SOCIETY
OF PETROLEUM ENGINEERS
Mid-Continent Section, Tulsa, Oklahoma
Abstracts courtesy of Ken Saveth, ksaveth@juno.com
Optimizing Artificial Lift Operations Through Use of Wireless Conveyed Real Time Bottom Hole Data - Tom Bandy, Earuch Broacha: ProTechnics
The use of an innovative wireless bottom hole pressure/temperature telemetry acquisition system in artificial lift operations can dramatically improve efficiency & optimize fluid producing rates in those wells. The tool is installed into the producing well in the vicinity of the perforations, measuring & transmitting the producing bottom hole pressures & temperatures to the surface for instantaneous control of the surface pumping motor speed. This insures the lowest possible fluid level back pressures, thus allowing the highest possible fluid entry into the wellbore from the reservoir’s capacity. Operating costs per barrel are lowered since the maximum oil production can now be realized from existing wells.
The telemetry tool is deployed with standard slickline equipment & is installed inside a well in a manner similar to ordinary pressure recorder tools. Several unique advantages of the tool are:
1) no moving parts; 2) no wireline to the surface; 3) real time measurement of bottom hole data; & 4) slickline retrievable. Future versions of the acquisition system tool will improve operating efficiency in the following ways:
Temperature monitoring & control of perforation scaling, tubular waxing, & tubular hydrating plugs.
Provide data necessary to create diagnostically predictive IPR curves through monitoring of reservoir in-flow rates.
Enabling early warning of water encroachment or lensing through fluid resistivity monitoring.
INTRODUCTION
A field demonstration of the application of the bottom hole pressure data, as received from Real Time Diagnostics’ wireless pressure transmission system, improved the efficiency of PanCanadian Petroleum Limited’s 8A-19-38-01-W4m well in the North Bodo field of northeast Alberta, Canada. The telemetry Acquisition Tools (PATÒ ) device, developed by Real Time Diagnostics (RTD), was installed in the production tubing below the producing zone perforations, where it was able to measure & accurately transmit bottom hole production pressures & temperatures of the well’s producing horizon to the surface. The real time pressure data was relayed into a voltage loop & a surface computer which contained software designed to output an analog process signal. This signal was then sent to the Wermac Electric Limited’s Variable Frequency Drive (VFD), which controls the speed & torque of the electric motor powering the bottom hole progressing cavity pump (PCP) system. PanCanadian was able to both increase the oil production & decrease the lifting coats per barrel by utilizing the actual bottom hole pressure response of the reservoir fluids flowing into the wellbore to optimize the daily rate of production.
DISCUSSION
Basic theory of signal transmission through electromagnetic wave propagation is not unique or novel; in fact, it has been around for many years. A typical oil field telemetry system includes a downhole frequency transmitter, which contains measurement sensors & a receiver located at the surface. A specially modulated electromagnetic frequency signal, representative of the measurements performed by the sensors located in the downhole transmitter, is injected into the formation where it propagates upward to the surface along the outside of the casing string, essentially creating a two wire path for the current flow to follow. By example, the casing represents one wire & the earth represents the return path or second wire. The electric signal is collected at the surface receiver system by measuring a voltage potential between the surface wellhead & a remote ground reference. The voltage potential is then amplified significantly & filtered to eliminate or reduce other electrical noises, which can be man-made or naturally occurring. These electrical "noises" can potentially interfere with the specialy modulated signal containing the downhole data. The amplified & filtered signal is then relayed into a surface computer where the data measured from the bottom of the producing well is processed & regenerated from the transmitted signal through the use of proprietary signal processing software.
In general, RTD’s PATÒ system consists of three sections (1) an electrical section containing a microprocessors as well as an abundance of downhole memory; (2) the data measurement section housing conventional pressure & temperature sensors; & (3) a battery section. The current process variables from the PATÒ unit, which are downhole pressure & temperature measurements, include part of an array of data set variables that the VFD will monitor & react to accordingly. The main signal process link will be a customized proportional integral derivative (PID) control loop that is based on the measured bottom hole pressure (BHP) in the wellbore. This BHP signal will input a speed derivative to the VFD for the electrically driven wellhead drive, based on PanCanadian’s preset desired bottom hole pumping pressure. This concept of the well being automatically on pump & maintaining daily oil production is analogous to the "cruise control" concept that optimally runs an automobile. It should be noted that at the same time that the VFD is maintaining this optimum production rate, it is simultaneously sensitive to other array inputs of "maximum &/or minimum flow line pressure", "maximum sucker rod torque & current", & maximum &/or minimum drive speeds". The full explanation of the control logic is not included in the scope of this paper.
In June of 1995, the prototype PATÒ tool was installed in the PanCanadian 8A-19 well where it was landed inside the production tubing below a perforated tubing pup joint, which is the downhole production pump intake. The specific configuration of the PATÒ installation within the bottom hole assembly (BHA) allows for an unrestricted flow path for the reservoir fluids to enter the production pump above the PATÒ system. The PATÒ system was pre-programmed to transmit pressure & temperature measurement updates every eight (8) hours. Each time the tool transmits, it sends 5-10 pressure & temperature measurements over a ten minute time span. These pressure & temperature readings are then relayed to the surface via the specially modulated electromagnetic signal where they are electronically verified for accuracy & authenticity just prior to the data being recreated at the surface by proprietary signal processing software. Each update consists of a multiple bit data package containing the pressure & temperature values of the producing horizon. Additionally, the wellhead vitals of speed, torque, surface pressure, & BHP are relayed by surface telemetry through a direct sequencing radio system to a host computer at the North Bodo field office. Presently all vital artificial lift equipment (ALE) operating characteristics are monitored. The speed of the rotary top drive currently controlled by the Wermac VFD through a speed signal that the operator inputs into the computer at the North Bodo field office. Any monitored values that are out of tolerance are instantaneously alarmed & result in immediate electronic notification to the field operator on duty, through an alpha-numeric pager. This has economically facilitated PanCanadian’s vision to have well operators go to the wells only when necessary as opposed to the tradition of having the operator visit the each well at least once a day. With the planned implementation of the PID loop in February 1996, the VFD drive will be able to automatically increase or decrease the speed of the bottom hole production pump based upon the BHP measurements & other dynamic variables that are specific to the personnel, environmental, & mechanical safety criteria.
FIELD RESULTS
The bottom hole wireless pressure monitoring system is being successfully run in PanCanadian’s
8A-19-38=01 W4m oil well at their North Bodo field. On September 5, 1995, the 8A-19 well was serviced to install a new prototype PATÒ gauge & the PCP speed was maintained at 300 RPM with 395 psi (2,723 kPa) bottom hole pressure until October 10, while producing 345 BPD (55 m3/D). At that point, the PCP speed was then increased to 370 RPM until November 10, resulting in an increased production rate of 616 BPD (98 m3/D) with 388 psi (2,675 kPa) bottom hole pressure. From November 10 to 21, the well had been slowed down to 50 RPM due to a turndown in the main pipeline system. After pipeline repairs were completed, the well was sped up to 400 RPM, resulting in a producing rate of 535 BPD (85 m3/D) with 397 psi (2,736 kPa) bottom hole pressure. Since the PCP was now obviously operating at its maximum allowable pump discharge pressure without the expected increase in fluid production, the well was serviced on December 9 to install a bottom hole production pump that was capable of producing 1,400 BPD (225 m3/D) at 1800 psi (12,410 kPa) pump discharge pressure. As of January 6, 1996, the pump speed has been steadily increased. The bottom hole production pump speed & torque are 325 RPM & 37.5 amps respectively. The bottom hole producing pressure has been reduced to 361 psi (2,482 kPa) & the well is currently producing 692 BPD (110 m3/D). Through better control of the pumping parameters, many well issues can be taken care of as a maintenance issue before they turn into catastrophic failures. The application of this technology has enabled PanCanadian to achieve production rates that begin to approach the reservoir’s capacity in a more progressively productive manner.
CONCLUSIONS
Recent improvements in wireless electromagnetic telemetry systems have created business opportunities for which routine oilfield operations can become more profitable & production can be automatically maintained or increased by measuring bottom hole production values & transmitting that data to the surface to use on a real time basis. This publication describes the unique application in which PanCanadian Petroleum Limited has been able to increase its oil production & decrease the lifting costs at the 8A-19 well in the North Bodo field through the application of real time bottom hole pressure information through wireless electromagnetic telemetry.
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