COALSEAM GAS PROMPTS MAJOR EXPANSION OF NEW MEXICO SYSTEM

Jerry Gollnick
Williams Field Services
Salt Lake City

Construction gets under way this fall to expand the 109-mile Manzanares coalseam gas-gathering system in the San Juan basin (SJB) of New Mexico.

This year's work will raise capacity to 575 MMcfd from 360 MMcfd in November 1990 when Williams Field Services (WFS) initially started up the system. By the end of 1993, the system will be able to handle 680 MMcfd.

Construction in 1992 will include installation of a supervisory control and data acquisition (scada) system, 5 miles of 10-in. line, 9 miles of 12-in. line, and 33,000 bhp in 11 new central delivery points (CDPs) along with dehydration and metering.

Additionally, 11.4 miles of 30-in. line will replace the same length of 20-in. line, and 11 miles of 20-in. will be replaced with 2 miles of 30-in. and 9 miles of 24-in. line.

Expansion to 680 MMcfd by the end of 1993 will involve an additional 15,700 bhp plus dehydration and measurement capacity for another 105 MMcfd along with 4.6 miles of 30-in. and 5.9 miles of 10-in., all looping pipeline segments.

At its commissioning in late 1990, the Manzanares system exemplified how the natural gas industry can bring significant new supplies into the market quickly and efficiently.

Development of the San Juan basin coalseam resource will be explained from the reservoir through the gathering pipelines and into the interstate and intrastate pipeline hub created for this extraordinary new supply source.

MODULAR DESIGN

The original scope for WFS' Manzanares project was to collect up to 360 MMcfd of coalseam gas at 100 psig from central points throughout the producing area, to remove the CO2 to El Paso Natural Gas Co.'s tariff level of 2%, and to deliver the residue gas to El Paso at 894 psig at the CDPs of collection on the Manzanares system.

This scope was based upon negotiated contracts for 122 MMcfd and additional potential contract volumes of 238 MMcfd.

The initial design of the Manzanares system employed a modular equipment design concept for flexibility and effectiveness of the overall system with a 22-in. backbone trunkline.

The 22-in. line was selected because, at the time, any pipeline 24-in. in diameter or larger required congressional notice, and contract timing was such that WFS' construction schedule could not afford the notice period.

Construction began in August of 1990 and first gas flow started in November at 40 MMcfd from the Horse Canyon CDP (Fig. 1).

The design for the 360 MMcfd initial facilities included the following:

Six CDPs for the volumes under contract, 122 MMcfd
Four CDPs for volumes being negotiated, 163 MMcfd
One CDP with a refrigeration process plant to move 75 MMcfd of conventional gas into the system
104 miles of 6 to 22-in. diameter new pipeline
11 miles of 20-in. existing pipeline
14,500 hp of existing Solar Mars booster compression modular packages
16,000 hp of leased compression in 1,000-hp modular packages
25,000 hp of purchased compression in 1,000-hp modular packages.

The design incorporated a mixture of purchased and leased equipment to provide for an anticipated production decline based upon the volume then under contract and to provide a means of project risk mitigation should reservoirs not perform as expected.

The scope and design for the Manzanares system has been under constant revision to upgrade it for additional volumes contracted. This year WFS is modifying the system to collect 575 MMcfd and, at the same time, designing and budgeting to handle 680 MMcfd in 1993.

The 575-MMcfd design modifications include the following:

11 additional CDPs for contracted volumes, 575 MMcfd
28,000 hp additional field compression in 1,000-hp modular packages
5,000 hp additional booster compression in 1,000-hp modular packages
Replacing 11 miles of 22-in. trunkline with 30-in. pipe and selling the 22-in. in place
Replacing 11 miles of 20-in. trunkline with 2 miles of 30 in. and 9 miles of 24-in. pipeline through an exchange with WFS' conventional system.

As mentioned, WFS plans to modify the system additionally in 1993 for 680 MMcfd of throughput and possibly for 800 MMcfd in 1994.

SUPPLY AREA

The San Juan basin occupies the portion of southwestern Colorado and northwestern New Mexico defined by the Fruitland formation surface outcrops (Fig. 1).

In Colorado, the SJB includes portions of La Plata and Archuleta counties; in New Mexico, parts of Rio Arriba, San Juan, Sandoval, and McKinley counties. The SJB is the largest coal-bearing area in New Mexico, occupying about 7,500 square miles.

The Continental Divide trends north to south along the east side of the SJB. The San Juan River drainage lies on the west side of the divide and the Rio Grande drainage on the east.

Land surface elevations within the basin range from 5,100 ft on the west where the San Juan River leaves the basin to more than 8,000 ft in the northern portion. The land surface is characterized by broad plateaus and mesas cut by steep-sided canyons.

Gas was produced with the first commercial well in the Dakota sandstone in 1921 and in the Mesaverde and Picture Cliffs formations in 1927. These three formations have accounted for the majority of gas produced from the SJB.

Coalseam gas from the Fruitland formation is now becoming a major producing horizon.

WFS, however, expects to see SJB coalseam-gas production reach 1.2 bcf in 1993 and possibly 1.8 bcf by 1995.

MARKETS

Gas produced into the Manzanares system can be directly marketed into four major market areas through the Blanco hub created to provide market flexibility for San Juan coalseam gas.

At the outlet of WFS' Milagro treating plant, producers may choose to go into four pipelines--Northwest Pipeline Corp. (NWPL), Transwestern Pipeline Co., El Paso Natural Gas Co. (EPNG), or Gas Co. of New Mexico--for no additional fee.

There is no rate between the gathering and treating company and the pipeline which the producer wants to serve. This condition adds value to the producer and facilitates development of the producing assets.

Manzanares coalseam gas serves four market areas:

The California market is served directly by EPNG and Transwestern; each of these pipelines is served directly through the Blanco hub by the Manzanares system.
The Pacific Northwest market area--Idaho, Washington, and Oregon--is served by NWPL through the Blanco hub.
The east of California market--Arizona, New Mexico, and West Texas--is served by both EPNG and Transwestern.
The New Mexico market is served by Gas Co. of New Mexico and receives gas from Manzanares through the Blanco hub.

Transmission take-away capacity from the Blanco hub is 2,260 MMcfd (Table 1).

A potential direct market currently being developed by EPNG is Mexico where plans exist to convert electric generation plants to natural gas.

GEOLOGY

The San Juan basin is asymmetric and roughly circular in shape except for the north-trending eastern boundary. The axis of the basin trends from the northwest to the southeast.

The area of the basin as mentioned earlier is approximately 7,500 square miles with its boundary identified by the outcrop of the Fruitland formation except for the eastern side where the Fruitland has been truncated.

The Fruitland formation was deposited during the final regression of the late Cretaceous epeiric seaway. Because of the nature of the depositional environment, Fruitland deposition cannot be described without a description of the deposition of the Pictured Cliffs formation as well.

The Pictured Cliffs formation is a marine sand deposited as a beach by the Cretaceous sea. The Fruitland is a fluvial formation deposited in a deltaic environment discharging into the Cretaceous sea.

As the sea level transgressed and regressed, the Fruitland and Pictured Cliffs formations were deposited as an intertonguing sequence of marine sands and shales with fluvial coals, sands, and shales. The Fruitland was deposited landward from and simultaneously with the Pictured Cliffs.

There were several small cycles of transgression and regression during the general regression of the Cretaceous sea. These small cycles explain the varied net thicknesses of the coal beds and marine sands which range in thickness from stringers up to 80 ft.

It is difficult to correlate the coals from one well to the next because of the deltaic nature of deposition. A combination of streams, coal-swamps, clastic lakes and bar sands all migrating laterally and vertically result in coals not being deposited or being deposited and later eroded away.

There are really no continuous coal beds. The coal zones can be replaced by a bar sand in wells no more than 100 ft apart.

Of the several ranks of coalification--peats, lignite, subituminous, bituminous, and anthracide--the Fruitland coals are subituminous to bituminous.

Typically, coalseam-gas wells initially produce large volumes of water. As the formation is dewatered, gas volumes will increase as water volumes decrease.

During the dewatering, the coal well can have an inverse production decline. Dewatering of coal wells can take months to years, and if production is curtailed, the process will have to begin again.

MANZANARES DESIGN

Currently, coalseam gas is gathered by the producer-operator from the wellhead to 13 Manzanares CDPs where the gas is measured for custody transfer, compressed, dehydrated, and check measured before entering a high-pressure collection system which carries the gas to the Milagro plant for CO, removal.

Gas leaving the Milagro plant can enter either the Blanco hub or El Paso Natural Gas Co.'s San Juan main line for transport to market areas both west and east of the producing area.

CDPs are strategically located throughout the most productive trend of the Fruitland formation. These CDPs range in size from 1 acre, accommodating 6 to 10 MMcfd, to 20 acres handling 95 MMcfd.

WFS has made the most use possible of modular grouping of facilities in the CDPs, which allows maximum flexibility and availability and minimum time required to increase or decrease the capacity of any CDP to match production requirements with economic objectives.

Modular custody-transfer meters are WFS' standard designs for 6 in. or 8 in. multiple, parallel meter runs. Daniel's Simplex orifice fitting is used for the 6-in. run and Daniel's Junior orifice fitting is used for the 8-in. runs.

The meter runs are covered by 7 x 9 ft insulated, heated buildings. Most CDPs have Barton chart recorders. Some meters have the three-pin chart recorder (flow measurement and temperature measurement), and some meters have two recorders, one for flow measurement and one for temperature measurement.

In addition, all CDPs have Y-Z proportional-to-flow, continuous samplers.

All CDP drivers on the project are turbocharged, BACT (best available control technology), lean-burn design, nominal 1,000 hp, natural gas-fired engines manufactured by Wakesha.

Compressors are four-throw, non-water cooled, reciprocating units of manufactured by Ariel. All accessory components are skid-mounted on a standardized skid with a standardized control package. The reduction in spare parts inventory represents a significant savings, and operator familiarity provides more savings in reduced downtime.

The modular dehydration packages designed specifically for the Manzanares system are unique, and WFS has developed four standard designs to fit the system requirements.

Two designs are for flow rates to 10 MMcfd and two are for flow rates to 12 MMcfd with one design in each category operating at 400 psig and the other at 1,100 psig. All designs include the following:

1/8 in. corrosion allowance to handle 16% CO2 in the gas stream
Extra trays and caps in the contactor, larger pumps, extra glycol-regeneration capacity, fin-tube glycol heat exchangers, and a gas-to-glycol stripper column
A glycol pump fuel-saver system which reduces pump fuel gas by 95% with a gas-recovery system delivering the fuel gas saved to the compressor fuel-gas system
Fin-tube glycol heat exchangers installed downstream of the contactor and eliminating any need to heat the gas stream before dehydration
Liquid separation on skid upstream of the contactor to minimize compressor oil and liquid fallout contamination of the glycol
Pilots, main burner, and flame arrestor modified to burn 800-900 BTU/cu ft of gas
Dehydration packages each containing a 4-in. meter run to balance the unit and provide for CDP outlet gas check measurement.

TWO DESIGN PRESSURES

WFS utilizes two MAOPs in the pipeline design: 720 psig for wellhead gathering and single stage-system lines, and 1,100 psig for the primary two-stage system lines.

A 14,500 bhp turbine booster station moves gas from the single-stage system into the two-stage system.

Virtual elimination of water from the primary gathering system controls internal pipeline corrosion from entrained CO2. To verify control, WFS uses a coupon monitoring system, analyzes liquid samples, pigs the pipelines, and can batch the pipelines with corrosion inhibitor, as necessary.

Elimination of water from the system as a means of corrosion control is superior to allowing water entry which requires constant pigging and batching of inhibitor.

The initial piping system design was 500 MMscfd at 1,000 psig minimum and 1,080 psig maximum; 22 in. OD x 0.281 in. W.T., API-5L, Grade X-65, DSAW (double submerged-arc welded) line pipe was selected for the main trunk lines. Smaller trunks and laterals 16 in. and smaller are also light-wall X-grades, but they are ERW (electric resistance welded) rather than DSAW.

All pipe was yard coated, the 22 in. with 14 mils of epoxy, and all other pipe sizes with 40 mils of extruded polyethylene (PE). The 22 in. San Juan River crossing and the Pump Canyon Road encroachment have extruded PE coating over the epoxy coating to ensure public safety, integrity of a trout fishery on the San Juan River, and longevity of the pipeline.

Pipeline facilities are designed and installed in accordance with ANSI B31.8. Once the facilities were installed, WFS tested the line with natural gas as specified in B31.8 utilizing the system compressors. This procedure eliminated the need for freeze protection, water permits, discharge permits, and hauling or pumping water. Pipeline dehydration after testing was also eliminated.

No leaks or failures were experienced, and WFS realized significant savings over hydrotesting. Public safety was ensured by hydrostatic pretesting of all river crossings, road crossings, and fabricated assemblies and by attaining test pressures only during night-time hours.

Welding was in compliance with WFS' qualified welding procedures. Additionally, all welders were tested and certified, radiographic inspection was performed in compliance with API-1104 standards of acceptability, and a minimum of 10% of all welds were X-rayed as required by B31.8 for a Class I (U.S. Department of Transportation) location.

CONSTRUCTION

Pipeline routing was dictated by the governmental agency utility corridor concept. The vast majority of lines run parallel to existing conventional gas gathering lines and roads; in most instances, multiple lines and a road.

Because of the rugged terrain and corridor requirements, multiple corridor crossings and working-side changes occurred. More than 1,000 individual line crossings were made in approximately 120 miles of construction.

Tie-ins were a major construction component rather than the typical minor component. Manufactured pipe fittings had to be utilized to accomplish drastic direction changes within the overcrowded corridor.

Right-of-way (ROW) limits granted for the project forced the working side over existing lines within the corridor. Extreme caution was required in this undesirable circumstance, and construction was slowed considerably.

Much of the line required spreading the ditch spoil over the working side to protect the existing lines during construction and reclaiming it to backfill and clean up.

Because of the nearness of existing high-pressure pipelines and the extremely restrictive ROW limits because of archaeology and terrain considerations, ripping and shooting of rock was virtually impossible.

To cope with this situation, the pipeline contractor used the largest conventional rock-wheel ditching machine in the world. In addition, the contractor used self-propelled padding machines for both padding and normal backfilling operations.

These two innovative techniques combined with brush-hogging of sagebrush resulted in excellent cleanup and minor rehabilitation expense. There was no sagebrush windrow to spread, no rock to bury or haul off, and most importantly, there were no citations for ROW limit violations.

The U.S. Bureau of Land Management created a video recording of the construction through rehabilitation phases of construction on the Manzanares project. This film is utilized as an example of "How-to-do-it" for both BLM staff and contractors prior to starting construction on new projects.

In addition to praise from the BLM, WFS was recently awarded the National Forests of New Mexico's 1991 "El Bosque" award for conservation excellence.

CDP DESIGN

CDP compression is in small blocks of nominal 1,000 hp units (background, Fig. 2). This technique lends reliability to the system: If one unit fails, a very small percentage of throughput is lost for a short time only, as the remaining units on site will make up the loss by increasing speed.

The individual CDP locations in the field provide all compression required to gather, process through the Milagro plant (Fig. 3), and deliver gas to the various pipelines at the Blanco hub.

Before construction, each CDP required an air-quality permit for exhaust emissions. Computer modeling was required for each site to predict emission levels both from the new source and existing sources within the area. A discharge plan for each site was also required.

The sites are designed to have no discharges; all equipment rests on foundations with leak containment piped to tankage. All fluids from daily operation and potential leaks or spills, including washdown and rainwater, go to tank for proper disposal.

Inlet pressure to the CDP is 100 psig. Once received, the gas is metered, filtered, compressed, and dehydrated. Because of the inlet meter upstream of compression being the custody meter, a dual-chamber, pulsation dampener is installed between metering and compression to eliminate meter error.

Two CDP designs were utilized: single-stage for 100-500 psig applications upstream of booster compression and two-stage for 100-1,100 psig applications. Design, installation, and testing comply with ANSI B31.8 for the MAOP required.

The CDP stations utilize a standardized module concept for all major components. This concept allows the addition, removal, or relocation of compressor, dehydrator, and meter skids without piping or concrete modifications (Figs. 2 and 4).

Compression, dehydration, and metering packages are sized to enhance the module concept. Single-stage compressors and dehydrators match up one-to-one at a capacity of approximately 12 MMcfd each; two-stage compressors and dehydrators match up at two compressors to one dehydrator; and meters follow the same concept.

Dehydration is by TEG utilizing skid-mounted units with on-skid metering to facilitate flow equalization between multiple units in parallel and to provide total station-outlet volume measurement. Condensed steam is collected to tank rather than to pit.

SCADA DESIGN

Scheduled for construction this month, the Manzanares scada system will provide operating and management personnel with real time data on the Manzanares gathering system.

The project includes the means of collecting information at the remote sites, communicating, organizing, storing, displaying, and reporting the information to Northwest Pipeline's gas-control center in Salt Lake City and to the Manzanares and Milagro plant offices in Bloomfield, N.M.

The system is based on, and will make maximum use of, the NWP scada system. Initially it will provide a basic level of service, but it is designed to be readily expandable to handle additional information and control and custody-transfer electronic flow measurement.

Pressures and flows into and out of each of 19 CDPs and one booster station will be measured. Pressure and gas quality will be monitored at the Milagro CO2-removal plant, and pressures and flows at the two delivery points out of the system will also be reported.

The system will monitor the status of individual compressors and be able to shut them down. The size of the CDPs range from 3 meters and 2 compressors to 7 meters and 14 compressors.

All transmitters will be supplied by Rosemount Inc.: Model 1151s will be used for differential pressures, Model 2088s for gauge pressures, and Model 444s with resistance-temperature devices (RTDs) for temperatures. Fisher Model 364 remote terminal units (RTUs) will collect the information, calculate flows, and monitor and shutdown individual compressors.

A 960 mhz radio system will communicate to the RTUs. Licenses have been obtained for two master stations which were chosen after path surveys. The master radios will be Motorolla Darcom 9000 NSWO Master F2681.

The remote radios will be Motorolla Darcom HRII F2750. Communication speed will be limited to 1200 baud to ensure accuracy under field conditions.

Communications between the master stations and Salt Lake City will be on a T-1 leased from Williams Telecommunications (WilTel). These circuits will operate at 19.2 kbps (1,000 bits/second). This T-1 will also be used for communications between the scada host and the local terminals.

Software provided by Valmet Automation Ltd., Calgary, and running on the NWP scada Vax computer, will control the system, poling each RTU at 2-min intervals and processing the data. The system will be monitored 24 hr/day by NWP gas control.

Access to all systems' data will be provided through NCD 17 in. 1024X768 Color X terminals at the Manzanares and Milagro offices and through Grid 1720 Notebook computers with modems which will be taken home at night and on weekends by operations supervisors on call.

The system is expected to improve the efficiency of WFS' Manzanares operation greatly by enabling supervisors to identify and respond to problems at the remote, unmanned CDPs quickly, and by providing control capability to respond to changes in transporter nominations.