A.D. Keen
Senior Editor-News
Regional Setting For Wilmington, Long Beach Unit (68255 bytes) The City of Long Beach and Thums Long Beach Co. (TLB) are pressing a campaign to revitalize their share of big Wilmington field off California in Long Beach Harbor.
It's an example of the way the petroleum industry is nursing along its grand old fields to wring the last possible drop of oil out of aging reservoirs.
Long Beach and TLB are using the newest technology to extend the economic life of Thums Long Beach unit (LBU) beyond the date envisioned in the unit's original development plan. Under the production and pressure maintenance program chosen by the city in 1965, LBU was to produce itself out of existence by April 2000.
The latest efforts to reduce operating costs while boosting oil recovery include acquiring 3D seismic data over the field and developing horizontal drilling capabilities for TLB's drilling program.
TLB since November 1993 has attempted nine horizontal wells on the LBU, including two in which coiled tubing was used to drill most of the horizontal section. In late January, the Geco-Prakla unit of Schlumberger Oilfield Services, Houston, completed a 20 sq km, 3D seismic survey in the harbor, as well as a vertical seismic profile (VSP) in a well on LBU's Island Freeman.
When LBU celebrates 30 years of operations in June, cumulative production from the unit will amount to 800 million bbl. TLB officials estimate the unit's remaining reserves at 150 million bbl, due in part to early redevelopment.
LBU is part of Wilmington field, a 1932 Los Angeles basin discovery with ultimate reserves nudging 3 billion bbl. That makes it a supergiant among U.S. giant oil fields - those with ultimate recovery of 100 million bbl or more (OGJ, Jan. 30, p. 80).
BASIS OF REDEVELOPMENT
Thums' redevelopment activity got under way in earnest in 1992 when TLB began a reporting system that allows closer management of field operations.
The company also reorganized LBU operating personnel into integrated profit center teams and unitized-formation teams and gave team members a larger role in planning and day to day operating decisions.
Armed with better information, newly empowered team members have played key roles in deciding which technological advances are most likely to make TLB field operations more effective.
Better teamwork has led TLB to revise casing and drilling fluid programs and to implement new drill bit and tripping procedures that have helped reduce the time needed to drill a well in Wilmington field to 12-15 days from about 40, trimming average well costs by 20% to $450,000-500,000.
Similarly, since it began to use coiled tubing in well workovers, TLB has reduced the average cost of sandfill cleanouts on LBU to about $10,000 from $55,000, a big savings because about half of LBU's 1,000 or so active wells must be cleared of sand each year.
James H. Davis, TLB president, said the new detailed financial information allows teams to make better decisions faster than was possible under the previous system.
The redevelopment program's overall results to date have been encouraging.
In 1991, LBU's production averaged 45,100 b/d (25330 bytes). By the time redevelopment began in 1992, production had slipped to about 43,000 b/d of oil and was forecast to continue sliding to about 35,000 b/d by January 1995. Instead, thanks to scores of gains resulting from mostly small operational refinements, Thums oil production climbed to an average 46,600 b/d in 1994 and about 47,000 b/d last January (25330 bytes)
LBU's profitability reflects the operating efficiencies TLB is achieving with tighter management oversight. The unit in 1994 generated a net profit of about $85.7 million on revenue of $220 million, up from $71 million, in 1991 on revenue of $233.5 million.
HORIZONTAL DRILLING
While most savings so far on LBU have flowed from improvements derived from increased teamwork, Davis said steadily improving mastery of new technology adapted to fit field parameters is expected to generate further improvements.
"More successes are beginning to come as we move up the technology learning curve," Davis said.
Fritz Gunkel, TLB vice-president of operations, said the thrust of the LBU horizontal drilling program is to intersect zones of oil, mostly in the Ranger interval at about 3,000 ft, bypassed in the past 3 decades by the unit's pressure maintenance waterflood program.
"We've found some pretty substantial sections of unswept sand with horizontal wells," Gunkel said. "Our objective is to produce significantly more oil with much less water than a typical field well."
Most of LBU's Wilmington wells produce about 10% oil and 90% water. However, TLB's first horizontal well in the field, D-709 on Island Freeman, came in at essentially 99% oil and last month still was producing 60-70% oil.
TLB drilled D-709 to 5,350 ft total measured depth, with an 860 ft horizontal interval at 4,490-5,350 ft.
In tests of its ability to drill horizontally with coiled tubing, TLB so far has drilled the upper part of well bores with a rotary rig, including part of each well's horizontal lateral, run and cemented casing, then drilled out from under the casing before moving off the rotary rig and inserting a coiled tubing string.
"So the coiled tubing was used in the best of all circumstances," Gunkel said. "All it really needed to do was take off drilling horizontally."
While less time and effort are needed to mobilize a coiled tubing unit than a conventional rig and less support is needed, Gunkel said, TLB likely would not have chosen to move a coiled tubing unit onto either of the horizontal wells had they not been considered field tests.
Since starting its horizontal drilling program, TLB has trimmed horizontal well costs to $550,000-600,000 from $700,000, depending on whether a well is a reentry or new hole.
While TLB has achieved better horizontal drilling efficiency, Gunkel said, from a reservoir management standpoint TLB's horizontal wells "have been a mixture of successes and head scratchers." The mixed results could indicate compartmentalization in the field, with some areas exhibiting virgin reservoir pressures if directional well-bores haven't penetrated all productive zones.
COMBINING CAPABILITIES
Officials hope that at some point on the learning curve TLB will be able to begin combining new technological capabilities on LBU to achieve even higher recovery rates at still lower costs.
That scenario has the company drilling horizontal wells, including some with coiled tubing units, designed to intersect bypassed oil imaged by 3D seismic data.
Given that objective, TLB's plans to acquire new seismic data over the field might never have been allowed by state and local officials if not for Geco-Prakla's survey design.
The company designed the shoot around a telemetric transition zone system that allowed normal harbor activities to continue undisturbed while the survey was under way. For example, on the weekend before the survey was completed a local yacht club staged a regatta in which 130 sailboats breezed through the survey area.
"We didn't interfere with them, and they didn't interfere with us," said Mike Spradley,
Geco-Prakla's manager of transition zone operations.
While Geco-Prakla's telemetric transition zone system (25330 bytes) is environmentally friendly, the company adapted the air-gun array on its energy source boat to fire at a water depth of 5 m, minimizing the likelihood of energy eruptions at the surface.
During data acquisition, the array released a burst of air into the water at 17 sec intervals, resulting in 8,000 shot points spaced at 25 m intervals. The survey consisted of four patches, each including four 8,000 m receiver lines with receivers placed at 25 m intervals and lines placed 300 m apart.
On the day after conclusion of the 3D transition zone survey, a Schlumberger wireline crew joined with Geco-Prakla to conduct a VSP survey in the D-630 well on Island Freeman using the same seismic source used on the 3D shoot.
VSP data allow a seismic contractor to obtain accurate time-depth information, calibrate the phase of seismic wavelet used in acquiring the 3D data, measure the seismic reflection response of the geological column in the well-bore, and correct for sonic log frequency dispersion.
Given the de facto moratorium on seismic surveys off California, Spradley said the survey likely was allowed only because of the environmentally friendly data acquisition system being used and because the survey area is owned and controlled by the City of Long Beach, a steadfast proponent of the shoot.
"The Thums 3D program could be the last seismic survey shot in California, or it could be the invitation to start environmentally friendly seismic exploration in state water," Spradley said.
BENEFITS OF 3D SEISMIC
TLB's Davis said data from the 3D survey should be available about mid-1995, providing the company with accurate data as deep as 12,000 ft.
LBU has stacked pays in three reservoirs: Ranger at about 2,500 ft, Terminal at about 3,500 ft, and UP-Ford at 5,000 ft.
To date, Ranger is the most productive of the three and has the most reserves. UP-Ford is the least developed with the least reserves but has the most potential for horizontal drilling based on 3D seismic data.
TLB plans to integrate 3D data into its Wilmington field data base to delineate the field's fault blocks in more detail. The new data also are expected to help TLB better identify and interpret stratigraphic changes in Wilmington's main pays.
"It will affect our routine, day-to-day well drilling and workover decisions, including which zones are to be recompleted or isolated, water injection patterns, everything," Davis said.
While LBU redevelopment focuses on use of better seismic data or improved horizontal drilling methods to recover what has been left behind, TLB Chief Geologist George Otott said some parts of Wilmington field have significant production potential.
Otott said, "On the west side of the field, we've drilled only one or two exploratory wells, and one of the key areas for 3D seismic was to image that side of the UP-Ford. Since we essentially have no west side UP-Ford development, the new seismic data should give us a lot of better insights into a possible development program on that side of the field."
Gunkel added, "I haven't heard of or been involved in a 3D seismic survey in any field that hasn't substantially changed the picture of what a company was dealing with, from a reservoir standpoint."
WATER INJECTION PROFILES
Better teamwork and closer management oversight are generating other, more subtle improvements across LBU.
Because city and state officials 30 years ago feared that producing Wilmington could cause severe surface subsidence, Thums' operating agreement includes a mandatory pressure maintenance program that requires contractor TLB to inject about 5% more water than the volume of fluids removed from each of seven fault blocks in the field.
As a result, Davis said, "We can only produce oil based on the limits of our injection capability".
To avoid that limitation, Davis said, TLB has been doing a better job of drilling and completing water injection wells, as well as keeping injection wells serviced and on line.
"We also have been injecting water in better patterns to optimize the sweep of the flood through the reservoir," said Xenophon C. Colazas, director of the city's oil properties department, LBU's operator.
Thanks to such improvements as revised water injection profiles and more efficient, effective well workovers, LBU officials have been able to resume production at dozens of idle wells across the field, Colazas said.
LBU operating costs could be lowered even more through more conventional strategies.
A test is planned later this year to assess the added cost savings possible by injecting water in the field from the city's water treatment facilities. The supply would cost less, and LBU officials also think it might help alleviate some recurring downhole problems caused by water supplied from its current source.
TLB could lower operating costs even more if it could trim spending for electrical power, currently about one sixth of Thums' yearly operating budget.
The company is considering use of more efficient experimental pumps as one way to reduce its power consumption.
Another proposed solution involves a 42,000 kw cogeneration project in which generators fired partly by gas produced on LBU would be installed at an onshore site. Planning on that project is under way, and field work could begin as soon as TLB obtains permission from the city to proceed.
THE BEGINNING
Creation of LBU to develop its share of Wilmington field from the first was conceived and planned as a cradle to grave project.
Long Beach voters in a February 1962 referendum agreed to allow the area to be developed as a unit from no more than four islands to be built in the harbor. The city was named operator of the development.
In February 1965, the city named a group of oil companies, including Texaco, Humble, Union, Mobil, and Shell, LBU's contract operator.
ARCO Long Beach Co. early in 1990 concluded negotiations aimed at buying out the last of the original Thums shareholders.
Copyright 1995 Oil & Gas Journal. All Rights Reserved.
