SPE 157126

Design of Sucker Rod Pumping Systems for Effectively Handling Solids and Sand

Mohamed Ghareeb and Anthony (Tony) Beck, Lufkin Industries, Inc.

Copyright 2012, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE International Production and Operations Conference and Exhibition held in Doha Qatar, 1416 May 2012.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

Subsurface pumps in sandy wells suffer mostly from abrasion of Sand (quartz). To prevent the pump from being stuck by sand grains and to reduce pump part failures due to sand, it requires understanding of sand problems and how they damage pump parts and cause stuck pumps. This can help with the design of the pump configuration in order to improve pump inherent reliability in sandy well conditions. Usually the common types of sand problems are

Plunger sticking in barrel

Pump sticking in tubing (insert pumps)

Sand damage to barrel, plunger and valves

Sand packing off in the pump

Sticking valves

The subsurface pump equipped with a sand screen and additional modifications worked out over the years with different oil producers have helped it become one of the best solutions for difficult sand laden wells. Where some sucker rod pumps and some exclusion devices are designed to keep solids from entering the pump. Certain pump configurations help in handling sand in terms of moving the sand through the pump with a minimum of wear.

This paper will discusses the main concepts in sand handling with highlighting some exclusion devices, and the most practical solutions for best sand handling pump and completion design as a function of conditions

Introduction

In sandy well conditions, understanding sand problems and how they can damage and stick the subsurface pumps will help with the design of the well completion and pump to improve its inherent reliability.

Rod pumps like other artificial lift pumping systems are not designed or able to pump Silica sand, proppant fragments for long period of time. The typical sucker rod subsurface pump configuration uses a plunger inside of a pump barrel connected to two check valves (standing and traveling valves) ball type. These two valves are opened by pressure and closed by flow. At the start of the upstroke of the plunger the traveling valve is forced closed and the standing valve is drawn open. Consequently fluid is flow from the wellbore to the pump barrel chamber during the upstroke. The standing valve will close and trap this fluid in the pump barrel chamber when the plunger reaches the top of the stroke and start the beginning of the down stroke (going down).

2

SPE 157126

The traveling valve opens during the down stroke of the plunger when the pressure below the travelling valve increased to a value higher than the pump discharge pressure. This process is continuously repeated, eventually bringing the well fluids to the surface (Figure 1).

Figure 1: Subsurface Sucker rod Pump princable of operation

Sand Problems in Rod Pumped Wells

In the production of fluid with particles (sand and/or abrasives), separation occurs as the particles travel up the tubing. The small particles usually stay suspended and are lifted to the surface; however, the larger, heavier particles fall down and settle on top of the rod pump plunger. The size and volume of the particles lifted to the surface will depend on the fluid viscosity and velocity. Sand usually represents the highest cause for the subsurface pumps failure. Figure 2 is a graph from the last study did by Welling & Company. It show particles (sand, solids, trash) represents the highest percentage of the pump Failures.

Figure 2: Pump Failures (Welling & Company)

SPE 157126

The major problems caused by sand are:

Sand Cutting

3

As pump plunger moves upward the well fluids are pumped from the well bore to pump chamber, sand and/or abrasives are pulled into the pump with the fluid. As plunger moving up during the upstroke the settled particles on the top of the rod pump plunger will work their way between the barrel, and the plunger. This is due to moving the plunger against the pump discharge pressure upward and this pressure pushes the particles downward. This will cause abrasion cuts, commonly known as sand cutting (Figure 3). When this occurs, plunger wills lose some of its sealing ability. Consequently the slippage volume of the fluid between the plunger and barrel will increase with increasing length and number of cuts. This results in decreasing the pump and total system efficiencies. Time accelerates the plunger and barrel wear and when the volume of the slippage fluid reach to an unsustainable rate, the rods must be pulled to replace the downhole pump.

Figure: 3: Plunger sand cutting and erosion with standard sucker rod pump

Rod Buckling

Another problem caused by sand is rod buckling. Presence of sand in around the pump plunger, it increases the friction between the pump barrel and plunger. This will restricts plunger movement downward freely which can result in rod buckling especially the lower part of the rod string. The buckled rods rub against the tubing, which causes wear on the rods, tubing, and pump. With time a hole can be worn into the tubing, which stops pressure and the flow of oil. Production must be stopped so that the rods and tubing can be replaced (Figure 4).

Figure 4: Rod Buckling due to Sand Friction Causes

SPE 157126

The continued pumping and separation& settling of sand in the tubing can cause sand cutting and rod buckling to occur over and over again during the life of a well. In order to combat the sand problem, some production companies have chosen to utilize the help of pump and tubing screens, which have proven in many cases to save the company time, money, and resources by extending pump life and increasing efficiency.

System Design to Minimize Sand Problems

When designing systems for handling solids and/or sand, we should be taking into consideration that this problem can often be minimized by one or a combination of the following approaches:

Prevent or minimize solids from entering the pump. (Enough rat hole should be available) Standard API rod Pumps with: Proper plunger/ barrel fit to either keep solids away from the plunger/barrel interface or let them pass through without sticking the pump. Use large valve ports to allow sand to travel through the valves without packing off. Grooved Plungers Specially designed plungers Special subsurface pump designed for fluid production with sand and particulates Pump accessories for minimizing sand and particulates problems

For any solution, operator should provide to the designer all the possible information about well and sand / solids production. This is in order to give practical recommendation and solution. Usually the minimum required data is:

Source and size of sand and particles. Are you dealing with formation or/and frac sands or larger abrasives? What are the major problems being experienced due to sand production? Well bore configuration Well Production rate and type of fluids and relevant fluid parameters

Downhole Sand Screens (Filters)

The main objective of using screens is to filter out large sand particles and other abrasives before fluid

enters the pump, this helps to maximize the life of the equipment. Sand screens usually come in

different sizes, models and systems of installation. The two main methods of installation are:- pump run, and tubing run.

A pump screen (pump guard) is run in place of the gas anchor on the bottom of the pump (Figure 5). It can be placed either below or above the casing perforations. The pump screen comes in various lengths and slot sizes.

A tubing screen is run in place of the perforated sub below the seating nipple, (Figure 6). It is designed in different shape and configurations. Usually made up of a screen jacket that is slipped over a piece of perforated tubing. Part of the success of this type of filter is that it has a large circumferential area.

Figure 5: Pump screen (pump guard) Figure 6: Tubing Screen

SPE 157126

5

The tubing screen can be placed either below or above the casing perforations. the tubing screen is screwed to the bottom of the seating nipple and a standard bull plug or purge check valve ( figure 7) is installed on the other end.

Although tubing and pump screens are the ideal solution to most sand problems, they do have limitations. The smallest slot size for a screen is 6/1000ths of an inch, if a well is experiencing problems with fine sand particles that are smaller than this screen size, the screen would be ineffective in reducing the flow of sand.

Another limitation of the screen is experienced when scale is encountered in the well. Over time, scale can build up on the surface of the screen, slowly coating the opening and restricting the flow of oil and gas. This is a problem that will clearly limit the ability of the screen to function properly and can cause the well to plug completely. However, if a proper chemical program is introduced at the same time as the screen is inserted into the well, the chemicals will break down the scale and allow the screen to function effectively without scale plugging.

Figure 7: Tubing Purge check valve (after HF Pumps)

The key to the success of the screen is preventing the particles greater than the screen sizeopening to pass through and all the smaller particles to pass through the screen opening without plugging the screen. The Vee-wire slot opening screen (the gap or opening between the Vee-wires) has proven to be one of the better designs. Because it is provides only two point contact with sand grains and cannot become easily plugged (Figure 8).

Figure 8: Vee Wire Screen

SPE 157126

Several filtration systems and techniques are available in the market. Each has proved to work well in

certain areas. The followings are some of the main common filtrations systems

Cavin Desanders: They are sized for the size of the particulates encountered. They use centrifugal

force from a swirling motion to throw sand towards the side walls of the tail pipe while the fluid stays in the center and enters the pump. These devices have proven to be effective in W. Texas installations. However, eventually you must clean out the well or the rat hole of the resulted debris.

Stren PumpGard and Stanley Filter: These are both filters that rely on excluding particulates from

the fluid stream. The PumpGard has an optional back flush device. These filters have problems with sticking or breaking if not protected by a mud anchor, especially if the assembly is tagged against fill. Heavy oil or high temp filters have mixed results as most filters have troubles with viscous oil

Prepack Screen and Liner: These are self-contained units that are most often used in unconsolidated

sand formations. The prepack unit has screens and sand with resin between the screens, while the screen and liner has only screens. Wells with scaling tendencies may present a problem with this type of device.

Determine the Optimal Screen

Proper selection of well screen is critical for successful wells and control. The screen performance is dependent on several factors. Screen should be selected for maximum sand retention and minimum productivity impairment.

Screen Opening

Screen opening (slot/micron rating) is dependent on particle size distribution. Table (1) shows the Particle size for different type of sand which can be use as guide line.

Table 1: Particulate size

Particle Size

Description

Below .003

Silt and clay

.003-.005

Very fine sand

.006-.010

Fine sand

.011-.020

Medium sand

.021-.040

Coarse sand

.041 and above

Very coarse sand

There are two main kinds of sand: formation sand and Frac sand. Formation sand is smaller than other kinds of sand and is usually irregular in size. Frac sand is larger than formation sand and is very uniform. Frac sand is usually the most abrasive kind of sand. It is important for the designer to know exactly what kind of sand is causing the problem in the well in order to choose the suitable slot size that will most effectively filter the sand and not restrict flow of fluids to pump.

The size of the slot determines the filtration size; with each slot measuring 1/1000th of an inch per slot (Ex. an 18 slot screen has an opening of 18/1000ths of an inch). The design inwardly enlarges to prevent particles from becoming jammed in the slot. The particles that are near in size to the slot opening simply pass through freely. The vee-wire slots types have proved to be an effective design.

SPE 157126

Table 2: Mesh screen size

Mesh Size Particle Size

140

100

65 48

0.012 35

28 20 14

MICRON= .00003937

Screen Length

7

The screens also come in a variety of lengths. Length is a critical factor in sand screen use. One of the main problems that can limit the ability of the screen is the selection of the wrong screen length for a particular well. Most plugging occurs when the fluid velocity is too fast, causing sand to become wedged in the opening. In fact, the longer screen length the slower the fluid velocity. A shorter screen will experience a faster or increased fluid velocity. A faster fluid velocity is more likely to pull solids into the opening of the screen, which can result in a build-up that will reduce the flow of fluid or even can cause plugging. The slower fluid velocity of a longer screen length is less likely to pull solids into the opening of the screen; therefore, the problems experienced by a shorter screen length simply do not occur. The key to success is the selection of a length that will, inhibit the formation and build up of sand particles on the surface of the screen, yet still allow a desired fluid velocity.

Subsurface Pump Configuration for Sand Handling

Unfortunately when sand is produced with well fluids by a conventional sucker rod pump it will accelerate wear of the plunger and pump barrel, and may also cause the plunger to stick in the barrel. Wear is generally caused when the sand grains are forced between the plunger and pump barrel. Sand grains can have a higher Rockwell hardness than the components of the pump, and can therefore abrade the plunger and barrel during the reciprocating motion of the sucker rod pump. The frictional heat generated by this wear can cause the pump components to gall, or fuse together.

Standard API pumps

When the standard subsurface pump is designed to run in well producing particles with the fluid, pump type and its parts should be carefully selected. Pump plunger, barrel, valves and hold-down are the most critical items.

Pump Components for Sand

Plungers, it are identified as either metallic or non-metallic, which refers to the sealing section of the

plunger itself. Outside plunger diameter is the basic pump size minus the specified clearance fit ("minus fit" or "tolerance"). A discussion of metal plunger fit must always recognize the need for at least 2% of the produced fluid as slippage for lubrication between the barrel and the plunger. There are several factors should be considered when determining pump clearance such as the size of produced sand, water cut, viscosity of produced fluid, and down hole temperature .However as a best practice for sandy wells, the following general rules for subsurface pump plunger/barrel clearance have usually proved to give a much longer service life:

The tight fit to exclude sand from barrel/ plunger interface works best with large grain size (0.020and above). Looser fit to allow sand to pass between the plunger and barrel interface when fine sand is present (medium to small grain size, 0.015and smaller).

SPE 157126

Users report longer plunger runs with grooved plungers in abrasive conditions, especially when large abrasive particles are being produced with the production fluid.

Pump Barrel surface treatments (chrome, carbonitrided and nickel carbide)

Pump Valves ( travelling and standing) , Experience has shown that two valves in series will give much

longer service than a single valve if the valve life is determined by wear or fluid cutting, rather than by corrosive action. This result appears entirely logical where sand or other solid material is lifted with the oil. In such cases, failure is likely to occur as a result of fluid cutting due to jetting action when a solid particle is caught between the ball and seat and prevents perfect sealing. The rate of damage is accelerated if the fluid jet carries solid material in suspension. When this condition exists, the fluid jetting through the entire length of the stroke causes severe damage to the ball and seat surfaces. The life of the ball and seat will depend largely upon the number of times it is subjected to damage by fluid jets. By using double valves, this damage can be greatly decreased since a jet cannot occur until both balls are held off their seats during the same stroke. Furthermore, if the two valves fail to seat, the pressure drop will be distributed between the two valves, and the cutting action will be less severe than

it would be with a single valve.

Standard pump cages were having many valve failures in pumps including PAMPA pumps. H-F rubber- lined design reduced valves failures and improved the pump performance due to the extremely large flow of the rubber lined cages. In lab tests the H-F rubber-lined cage out flowed all of the other valves tested including the petro valve. This allows sand and even small gravel; broken scale and other particulates to pass through the valves without sticking or damage.

Hold-down Seal Assembly, it seals the pump to the tubing. These are classified either as cup-type or

mechanical-type. Where pumps are sanding in and cannot be pulled and cause pulling problems, the mechanical holddown has an advantage since there is not a "no-go" ring of dimensions greater than the barrel and cage outside diameter to contend with. Top holddown assembly either cup-type or mechanical are the recommend pump type for wells producing particles with fluids.

The main disadvantage to any bottom hold-down pump is in a sandy well where the sand can drop back in the annulus between the pump and tubing and stick the pump. Then the rods and tubing have

to be stripped out to retrieve the pump.

Special Subsurface Pumps

There are several pumps and configuration in the market which have proved to be suitable for certain condition in sandy wells. Each has advantages and disadvantages such. The most commonly used and field proven pumps are:-

The traveling barrel API pump (Figure 9): The travelling barrel pump is a versatile pump. It operated

in sandy wells with good results. The pump has the travelling valve assembled with the barrel and the standing valve on the plunger. The traveling valve system acts as a sand check and prevents sand from settling on top of the plunger when the well is shut down. The surging of fluid in and out of the lower end of the barrel causes turbulence and prevents sand from settling around the pump and sticking in the tubing. The pressure is equalized in this type pump as it is in the stationary barrel bottom hold-down type pump. The traveling barrel pump has a greater resistance to bursting than a top- anchored pump. The problem of this pump is it will gas lock easier than the stationary barrel type pump because the standing valve is smaller than the traveling valve and due to valve placement.

In crooked or slanted holes, the traveling barrel pump will operate with more friction than a stationary

barrel type pump and thereby place the rods in compression, reducing the effective stroke. The barrel

SPE 157126

9

will be subject to outside diameter wear also. For these reasons, it is recommended that a guide be run on all traveling barrel type pumps. The high position of the valves does not make it a good application

for low fluid level wells.

Pampa Pump (Figure 10) is a tight fitting pump with a long plunger and a relatively short barrel or liner

section. It designed to eliminate any sand or foreign matter from getting between the plunger and liner.

The Pampa pump is especially suited to production of fine sand in well fluids.

The Pampa Pump is available in three configurations: Pampa Tubing Pump, Pampa Traveling-Barrel Insert Pump and Pampa Stationary-Barrel Insert Pump. All use the concept of a longer-than-normal plunger and shorter-than-normal barrel. The plunger length is selected based on stroke length and the barrel length is selected based on pump depth, just the opposite of a standard API-style pump These pumps are all excellent choices for rod-pumping situations where normal-style pumps have a tendency to stick or hang-up due to particulates becoming trapped between the barrel and plunger. Since the plunger is longer than normal, it always strokes out of the barrel and washes clean with production fluid. Another feature is that the Pampa Plunger is pulling the particulates away from the plunger/barrel interface on the upstroke, rather than running over the particulates and trapping them between the plunger and barrel. When the pump is shut down, the traveling valve on top of the plunger closes and prevents sand in the tubing string from settling inside the pump.

Figure 9: Traveling Barrel API Pump Figure 10: Pampa Pump

HF Sand PRO Pump (Figure 11), is uses two plungers connected in tandem to separate the

produced sand from the leading edge of the lower sprayed metal plunger. The upper soft packed plunger has no pressure across it that would force the sand into the cups and cause premature wear. The lower metal plunger has no sand at its leading edge preventing damage to it.

Quinn Frac Pump (Figure 12), is a unique configuration of both new materials as well as an improved

pump design. The design creates a virtual plunger seal to prevent any particulates from coming in between the plunger assembly and the barrel. This minimizes wear as well as increases pump efficiencies by eliminating most of the slippage. This is accomplished by using new processes, including duplex chrome plating and new advanced carbide and polymer materials.

10

SPE 157126

The Quinn Texas T Pump (Figure 13), is designed to help pump abrasive materials often found in

pumping situations. This pump is used in situations where Frac sand or formation fines are causing a pumping problem, and where depth issues often limit other designs.

This pump works by allowing solids to pass through the pump and up the tubing by sealing the O.D. of the plunger and barrel from solids that would normally seize a small barrel that also acts as a wiper. On the upstroke fluids and solids are allowed to enter a lower barrel. On the down stroke, fluid and solids are moved up through the plunger and into the tubing. On the next upstroke, left over solids and fluid are wiped off the plunger, by the upper barrel and allowed to mix with the new fluid so they can travel through the pump in a continuous cycle. This pumps have several advantages where, it helps allow solids to pass through the pump , it can be ran as a top or bottom hold down, it excellent application for wells with timers and automation and pump design strength allows this pump to be ran at extreme depths.

Figure 11: HF Sand PRO Pump Figure 12: Quinn Frac Pump Figure 13: Quinn Texas T Pump

Completion Configurations

Minimizing sand problems should be done during initial well completion (i.e. gravel pack, or through implementation of a post completion sand consolidation treatment). Properly designed completions will achieve increased equipment running life, consequently increased production and lower production cost.

In a standard beam rod pumping completion, the tubing and the pump seating nipple are the essential parts in the completion string. But for moderate and deeper wells, a tubing anchor catcher (TAC) became the third important part for successful well operations. It is designed to anchor the tubing to the

casing at depth in order to pull and maintain tension of the tubing. Tubing size should be selected to

achieve maximum fluid velocity. This is in order to allow fluid to cay the produced sand to surface.

Pump setting (seating nipple) and tubing anchor depths are very critical especially for depleted and high gas/oil ratio wells where the pump should be set as deep as possible and at least the tubing intake usually set below the bottom of perforations. In case of heavy sand production and/or not enough rat hole, the tubing intake should be set two to three joint above the top of perforations. In all cases the tubing anchor should be set above the perforations

SPE 157126

Conclusions and Recommendations

11

Sand reduces run life but with proper choices of equipment and techniques, sand laden fluids can be produced with beam pumping systems. For Sand packing-off or sticking valves; the use of rubber-lined cages have pretty well eliminate this problem. Design of the proper barrel/plunger clearance is very critical in sandy wells. For large grains of sand a tight fit clearance gives good results. In case of small to medium sand (powder size /powder and sugar) ,plunger clearance should be designed to allow sand to pass and not stick the pump The filtration system to the pump intake (pump and/or tubing screen) can reduce the amount of sand entering the sucker rod pump. Tubing screen with large slot (.025to .030) attached to the pump intake to exclude the large grains that damage the pump has given very good results. However sand sieve analysis helps to select proper screen size. Special pumps such as Pampa pump (long plunger and short barrel) are all excellent choices for rod-pumping situations where normal-style pumps have a tendency to stick or hang-up due

to particulates becoming trapped between the barrel and plunger.

Experience has show that double valves will give longer service life downhole than single valves in the same pump. In the case of sandy wells, selections of the correct subsurface completion components are necessary to minimize sand problems. Properly sized tubulars aid in fluid velocity.

References

Mills, Kenneth N,Plunger Fit Sets Pump Performance, the Petroleum Engineer (April 1955) B37-B40. Benny Williams Beam Pumping with Particulate Production paper presented to 2008 Southwestern Petroleum Short Course. G.M. Muth, SPE, Muth Pump Company LLC, and T.M. Walker, SPE, Evans, Frey and Walker Extending Downhole Pump Life Using New Technology SPE 68859, paper presented at the SPE Western Regional Meeting held in Bakersfield, California, 26-30 March 2001 Harbison-Fischer web site www.hfpumps.com Odessa separator web site www.Odessaseparator.com Quinn pump (Lufkin) web site www.quinnpumps.com Russell Franklin The Ultimate Filtration Tool The Utilization Of Tubing Screens And Pump Screens In Down Hole Pump Operations report published by Odessa separator, May 2010