Louis P. Zylstra
IDS
Santa Ana, Calif.
Several leaking oil wells drilled in the late 1800s in the surf zone in Southern California required a specially built rig and platform for proper abandonment. The abandonment operations were complicated because the beach is heavily used by the public and the condition of the wells was unknown.
A mobile sled was designed to support a drilling rig safely in the rough surf zone. The surf sled vehicle has a modular design for efficient assembly on the beach with minimal disturbance of the environment. No structures had to be built on the beach or in the surf zone to access the wellheads, thereby reducing costs and environmental impact.
The surf sled vehicle used special equipment to keep the drilling rig level and to prevent oil spills or contamination during the drilling and abandonment procedures. The wells were abandoned safely and in a timely manner, despite the challenges of working in such a sensitive area.
LEAKING OIL WELLS
Beginning in 1886, numerous wells were drilled in the Summerland oil field offshore and along the beach near Santa Barbara Calif. (Fig. 1). A cluster of five Summerland oil field wells were abandoned about 1907 using the accepted technology of the time the wells were blasted with dynamite and subsequently plugged with telephone poles. Unfortunately, this type of abandonment was not competent, and oil and gas eventually leaked through and around the casing strings.
In 1990, the California State Lands Commission declared these five oil wells a hazard, and state funds were allocated to abandon the wells properly.
Two of the wells were on the beach, and three were located in the surf zone, posing a unique challenge for positioning drilling equipment at the work site. No infrastructure was available to support the abandonment operations. The project required an inexpensive solution because of limited state funding.
WELL ACCESS
Limited site access, the need to place equipment on a 70 ft high bluff, and heavy public use of the Summerland beach were the major impediments to conducting normal oil field operations. No piers were available (or economical to build) for the surf zone abandonments.
The surf zone environment presents several challenges for oil field operations. In the surf, floating equipment cannot be safely anchored, nor can it provide a stable work platform for drilling operations. Environmental concerns are of utmost importance, and pollution control methods must be fail safe because of the sensitive nature of the beach area.
Because of these difficulties and permit requirements, the drilling support equipment had to be compact and located 70 ft above the work site at the top of the bluff, a quarter mile away. These restrictions presented problems for transporting drilling mud to the work site and for handling waste disposal from the rig site. Furthermore, because of the age of the wells, most of the information on well bore design and piping configuration was no longer available.
SURF SLED VEHICLE
To abandon the wells, IDS used a surf sled vehicle to provide the same support as a pier in the surf/tidal zone but without the high cost and without significantly affecting the public use of the beach. The mobile surf sled vehicle was modified to meet the specific requirements of the Summerland abandonment operations.
The surf sled vehicle was originally designed to provide stable surf zone support for diving and heavy construction operations. It was first used in August 1992 to install support clamps on a pipeline in a high energy surf zone at the environmentally sensitive San Elijo state beach at Cardiff, Calif. The surf sled vehicle was originally designed to float using two removable pontoons as ballast. For the San Elijo project, the vehicle was positioned with a winch on the beach and a winch on a ship anchored on a fourpoint mooring.
For the Summerland wells, the vehicle was designed to support large drilling rig hook loads of up to 60 kips and to remain stable with 12 ft wave loads.
An important feature of the sled is its modular design for ease of assembly and disassembly. The sled measures 35 ft by 35 ft and is supported on two 36 ft long pontoon type skids. This compact design allows the surf sled vehicle to work in size restricted sites.
Using a winch pull, the sled can be set accurately over any wellhead or pipe. For the Summerland wells, the vehicle was taken apart, and the component sections were placed on the beach with cranes operating from the top of the bluff (Fig. 2).
The surf sled vehicle was reassembled on the beach and positioned in the surf zone using four D8 Caterpillar tractors (Fig. 3).
ENVIRONMENTAL CONCERNS
Because of the extensive public use of the Summerland beach, extra attention was put on preventing beach contamination, hydrocarbon spills, and drilling mud waste.
A temporary tank farm was set up off the beach and away from the work site in a location central to all five wells. Three temporary 31/2 in. OD lines were constructed to transport freshwater and clean drilling mud to the site. A flexible hose was used between the return line and two centrifugal pumps, placed outside of the surf zone, used to remove well fluids which were then transported to the remote tank farm.
The tank farm included a shale shaker, equipment for hydrocarbon separation and storage for the return fluids, mud mixing equipment, and kill fluid storage.
DRILLING OPERATIONS
The surf sled vehicle was designed to support an API Class 11 blowout preventer (BOP). The BOP was hung below deck level because no structural support was available from any of the casing strings. The BOP accumulator and block valves were located on the deck of the sled.
All drilling support equipment, including tanks, mud mixing equipment, and filters, had to be located away from the wellheads at the top of the 70 ft bluff. Thus, the operation required special planning for handling the drilling returns, which had to be pumped vertically up the cliff to the temporary facilities.
After the sled was assembled on the beach, a 28,000-lb drilling rig was placed on it by a crane from the bluff. To counteract uneven beach topography and to keep the drilling rig level during operations, the rig was mounted on the sled with hydraulic rams at each corner. The rams were individually actuated to compensate for uneven or moderate grades (Fig. 4).
ABANDONMENT
The Summerland wells were abandoned using standard plug and abandonment procedures with some minor modifications.
During the abandonments, it was discovered that the existing casings were substandard 10 in., 8 5/8 in., and 6 5/8 in. schedule 10 or thin wall seamed pipe manufactured in the late 1800s.
To make the transition to a standard API flange, a slip on spool piece was welded to the existing casing string during low tide or from within a cofferdam (a water tight enclosure placed underwater and pumped dry to permit construction work).
On one well, a 12 in. conductor pipe was driven over the production string, and the annulus was cemented prior to the installation of the BOP.
Each abandonment operation included a clean out run, a cavity shot, and solid cement plugs set to surface. Additionally, each well's casing was cut 5 ft below the sand line.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
