Oligocene Trend Research Articles

Eocene–Miocene carbon-isotope and floral record from brown coal seams in the Gippsland Basin of southeast Australia

The carbon-isotope and palynological record through 580 m thick almost continuous brown coal in southeast Australia's Gippsland Basin is a relatively comprehensive southern hemisphere Middle Eocene to Middle Miocene record for terrestrial change. The carbon isotope δ 13C coal values of these coals range from − 27.7‰ to − 23.2. This isotopic variability follows gymnosperm/angiosperm fluctuations, where higher ratios coincide with heavier δ 13C values. There is also long-term variability in carbon isotopes through time. From the Eocene greenhouse world of high gymnosperm-heavier δ 13C coal values, there is a progressive shift to lighter δ 13C coal values that follows the earliest (Oi1?) glacial events around 33 Ma (Early Oligocene). The overlying Oligocene–Early Miocene brown coals have lower gymnosperm abundance, associated with increased % Nothofagus (angiosperm), and lightening of isotopes during Oligocene cooler conditions. The Miocene palynological and carbon-isotope record supports a continuation to the Oligocene trends until around the late Early Miocene (circa 19 Ma) when a warming commenced, followed by an even stronger isotope shift around 16 Ma that peaked in the Middle Miocene when higher gymnosperm abundance and heavier isotopes prevailed. The cycle between the two major warm peaks of Middle Eocene and Middle Miocene was circa 30 Ma long. This change corresponds to a fall in inferred pCO 2 levels for the same period. The Gippsland data suggest a link between gymnosperm abundance, long-term plant δ 13C composition, climatic change, and atmospheric pCO 2. Climatic deterioration in the Late Miocene terminated peat accumulation in the Gippsland Basin and no further significant coals formed in southeast Australia. The poor correspondence between this terrestrial isotope data and the marine isotope record is explained by the dominant control on δ 13C by the gymnosperm/angiosperm abundance, although in turn this poor correspondence may reflect palaeoclimate control. From the brown coal seam dating, the coal appears to have accumulated during a considerable part of the allocated 30 Ma Cenozoic time period. These brown coal carbon isotope and palynological data appear to record a more gradual atmospheric carbon isotope change compared to the marine record.

Circulation in the Southern Ocean during the Paleogene inferred from neodymium isotopes

Long-term records of neodymium (Nd) isotopes from sedimentary archives can be influenced by both changes in water mass mixing and continental weathering. Results of Nd isotopic analyses of fossil fish teeth from ODP Site 689 (Maud Rise, Southern Ocean) provide a long, continuous, high-resolution marine sediment Nd isotope record (expressed in ɛ Nd units). Correlation of down core secular variations between the ɛ Nd record, δ 13C values from benthic foraminifera, and clay mineral assemblages demonstrates that long-term variability of Nd isotope ratios reflect changes in ocean circulation, and that only minor fluctuations in ɛ Nd values are associated with changes in continental weathering on Antarctica. Nonradiogenic ɛ Nd values at Site 689 during the middle Eocene require the contribution of an end member with ɛ Nd<−9.5. Southern Ocean deep water may have been too radiogenic in the middle Eocene ( ɛ Nd=−8.5), though this end member may not be fully characterized. A possible source of deep water outside of the Southern Ocean in the middle Eocene is the Tethys Sea ( ɛ Nd=−9.3 to −9.8). The presence of Warm Saline Deep Water (WSDW) on Maud Rise is consistent with the Nd isotope results. The onset of more radiogenic ɛ Nd values at ∼40.8 Ma coincides with other changes at Site 689 which are consistent with a switch from a warm bottom water mass in the middle Eocene to a colder bottom water mass in the late middle Eocene. A rapid shift to radiogenic ɛ Nd values beginning at 37 Ma is best explained by the opening of Drake Passage. The shift coincides with increases in phytoplankton production throughout the Atlantic sector of the Southern Ocean that document the development of upwelling cells presumably related to more effective latitudinal circulation. After the Eocene/Oligocene boundary when large-scale ice sheets developed on Antarctica, Southern Ocean sourced water masses, such as Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW), had a greater influence on the hydrography of the study area. An early Oligocene trend to nonradiogenic compositions resulted in similar values to the modern ɛ Nd values of these water masses. The modern ɛ Nd values of AAIW and AABW reflect a significant contribution of North Atlantic Deep Water (NADW), thus decreasing ɛ Nd values in the early Oligocene may have resulted from the export of Northern Component Water (NCW, similar to modern NADW). During the late Oligocene and early Miocene, the long-term trends of the record follow benthic δ 13C values. Variability in the Nd isotope record most likely reflects fluctuations in ocean circulation arising from changes in the relative contributions of different end member water masses to the Southern Ocean. An interval where ɛ Nd values and δ 13C values are not correlated may reflect the influence of a short-lived weathering event on the ɛ Nd record. Early Miocene ɛ Nd values resemble those of modern Southern Ocean water masses, indicating a shift toward present-day patterns of ocean circulation.

Oil and Gas Developments in Louisiana Gulf Coast Onshore in 1989

All three of the principal indicators of oil and gas activity fell significantly in onshore south Louisiana in 1989 after posting modest gains in 1988. Drilling activity in 1989 decreased 28% from the 1988 level of 696 wells to 500 wells. As in 1988, this drop was largely at the expense of development wells; a larger proportion of extension wells and a similar number of wildcat wells were drilled in each year. Operators drilled 56 new-field wildcats, 100 other exploratory wells, and 344 development wells. Overall success rate declined from 51% to 47% due to the decreased emphasis on development drilling. Six new-field discoveries were completed: 2 each in the Miocene and Eocene trends, and 1 each in the Oligocene and Cretaceous trends. There were 25 significant extension wells with 6, 14, 4, and 1 successful tests in Miocene, Oligocene, Eocene, and Cretaceous rocks, respectively. Land acquisition declined 20% relative to 1988 activity from 336,136 ac leased to 267,276 ac. The preferred leasing sites were Vermilion, Terrebonne, Calcasieu, St. Martin, East Feliciana, and Acadia Parishes. The Oligocene trend had the most leasing activity with more than 45% of industry activity, followed by the Miocene trend with 28%. Geophysical acquisition also dropped from 436.5 crew-weeks in 1988 to 327 crew-weeks in 1989, a decrease of 25%. Favored locales were Cameron, Vermilion, Calcasieu, Plaquemines, and Lafourche Parishes. Geophysical prospecting in the Miocene and Oligocene trends predominated, capturing 48% and 37% of industry interest, respectively.

The Maurice Field: New Gas Reserves from Buried Structure along the Oligocene Trend of Southwestern Louisiana: ABSTRACT

ABSTRACT Significant new gas reserves have recently been discovered in the Marginulina texana sands along the Oligocene trend at the Maurice field. Detailed subsurface maps and seismic data are presented to exhibit the extent and nature of this local buried structure and to demonstrate future opportunities along the Oligocene trend. Since discovery in 1988, the MARG. TEX. RESERVOIR C has extended the Maurice field one half mile south and has established 200 feet of Marginulina texana pay. Estimated reserves are in the order of 160 billion cubic feet of gas with limits of the reservoir still undefined. This reserve addition would increase the estimated ultimate of the Maurice field by over 70 percent from 220 billion cubic feet of gas to 380 billion cubic feet of gas. Cross sections across the field depict the new reservoir trap as a buried upthrown fault closure with an anticipated gas column of 720 feet. Interpretation of the origin of this local structure is that of a buried rotated fault block within an overall larger depositional structure. Detailed subsurface maps at the Marginulina texana and the overlying Miogypsinoides levels are presented. These maps indicate that one common fault block, FAULT BLOCK AB, is productive from two different levels. The deeper Marginulina texana sands are trapped on north dip upthrown to a southern boundary fault, FAULT B. The overlying Miogypsinoides sands are trapped on south dip downthrown to a northern boundary fault, FAULT A. The northern fault, FAULT A, was the Marginulina texana expansion fault and rotated that downthrown section to north dip. Because of the difference in dip between the two levels the apex of the deeper Marginulina texana fault closure is juxtaposed by one mile south relative to the apex of the overlying Miogypsinoides fault closure. Analysis indicates that important structural growth occurred during Marginulina texana deposition with a local unconformity covering the apex of the upthrown fault closure. State-of-the-art reconnaissance seismic data clearly exhibit this buried rotated fault block. Similar buried structures are predicted to exist along the Oligocene trend. Such occurrences will open to explorationists opportunities for the discovery of significant gas reserves throughout the 1990's.

Oil and Gas Developments in Southeastern States in 1989

Total drilling activity in Mississippi, Alabama, Florida, and Georgia, including both exploratory and development wells, increased 72.5% from 608 wells in 1988 to 1049 wells in 1989. Most of the increase was a result of development drilling for coalbed methane in the Alabama portion of the Black Warrior basin. Exploratory drilling in 1989 in the southeastern states decreased 13.6%. Of the 229 exploratory tests in 1989, 55 were successful for a 24.0% success rate. This compares to 1988's 50 successful completions of 265 tests and an 18.9% success rate. The Paleozoic trend of northeastern Mississippi and northwestern Alabama accounted for 31.0% of the exploratory tests. This active trend had 13 new-field discoveries in 1989 compared with 17 in 1988. The Jurassic trend, with 22.3% of the total exploratory effort had 4 new-field discoveries in 1989 compared with 8 in 1988. The Upper Cretaceous trend accounted for 20.5% of the exploratory tests. This trend had 2 new-field discoveries in 1989, the same as in 1988. The Eocene, Lower Cretaceous, Oligocene, and Miocene trends accounted, respectively, for 16.2%, 5.2%, 3.9%, and 0.9% of the total exploratory tests. Four new-field discoveries were reported in the Eocene, 2 in the Lower Cretaceous, 2 in the Oligocene, and 2 in the Miocene.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1989

Onshore drilling in the upper Gulf Coast of Texas during 1989 totaled 638 wells, a 21.6% decrease from 1988's total of 814 wells. Exploratory drilling remained at the same level, but development drilling declined 30.2% from 1988. Thirty-four new-field discoveries resulted from drilling 141 new-field wildcat wells in 1989, a 23.6% success rate. Fifty-three other wildcat discoveries resulted from drilling new-pool, deeper pool, or extension wells with a 60.2% success rate. The Eocene trend was once again the most active exploratory trend onshore with 40.6% of the onshore drilling; the Oligocene and Cretaceous trends had 25.3% and 3.1% of the onshore exploration activity, respectively. Offshore exploratory drilling in 1989 totaled 74 wells, a 32.1% decrease from 1988. Development drilling offshore nearly tripled with 174 development wells drilled in 1989 compared to 64 wells drilled in 1988. The exploratory success rate offshore was 31.1%. Exploration activity resulted in 20 new-field discoveries and 3 new-pool, deeper pool, or extension discoveries. Forty exploratory dry holes were drilled offshore in 1989. Offshore, the Miocene trend was most actively explored with 8.1% of the exploratory drilling in 1989 (66 wells were listed as undesignated).

Oil and Gas Developments in Upper Gulf Coast of Texas in 1987

Onshore drilling in the upper Gulf Coast of Texas during 1987 totaled 822 wells, a 19.8% decrease from 1986's total of 1,025 wells. Exploratory drilling declined 17.5%, and development drilling decreased 20.5% from 1986. Twenty-two new-field discoveries resulted from drilling 123 new-field wildcat wells in 1987, for a 17.9% success rate. Forty-five other wildcat discoveries resulted from drilling new-pool, deeper pool, or extension wells, with a 64.3% success rate. The Eocene trend was the most active exploratory trend onshore with 38.9% of the onshore drilling; the Oligocene and Cretaceous trends had 27.4% and 26.4% of the onshore exploration activity, respectively. Offshore exploratory drilling in 1987 totaled 64 wells, an 18.5% increase from 1986. Development drilling offshore declined 51.0% with 50 development wells drilled in 1987 compared to 1986's total of 102 wells. The exploratory success rate offshore was 17.2%. Exploration activity resulted in 6 new-field discoveries and 5 new-pool, deeper pool, or extension discoveries. Fifty-three exploratory dry holes were drilled offshore in 1987. Offshore, the Miocene trend was most actively explored, receiving 59.4% of the exploratory drilling in 1987.

South Lake Arthur Field and Occurrence of Buried Structures Along Oligocene Trend of Southwestern Louisiana: ABSTRACT

South Lake Arthur Field and Occurrence of Buried Structures Along Oligocene Trend of Southwestern Louisiana: ABSTRACT

Oil and Gas Developments in Louisiana Gulf Coast Onshore in 1986

The oil price collapse of January 1986 caused all oil industry indicators to plummet as the industry entered its worst depression in recent memory. Although much oil field activity was suppressed, those few companies with well-managed sources of cash flow and with little debt took advantage of bargain-price services to continue exploration. As in the last few years, companies adopted conservative tactics to husband their capital. These strategies included low-risk operations such as development drilling or exploratory efforts in the established Miocene and Oligocene trends. Stringent economic criteria forced operators to target wells for shallower, oil-prone objectives, and to spread risk through the formation of partnerships. Operators drilled 991 wells in onshore south Louisiana in 1986, a decrease of 29% from 1985 and a fall of 37% from the peak year of 1981. Industry drilled 113 wildcats, 136 other exploratory tests, and 742 development wells. Total footage dropped 41% to 8,721,992 ft, and average footage also fell to 8,801 ft/well from 10,575 ft/well in 1985. The industry success rate was 43%, with 13 new fields discovered and 33 significant extensions completed. Leasing activity in south Louisiana was crippled, with the total amount of leased acreage (268,925 ac) decreasing 56% compared to 1985 and 85% compared to the high in 1981. Allen, St. Bernard, Cameron, Lafourche, Acadia, and Vernon Parishes were the leading lease sites. Geophysical activity fell 56% from 1985 and declined 74% from peak 1981 levels as 441 crew-weeks of seismic were shot. Interest was heaviest in Vermilion, Calcasieu, Terrebonne, Beauregard, Cameron, and Plaquemines Parishes.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1986

Onshore drilling in the upper Gulf Coast of Texas in 1986 was down 52.2% from 1985. Onshore exploratory drilling was down 46.3%, and development drilling was down 53.7%. Offshore drilling was down 22.0% from 1985. Offshore exploratory drilling was down 34.1%, but development drilling was down only 13.6%. The Eocene and Oligocene trends were the most active in the onshore area. The Miocene was the most active offshore trend. Onshore seismic activity was down 12.7% from 1985. The Eocene trend had more than half of the seismic activity in the onshore. Offshore seismic activity was down 31.7% from 1985. More than half of the offshore activity was conducted in the High Island area. Although the onshore rig count dropped 58% during 1986 and spot gas prices fell by 48%, signs of stabilization in gas prices could set the stage for future improvements in industry activity.

Oil and Gas Developments in Louisiana Gulf Coast Onshore in 1985

All oil and gas exploration and operation indicators in the south Louisiana onshore region decreased in 1985. The industry has apparently entered a significant downturn with both oil and gas as surplus entities, and many factors point to lower oil prices. Companies opted to continue and expand the conservative tactics they embraced in earlier years. These tactics involve preferential drilling for oil rather than gas, an amplified number of development wells, acquisition of reserves through field purchases and company mergers, and heightened emphasis and company mergers, and heightened emphasis on drilling and exploration activities in the proven Miocene and Oligocene trends. Oil companies drilled 1,402 wells in onshore south Louisiana in 1985, a 3% decline from 1984 levels and an 11% decrease from the peak year of 1981. Total footage ebbed slightly from 15,324,733 ft in 1984 to 14,826,231 ft in 1985, whereas average well depth increased slightly. Operators drilled 218 wildcats, 229 other exploratory tests, and the highest number of development wells (955) in recent history. Twenty-one new fields were discovered in 1985: 6 fields in the Miocene trend, 7 in the Oligocene trend, 6 in the Eocene trend, and 2 in the Cretaceous trend. There were 38 significant extensions, of which 28 were established in Oligocene or Miocene rocks and 5 each completed in Eocene and Cretaceous sediments. Leasing activity fell 30% from the 1984 mark to 618, 618,033 ac, and plunged 65% from industry heights in 1981. Most active lease sites were Allen, Lafourche, St. Martin, Cameron, and Calcasieu Parishes. Seismic surveying also fell significantly from 1,259 crew-weeks registered in 1984 to 993 crew-weeks in 1985. Vermilion, Cameron, Plaquemines, and St. Mary Parishes recorded the highest levels of geophysical activity.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1985

Onshore drilling in the upper Gulf Coast of Texas during 1985 totaled 2,143 wells on an as-reported basis, a 4.5% increase from 1984's total of 2,050 wells. Exploratory drilling was up 7.4%, whereas development drilling increased 3.8% from 1984. Four hundred thirty-six exploratory wells and 1,707 development wells were drilled during 1985. There were 45 new-field discoveries onshore in 1985 out of 257 new-field exploratory wells, for a 17.5% success rate. The average depth for these wells was 9,716 ft. There were 148 other wildcat discoveries and 31 failures for an 82.7% success rate in the category of new-pool, deeper pool, and extension wells. The Oligocene trend was the most active trend onshore in 1985 with 45.1% of the drilling, followed by the Eocene trend with 36.9%. Offshore exploratory drilling in 1985 totaled 82 wells on an as-reported basis. Fourteen gas discoveries, 2 oil discoveries, and 66 dry holes were reported. The overall success rate was 19.5%, a significant increase from the 12% success rate reported in 1984. Onshore geophysical activity decreased significantly in 1985 to 385 crew-weeks from 1984's total of 937 crew-weeks. Offshore activity was also down in 1985 with 202 crew-weeks compared to 317.5 crew-weeks reported in 1984.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1984

Wells drilled in the Upper Gulf Coast of Texas during 1984 totaled 1,973, almost the same as 1983's total of 1,979 wells. Onshore exploratory drilling continued to decrease, with 329 wildcats drilled compared to 426 in 1983 and 505 in 1982. Development drilling accounted for 83% of all onshore wells, up 6% from the 2 previous years. There were 36 new-field discoveries in 1984 with an average depth of 10,163 ft and a success rate of 20%. The 96 other exploratory discoveries had a success rate of 64%. The Oligocene trend was the most active, with 43% of the wildcat drilling, followed by the Eocene trend, with 39%. Offshore exploratory drilling was up sharply from 1983. A total of 57 wildcats were completed during 1984, up from 37 in 1983. Seven wildcats were successful gas completions for a 12% success rate (there were no oil completions). An additional 38 wildcats drilled during 1984 were classified as suspended at year end. Onshore geophysical activity increased in 1984 to 937 crew-weeks from 1983's 894 crew-weeks. Offshore activity hit an all-time high for the third consecutive year with 317.5 crew-weeks.

Oil and Gas Developments in Louisiana Gulf Coast Onshore in 1984

A decrease in operating and exploration costs prompted a rise in drilling, leasing, and geophysical activity in the south Louisiana onshore region in 1984. However, because of a persistent gas surplus and uncertain oil prices, operators adopted a conservative strategy for reserve replacement that included an increase in development drilling, an acceleration of enhanced oil recovery projects, and a concentration of extension and exploration drilling in the established Miocene and Oligocene trends. Operators drilled 1,447 wells in 1984, an increase of 15% over the 1,230 wells drilled in 1983. Total footage also rose from 13,453,752 to 15,324,733 ft. Oil companies drilled 245 wildcats, 302 other exploratory tests, and 900 development wells (development drilling increasing 18%). Seven newfield discovery wells were completed in 1984, of which 4 produced from Wilcox (Eocene) sandstones, 2 were perforated in the Oligocene, and 1 well was completed in the Austin Chalk (Cretaceous). There were 36 significant extensions, of which 33 found production in rocks of Miocene and Oligocene age. Leasing activity increased 10% to 885,903 ac. This level is far below that of 1980, 1981, and 1982 when more than 1 million ac were leased each year. Leasing activity was heaviest in Lafourche, St. Tammany, Vermilion, Calcasieu, and Beauregard Parishes. Geophysical activity also had a slight increase of 4% in 1984. A total of 1,259 crew-weeks of seismic shooting was recorded as compared to 1,212 crew-weeks in 1983. Cameron, St. Martin, Jefferson, Lafourche, Plaquemines, and Vermilion Parishes recorded the highest levels of geophysical activity.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1983

Wells drilled in the Upper Gulf Coast of Texas during 1983 totaled 1,979, down 23% from the 1982 total of 2,581. Onshore exploratory drilling continued to decrease, with 426 wildcat wells drilled compared to 505 wells in 1982 and 581 in 1981. Development drilling accounted for 77% of all onshore wells, virtually unchanged from the previous 3 years, but the 1,422 wells drilled was 25% fewer than in 1982. There were 58 new-field discoveries in 1983 with an average depth of 10,393 ft and a success rate of 22%. The 119 other exploratory discoveries in 1983 had a success rate of 73%. The Oligocene trend was the most active, with 43.9% of the wildcat drilling, followed by the Eocene trend. Offshore exploratory drilling slipped from 42 new-field wildcats in 1982 to 38 completed wildcats in 1983. Four new fields were discovered and 2 were extended. Average depth of an offshore exploratory well was 10,250 ft. With 61 wells listed as suspended operations at year end, the success rate of offshore exploratory wells could increase sharply. Onshore geophysical activity increased slightly in 1983 to 894 crew-weeks. Offshore activity hit an all-time high for the second year in a row with 288½ crew-weeks.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1982

There were 2,412 wells drilled in the Upper Gulf Coast of Texas during 1982, a slight decrease (4%) from the 1981 total of 2,502. Onshore exploratory drilling decreased 14%, with 505 wildcats drilled in 1982 compared with 581 in 1981. Development drilling accounted for 79% of the total, with the 1,907 wells drilled in 1982 showing little change from the 1,918 development wells drilled in 1981. There were 55 new-field discoveries completed in 1982 with an average depth of 9,431 ft and a success rate of 18.5%. There were 134 other wildcat discoveries in 1982 with an average depth of 9,475 ft and a success rate of 64.7%. The Oligocene trend remained the most active, with 40.6% of the wildcats, followed by the Eocene trend with 34.6%. Most of the significant new-field discoveries were made in the Oligocene Frio and Eocene Wilcox Formations. After a 6-year low in offshore exploratory drilling in 1981 (42 wildcats), 1982 saw a solid rebound with 70 exploratory wells drilled. However, the success rate for new-field wildcats continued to fall (to 3.6%). Onshore geophysical activity hit a 4-year low in 1982 with only 872 crew-weeks worked. Offshore geophysical activity hit an all-time high in 1982 with 225 crew-weeks worked, probably in response to the 1983 expanded federal OCS sales.

Oil and Gas Developments in Upper Gulf Coast of Texas in 1981

Wells drilled in the Upper Texas Gulf Coast during 1981 totaled 2,502, up 37% from the 1980 total of 1,826. Onshore development drilling accounted for 76% of the total with 1,910 wells, a 36% increase over the previous year. Onshore exploratory drilling also had a 37% increase, with 581 wildcats drilled in 1981 compared with 420 wildcats drilled in 1980. There were 65 successful new-field discoveries in 1981 with an average depth of 10,549 ft and a success rate of 19.6%. The Oligocene trend remained the most active exploration trend with 44% of the wildcats; however, the Eocene trend, particularly the Yegua Formation, was the target of the most significant discoveries. Offshore, exploratory drilling decreased dramatically by 54% with only 42 wells drilled compared with 90 the previous year. Offshore development drilling increased 27% in 1981 with 88 wells drilled compared with 64 in 1980. Onshore, geophysical activity decreased slightly with 1,064 crew-weeks worked compared with 1,174 crew-weeks in 1980. Offshore geophysical activity also decreased with only 97.5 crew-weeks worked compared with the 156 crew-weeks of the previous year. In 2 state lease sales and 1 federal lease sale held in 1981, the industry spent $1.13 billion to acquire 476,530 acres.

Upper Gulf Coast of Texas

Wells drilled in the Upper Texas Gulf Coast during 1980 totaled 1,826, up over 35% from the previous year total of 1,344 and over 13% from the 1977 decade high of 1,584. Onshore development drilling accounted for most of the increase; activity was up 50% from 1979. Onshore exploratory drilling continued to climb, up from 406 wildcats in 1979 to 420 in 1980. Of these, 42% were in the Oligocene Trend, which remains the most actively explored trend in the coast. The onshore success rate was also up slightly, from 50 to 51 discoveries this year. Offshore exploratory drilling was on the rise in 1980, up 15%, while development drilling continued the 1978 decline trend, down 21% this year. Onshore geophysical activity totaled 1,174 crew weeks, up 224 from the 950 crew weeks in 1 79 and up 182 from the decade high of 992 in 1978. Offshore seismic activity increased to 156 crew weeks, a record high for the last 6 yr. In two state and one federal lease sales, the industry spent $1,480,820,025.03, acquiring 1,357,485.52 ac.

Developments in Upper Gulf Coast of Texas in 1979

Wells drilled in the Upper Texas Gulf Coast during 1979 totaled 1,351, a slight decline from the previous year's total of 1,540. The onshore Oligocene trend remained the most actively explored trend in 1979. A total of 406 exploratory wells was drilled resulting in 50 new-field discoveries. Onshore geophysical activity totaled 950 crew-weeks, keeping pace with the record high of 992 in 1978. The U.S. Department of Energy-sponsored geothermal/geopressure project well reached total depth and entered its 2-year testing phase. Offshore development drilling dropped 42% as did exploratory drilling which decreased 18% in 1979. In 2 state and 2 federal lease sales companies spent $327,361,042 leasing 494,953 acres.

Developments in Upper Gulf Coast of Texas in 1975

The Upper Gulf Coast of Texas had a slight increase of 2.2% in drilling activity this year. The total number of wells drilled (exploratory + development) was 1,130 versus 1,106 last year. The increase is due to a 8.5% increase in development drilling while exploratory drilling declined by 3.6%. The success for all drilling was 54%, most of which is attributable to the 76% success rate for onshore development wells. The Eocene-Paleocene trend and the Oligocene trend were the most active onshore areas and the Pleistocene trend continued to dominate the offshore activity. Six platforms had been set in the Pleistocene trend by year end and 14 more were scheduled to be set. Six lease sales were held this past year; 3 were state sales and the others were federal offshore-contin ntal-shelf sales. Federal Sales OCS 37 and 38-A offered acreage in the Upper Gulf Coast area and drew record low bids.