Patent ID: 12196199

DETAILED DESCRIPTION

Conventional seal packing technology utilizes several different types of metallic and/or elastomer seal components inserted into a stuffing box during installation into the fluid end of a pump. The seal packing assembly may include, multiple individual annular metallic and/or elastomer seal components inserted into a stuffing box successively to form the packing during installation. This seal stack is retained by a packing nut that is also installed in the machined contours and threading in the fluid end. The packing nut preloads and energizes the seals to ensure their positive engagement with the plunger. The typical seal stack includes a junk ring, header ring, pressure ring, adapter, spacer, lantern ring, and wiper ring. In the conventional seal stack configuration, a lubrication port is formed in the lantern ring to allow a lubrication or coolant fluid to be supplied to the seal stack. The lantern ring is typically one of the seals that is the furthest from the pressure chamber. Sand and other abrasive elements in the frac fluid have a tendency to migrate past the junk ring and header ring, typically closest to the pressure chamber, and end up at the interface between the plunger and the packing seals. There, the stroking action of the plunger causes abrasion and damage to surfaces of the plunger and the seals, which in turn leads to premature wear, leaks, and seal failure.

FIG.1is a partial cross-sectional side view of an example embodiment of an intermittent flushing plunger packing assembly10for a reciprocating pump. The innovation described herein is to inject a pressurized flushing fluid at one of the seals closest to the pressure chamber12, such as adding a flushing fluid port14and a cavity that forms a flushing chamber16in the junk ring. The function of the flushing chamber ring or modified junk ring16is to keep the “junk” in the frac fluid out of the seal stack. The use of a pressurized flushing fluid around the flushing chamber ring16creates an added barrier that would prevent entry by the frac fluid. The flushing fluid is drawn from a fluid source20and is pressurized with a pump (not shown) to supply the flushing fluid to a flushing chamber/cavity16incorporated in the first seal component18of the seal stack via a check valve22in a flushing port14. Previously called a junk ring, this new seal can be termed the “flushing chamber ring.” or “flushing cavity ring”18.

The flushing fluid for the flushing chamber may be any suitable clean fluid such as water, lubrication fluid, etc. The check valve22ensures that fluid can only enter the flushing fluid chamber16in the seal stack and not allow the high pressure frac fluid to enter. The amount of flushing fluid that is consumed or supplied to the flushing chamber ring18can be monitored using a suitable monitor (including, e.g., flow, temperature, and pressure sensor(s), microprocessor/microcontroller, and data communication interface)24to help assess the health of the system. For example, if a greater than normal amount of flushing fluid is being consumed, then it may indicate that the flushing fluid is escaping into the fluid cylinder and that the packing seals are worn and should be replaced. If little or no flushing fluid is being consumed, then it may indicate that the check valve22, the fluid source20, and/or flushing fluid pump may be malfunctioning. Therefore, the monitor24may provide data that may be used to assess the operating status of the seal stack.

Behind the flushing cavity ring18is a header ring26that incorporates a scraper28that has an inner diameter profile defined by a plurality annular ridges30. These ridges30provide additional barriers against entry by sand and other elements in the frac fluid. A pressure ring32, adapter34, spacer36, and lantern ring38are the remaining components of the seal stack. The spacer36may incorporate an annular groove40. The lantern ring38may incorporate passages42to allow a lubrication fluid to enter the seal stack via a lubrication port44. A packing nut46is securely fastened in the plunger bore against the seal stack, which energizes the packing stack, and adjusts the height of the packing stack and the packing load. The packing nut46may incorporate a wiper seal48as shown inFIG.1.

FIG.2is a pressure versus time plot of the flushing fluid and frac fluid in a preferred operation of the intermittent flushing fluid plunger packing assembly10in the positive displacement pump. It may be seen that the clean flushing fluid is injected at approximately 300-500 psi during the retraction portion of the stroke. During the discharge portion of the stroke, the flushing fluid can be lowered to near zero pressure. Alternatively, the flushing fluid can be maintained at a constant pressure that is always greater than the fluid cylinder pressure during the retraction portion of the stroke. By injecting a clean flushing fluid into the flushing chamber16in the flushing cavity ring18, a liquid barrier is created between the elastomer header ring26and the frac fluid. The use of the pressurized flushing fluid in the flushing cavity ring18or another seal element close to the fluid cylinder helps to reduce the amount of sand and other corrosive elements in the frac fluid that would get past the junk ring and header ring, and to lessen the amount of premature wear and abrasion in the plunger and seal elements. As a result, the packing seal would last substantially longer and the cost of maintenance and repairs would be drastically decreased.

FIG.3is a pictorial representation of an exemplary positive displacement pump60that may incorporate the intermittent flushing plunger packing assembly10described herein. The positive displacement pump60has two sections, a power end62and a fluid end64. The fluid end64of the pump60includes a fluid end block or fluid cylinder, which is connected to the power end housing via a plurality of stay rods66. In operation, the crankshaft (not explicitly shown) reciprocates a plunger rod assembly between the power end62and the fluid end64. The crankshaft is powered by an engine or motor (not explicitly shown) that drives a series of plungers (not explicitly shown) to create alternating high and low pressures inside a fluid chamber. The cylinders operate to draw fluid from a suction manifold68into the fluid chamber and then discharge the fluid at a high pressure to a discharge manifold70. The discharged liquid is then injected at high pressure into an encased wellbore. The injected fracturing fluid is also commonly called a slurry, which is a mixture of water, proppants (silica sand or ceramic), and chemical additives. The pump60can also be used to inject a cement mixture down the wellbore for cementing operations. The pump60may be freestanding on the ground, mounted to a skid, or mounted to a trailer.

In a typical positive displacement pump as shown inFIG.3, the crankshaft is mechanically connected to a motor. In one embodiment, a gear is mechanically connected to the crankshaft and is rotated by the motor through additional gears. A connecting rod connects to a crosshead through a wrist pin, which holds the connecting rod longitudinally relative to the crosshead. The connecting rod is pivotally secured by a bushing, which holds the connecting rod longitudinally relative to the crosshead. The connecting rod pivots within the crosshead bushing as the crankshaft rotates with the other end of the connecting rod. A pony rod extends from the crosshead in a longitudinally opposite direction from the crankshaft. The connecting rod and the crosshead convert the rotational movement of the crankshaft into the longitudinal movement of the pony rod, which is connected to a plunger that draws and pushes the pump fluid passing through the cylinder housing. The plunger extends through a plunger bore and into a pressure chamber formed inside the fluid cylinder.

It should be noted that the intermittent flushing plunger packing assembly10may be utilized in pumps of other configurations, such as a linearly actuated pump having a centrally-disposed drive system coupled to two fluid ends at either end along the linear axis, where the drive system drives the plunger rod to move the fluid in both fluid ends. In an example embodiment, an electric linear pumps may use a planetary screw drive (e.g., planetary gears surrounding a threaded rod to convert rotational motion of the planetary gears to the linear translation movement of the threaded rod) to linearly move (i.e., translate) plunger rods instead of the traditional diesel engines. The threaded rod coupled to the drive system has plunger sections on both ends such that when the plunger rod moves in either direction, one of the two ends will be pumping out fluids while the other drawing in fluids. In other embodiments, the electric actuator may be in the form of a winding that uses electric current to create a magnetic field to move the rod along its axis (e.g., similar to solenoid actuation). A fluid end is coupled with each of the two plunger ends to control fluid charging on the suction stroke and pressure discharge on the power stroke.

The intermittent flushing plunger packing assembly10may be utilized in a second embodiment of the linear actuated pump that includes a centrally-disposed fluid end coupled to two hydraulic actuators on its two sides along a linear axis. The hydraulic actuators are in fluid communication with a hydraulic drive system that incorporates a planetary screw drive or a solenoid drive system. In this configuration, the stroke length of each plunger rod can be halved and a smaller screw drive system may be employed and still achieve the same horsepower and fluid rate output as in the first embodiment pump described above. In this more compact configuration, the overall length of the pump assembly is reduced by the size of one fluid end. Further, because of the shorter stroke length, it is easier to achieve and maintain accurate alignment of the fluid end and hydraulic drive components.

The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the intermittent flushing plunger packing assembly for the packing bore described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.