The Oligocene Hackberry onshore the Texas and Louisiana Gulf Coast has long been recognized as a prolific reservoir, but it was a confusing and difficult play that frustrated explorers for many years. Adding to the complications was a geologic model that, although widely followed, was not representative of the subsurface reality. That paradigm changed abruptly with the development of a new geologic model and the application of 3-D seismic, and specifically amplitude variation with offset (AVO) techniques. Suddenly, operators armed with fresh ideas, seismic volumes and amplitude extractions could easily pinpoint likely Hackberry prospects. Success rates zoomed in the trend, which stretches from Chambers, Jefferson and Orange counties, Texas, into Calcasieu, Beauregard, Jefferson Davis and Allen parishes, Louisiana. Private Midland-based Mayne & Mertz is credited by its industry peers as kicking off the second coming of the Hackberry. Formed in 1982 by partners Taylor Mayne and Len Mertz, the firm focused mainly on the acquisition and development of properties in the Permian Basin. The owners witnessed the heyday of onshore 3-D seismic in West Texas and appreciated its provocative potential. Mayne & Mertz decided to open a Houston office and apply the technology to the Gulf Coast. It hired James Allen and Mike Puzio-Allen was a well-known expert in AVO interpretations and Puzio had worked the enigmatic Hackberry trend for years. "Classically, the Hackberry was perceived to be a canyon and turbidite sequence underneath a deepwater shale. But, there was no predictability with that type of model," says Puzio, the exploration manager. Since geologists thought the sands were deposited on top of an erosional unconformity, they would map sand thicknesses from well to well and project the trends as sand channels. Unfortunately, a typical outcome of a Hackberry program was one or two nice producers ringed by three or four dry holes. "People used to joke that the worst thing they could do was find production in the Hackberry, because then they would have to offset it." From his study of the play and his own drilling experiences, Puzio came to believe the Hackberry was a rotated slump-block play with sands preserved below an unconformity. "It is a totally different way to project the sands, and it's logical and predictable." Along with 3-D's ability to accurately image the structural positions of the slump blocks, it could also be used to directly detect hydrocarbons. The Hackberry sands, when charged with gas, possessed just the right characteristics to make them light up the seismic with amplitude anomalies. Also, plenty of opportunities remained. Although more than 2 trillion cubic feet (Tcf) of gas had already been found (with very low success rates) in the Hackberry, the play was certainly not mature. In the early 1990s, about 550 square miles of prospective acreage remained undrilled. "We believed that with our new geologic idea and with the ability to image the slump blocks with 3-D, we would be able to find a lot more oil and gas." That has unquestionably been the case. To date, Mayne & Mertz has drilled 34 producers out of 43 attempts, for an 80% success rate. This is true exploratory success, since the Hackberry accumulations are discrete and are usually able to be drained with a single well. Even more impressively, Mayne & Mertz has not drilled a development dry hole on any of its discoveries-the 3-D offers the proof needed to avoid the sometimes almost overwhelming temptation to offset an excellent producer. The foundations for the firm's success are three proprietary 3-D seismic databases that it put together in Calcasieu Parish. It also participated in one 20-square-mile survey in Texas, but it quickly determined that it preferred the Louisiana portion of the play. "There were many more large land owners in Louisiana, and that let us tie up quantities of acreage very quickly; we also liked Calcasieu's surface working environment, with its abundant high ground." And, the play extends from depths of 7,000 feet to more than 14,000 feet in the parish, giving an operator a wide continuum of situations from which to chose. Mayne & Mertz decided to head into the mid- to downdip portions of the play. "We expected to find fewer but larger opportunities as we moved basinward, because the faulting is not as complicated." Its two most recent discoveries, the #1 Opal Grey Trust 26 and #1 Stream 25, both in Township 11s-Range 13w, each flowed more than 1,000 barrels of oil and several million cubic feet (MMcf) of gas per day. Much of its area requires intermediate casing-the bottomhole pressure of its deepest well, at 14,200 feet, was more than 11,500 psi. The accumulations it targets in its area span from 80 to 150 acres in size, and they can be accurately delineated with the seismic. Limits to the technique exist, however. "We're not able to determine from the seismic how thick the pay interval will be before we drill a prospect," he notes. "Our thickest pay is 150 feet; our thinnest, 12 feet." Too, whether an anomaly will be primarily gas- or oil-filled cannot be determined predrill. "We do get an AVO response from oil pay, either because it contains just enough associated gas or because a thin gas cap overlies an oil leg." The company still has more than a dozen prospects to drill, all in Calcasieu Parish. It hopes to finish the package this year, but rig availability problems may push that goal back, says Puzio. San Francisco and Denver-based HS Resources Inc. is another leading player on the Louisiana side of the play. "We've shot more than 1,000 square miles of 3-D data in seven separate programs strictly for the Hackberry," says Wayne D. Williams, vice president, geophysics. In late 1995, HS and private firm Aspect Resources , based in Denver, formed a joint venture called SouthTech. It entered the play via a small acreage position that SouthTech owned inside of a Mayne & Mertz-operated 3-D seismic project called Buhler, in Calcasieu Parish. That first deal spawned successful wells, proving to HS that both the geological model and the AVO technique were suited to the Hackberry. HS and Aspect then headed north of the Buhler shoot, putting together successive ventures in the up-dip portion of the play. Because land on the Texas side was largely tied up, it chose to stay in Louisiana. HS does, however, work both the Vicksburg and Frio plays in Texas, abutting the southwest edge of the Hackberry trend. Since that initial project, HS and Aspect have continued to partner in the Hackberry in Louisiana. Within their area of mutual interest, HS handles all the drilling operations for the Hackberry, and Aspect and HS split operations of the seismic shoots. Interpretations of the seismic data volumes are performed in parallel by HS, Aspect, SouthTech and Resource Solutions, a consulting group that has played an essential role in the Hackberry success. In its area, the Hackberry wells range from 9,000 to 12,000 feet in depth, and usually are normal pressured and don't require an intermediate string of pipe. Total costs per completed well in 2000 were about $1.4 million for the company. A successful well will recover an average of 4 billion cubic feet of gas equivalent (Bcfe), but individual reserves can range up to 10 Bcfe per well. Most units it forms on the Louisiana side are 160 acres in size, and leases easily go for several hundred dollars per acre. Seismic is king in the Hackberry, and companies interested in the play must be willing to invest large amounts of money in acquiring and processing the necessary data, says Williams. HS generally shoots programs of 70 to about 140 square miles, with acquisition costs running $40,000 to $70,000 per square mile. Through a contractor alliance that Aspect and HS formed with Veritas DGC Inc. , sesimic acquisition costs have been brought down to around $40,000 per square mile, excluding permits. Correct processing is another crucial factor. This year, the company is putting together two more proprietary shoots on the eastern edge of the play. HS goes for the big picture, says Williams. "We've taken all our 3-D surveys along the Interstate 10 corridor and merged them together, and then we've done a prestack time migration on the entire volume. We have one contiguous dataset from the Texas border all the way to the east side of our Hathaway shoot in Jefferson Davis Parish. It's an incredible competitive advantage for us." All of HS' Hackberry prospecting is based on AVO analysis, structural mapping and amplitude work. The targets are smaller than those to the south, with areal extents of just 30 to 60 acres. The strong AVO contrast generated by the gas-filled sands drives the play, but HS looks at other wavelet characteristics as well. HS' results are sterling: its success record is 72%, with 44 producers out of 61 wells drilled. No question, the economics of the play are very strong. "Overall, our company has a finding cost of $1 per thousand cubic feet of gas equivalent (Mcfe) in the Hackberry play," says Williams. "That includes the capital for 3-D surveys that contain prospects that are not yet drilled. On projects such as North Gillis where the 3-D is largely exploited, our finding cost is 40 to 60 cents per Mcfe." Still, HS is reevaluating its 2001 Hackberry program. Last year, the firm drilled 24 wells and it presently operates three rigs in the play. It has a several-year inventory of drillable prospects, and it had planned to keep six rigs running in the play throughout the year, but the soaring cost of drilling is giving it pause. "Costs, both tangible and intangible, have gone up anywhere from 20% to 50%, and that obviously affects the economics. Rig availability is another issue." Point Comfort, Texas-based Neumin Production Co. has also been quite active on the Louisiana side. The firm was originally part of Alcoa, and began drilling for oil and gas in the 1940s. Since 1988, Neumin has been owned by Formosa Plastics . Its parent company burns 130 MMcf of gas per day just in its Point Comfort plant, so Neumin's production acts as a fuel-cost hedge. The company explores throughout the Gulf Coast, and in recent years has concentrated in Calcasieu Parish, Louisiana, and Lavaca, Colorado, Wharton, Jackson, Calhoun and Victoria counties, Texas. It entered the Hackberry in 1995, when it started shooting proprietary 3-D surveys with partners. Neumin drilled its first well in the trend in late 1996. Aside from a small survey in Texas, Neumin has stayed in Calcasieu Parish. Today, it has about 300 square miles of proprietary data. One of its wells, the #1 State Tract 15155, spudded at a surface location in Orange County, Texas, and bottomed across the state line in Calcasieu Parish. "The well has a 6,000-foot lateral," says John Foester, geologist. "We drilled it that way because of surface access-it was in a marsh refuge area in Louisiana." The company has drilled or participated in 31 Hackberry wells, 12 of which were in the pressure regime. Its success rate is 77%, with 24 producers. Like the other active players, Neumin bases all its Hackberry locations on 3-D seismic and AVO analysis. Its wells range from 7,000 to 8,500 feet in the normal-pressured area, and its pipesetters range from 8,500 to 11,000 feet. Last year, drilling a well without intermediate casing cost about $650,000; this year, that figure is reaching $800,000. The drilling cost doubles when pipe has to be set, but the reserves rise correspondingly. From its 14 wells in the normal-pressured Hackberry, Neumin has produced 24 Bcfe to date; from its 10 pipesetters in pressure, the company has produced 34 Bcfe. Per-well production has averaged 1.7 Bcfe for the nonpipe wells and 3.4 Bcfe for the pipesetters. This year, the company planned to drill or participate in more than 30 wells, says Jim Gilstrap, landman. "But, it's probably going to be more like 20 or 25 wells because of the rig situation." Neumin operates most of the wells in which it holds interests; Mitchell operates a handful of the Hackberry wells in which Neumin holds nonoperated interests. "We like the Hackberry because it's an amplitude-based play, generally sitting on a structure," says Foester. "Especially in the normal-pressure portion, we have a pretty good idea of what we're going to produce before we drill." The pressured portion of the play is not quite as predictable, he notes. A common denominator on both the Louisiana and Texas sides of the play is Aspect Resources. The company has been in the Hackberry since the beginning of this latest go-round, joining with Mayne & Mertz for its first 3-D shoot in Louisiana. Since then, Aspect has shot approximately 2,000 square miles of 3-D data in the Hackberry, says Alex Cranberg, president. "We've shot far more data than any other firm." Aspect works in partnership with HS Resources on the Louisiana side, and with Tulsa-based Helmerich & Payne Inc. and Houston-based Esenjay Exploration Inc. on the Texas side. Its interests vary on a project basis, and it operates wells in Texas and seismic shoots in both states. While the two halves of the play are fairly similar, more of the Texas side is in pressure, says Cranberg, requiring intermediate strings of pipe. The Louisiana side hosts more of the normal-pressured Hackberry. "The play is getting pretty mature on both sides, but there's still quite a bit of drilling left to do. Because of the recent gas prices some of the smaller prospects have become economic." The Hackberry play has been an unusual opportunity, he says. "It's an exceptional, very highly profitable play." One of Aspect's partners in Jefferson County is Esenjay Exploration. It acquired a position and started drilling in 1998, says David Berry, chairman. "We drilled one of the first geopressured wells in the Hackberry. At first, we didn't know if we would be able to image the subsurface properly in the geopressured environment, and in fact our first well was dry." After that, the company went on a tear. It has drilled 20 producers out of 27 attempts, for a success rate of 74%. Esenjay has been involved in six contiguous 3-D seismic surveys in Jefferson County, covering more than 275 square miles. Last year, the firm drilled eight successful Hackberry wells out of 11 attempts. One of its notable discoveries was the 11,150-foot Klaver #1, operated by Helmerich & Payne and drilled in the Lovells Lake 3-D survey. That well flow tested at rates of more than 20 MMcf of gas and 1,200 barrels of condensate per day. The Klaver, which began producing into the pipeline in July, had already made 1.8 Bcf of gas and 100,000 barrels of condensate by mid-November 2000. Another, the O'Brien #2, was drilled in the Cheek 3-D survey, also by Helmerich & Payne. That test flowed 4.5 million cubic feet of gas and 87 barrels of condensate per day from Hackberry. Presently, Esenjay has an inventory of 11prospects on its existing seismic database. This year, it is currently drilling one well and plans four more. A generic Hackberry well in Jefferson County's nongeopressured area costs about $800,000 to drill, and another $500,000 to complete. A geopressured well costs about $1.4 million to drill and another $500,000 to complete, although like all the other companies Esenjay is experiencing rapid drilling-cost escalations. "There may be a better place to use 3-D seismic to alter risk, but I don't know of it," says Berry. "Our experience is that the success rates in the area prior to 3-D were below 10%, and now they are in the range of 75%." Significantly, those numbers don't include marginal wells, because the rock quality is so superior in the Hackberry that the successful tests are all high-rate producers. Average per-well reserves in its Jefferson County area are between 2.5- and 5 Bcfe, and some will ultimately produce up to 20 Bcfe, he says. "So much money was spent on 3-D seismic with so much expectation, and there were many disappointments. Often, it was used in areas where it didn't help a lot, or where large land holdings were tied up but the geology and geophysics were not appropriate. But here, 3-D is a genuine success." Houston-based SK Resources Inc. jumped into the Hackberry just two years ago. It was motivated to get into the Jefferson County portion of the play by the impressive discoveries there, says Greg Kane, vice president of land. "It's ideal because the wells are high-rate, the success rates are tremendous, and the pipeline infrastructure is excellent." Zackson Resources , SK's operating arm, has drilled one Hackberry well to date and participated in several others. At press time, it had another location ready to spud, and it plans to ultimately drill five or six additional Hackberry tests. The company has not shot its own proprietary surveys; instead it is relying on speculative 3-D shoots that it has purchased. "We've been working from several of the large spec shoots that are available in the area," says Keith Hatch, vice president of geophysics. "There appear to be a fairly large number of anomalies, and the key is to make sure they are large enough to contain economic reserves. The ones we are commercially interested in vary in size from 18 to 50 acres." Kane believes the Hackberry play is not over. "We see plenty of opportunity. Most of the leasing in our area of interest was done in 1998 and 1999, and that acreage is all going to roll over this year and the next. There's no way that the present leaseholders can drill all the anomalies before their leases expire." Many more 2- to 5-Bcfe wells will continue to be drilled in the Hackberry, he says. "The big stand-out bright spots are getting drilled now, and what's left may be second-tier opportunities. But, the recent rise in gas prices has made that less of a concern. Anyone can do the math-this is a wonderful play."