Agitating – Mortar mixer type – Methods
Reexamination Certificate
2000-12-04
2001-09-11
Soohoo, Tony G. (Department: 1723)
Agitating
Mortar mixer type
Methods
C137S008000, C137S012000, C137S599010
Reexamination Certificate
active
06286986
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a blending apparatus. Specifically, the present invention relates to a blending apparatus used in well fracturing operations. More specifically, the present invention relates to a blending apparatus having multiple mixing tubs.
BACKGROUND OF THE INVENTION
To increase the production of an oil, gas, geothermal, or other type of well, the producing zone of the geological formation surrounding the well is fractured to allow the desired fluids to flow more freely through the formation and into the well. Fluid is pumped into the formation under high pressure to fracture the producing zones. However, if fracturing fluid is pumped into the formation during the fracturing operation without some accompanying solid, the geological formation pressures will cause the fractured areas of the formation to close when the pumping of fracturing fluid stops, thus restricting the flow of the oil or gas.
A slurry of particulate material, such as sand blended with the fracturing fluid, may be forced into the fissures in the geological formation to keep the formation open after the slurry has been pumped into the well. Well servicing equipment incorporates blending apparatus to mix the particulate material with the fracturing fluid. The blender discharges the slurry to a high pressure, downhole pump that injects it into the well and into the producing zones. It is important that the discharge pressure of the blender remains constant to prevent the downhole pump from cavitating, a condition in which inlet fluid flow is reduced or air is passed through the pump and downhole pressure is lost. When cavitation occurs in the downhole pump, the fracturing operation fails.
It is desirable to use multiple blending tubs in the blending and fracturing operations. Multiple blending tubs increase the flow rate and provide a failsafe backup system in the event that one of the tubs fails. However, because of cavitating and other downhole pump problems, it has been difficult to use multiple tubs simultaneously. It is crucial to a cost effective fracturing operation that a high flow rate of slurry is reliably delivered at a relatively constant pressure to the downhole pumping equipment.
INFORMATION DISCLOSURE STATEMENT
The Stegemoeller patents (U.S. Pat. Nos. 4,490,047, 4,802,141, 4,850,701 and 4,913,554) disclose a structure which combines a single mixing tub mounted on a vehicle and having in conjunction an engine for driving hydraulic pumps, additive tanks for use in producing the slurry mixture from the mixing tub, and a control station for operating and monitoring the operation of the system. Throughout these patents, there is considerable discussion concerning the shape and size of the mixing tub. However, there is no teaching in any of the Stegemoeller et al. patents of manifolding multiple blending tubs together to provide a constant outlet pressure.
The Cooper patent (U.S. Pat. No. 4,159,180) discloses a mixing tub mounted on an articulated truck bed. The purpose behind this mechanism is to allow the mixing tub to be rolled off of the truck chassis so that it is resting upon the ground. It is stated that this lower position for the mixing tub allows the tub to be charged with conventional loading equipment instead of having to provide a loading mechanism on the truck itself. The entire system is returned to the truck chassis for transportation purposes. The Cooper patent teaches a single mixing tub and does not disclose the use of multiple tubs.
The Althouse patent (U.S. Pat. No. 4,453,829) discloses a type of mixing tub which utilizes a special impeller for the mixing and blending of the ingredients to form the outlet slurry. This embodiment uses a relatively flat casing with a first impeller having a slinger and a second impeller fastened to a vertical shaft. The second impeller is positioned beneath the slinger portion. The slinger has a toroidal shape which is stated to provide a good pressure balance within the fluid composition for circulating and mixing within the casing. The mixing tub utilizes a reverse centrifugal pump. This mixing tub is used in the servicing of oil wells. The Althouse patent does not teach the use of multiple blending tubs.
The Paulus et al. patent (U.S. Pat. No. 3,050,159) and the Ross et al. patent (U.S. Pat. No. 3,295,698) disclose mobile mixing systems. Both of these patents, however, are directed to batch plants usually for the mixing and pouring of concrete. The Paulus et al. patent discloses a self-erecting portable mixing plant which is transported to the site on a trailer type structure. Upon reaching the site, the structure is erected or elevated into position with the mixer and loading distribution bin elevated to a considerable height to allow the contents of the mixer to be dumped directly into a hauling vehicle. The Ross et al. patent also shows a trailer mounted batch plant whereby a concrete silo is erected into a vertical position with conveyers used for automatically charging a portable mixer with the proper ingredients for concrete. These last two patents are not directly on point, but disclose various types of trailer mounted structures which are used for mixing purposes. These references do not disclose multiple tubs manifolded together to allow the use of two or more tubs simultaneously.
SUMMARY OF THE INVENTION
The present invention provides an improved well servicing apparatus for blending and delivering a slurry of fracturing fluid and particulate matter at a constant flow rate and pressure to a downhole pump. Multiple blending tubs are mounted on a trailer, skid, or other type of supporting vehicle or structure and are manifolded together with a slurry discharge manifold. Pipe sections of equal length connect the blending tubs to the slurry discharge manifolds. The slurry discharge manifold and equal length pipe sections provide balanced pressure between the individual blending tubs. Connections to the manifold are provided on both sides of the support structure for convenient operation from either side. A fluid intake manifold on either or both sides of the apparatus may be included to deliver fracturing fluid to the blending tubs. A source of fracturing fluid, such as a tanker truck, is attached to one or more connections on the fluid intake manifold. A conveyer system delivers particulate matter, such as sand, to a distribution bin located above the blending tubs.
Each blending tub may be cylindrically shaped and powered by a rotating impeller attached to and suspended from a vertical drive shaft. Particulate matter is fed by gravity through the distribution bin into an opening in the top surface of each blending tub. Fracturing fluid is introduced into the blending tub from a tangential inlet located on the upper portion of the blending tub. A plenum space is provided in the tub directly below the rotating impeller. As the fracturing fluid and particulate matter gravitate downward through the tub, they are mixed to form a slurry which exits through a tangential discharge outlet located on the lower portion of the tub adjacent to the plenum. Control valves are located near the inlet and outlet of each blending tub. These valves are used primarily to isolate a blending tub when it is not in use.
Because the inlet and outlet piping to the individual tubs are identical on each tub, the pressure drop in these pipes are relatively the same. This characteristic allows the tubs to automatically balance the pressure within the tubs and manifolds and thus provide a constant outlet pressure to the downhole pump. This self-balancing of the pressures within the tubs and thus the outlet manifold is a critical and unique feature of the present invention.
The start up operation of the blending tubs proceeds as follows. The slurry is mixed in one blending tub with the impeller rotating at 600 rpm or more and the inlet and outlet valves open. The suction pump is operated to provide a pressure of between approximately 25 psi and 38 psi. The impeller of the second tub is brought up to a speed of approximately 600
Anderson Timothy Lloyd
Grimland Kristian E.
Maverick Stimulation Company, LLC
Pittenger & Smith, P.C.
Soohoo Tony G.
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