HDESP Applications in Common Oilfield Environments

HDESP pumps are designed to withstand aggressive chemical environments downhole, including environments containing H2S, CO2, and organic chemicals.  The basic pump structure is stainless steel, with duplex stainless steel used for critical high strength structures such as the pump case.  Stellite (DuMore) balls and seats are standard, with other alloys available upon request.  The pumping diaphragms are made from nitrile rubber.  All materials in contact with the well environment are either made of stainless steel, stellite, or nitrile rubber.

The diaphragms and electrical insulation used in the pump are exposed to the well fluid and will react to exposure over a period of time.  Generally, rubber materials will swell (change volume) in the presence of aggressive chemicals, and change mechanical and electrical properties.  All rubber materials used in the HDESP pump are nitrile rubber, formulated to resist exposure to hydrocarbon materials and H2S.  Unlike other pumps (such as PCP pumps) these materials can  swell to some extent upon exposure to aggressive chemicals, and not hinder the normal operation of the pump.  Upon exposure to high levels of H2S (greater then 3% at temperatures up to 150 F) degradation and mechanical failure of the diaphragm will occur over time, and may shorten pump life.  Exposure to concentrations greater then 10% CO2 has produced blistering of the diaphragm materials upon decompression, but otherwise normal operation.  Exposure to amines is not recommended in concentrations greater then 100 PPM due to rapid degradation of the diaphragm

In the field, exposure to less then 3% H2S and less then 10% CO2 have been experienced with relatively little corrosion of the stainless steel structure.  Stellite balls and seats are not recommended at high CO2 concentrations (> 5%) due to cobalt depletion.  Ball and seal selection can be tailored to local conditions by contacting SmithLift.    Protection of stainless steel depends on the maintenance of a passivating layer by an oxidizing environment.  A non-oxidizing environment such as a high PH environment and/or chlorides (such as salt) can breakdown protection, and lead to rapid corrosion. 

Evaluation of corrosion potential of a particular well can require considerable skill but a general rule of thumb is that any condition that causes rapid corrosion of stainless steel will also cause rapid corrosion of the pump.  Stainless materials perform well in acid environments, and chemical treatments (such as acidizing) have been done with the pump in place, saving the operator the expense of pulling the pump during treatment.  The rubber materials used in the pump have shown resistance to H2S, CO2 and most common well treatment chemicals in the field.  Nitrile is extremely resistant to fully saturated hydrocarbons such as those found in condensate, oil and natural gas.  A few organic materials, such as amines have caused excessive swelling of nitrile rubber, and should be avoided.  Experience with other nitrile rubber tools (such as packers) in the well environments will provide the best indication of the performance of the rubber materials in the pump.

In addition to corrosion and chemical attack, the formation of scales and deposits can cause pump problems.  Most commonly, scale will occur at the pump inlets or directly above the pump where the velocity of the pumped fluid drops in stagnant areas such as larger diameter production tubing.  Deposits within the structure of the pump are rare due to higher temperatures and higher velocities within the pump.  In most cases, failure occurs when the fluid paths either into or out of the pump are blocked, causing pumping to cease.  Deposits can be paraffin, reaction products (such as iron sulfide), or sands such as formation or frac sand.  As a general guide, if deposits occur with other types of pumps, deposits will also occur with HDESP type pumps.

In summary, HDESP pumps are designed to withstand severe environments found downhole.  HDESP pumps can be used successfully if the well fluid is compatible with stainless steel and nitrile rubber.  If the well tends to deposit materials such as iron sulfide and paraffin, the possibility exists that HDESP pumps will become clogged, and a treatment program may be needed to prevent damage to the downhole pump.  Normal oilfield chemical procedures such as scale or acid treatments can be conducted with the pump in place as long as the treatments are compatible with stainless steel and nitrile rubber and do not cause excessive temperatures.