bores of the rotor. These cavitation events, in turn, generate highly energetic shock waves that propagate from the cavitation bores through the drilling fluid in the cavitation zone. The propagating shock waves result in extreme and very rapid pressure fluctuations within the drilling fluid. When the flow rate of the fluid, its temperature, and the rotation rate of the rotor are properly chosen, the dwell time of the fluid in the cavitation zone and the shock wave and pressure variation energy in the cavitation zone are sufficient to tear apart the cellular structure of bacteria and other microorganisms in the fluid, thereby destroying and exterminating them.
An advantage of the present invention it is that it should work at nearly any flow rate, rotor rotation rate, and temperature with corresponding varying degrees of efficiency. In other words, some microorganism mortality occurs at just about any combination of these factors. Typically a starting temperature of a drilling fluid is between about 32° F. and 70° F. Preferably the drilling fluid is heated to a higher temperature between about 75° F. and 150° F. before being treated in the controlled cavitation reactor. Maximum elimination of living microorganisms occurs at higher temperatures and/or higher delta temperatures, but some beneficial effect would be expected at lower fluid temperatures.
Effectiveness of the treatment of drilling fluid in the controlled cavitation reactor also can vary with the source and type of fluid and the physical robustness of living microorganisms found in differing locations and during different seasons. The best practice is to take the “free” microbial extermination that comes from pre-heating the drilling fluid to a target temperature, and then multiplying that microbial kill by choosing an appropriate flow rate and rotor RPM in the controlled cavitation reactor. Of course, it is not possible to kill every microbe that might reside within a drilling fluid, but the higher the microbe kill rate using the present invention, the lower the volume of antimicrobial chemicals needed even to the elimination of the need for such chemicals.
The molecular and particle agitation caused by the energetic pressure variations in the cavitation zone 61 result in friction in the drilling fluid. This, in turn, causes the temperature of the drilling fluid to rise further. As the treated and heated fluid exits the controlled cavitation reactor 52 through the outlet 58, it is directed in this embodiment to a heat exchanger 76. Here, excess heat imparted to the fluid in the controlled cavitation reactor can be extracted if required before the fluid is delivered through slurry pipe 17 back to the holding tank 12 or to a remote location for use. In the embodiment shown in
The invention has been described herein in terms of preferred embodiments and methodologies considered by the inventor to represent the best mode of carrying out the invention. It will be clear to the skilled artisan, however, that a wide gamut of additions, deletions, and modifications, both subtle and gross, may be made to the exemplary embodiments described above without departing from the spirit and scope of the invention. All such additions and deletions should be construed to fall within the scope of the invention.
Priority is hereby claimed to the filing date of U.S. provisional patent application 62/161,639 filed on May 14, 2015 and entitled Reduction of Microorganisms in Drilling Fluid Using Controlled Mechanically Induced Cavitation.
Number | Date | Country | |
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62161639 | May 2015 | US |