Pump Stroke Optimization: A Better Way

Transcription

1 11 th Annual Sucker Rod Pumping Workshop Renaissance Hotel Oklahoma City, Oklahoma September 15-18, 2015 Pump Stroke Optimization: A Better Way to Operate a Rod Pumped Well Bill Elmer, P.E. Encline Artificial Lift Technologies LLC Author s Logo

2 Pump Stroke Optimization The pump fillage problem What is Pump Stroke Optimization? How PSO works Why it works Proven results Compelling economics 2015 Sucker Rod Pumping Workshop 2

3 First problem: Today s rod pump controllers were designed for vertical wellbores In vertical wells, small pump speed changes can quickly match pump capacity to production. Horizontal wells have fluctuating flow regimes. Short-term events (waves, slugs) can mislead a rod pump controller into making unwanted speed changes, rapidly cycling between maximum and minimum pump speeds. The result: Poor pump fillage Sucker Rod Pumping Workshop 3

4 How do operators handle poor pump fillage today? By manually setting pumping speed Limiting maximum pumping speed Reducing the minimum pumping speed The current approach requires Regular monitoring by personnel Resetting pumping speeds as wells continue to deplete Sucker Rod Pumping Workshop 4

5 How PSO works PSO device continuously learns how to run a pumping unit at its optimum speed for the well Infers RPC setpoints on Minimum and Maximum Working Speeds. Infers when the pumping unit is on the upstroke or downstroke. Calculates average pumping speeds Counts frequency of pumpoff events. Delivers an alternate speed signal to the VFD that keeps the maximum speed more in line with the recent average pumping speed PSO algorithm automatically resets pumping speeds as wells deplete or are enhanced (by offset fracs) 2015 Sucker Rod Pumping Workshop 5

6 PSO decreases slippage, increases pump fillage, and is better for the rods For RPCs that permit a downstroke speed that is slower than the upstroke speed, the PSO algorithm preferentially reduces the downstroke speed This can result in substantially less pump slippage Less pump slippage translates into high efficiency and less strokes per day for same amount of production Other benefits of slow downstroke speed More time for evolving gas to exit gas anchor Higher minimum rod loads reduce buckling tendencies and allow for higher maximum rod loads 2015 Sucker Rod Pumping Workshop 6

7 Example: Conventional unit setup to run 10 SPM, but only needs to run at 3 SPM On VFD, 3 SPM would be 30% of 60 Hz, or 18 Hz Total stroke duration is 20 seconds Upstroke duration is 10 seconds (50% upstroke duration) By increasing the upstroke speed in relation to the downstroke speed, less of the stroke duration is spent on upstroke 6 SPM (36 Hz) on upstroke, a 5 second duration 2 SPM (12 Hz) on downstroke, a 15 second duration Total stroke duration is still 20 seconds with 3 SPM but the upstroke duration is now only 25% of each cycle, not 50% (5/20 instead of 10/20) 2015 Sucker Rod Pumping Workshop 7

8 Example: Pumping at 3 SPM with PSO 2015 Sucker Rod Pumping Workshop 8

9 Extended Example: Pump slippage equivalent to pump capacity at 1 SPM For the previous example where the fixed speed was 3 SPM, the net SPM was 2 SPM By reducing the upstroke duration from 50% to 25%, the pump slippage is therefore reduced to 0.5 SPM 1 SPM Slippage rate x (25%/ 50%) = 0.5 SPM Slippage rate The net SPM is therefore increased from 2 to 2.5 SPM This is 25% higher than needed Well is now overpumping 2015 Sucker Rod Pumping Workshop 9

10 Extended Example: Continued PSO Algorithm will reduce the pumping speeds to cut the net from 2.5 back down to 2.0 SPM New upstroke duration of 5.3 seconds (5.66 SPM) instead of 5 seconds New downstroke duration of 18.7 seconds (1.6 SPM) instead of 15 seconds Total stroke duration: = 24 seconds 24 second stroke = 2.5 SPM, netting 2.0 SPM Ratio of upstroke duration now: 5.3 / 24 = 22% New amount of pump slippage: 1 SPM x (22%/ 50%) = 0.44 New net SPM: = 2.06 STILL OVERPUMPING 2015 Sucker Rod Pumping Workshop 10

11 Extended Example In this example, the SPM was reduced from 3 down to 2.5 Reduction of 17%, or 720 strokes per day, more than a quarter million per year Net pump output still higher Original fixed speed net SPM was 2 SPM New net SPM with PSO is 2.06 SPM, 3% higher PSO Algorithm will continue to whittle this down to 2 SPM, for additional stroke count reduction 2015 Sucker Rod Pumping Workshop 11

12 Why does a longer duration downstroke increase pump fillage? Hypothesis: A longer duration downstroke yields: Additional quiet time for gas bubbles to rise and exit the gas anchor, bringing less gas in the pump Additional time for gas bubbles to rise from the bottom of the pump, leaving a gas-free almost incompressible fluid between the standing and travelling valves at the end of the downstroke. This fluid, having degassed during the upstroke at low pressure, will evolve few gas bubbles when the upstroke begins. This allows the standing valve to open sooner, as evidenced by the straighter upper left hand portion of the example dyno card This results in more liquid entering the pump, for an effective longer net stroke length, and better pump fillage 2015 Sucker Rod Pumping Workshop 12

13 Another explanation for the below card is less pump slippage Sucker Rod Pumping Workshop 13

14 Field Trial Results Methodology: Capture XSPOC data on two test wells prior to hardware installation, install hardware, set initial parameters, monitor performance. The test wells: Horizontal oil wells, about 3 years old Producing laterals 10,700-11,000 feet deep TVD, Perforated intervals between 4,500 5,000 feet long. Well #1 Toe up, Well #2 Toe down 30 to 110 BPD total fluid [95% oil cut] GOR range of scf/bbl Pumps set above the kickoff point, 9,700-10,200 API RP11L pumping system 2015 Sucker Rod Pumping Workshop 14

15 Well #1: 35% reduction in strokes per day, oil production not significantly affected Well #1 averaged 5155 strokes/day for the two weeks prior to PSO installation. The average after PSO installation was 3345 strokes/day, a 35.11% reduction. Oil production rate not significantly affected. Pump fillage increased from 76% up to 90%, an 18% increase Sucker Rod Pumping Workshop 15

16 Well #1: Minimum load increased by 1000 pounds, maximum load mostly unchanged This is better for rod loading, and should result in less rod buckling and compression, hence less wear. Slower downstrokes have mitigated many of the outlier instances of very low minimum rod loads Sucker Rod Pumping Workshop 16

17 Well #2: 25% reduction in strokes per day, oil production not significantly affected Well #2 averaged 5557 strokes/day before PSO installation. After PSO installation, the well averaged 1361 fewer strokes/day. Average pump fillage increased from 79% to 84.5%. Minimum pump fillage increased to around 75%, from 55%-65% Sucker Rod Pumping Workshop 17

18 Well #2: Minimum load increased 1000 pounds as did the maximum load This is because there was less gas in the pump, due to increased pump fillage. The maximum load increase is tolerable, and benefits from reduced buckling should outweigh any issues related to higher sideloading Sucker Rod Pumping Workshop 18

19 Why it works PSO logic creates maximum working speed setpoints that are better aligned with the daily production rate. This prevents over-reacting to high pump fillages often seen at the beginning of a slug event. Keeping the maximum pumping speed slightly higher than average pumping speed helps avoid low pump fillage events Sucker Rod Pumping Workshop 19

20 Compelling economics Although there are clear paths for rod failure deferral, PSO can be justified by energy cost savings alone Sucker Rod Pumping Workshop 20

21 Conclusions PSO reduces pumping system losses by Saving energy that would otherwise be lost to pump slippage Minimizing mechanical and hydraulic losses associated with wasted (poorly filled) strokes Power savings should quickly pay for PSO PSO improves the operating climate of rods Slower downstroke speed helps keep rods in tension Less inertia and friction resisting the downstroke Time for gas in the pump barrel to separate Greater average pump fillage reduces pound events 2015 Sucker Rod Pumping Workshop 21

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