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PDL/CDi History Version 1.0: PDL1 to PDL4 Datalogger
PDL/CDi History Version 1.0: PDL5
PDL/CDi History Version 1.0: CDi2/PDL6, the PDL that Wasn't
PDL/CDi History Version 1.0:
PDL/CDi History Version 1.0: Pembina Lake Erie Datalogger
PDL/CDi History Version 1.0: P5 Switcher
PDL/CDi History Version 1.0: P7 Switcher
PDL/CDi History Version 2.0

PDL/CDi History Version 1.0: ZDL5 Switcher
PDL/CDi History Version 1.0: CDi3.FTe Switcher
PDL/CDi History Version 1.0: CDi3.RMe Switcher
PDL/CDi History Version 1.0: Remote 900 MHz RF Link
PDL/CDi History Version 1.0: CDi99 Libby Flow Meter
PDL/CDi History: Dan Sparkes Production Paper from August 2000
The reader needs to pay attention to the fact the Danster is describing intermitters and plunger lifts we had in the 90s here. The Danster's passion for the gadgetry and the work was immediately obvious as soon as he showed up in early 2000. He would still be here if his passion for Scotland was just a bit weaker. Aberdeen and the North Sea won, lake Erie lost, but in the short time he was here he did manage to make some friends... and write this paper which I consider the PDL/CDi bible. Adam 2017/01/20
Production Technology for Lake Erie Gas
How to Gain Control of the Lake and Improve the Bottom Line

Prepared by:

Dan Sparkes

Ontario Operations Co-op Student
Talisman Energy/University of Alberta

August 17, 2000

Original pdf here:

For many years, the former owners of the Lake Erie gas properties had been trying to efficiently gather quality data on gas flows and pressure throughout the gathering systems. These efforts have resulted in such overblown projects as full size chart recorders being sunk to the bottom of the lake contained in massive steel aquariums and primitive electronic recording devices powered by multiple submerged truck batteries and connected with an intricate mess of hoses and wiring. Through the evolution of better electronics and custom design work for lake Erie, a new data logger and controller has emerged. This data logger also enables the use of new technologies to control water in the system, arguably the main enemy of production in lake Erie. New electronic technology can also enable remote data gathering and valve operation on a continuous basis. These features aid in intelligent decision making, increasing production, decreasing downtime and reducing costs.
Lake Erie gas production is plagued by problems of water in the wellbores and garnering system, high operating costs, inefficient gathering systems and other problems. Solutions to these problems are proposed in this document that involve active (mechanical) production technology, better offshore automation, and automated data gathering. The key to the success of these technologies depends on making an investment in a network SCADA system that will utilize pipeline based communication between specialized data loggers that nave been designed specifically for lake Erie gas production and are currently in "stand alone" use. Networking in the lake is extremely low cost due to the local private electronics developer and has both immediate and longer term benefits in increased production, reduced costs and drilling failures, and reduction of substantial risk.
1. The SingleChips PDL
1.1 Investment already Made
Development work by Adam Giannopoulos, creator of the lake Erie production data logger (PDL), represents 7 years and close to $1 million in installations. This work has produced a unique, simple, low power, product of great value to Talisman.

The modern lake Erie PDL mounts directly on the "Camco" orifice plate holder and requires no further connections except for one cable, used to communicate with a computer and charge the battery simultaneously. A simple four wire, quick connect, cable is normally run to surface on an ordinary wooden or PVC buoy so that data can be downloaded, the battery charged, and PDL functions changed without the need for a diver.

The modern PDL is capable of receiving additional input channels and controlling equipment such as plunger lifts, intermitters, and emergency shut down valves (ESDs). PDLs have already been used successfully in these applications.

1.2 Uniqueness of Lake Erie
Lake Erie operations are unique not only in that they are offshore, but they are different from other offshore operations with a land-based style exposed gathering system and equipment. There are several barriers to system Control and Data Acquisition (SCADA) systems in the lake.
1.2.1 Water Environment
Water proofing and pressure proofing are the most obvious concern for electrical devices in the lake. This problem is actually quite minor and has been successfully overcome by selecting durable absolute pressure transducers and developing a simple, compact PDL that is well encased.
1.2.2 Minimizing Diving
Due to the high cost of diving and inability to dive in winter, diving to retrieve data and maintain excess equipment must be kept to a minimum. This means that PDLs must be completely self-contained with the ability to be reprogrammed, charged, and downloaded from a buoy on surface. The Singlechips PDL has already met this challenge successfully through a design that utilizes a simple and inexpensive cable connection that enables simultaneous battery charging and communications.
1.2.3 Power Consumption
In order operate for an extended period of time without costly boat visits for charging, the PDL must consume only an extremely small amount of power. This is one of the most unique and important features of the SingleChips PDL, which can operate for over a year (length depends on recording interval - see section 1.3.4) on a battery one tenth Fig 1.1: PVC Wellhead Buoythe size of a truck battery. This low power consumption is in contrast to other electronics such as the Multi brand plungerlift controller, which would exhaust an equivalent power supply in a matter of hours. Networking combined with solar panels would even eliminate the need for a boat to visit the sites periodically.

An option exists such that a solar panel could he installed on the existing PVC buoy above each PDL location. This would altogether eliminate the need for charging from a boat and would pay quickly since diveboats downloading PDLs do not stay on location long enough to properly charge the battery.

1.2.4 Communications
The next logical step in PDL development is to enable communications between the dataloggers and create a windows based network that will enable data acquisition and control administered from the respective compressor station, the Port Colborne office, or even Calgary. This reality is only several months of development time away when a commitment to purchase several loggers is made. Networking represents the opportunity to revolutionize operations in the lake as it is the key to successfully gathering data and automating equipment.

It is essentially impossible to transmit a radio signal from lake bottom to shore and vice versa. Buoy mounted antennas would be an option, however this would still consume a sizeable amount of power and communication would be lost whenever the buoy rope snapped or the buoy became submerged (both of which happen often, particularly in winter).

The solution to the communication problem has not yet been implemented, but will rely on custom technology once again. Since the entire gathering system is composed of steel pipe (with the exception of some hoses and clamps) this pipe, together with the water, can be used to carry an electric current in the same fashion that current is applied to pipelines for cathodic protection. If alternating current is used, the frequency can be modulated (FM) and a signal can therefore be transmitted.

In a test conducted this summer, a low-frequency signal was applied to the pipeline and received offshore, confirming that communication through this means is possible.

1.3 Technical Description
The basic Lake Erie data logger records pressure on either side of an orifice plate, along with water temperature. Readings are taken at whatever interval is specified by the user and stored until a boat downloads them. The PDL is designed so that two pressure transducers attach directly to the pressure taps on a Camco orifice holder. The circuit board is contained within a 3/4" aluminum box, and sealed with a potting compound for extra water proofing. After attaching the pressure transducers, the box is clamped to the pipe. A quick-connect marine cable can be run to surface on a buoy for downloading and battery charging without the need for a diver.
1.3.1 Input Channels
The Singlechips PDL is built with 8 programmable input channels so that it can be customized for new applications beyond pressure, temperature, flow recording and valve control. These may include extra pressure sensors or inputs such as plunger arrival sensors for plunger lift installations.
1.3.2 Pressure Transducers
In standard orifice flow measurement of gas, a differential pressure transducer is utilized to accurately measure small differentials across the orifice plate. Unfortunately there are no commercially available differential pressure transducers that are durable enough to withstand the pressure surges and harsh conditions experienced in the lake. For this reason, the Singlechips PDL has unique features to match the performance of two different static pressure transducers. The individual transducers all behave slightly different as their temperature changes. To accommodate for this, transducers are matched at different temperatures and paired up accordingly. There is also a differential channel in the PDL in addition to the two static channels which has an adjustment for the deviation of the individual pressure transducers with temperature.
1.3.3 Data Storage
The Singlechips PDL has 1MB (1024kB) of data storage capacity. The "wake-up" and recording interval can be set anywhere from minutes to days. Recording 4 channels every 30 minutes for 1 month consumes 20kB of memory. Therefore, under these conditions, there is enough memory for 51 months of data storage between downloads. Naturally, the length of time between necessary downloads is directly proportional to the length of the interval between recordings and inversely proportional to the number of channels being recorded.
1.3.4 Intermitter, Plunger Lift, ESD
The PDL is capable of controlling two solenoid valves to control gas supply for opening and closing pneumatic actuated valves. These valves have already been used for plunger lift operation and pipeline intermitter operation. ESD is already built into the system software as well. Valves can be set-up for either fail-open (plungerlift/intermitter) or fail-closed (ESD) operation.
1.3.5 Power Consumption
As mentioned above, likely the most important feature of the Singlechips PDL is low power consumption. The system only consumes power during the pre-set recording interval, the rest of the time it "sleeps", using electrical power to run only the clock chip. Running at the 30 minute recording interval mentioned above, the 6V, 12A-hour lead-acid battery will last for two years without recharge. Current limiting hardware to prevent gas build up in the lead-acid battery automatically controls recharging. Charging begins as soon as the communication cable is connected for download or reprogramming. Low power consumption means that the PDL battery could stay charged continuously if only a small solar panel was installed on the existing buoy. The low cost for the panel of about $20 would make it disposable in the case of buoys that are destroyed by ships or ice. Provided a reasonable recording interval is selected, the solar panel would only need to get light for several hours per day for only a portion of the year to maintain a charged battery indefinitely.
1.4 Alternatives to SingleChips Electronics
In 1988, two plunger lifts were installed using Multi controllers adapted for underwater use. Though they did function, they were plagued by control problems stemming from high power requirements, improper motor valve operation due to ambient hydrostatic pressure and other problems. In the early 1990s, after the acquisition of Telesis Oil & Gas by Pembina, several years were spent experimenting with adaptation of commercially available dataloggers. As had Anchutz before, Pembina spent hundreds of thousands of dollars in bulky, complex equipment in an attempt to measure flow from points offshore. Little success was had with this equipment as it was expensive, awkward, and required a large power supply. One such venture involved a very large buoy covered with solar panels and radio transmission equipment for a project cost rumored to be in the $100,000s.

In short, very little existing technology is available that is well suited to this lake application by meeting the requirements of low power consumption, in particular. For example, Multi brand plunger lift controllers were tested and found to consume far more power than could reasonably be supplied to the Lake floor through batteries or a small solar panel. The circuitry also cost approximately 8 times more than the circuitry employed in the Singlechips data logger.

Other dataloggers and controllers commercially available are very costly and are not set up with communications protocols that would be suitable for the lake. Radio communications would require high power and would not be suitable. No commercially available system is currently set up to communicate along the pipelines with low power and customization of commercial products would be very costly. Since no "canned" packages are available, only a major discovery could warrant the development expenditure to develop and repackage technology for this application.

2. Economics of Networking
2.1 Direct Savings
2.1.1 No boat trips to adjust plunger lifts
Though plunger lifts are very effective and reliable systems, they do require frequent attention to check their performance and change their time / pressure based switching settings. Several visits are necessary immediately after installation and periodic checks are necessary as are for any mechanical installation. Offshore networking is crucial to the success of a plunger lift campaign on numerous wells. With boat time costing well in excess of $100 per hour, the only way to monitor and optimize multiple plunger lift wells is with a network that will allow data gathering and programming from shore.
2.1.2 Reduced down time 80% or better
As can be imagined, trying to find lost production in gathering systems that contain hundreds of kilometers of pipeline and nearly as many wells can be quite time consuming and costly. This is especially true when a diver must be hired every time a line pressure is measured or a valve is checked in a new location. This problem is compounded severely in winter when ice can cover most of the lake.

Large production losses in winter can be cause for implementing the emergency response plan. It is usually necessary to fly over the lake to look for severe leaks or catastrophic failures. S large ice breaking boat may then be needed to get divers to locations and divers must go down in dangerous ice conditions to locate the source of the problem and correct it. Though networking will not enable remote repairs, it can eliminate the need to spend days to weeks searching for the source of the lost production in dangerous conditions and with a looming emergency by pinpointing the pressure or flow anomaly immediately.

Remotely actuated valves in important locations would enable shutting in of sections of the system in the case of a catastrophic failure and need to invoke emergency action. If ice conditions did not permit divers to reach the source of the venting gas for days or weeks, as has happened before, remotely actuated valves could turn off the supply of gas until the failed pipe could be serviced by divers.

Estimates by Port Colborne staff indicate that savings in quick location of lost production could easily amount to between $50,000 and $100,000. Dive costs from November to February totaled over $210,000 in 1997 and over $130,000 in 1998. Costs and lost production due to the Alma line blockage in winter 1999-2000 totaled over $500,000 (though networked PDLs would have been little help in this particular situation).

2.2 Other Key Benefits
2.2.1 ESD
The lake currently contains both isolated automatic and hydraulic (controlled from shore) emergency shut down (ESD) valves. The hydraulic lines were not only expensive to install many miles out into the lake, but have ruptured and leaked into the lake and have been snagged numerous times by fish trawling anchors. The isolated mechanical ESDs have required diving to pin open and have been somewhat problematic in the past. They must also have a diver visit to reset them, of course. The Singlechips PDL is fully capable of ESD operation with the actuated valve powered by line pressure or a charged gas bottle.
2.2.2 Production information to evaluate pools for further drilling, Workovers
Some consideration should be given to the benefit of good production data to exploration and development. We have clearly seen the importance of production bubble mapping in exploration onshore. With real production and pressure data, pools can be better delineated and exploration can be directed towards more prolific areas.

Of course it is hard to put a dollar value on missed drilling opportunities due to poor production data, but it is something to consider given the impact that success or failure of any one well can have.

2.2.3 Identification of optimization potential
As discussed the section 3, the network can provide not only the means, but the information necessary to optimize an estimated 25% of impact wells (wells that can make a difference at the sales meter) making for substantial gains in productivity. For example, the most difficult part of making an effective plunger lift system is choosing the candidate well when all that is often available is an annual flow rate with no water volume, and sometimes no meaningful annular pressure (if well has packer for example).

It is known that there are many wells and sections of pipe that have restricted production due to water, improper sizing, solids restrictions and blockages, leaks, hydrate problems, and more. Locating these problems is virtually impossible without more data than annual flows and inspections. With better monitoring, bottlenecks and outright blockages can be located and corrective action can be taken, be it pipe replacements and diameter changes, plunger lifts, intermitters, or better pigging practices.

2.2.4 Regain Control of the Lake
Though many efforts are made to increase communication between Talisman staff and "permanent" contractors (divers), there still exists a large gap that is hard to fill with meetings, dive boat visits, and phone calls. To solve problems more effectively offshore, technical staff need to be properly tuned in to field issues (a good reason to have field engineers). Divers also need proper understanding of the reasoning behind dictated tasks so that they can provide feedback and feel involved to encourage constructive ideas and practices. Better understanding of the field conditions by the plant operators helps them to deal with surges and losses of production, handling of liquids and locating lost production.

Remote monitoring will enable all Talisman staff to get a much better picture of flow conditions on the lake and should help to reduce doubt and discrepancy with respect to pipeline conditions and the benefits of maintenance work such as Well servicing, pigging, and leak control.

2.2.5 Proper Allocation
Better flow measurement will enable proper allocation to deal with different working interests of the partners. For example: if a new well is tied in on the line running to Port Alma, it will back out all wells to some extent. This includes a well owned 100% by Anchutz. If the backout on the Anchutz well is not correctly accounted for, it could artificially reduce Talisman net production and give free gas to Anchutz.
2.2.6 Reserves and Production Forecasting
In fields such as Port Stanley, several distinct areas are commingled into group lines. When compression was installed (Timesaver II offshore compressor), it was determined through group metering that up to 50% more of the increased production came from one of the two major area divisions. This was largely due to pipeline diameter constraints. The knowledge of where gas is coming from will enable reserves to be booked more accurately and production to be better forecasted to evaluate major and long-term projects such as offshore compression and pipeline diameter changes. Both of these projects have been undertaken in the Port Stanley field without extra knowledge from data loggers; as a result, many questions have been raised as to the correct sizing of the pipeline and the effectiveness of the compression at all wellheads.
2.3 Costs
Each networkable data logger will cost approximately $6000, however, since Talisman already owns about 40 pressure transducers, the cost of the next 20 new PDLs will be reduced to $4000. Other equipment is also owned that can be taken advantage of in this way.

Installation of the onshore portion of the network will be nearly insignificant, likely at a total cost of less than $1000. As the network could be primarily installed during annual required well visits, diving costs to install the loggers in the Morpeth field (location selected for first network) should be minimal but could still amount to a several thousand dollars.

Installation of group metering points is the most costly part of data logger installation. This is because diving is required to rework piping to direct flow through an orifice plate. Many group-metering points have already been installed throughout the lake and the cost to install networked loggers on them should be minimal. No group metering points are yet available in the Morpeth field, but by placing dataloggers on approximately 7 big producing wells, production losses could be located quickly and gathering system pressure distribution could be effectively modeled.

Networking of dataloggers is not likely to reduce diving overall, as there will be more equipment in the lake and, realistically, some units will leak or break down otherwise and require maintenance from a diver. Redundant dive time such as for pressure & flow data should be cut however, as will production down time. In particular, diving in search of lost production, gathering production and pressure data for engineering purposes, and the majority of winter diving, boating, and flying should be reduced drastically. Many dollars are spent each year searching for lost production. Each time this happens in poor winter conditions, it must be regarded as an emergency situation.

Annual boat and diving costs run around $1.5M. Of this, over $0.5M is spent on initial well visits for the year. This number cannot be reduced unless some wells are abandoned or governmental approval can be granted for not visiting every well annually. This approval may be realistic if real-time data can be obtained from the wells to show that no problems are underway. Possibly a surface inspection would be all that is necessary to check the buoy and look for bubbles. Group meter volumes can be prorated by inline orifice tests performed on the wells every two years, as is acceptable accounting practice and built in to Field Data Capture (FDC) software.

3. Production Optimization
3.1 Wellbore (Plunger Lift)
It is a known fact that many of the wells in the lake are loaded up with liquids and could produce at many times their current gas rates if unloaded with a plunger lift or adjusted through other changes in wellbore configuration (tubing size, etc.). Identifying these wells requires several dives to service the well (lift liquids by venting to atmosphere) and to measure flow and pressures afterward. All this extra diving and work makes looking for problem wells uneconomical and leads to producing many liquid loaded wells in the neighborhood of 10mcf/d rather than 200mcf/d.

It is thought that a large fraction of the wells in the lake could be optimized to increase production significantly. In fact, a quick review of the wells in the Morpeth system to look for plunger lift candidates resulted in just under 50% of the wells identified as having probable optimization potential through choke changes and/or plunger lift installations.

A testament to the fact that tubing water loading is a significant problem is that each year, when active well servicing used to begin, steady declines in production from the lake showed a slowing to reversing effect. Well services were not stopped due to lack of effect on production, but rather due to lack of economic success. Unloading a well can have a dramatic effect on gas rates, however that well will load up again in a time from days to hours or even minutes. Servicing 2-5 times annually at roughly $1k per service is not an economical means of keeping wellbores free of liquids. Plunger lifts on the other hand, at $10-15k per installation, can have a lasting impact on production as they will continuously de-water the wellbores, effectively servicing the well multiple times per day.

Again, it is difficult to put a dollar value on "missed opportunity due to lack of information and control", but with nearly 500 producing wells under the lake and a large fraction of those estimated to benefit from some kind of work, one can see that the potential is likely enormous.
Refer to Appendix A: Plunger Lift Case Study

3.2 Gathering System (Intermitter)
Pigging of the main lines, particularly in the Port Maitland system has proved that water loading, combined with salt blockages, in the pipelines can hold back several hundred thousand cubic feet of daily gas production. Due to diving expense it is not practical to pig lines frequently and they are currently pigged on a schedule primarily based on maintenance needs to remove solids buildups before they become too great.

Sweet gathering systems are nearly drawn down to their discharge limit, with only 30psig suction pressure at the Port Maitland Compressor. Despite this, wellbores at the back of the system are forced to produce against pressures over 100psig. Though this is not particularly high, it can be lowered through clearing of the pipeline and increase production at the station.

One way to keep the gathering system clear and also to keep the pressure low is to run an intermitter. The intermitter alternately switches different arms of the gathering system from production to shut in. This reduces the pressure in the gathering system and increases the velocity thereby more effectively sweeping the water into the station and producing the wells against lower backpressure.

A major intermitter project was installed on the Trustco line immediately after the Talisman purchase of Pembina. The project was considered a failure due to unsustainable gas flow in some locations. Poor location selection and valve timing were also problems, with boat visits to each site required to set new cycle times and collect data. The recorded flows did show, however, that the intermitter principal worked in several locations (that total production with downtime was greater than total production without the intermitter).

A project similar to the above, enhanced by networked PDLs would enable real-time switching to optimize the intermitter system and ensure no accidental or extended time shut-ins. Networked PDLs would also enable better location selection for the intermitter valves by providing better production data.

Intermitters are less likely to show great improvement in the lake than plunger lifts, but could still be economic projects in the massive gathering systems once network technology is available.

3.3 Passive Production Optimization
It has been observed time and time again through the tieing-in of new wells, stimulations, and even the installation of offshore compression that pipeline restrictions are preventing production from many areas from reaching the plant. Poorly sized pipelines need to be changed in some cases, and new pipeline installations have to be properly sized to manage declining or expanding production from different areas of the lake.

In order to correctly locate the improperly sized lines and select correct sizes to replace them with, pipeline models must be used due to the complexity of the looped gathering systems. These models require flow and pressure data, especially data that encompasses different flow rates in time that can be used to "tune" the models.

The Timesaver II offshore compressor has particularly shown the impact that pipeline restriction can have, as it could be seen from dataloggers in the Port Stanley system that one of the major legs of the system accounted for much more of the production gain than the other. The reduced pressure was transmitted along the less restricted line more effectively than the undersized line. Since this line had to be replaced due to leaks anyway, it was upsized to accommodate lower pressure gas flow more effectively.

There are also passive changes that can be made in the wellbores, facilitated by better flow and pressure data. Wellbores can of course be modeled in the same fashion that the pipelines can and chokes and tubing can be sized more effectively with less guesswork.

Appendix A: Plunger Lift Case Study 222-V-1
A plunger lift was installed this summer on well 222-V-1 in the Morpeth field.
This well was drilled in 1977 but was left suspended until it was worked over and stimulated in 1997. The well has produced steadily since the workover, at a rate between 10 and 20Mcf/d. Virgin reservoir pressure was measured at 722psi and the well is still capable of building 700psig on the annulus at surface. Through servicing the well, it has been shown that when the wellbore is unloaded of water, it can deliver gas at rates between 200 and 350Mcf/d.

This well is a perfect example of a gas well that is undepleted and has formation deliverability but cannot produce due to the hydrostatic head of the water that fills the tubing. When the choke was pulled to install the plunger lift, a fluid level was encountered in the tubing about 300m above the perforations.

Logged data (see Fig. A1) from the plunger lift indicates that this well can build to over 100psi to over 600psig annulus pressure in under 10 minutes. After plunger unloading the tubing is once again loaded with fluid by the end of 30 minutes. This indicates the frivolousness of well servicing ($500-$800 each) to increase production.

It can also be seen from the logged data that the plunger is able to partially unload the well without the intermitter valve functioning, although it is less effective. This is indicated by the horizontal line on the annulus pressure in between shut in and unloading periods. It can he seen when the plunger got stuck that the annulus pressure suddenly climbed, indicating that the plunger had been partially unloading the well in between intermitter valve cycles (See Fig A2).

It can also he seen from the data that the well was able to unload through use of only the intermitter valve when the plunger was out of the well temporarily, though again not nearly as effectively. This unloading came to an end when the plant compressor was down for several hours and the well loaded up more extensively (See Fig A3).

Logged data from the plunger lift indicates that a net increment of at least 150Mcf/d should be seen at the plant, though unfortunately this amount is within routine fluctuation and fluctuations due to maintenance and construction in plant production and the sales increment could not be positively confirmed.

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