PAPUA NEW GUINEA PIPELINE OVERCOMES ADVERSE CLIMATE, TERRAIN

James B. PriceChevron Niugini Pty. Ltd. Port Moresby, Papua New Guinea
Gerald F. LeipertWilliams Bros.-CMPS Engineers Brisbane

Construction of the Kutubu oil-export facilities in Papua New Guinea illustrates the importance of proper planning and flexible execution in completing on schedule and within budget a project through difficult and remote terrain.

In June 1992, Chevron Niugini Pty. Ltd. completed construction of and began exporting crude oil through the 264-km, 508-mm OD (164 mile, 20 in.) pipeline (OGJ, June 29, 1992, p. 44).

As part of the Kutubu petroleum development project, the pipeline transports crude oil from a central production facility (CPF) in the southern highlands to a marine terminal located in the Gulf of Papua (Fig. 1).

The terminal facilities include a manned platform (Kumul) for pressure reduction, flow control, and custody transfer and a single point mooring (SPM) buoy in 25 m of water for loading an open fleet of export tankers.

Chevron is operator of the development project in joint venture with Ampol Exploration Ltd., BHP Petroleum (PNG) Inc., BP Australia Ltd., Merlin Petroleum Co. Ltd., Oil Search Ltd., and the government of Papua New Guinea's Petroleum Resources Kutubu Pty. Ltd. (An assay of Kutubu crude oil appears on p. 73 of this issue.)

Chevron drilled the initial discovery well at Iagifu in 1986, followed by Hedinia in 1988 and Agogo and Usano in 1989. Project planning began in 1987, with field surveys and preliminary design in 1988, and final design in 1990.

Construction of the pipeline and marine terminal began in early 1991 and was completed in July of last year.

The pipeline consists of land and marine sections which are tied-in at the landfall on the Kikori River above Ogomobu.

The land section is 171 km (106 miles) long from the CPF to the landfall (Fig. 2). The marine line is 90 km (56 miles) long from landfall to Platform Kumul (Fig. 4, OGJ, Aug. 3, 1992, p. 52) plus a 3.6-km loading line from the platform to the SPM.

Chevron engaged Williams Bros.-CMPS (WB-CMPS) to conduct field surveys and design the land pipeline. An affiliate, R. J. Brown-CMPS (RJB-CMPS), designed the marine pipeline and platform. Chevron managed the construction with an integrated team whose members came from Chevron, WB-CMPS, and RJB-CMPS.

LAND LINE CONSTRUCTION

The land line was built in tropical rain forest where access and logistics were difficult with virtually no existing infrastructure. Weather conditions with up to 300 mm (12 in.) of rain per day and up to 1 m of rain per month made access more difficult due to flooding.

Extremely rugged terrain in some sections contrasted with large swamps in other areas. Numerous creeks and major river crossings posed additional obstacles.

Finally, working with local landowners who are still tribal in nature and dealing with malaria and poisonous snakes were all part of the challenge of building this line.

The area along the pipeline consists predominantly of limestone. Surface conditions range from rugged limestone karst to areas of overlying alluvial clays and large sago swamps.

Limestone pinnacles 100 m high are scattered along the pipeline route along with numerous sinkholes and underground caves. Underground rivers are prominent with most of the rainfall absorbed by the limestone and very little surface runoff. A dense growth of tropical rain forest covers the entire area.

Work on the land pipeline began with route selection in April 1988. With aerial photography, Chevron selected a possible route. Then a team of surveyors and geotechnical representatives were mobilized to the site to complete the route selection.

Helicopters were the only means of access to most of the right-of-way. Local laborers cleared helipads at 5-km intervals along the proposed route. Survey markers were established at these locations and later tied-in through a global positioning system (GPS) survey.

Route refinement continued to September 1988 when the field survey was completed. With information gathered during the field survey, personnel assessed the constructability of the line and prepared a preliminary design and cost estimate.

Final design, including development of material and construction specifications, began in 1990.

Planning proceeded in parallel with pipeline design to establish a communications system in the project area. Inmarsat telephone and HF radios were used during the field surveys. A microwave communications network was designed to provide both VHF radio communication and telephone service plus data channels for the monitoring and control system (MACS) on the pipeline.

VHF communication was available at the start of pipeline construction with telephone service established shortly thereafter.

Chevron issued invitations to bid for the pipeline construction in May 1990, and a bid walk with representatives from short-listed contractors occurred on site. These representatives could view the pipeline route from helicopters and could walk along tracks that had been cleared through some of the more difficult construction areas.

Bids arrived in August 1990, and following an extensive evaluation, Chevron awarded contract for the pipeline construction to a joint venture of Spie-Capag SA and McConnell Dowell Constructors PNG Pty. Ltd. in December 1990.

CONSTRUCTION CHALLENGES

Work commenced on site in February 1991 with the development of a main camp and marshalling yard at Kopi situated on the Kikori River near the southern terminus of the land pipeline (Fig. 1). All equipment, materials, and supplies for the project would eventually be brought by boat up the Kikori River to the marshalling yard at Kopi.

To reduce the time required for the contractor to get established, the site had previously been cleared and a base of crushed limestone laid down over geotextile. Two jetties, 60 ton and 100 ton, respectively, were constructed almost immediately. This was followed by establishment of a camp and office complex for the project's main base.

The camp eventually accommodated up to 400 people. Diesel and jet-fuel storage and distribution systems were established along with maintenance facilities and helipads.

Major workhorses for the project were 46 new Caterpillar D300 trucks. These initially functioned as dump trucks for road construction (Fig. 3) and later converted with special trailers for pipe hauling and moving fuel and containers. Earth-moving equipment dominated the equipment list.

The bulk of the employees working on the construction were from PNG with approximately half coming from the local area. An extensive training program involving both formal courses at an on site training center and on-the-job training provided the necessary qualified labor. More than 750 people completed 60,000 man-hr of training.

Initial construction activities involved staking the center line for the pipeline corridor and obtaining rights of access from landowners. Although the terms of compensation had been established when the petroleum development license was approved, obtaining the agreement of the local landowners was often challenging.

In the local culture, a show of strength is part of successful negotiating procedures. An entire village would converge on a camp site to discuss some item of concern. While typically carrying bush knifes and axes, on occasion the villagers would also be accompanied by painted-face warriors carrying bows and arrows.

Despite work stoppages during construction, all issues were resolved without violence.

CATCH-UP PLAN

The single most significant factor in successfully completing the job was establishing access along the pipeline right-of-way.

In some areas the limestone karst could be blasted and graded to provide an acceptable access track along the pipeline. For most of the length of the line, however, a road had to be constructed along the right-of-way.

Quarries were established at limestone pinnacles located along the right-of-way. Trucks then hauled material won by blasting and placed it to form a road alongside the surveyed ditch line. Limestone material was placed over a layer of geotextile to reduce the amount of material required in the soft clay and swampy sections of the road construction.

Progress was initially slow mainly because of access difficulties along the right-of-way.

Utitu Creek provided a major obstacle for construction a few kilometers north of Kopi. Pontoons ferried equipment but were unacceptable for transporting loaded trucks across the creek.

The first Bailey bridge (temporary bridge, rapidly built of interchangeable latticed steel panels) constructed across the creek was taken out of service after 1 day because of instability in the creek bank and subsequent failure of the supports on the south approach.

The repaired bridge was returned to service in July 1991. During the second day of operation, however, a D300 truck hit the side of the bridge about mid-span, resulting in the collapse of the bridge and the deaths of 2 people.

Access track and pipeline construction continued with materials and equipment being transported by boat 40 km up the Kikori River to near Kaiam.

Transportation was extremely difficult as the water level in the river changed rapidly.

Under low water conditions the depth was insufficient to allow boats up the river; under high water conditions, the strong current prevented navigation of the river. Road access between Kopi and Kaiam was achieved in October when a reconstructed bridge over the Utitu Creek became serviceable.

To allow creeks to be crossed, numerous log bridges were installed along the access track. Bailey bridges were installed at three of the larger creeks. The initial plans included installing a bridge across the Kikori River. A suitable crossing site could not be located, however, and a ferry crossing was used instead.

The rainy season extends from April to October, and heavy rains early in the season resulted in extensive flooding of about 10 km of right-of-way north of Kopi. In August, 1 m of rain caused severe flooding that forced the abandonment of all camps north of Kopi and resulted in a 2-week shutdown of construction. By the end of August 1991, the project was 2 months behind schedule.

The contractor developed a revised construction plan to bring the project back on schedule.

Key to completing the job on time was getting crews and equipment working on right-of-way preparation and access-track construction in the rugged terrain north of the Mubi River as soon as possible.

Investigation of the Kikori River indicated that while the river was almost impassable immediately north of Kaiam, the water was significantly deeper in the section from near kilometer post (KP) 88 to the Mubi River. A shallow draft landing craft was mobilized to the site to use in this section.

Once the access track reached KP 88, it was then possible to use the river to support operations from Mubi north instead of having to wait until the access track reached the Mubi River. Upon completion of the access track to the Mubi River, this landing craft would be used to ferry traffic across the Mubi River.

This plan resulted in a 2-month improvement on the schedule.

PIPE, VALVES

API 5L Grade X-65 ERW (electric-resistance welded) pipe was supplied for the project from Korea. The main line was constructed of 7.5 mm W.T. pipe with 9.5 mm W.T. pipe used for water crossings and where required for hydrotest sections with large changes in elevation.

Bare pipe was supplied to site. Chevron contracted Shaw Pipe Protection Pty. Ltd. to apply a 1-mm (39 mils) thick coating of high-density polyethylene (HDPE) to the pipe on site. A coating plant, set up at the Kopi marshalling yard, completed all coating by the end of 1991.

The entire length of the line was concrete coated because of the absence of suitable bedding and padding material in the area for the rock ditch. Shaw also applied the concrete coating at Kopi for the construction contractor.

Shaw coated the majority of the line with a 25 mm coating of concrete rock-jacket. Concrete weight coating was installed on 6 km of pipe for installation in wet areas, water crossings, and through rocky areas where additional pipe protection was needed.

Civil work dominated the construction activities from beginning to end.

In addition to the road building, major earth works were required through rugged terrain north of the Mubi River. Two sections, one from KP 66 to KP 62 and the second from KP 11 to KP 6 resulted in an elevation change of more than 1,000 m (Fig. 2).

Extensive blasting through these areas provided a route for pipeline construction and to transport equipment and materials along the right-of-way. A total of 1,000 tons of explosives was used in the overall construction.

Backhoes did most of the ditching, but two rock saws cut solid rock areas and a wheel ditcher ploughed clay areas wherever possible. Manual welding used stick electrodes. Some pipe laying took place in July and August, but it was not until September 1991 that the main line pipe gang got fully under way.

Although some initial problems arose with high water levels and flooded ditches, the pipe laying in general progressed smoothly and was basically completed by the end of May 1992.

River crossings were directional drilled for Utitu Creek, Kikori River, Wah River, and Mubi River. Significant problems were encountered both in the drilling and in the pulling operations because of discontinuous rock formations, below-ground voids, and large cobblestone areas.

Initial attempts to pull the pipe through the bores indicated that the rock-jacket coating did not have the strength necessary to withstand the pulling force. Pulls at the Utitu and Kikori crossings were abandoned, and the pipe was removed from the holes.

Problems were eventually overcome by installation of 24-in. OD casing over the pipe prior to pulling; all subsequent bored crossings used this process. It permitted relatively smooth pulls and ensured the integrity of the pipe and coating.

Work commenced on the first crossing in October 1991, and the last crossing was completed in May 1992.

Four aboveground valve stations were located along the line. All valves received electric operators and are capable of being remotely controlled through the monitoring and control system.

Communications towers at each site allowed communications through the microwave system to the control rooms at the CPF and at platform Kumul. Power arrived at each site through solar panels with back-up diesel generators.

Rectifiers were also installed at each site as part of the impressed current cathodic-protection system.

Elevation changes dictated that the line be divided into nine sections for hydrostatic testing.

A gauging plate sized at 95% of the nominal ID was run through all sections. Most sections were also checked for dents and ovalling with a calliper pig. Test pressures were established for each section on the basis of a maximum stress level of 100% of specified minimum yield strength (SMYS) during testing.

Testing began in January 1992 and finished in the last section on June 12, 1992. Following testing, final tie-ins were completed, including the tie-in to the marine pipeline, and the line was filled with water in preparation for commissioning.

MARINE ACTIVITIES

Construction of the river section presented the most difficulties for the marine pipeline.

Water levels varied by 4 m between high and low river conditions as a result both of tidal effects and of runoff from the Kikori River catchment area. Significant variation in rainfall during construction led to periods of very low water conditions as well as periods of relative flood conditions.

Shallow sections of the river with water levels less than 2 m effectively limited the draft of the construction spread which could be utilized. Coping with current velocities of 5 knots observed near the mouth of the river and being able to maneuver and set anchors in the tight radius bends and shallow water sections of the river required a significant mooring capability.

Work on planning the marine pipeline began in 1988. The initial concept called for continuing from the onshore pipeline terminus across the marsh islands in a straight line to a point where an offshore barge could begin laying out to deep water.

As planning progressed an alternative route arose in which shallow water equipment would be used to lay the pipeline down the river to a point where an offshore barge could continue to lay pipe as planned to the marine terminal. This alternative was attractive because it was more efficient to build and entailed less risk.

The river route involved less equipment than construction across marsh islands with numerous river crossings and took less time to build. It also caused less disruption to the marsh islands' ecological system.

Data from bathymetric and geotechnic surveys conducted in 1989 were used to select a 40-km route down the Kikori and Nakari Rivers: the longest known pipeline built down a river.

Chevron prepared a bid package for fabrication of the platform, transportation of line pipe, platform, and SPM, and installation of pipeline, platform, and SPM. The company issued the bid documents in May 1990, and a bid walk occurred on site for contractor representatives to familiarize themselves with the environment and logistics constraints.

Bids arrived in August 1990 and, in December 1990, Bouygues Offshore Singapore Pty. Ltd. received contracts for fabrication, transportation, and installation.

RIVER CONSTRUCTION

Work began in Papua New Guinea in August 1991 when a survey crew was mobilized to establish positioning and control stations and begin the bathymetric survey before pipe lay.

The river construction spread was mobilized in September 1991 and included the shallow water lay-barge TAK 300 with a 2.5 m draft and the accommodation barge Melati 1803 to house the crew required to weld and lay pipe 24 hr/day.

The pipeline was pulled ashore at landfall on Oct. 3, 1991, and 37.5 km of pipe were laid out to a point where the BOS 355 derrick-lay barge could recover it and continue the offshore section to complete the line to the terminal.

The TAK 300 completed the river pipelay on schedule even though it lay aground for periods of up to 9 hr/day in the shallowest sections of the river. A hull cooling system enabled the barge to maintain power even when aground for long periods (Fig. 4).

With the same shallow water spread, trenching of the river pipeline followed the line's being laid.

A post trenching machine made an initial pass over the shallow water sections but did not achieve the trench depth required at several locations. This equipment did not move enough bottom material (sugar sand) to allow the pipeline to settle to grade. Additional passes were made with Toyo pumps suspended on either side of the line from a frame supported by the TAK 300.

These pumps effectively lowered the top of pipe to meet the trenching requirement of the lesser of - 3.4 m, or 1 m of cover.

By the time construction culminated, the pipeline had buried below the river bottom in many areas. High river currents move a significant amount of bed load material which is expected eventually to cover the entire line.

At one location, the pipe was laid on bottom in water -4 m. The river moved 2.6 m of sand over the pipe by the time divers returned to recover the electrical cable pig tail 5 months later to tie-in with a test point station. Subsequent surveys planned during operations will monitor the extent of burial.

Vessel impact dented three sections of pipe before the construction including burial was complete.

In the first two cases, the damaged sections were recovered to the surface on the TAK 300 and new sections fitted and welded into place, followed by field joint coating and lowering to the bottom.

In the third case, a coffer-dam was constructed and dewatered so that the pipeline could be repaired in place. All welds were 100% radiographed to API 1104 acceptance criteria.

The pipeline was accepted for first oil after the running of a gauge plate sized at 95% of the minimum ID and completion of a 24-hr hydrotest at a pressure equivalent to 150% of the design pressure.

Approximately 35% of the marine work force was from Papua New Guinea and worked as surveyors, tug crew, welder helpers, coating helpers, riggers, caterers, and security personnel. The rest of the workers were from 21 other countries and had highly specialized skills.

Landowners were employed to clear sites for survey control stations and for the three impressed-current stations and two test-point locations. All landowner and community relations issues were handled by Chevron.

Construction personnel held periodic meetings and tours of the facilities to explain the status of the work and future plans to the landowners. No significant land-owner or community relations issues disrupted the work.

COATING

Marubeni in Japan supplied API 5L Grade X-60 DSAW pipe and transported it to Bredero Price in Kuantan, Malaysia, for 500-m, fusion-bonded epoxy corrosion coating and concrete weight coating.

The majority of the marine line was 11.1 mm W.T. X 50-mm concrete weight coat. To provide stability, 90 mm concrete weight coat was used in the surf zone. Pipe wall thickness was increased to 12.7 mm for the risers at the platform. All offshore tie-ins were made by divers.

COMMISSIONING

The line was officially turned over for commissioning on the scheduled completion date of June 18, 1992. Actual commissioning of the entire export pipeline began 3 days later.

The original schedule was met because the people on site could do what was required to complete the work. Extreme care had to be exercised in the early stages of commissioning as the increased head, caused by having water in the line as opposed to oil, resulted in pressures marginally above the line maximum allowable operating pressure.

Back pressure was initially maintained at Kopi to control the line filling operation. Control was transferred to the marine terminal when oil approached the Kopi valve station.

The location of the oil as it moved down the pipeline was monitored through the use of a slug of dyed water in front of the oil and a pinger installed on the last pig.

Filling occurred at rates up to 80,000 b/d and was finished in 6 days. With the start of loading of the first tanker on June 27, 1992, the export pipeline was turned over for production operations.