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A Coupling to Boost Well Efficiency

The deviation and side loading in deep, unconventional wells presents challenges for sucker rod pumping when rods flex during the down stroke of the pumping unit and sucker rod couplings wear into the inner wall of the production tubing. For example, a well pumping at six strokes per minute will cycle 8640 times per day and any given point on the sucker rod string can travel up to 23 miles per day. With so much potential contact between the sucker rod string and production tubing, there is plenty of opportunity to reduce frictional drag and loading on the system. Tubing leaks and coupling failures have historically accounted for nearly half of the failures in rod pump wells, with the root cause of these leaks frequently identified as coupling on tubing wear.

The copper alloy couplings reduce overall friction on sucker rod strings.
The copper alloy couplings reduce overall friction on sucker rod strings.

A standard spray metal coupling is abrasive to steel production tubing with its hard-nickel coating. While standard T couplings are not coated nor as hard as spray metal couplings, tubing wear occurs by a steel-on-steel galling mechanism. T couplings are also more susceptible to corrosion. In an effort to alleviate these effects and associated tubing wear, Materion developed a new low friction, high strength copper alloy. The ToughMet® alloy is a highly durable, spinodal bronze made of copper, nickel and tin. Naturally anti-galling to steel production tubing, it features high impact strength, offers improved corrosion resistance and can reduce overall friction on the sucker rod string.

Eliminating frequent workovers

ToughMet sucker rod couplings were initially successfully qualified in deviated wells with higher than average rates of failure. Hess, one of the largest producers in the Bakken, more than tripled its mean time between failures after introducing the couplings to deviated sections of their wells and went on to include the couplings in its standard production practice. Discovery Natural Resources LLC, an oil and gas company operating more than 1000 wells in the Permian Basin, owned some extremely deviated wells that were experiencing failures every 60 to 90 days, as a result of rod-on-tubing wear. After introducing ToughMet couplings, the company reported one well running for more than 385 days without failure. Clearly, these operators were able to eliminate frequent workovers and effectively improve their production efficiencies by utilizing a sucker rod coupling that actively mitigates coupling-on-tubing wear.

Observing improvements in overall efficiency

However, it has now been established that there is a range of unanticipated and significant added benefits of using the new couplings, beyond simply a reduction in workover costs for deviated wells. Identifying well performance benefits in addition to reduced tubing failures was of great interest to eight different operators. Between these eight different operators, 11 wells are currently running entire sucker rod strings of ToughMet couplings to investigate and quantify the full range of benefits observed by reducing frictional drag in the well. After analyzing their data, the following observations and predictions can be made on behalf of wells modified to run entire sucker rod strings of ToughMet couplings, where no other design alterations are made:

  • 88% of wells will experience an increase in oil production.
  • 93% of wells will experience increased downhole stroke.
Probability chart showing population percentiles for determining the coupling’s potential impact on production rates. It’s 88% probable that a well will have improved oil production with a mean increase of 37%.
Probability chart showing population percentiles for determining the coupling’s potential impact on production rates. It’s 88% probable that a well will have improved oil production with a mean increase of 37%.

Downhole stroke is usually much shorter than the stroke length measured at the surface because rods stretch, contract and deflect. Lowering frictional drag on the sucker rod string allows it to travel more smoothly and with more velocity, translating into greater downhole stroke. Capturing more pump stroke improves compression and allows the well to operate at maximum capacity.

  • 87% of wells will experience decreased fluid level above the pump. Decreasing the fluid level is desirable and indicates efficient sucker rod pumping.
  • 81% of wells will experience improved pump fillage. Operation is more efficient if the pump is filled with fluid. If so, lower electrical power usage will result.
  • 98% of wells will experience gearbox load reduction. Loading on the gearbox is directly related to power requirements necessary to operate a well on rod pump. The gearbox drives the polished rod and provides the torque to rotate the counterweights.
  • 95% of wells will experience peak polished rod load reduction. The polished rod holds the entire weight of the sucker rod string below, the weight of the fluid and the added inertial effects as the unit reciprocates. Frictional drag on the sucker rod string increases the load on the polished rod.
  • 93% of wells will experience improved system efficiency. Higher system efficiency indicates the well is using less power for more fluid production and the costs of operation are directly related to this metric.
Fig. 3. Probability chart showing population percentiles to predict the coupling’s potential impact on gearbox loading. It’s 98% probable that a well will experience gearbox load reduction with a mean decrease of 16%.
Fig. 3. Probability chart showing population percentiles to predict the coupling’s potential impact on gearbox loading. It’s 98% probable that a well will experience gearbox load reduction with a mean decrease of 16%.

The data supports the hypothesis that ToughMet couplings not only reduce tubing wear, but also minimize frictional drag on the sucker rod string. When the sucker rod string can travel more smoothly, wells are able to capture lost downhole stroke and return more efficient fluid production. The couplings may serve to extend the life of surface equipment and sucker rods as indicated by smoother pump cards and reduced loads on the gearbox and polished rod. Minimizing frictional drag will also likely improve a well’s operating efficiency and offer power savings associated with it.

The following case studies detail the observations made to improvements in overall efficiency when running entire sucker rod strings of ToughMet couplings.

Case study 1: Permian Operator B, Well 1

126 ToughMet couplings were installed into Well 1 in August 2017.

Well efficiency improvements

Through April 2018, the well experienced overall improved oil production and downhole stroke, while pump fillage stayed relatively the same before and after ToughMet couplings. Oil production increased an average of 35 bpd to 145 bpd compared to 110 bpd with spray metal couplings. Likewise, downhole stroke length increased by an average of 49 in. to 175 in. compared to 126 in. with spray metal couplings. Loads on the surface equipment also reduced significantly. Gearbox loading was designed to be at 76.5% of its suggested maximum load and averaged 74.6% with the spray metal couplings. After ToughMet couplings were installed, the average gearbox load averaged 63%, which was 12% lower than the spray metal average or 14% below the designed target. Average peak polished rod load decreased by over 8500 lbs, a 27% improvement. This well continues to run the ToughMet couplings, but failed after 8.3 months in May 2018 due to a rod part. After 2,560,320 cycles, the couplings showed close to no wear and the serial numbers on the faces were still visible. All of the ToughMet couplings were reinstalled.

 Case Study 2: Permian Operator B, Well 2

A Permian operator installed an entire sucker rod string of consisting of 186 ToughMet couplings into a horizontal well in August 2017. This well ran on rod pump with both spray metal and T couplings prior to the ToughMet couplings. Historically, it had failed every 6 to10 months due to a tubing leak or rod failure. Upon workover, the same 1.75 in. pump was rebuilt and reinstalled and fiberglass rods, tubing rotators, rod rotators and rod guides were maintained. Half of the L80 production tubing was also replaced upon workover. The pump was set in the curve at 6656 ft and side loads average 240 lbs. The designed stroke length was 130 in. and the well is running at 7 strokes per minute on a variable speed drive. Since ToughMet couplings were installed, this well has been running for more than a year.

Well efficiency improvements

Over the first six months of operating with the new couplings, oil production averaged 130.5 bpd compared to 110 bpd prior. When Well 2 was running with spray metal and T couplings, the downhole stroke length was 132 in. vs. 130 in. design. After the new full string of couplings was installed, the well’s downhole stroke recorded between 150 in. and 155 in., gaining an additional 18 in. to 23 in. Pump fillage ran between 92 and 99.9% compared to 90% before. Likewise, loads on the well’s gearbox as a percentage of its designed max load changed from 84% down to 59%-64%, suggesting possible decreased power usage and potential extended gearbox life. Lastly, the peak polished rod load averaged more than 3000 lbs below the historical average.

In April 2018, the operator indicated that the well’s fluid levels were rising because of fracking nearby, therefore data obtained during this time period has not been used to evaluate the performance of the well. 

Case study 3: Permian Operator C, Well 3

An entire sucker rod string of 456 ToughMet couplings was installed into an 11,411 ft Permian vertical well in January 2018. This is a lower producing well that previously ran spray metal and T couplings. Historically, its failure frequency was an average 119 days due to various failure modes. Upon workover, the same 1.25 in. pump was reinstalled and no tubing rotators, rod rotators, or rod guides were implemented to maintain the same well design.

Well efficiency improvements

After a month of run time, reduced friction and loading data were observed alongside increased production, effective net stroke length and pump fillage. The operator noted the following comparisons between the well’s prior performance with spray metal and T couplings and the current performance with ToughMet couplings:

  • Oil production increased from 19 bpd to 22 bpd (16%).
  • Gearbox loading declined from 87% to 77%.
  • Pump stroke improved from 70 in. to 77 in. (10%).
  • Pump fillage increased from 80% to 100%.
  • Pump friction lessened from 987 lbs to 776 lbs (21% decrease).
  • Pump volume efficiency increased from 55% to 64%.
  • Structural unit loading was 2% with ToughMet couplings.
  • Maximum rod loading was 4% lower with ToughMet couplings.

After two months’ of run time, the variable frequency drive was removed and replaced with a pump off controller because the well started to fight gas interference. Now, the well does not operate 24 hours a day and idles whenever pump fillage falls below 60% to allow the wellbore to fill.

After three months’ of runtime, the operator reported that oil production averaged 19 bpd, which is equal to the historical production rate. However, because the well is now operating 14.6 hours per day compared to 24 hours per day with the previous design, fluid production cannot be validly compared. Despite this, other benefits were measured:

  • Downhole stroke improved even further to 80-85 in. from to 70 in. Similar wells in the field were only capturing 70-75 in. pump stroke.
  • Pump fillage was 100% when the well was not affected by gas interference.
  • Pump volume efficiency improved to 76% compared to 55% before.
  • Structural unit loading decreased to 85% compared to 90% before.
  • Gearbox loading increased slightly to 81% but was still below pre-ToughMet averages.
  • Max rod loading decreased to 97% compared to 114% before.

In April 2018, Well 3 failed due to a broken rod likely caused by paraffin build up. The couplings showed no wear and were reinstalled. Performance updates will be gathered and averaged over a longer period of time as the well continues to run.

Case study 4: Permian Operator D, Well 4

In February 2018, 286 ToughMet couplings were installed into a 9200 ft deep horizontal well. Prior to ToughMet coupling installation, Well 4 was operating at 6 SPM on a variable speed drive with spray metal couplings, fiberglass and steel rods and L80 production tubing. This well did not use rod rotators or rod guides. The operator noted that this well fights gas interference and experiences rod buckling in the bottom section of the sucker rod string. To help alleviate gas interference issues, Well 4 is designed to shut off when pump fillage falls below 70%.

Historically, the daily well run time recorded between 20-45%, pump fillage was 81-85% and oil production was 26 bpd. Gas averaged 35 mscf per day and water averaged 25 bpd. Upon workover, 17 spray metal couplings could not be broken out. However, no other design changes were made to the well when ToughMet couplings were implemented.

Well efficiency improvements

After 2.5 months of operation, the operator was surprised to see daily run time double to 60-80% for Well 4. The run time per day increased with the ToughMet couplings because typical pump fillage was 99.5% and thus remained above the 70% trigger point for shutting off the well more often. The operator suggests that the low friction couplings have helped to alleviate the buckling in the bottom section of the rod string, allowing for improved compression in the pump, better plunger movement, greater pump fillage and a faster recovery rate. The oil production rate also increased 15% to 30 bpd. Gas and water averaged 49 mscf per day and 23 bpd, respectively. The operator noted that Well 4 had not produced 30 bpd since October 2017.

Summary

The early results from these field trials show that changing out standard couplings to ToughMet couplings has a substantial effect on well performance. The statistics suggest that ToughMet couplings have increased or accelerated the oil production rate 21% on average in these wells. The statistics also confirm the hypothesis that ToughMet couplings allow wells to capture extra downhole stroke length, increase pump fillage, decrease fluid levels, minimize gearbox wear and tear and alleviate loads on the sucker rod string. 

Probability plot with population percentiles to deduce the coupling’s potential impact on average system efficiency. It’s 93% probable that a well will experience improved system efficiency with a mean increase of 37%.
Probability plot with population percentiles to deduce the coupling’s potential impact on average system efficiency. It’s 93% probable that a well will experience improved system efficiency with a mean increase of 37%.

As operators continue to provide updates on their wells running ToughMet couplings, the changes measured will be added to the probability charts shown in Figures 1, 2 and 3. These probability charts express the likelihood that a well will experience a significant change to the performance metrics discussed if ToughMet couplings are implemented. By summarizing the field data in this way, operators can more clearly see the effects of reducing friction in their wells and how likely it is that they will capture those benefits by running ToughMet couplings.

Conclusions

To date, 28 operators have installed ToughMet couplings in more than 900 wells between the Bakken and Permian Basin. The case studies demonstrate that, besides reducing failure rates and avoiding costly workovers, ToughMet couplings have a measureable effect on a well’s performance. Each well is operating more efficiently with improved sucker rod string movement, greater downhole stroke, increased pump fillage and accelerated fluid production. In addition, simply switching coupling materials has resulted in decreased loads on the gearbox and polished rod, which suggests that surface equipment life can also be extended.

Switching sucker rod couplings from standard T or spray metal to the copper alloy couplings achieved the following (on average):”

  • Oil production increased 21% on average
  • Downhole stroke increased 23% on average
  • Pump fillage increased 9% on average
  • Peak polished rod load decreased 16% on average
  • Decreased alternating stress on the polished rod by 16% on average
  • Gearbox loading decreased 16% on average
  • Fluid level above the pump reduced by 28% on average
  • System efficiency increased by 37% on average

Although this study reports only on the initial findings of field trials that targeted well optimization by using ToughMet couplings, statistical analysis based on a normal distribution model suggests 93% of wells will experience improved system efficiency.

Bill Nielsen, V.P./General Manager at Materion Performance Alloys, said, “We want to thank all the operators who are participating in this project. Innovation is, of course, always exciting to experience. From the business perspective, having good data from which to draw risk-adjusted financial expectations is essential. The probabilities of increasing revenue while simultaneously reducing cash OPEX and CAPEX eclipse the minor marginal cost of adopting this technology. We expect widespread adoption to continue, and we've invested to assure we are aligned to sustain a rapidly accelerating demand trajectory.”

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