Adjustable Speed Drives (ASD): Failure Reduction and Production Optimization

Frank Ochoa07/25/2007

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Introduction

• The Adjustable Speed Drive utilizes sensorless vector software to determine load and position. In a dynamic well environment, the ASD can seek the optimum Strokes Per Minute (SPM) to maintain a fluid level just above pump off, without shutting the well down. This results in a reduction of equipment loading, reduces failures, and maximizes fluid inflow to the wellbore.

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Agenda

– Capabilities of the ASD– Case Studies– Applications of the ASD– Selection Process– Results and Projections

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Capabilities of the ASD– Continuously Adjusts

Motor Speed to Match Productivity of the Well

– Intra-Stroke Speed Variation

• Slower Down-stroke

• Faster Upstroke

– Internal Pump Off Control or paired with Lufkin SAMS Controller

– Converts Single-phase Power to Three-phase

– Soft Start

– Drive Software• Motor Torque is

sensed and used to control the drive

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ASD Provider– Lufkin ASD

• Crane, TX

– Original Drive Tested

• Cutler Hammer SVX-9000

– Current Drive• Toshiba

– Software• SALT

Sensorless Artificial Lift Technology

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Vendor Stated ASD Lift Applications

– Conventional Pumping Units• Most common artificial lift unit.

– Rotaflex Units• A Rotaflex is an “ultra” long stroke pumping unit

that is used primarily for deep high-volume wells. Fills a niche between conventional and ESP units.

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Case Studies

Objectives– Validate ASD

Applications– Develop Selection

Criteria– Develop Standard Setup

• Wells– #43 Sec. 198 – #402 Sec.198

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#408 Section 198

– Rotaflex Unit– 20 BOPD, 700 BWPD– 2 ¾” Big Bore Pump– SPM: Constant 4.3– 288” Stroke Length– Hard Pump Off

Job Reason Date Rod String Failure 9/15/2006 Rod String Failure 9/29/2003 Tubing Failure 8/29/2003 Rod String Failure 10/5/2002 Pump Failure 4/19/2000

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#43 Section 198

– Conventional 640 Pump Unit– 120 BOPD, 200 BWPD– 2 ¾” LB Pump– SPM: Constant 8.6– 168” Stroke Length– High Cycle Rate

– 3 Failures in 12 Months

Job Failure End Date

Rod String Failure 6/23/2006

Stroke per Minute Decrease 2/16/2006

Rod String Failure 2/9/2006

Tubing Failure 6/21/2005

Rod String Failure 1/22/2005

Rod String Failure 10/5/2004

Rod Pump Failure 3/14/2004

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ASD Applications– Failure Rate Reduction

• Eliminate Fluid Pound• Reduce Rod Buckling• Reduce or Eliminate Cycling

– Conventional, ESP, and Rota-flex

• Smooth Upstroke/Downstroke Transition• Reduce Motor Temperature

– New Well Stabilization

– Rota-flex Optimization

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Eliminate Fluid PoundFluid pound is caused by

Incomplete Pump Fillage.

It can lead to:

– Shock Wave• Gearbox Wear

• Loss of Coupling Displacement

– Equipment Failure• Rod Fatigue

• Rod Wear

• Tubing Wear

• Pump Component Failure

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Reduce Rod Buckling

Rod Buckling is the primary cause of tubing and rod wear failures. Rod buckling can be caused by:

– Fluid Pound– Downstroke Compressive Forces

• Sucker Rod Velocity

• Crooked Hole

• Pump Sticking

The ASD can reduce rod buckling by:– Maintaining a fluid level above pump-off so that

fluid pound does not occur.– Slowing the downstroke while speeding up the

upstroke to minimize compression.

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Eliminate Cycling

• When the ASD detects pump-off, it slows the pump down instead of shutting it off. This allows the well to recover while maintaining fluid flow into the pump. This is advantageous for many reasons:

– Less starting/stopping of the Equipment

– Solids Control• Continuous fluid flow eliminates sand, iron sulfide, etc. from falling back onto the

pump.

• Continuous fluid flow reduces scale, paraffin and asphaltine buildup.

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Upstroke/Down-stroke Transition

– Slower transitions reduce loads and stresses on both surface and down-hole equipment

– Applicable to Conventional Units

– Will be tested on Lufkin Mark Unit

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New Well Stabilization

– Match changing well production

– Keeps solids moving during cleanup

– Compensate for minor design inefficiencies

– Maximize inflow by maintaining minimum fluid level in the wellbore

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Rota-Flex Optimization

• The ASD can optimize these units by: – Upstroke/Down-stroke

Speed Variation– Transition Load Reduction

This translates into:– Less Failures– Less Wear on Equipment– Longer Runtime

• Rota-Flex Unit

• Down-hole Equipment

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ASD Candidate Selection Process– New Wells

– Rota-Flex Units above 3.5 SPM

– ESP’s that cycle due to fluctuating production

– High Failure Rate Wells meeting certain Criteria• We identify wells listed with 2 or more failures in the last 12

months.– WellServ– Lowis– Catalyst

• We then sort the wells based on failure mode and operating conditions that the ASD could effect.

– Rod and Tubing Wear, Pump Failures– SPM, Runtime, Stroke Length

– Meet with Artificial Lift/Corrosion Rep for final review and candidate selection

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ASD Selection Process

– Reviewed Rota-flex SPM

– Repeat Failure Candidates• 9% of wells account for 51% of failures• Wells sorted by failure type

– Reviewed with Artificial Lift Rep

– Submit Recommended Wells

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Results and Projections

Adjustable Speed Drives have a definite benefit in the oilfield. When placed in the correct application, the ASD can:

– Reduce Failures– Optimize Production– Reduce Equipment Changes– Reduce Operating Expenses– Reduce Downtime– Fast Payout

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Potential Benefits

– Power Savings– Optimize Paraffin Treatment Schedule– Efficiency Increases

• Nema B Motor v. “high-slip” Nema D Motor

– Power Factor of .97

Potential Concerns– Potential Harmonic Effect