Eocene Trend Research Articles

Climate Change and Trophic Response of the Antarctic Bottom Fauna

BackgroundAs Earth warms, temperate and subpolar marine species will increasingly shift their geographic ranges poleward. The endemic shelf fauna of Antarctica is especially vulnerable to climate-mediated biological invasions because cold temperatures currently exclude the durophagous (shell-breaking) predators that structure shallow-benthic communities elsewhere.Methodology/Principal FindingsWe used the Eocene fossil record from Seymour Island, Antarctic Peninsula, to project specifically how global warming will reorganize the nearshore benthos of Antarctica. A long-term cooling trend, which began with a sharp temperature drop ∼41 Ma (million years ago), eliminated durophagous predators—teleosts (modern bony fish), decapod crustaceans (crabs and lobsters) and almost all neoselachian elasmobranchs (modern sharks and rays)—from Antarctic nearshore waters after the Eocene. Even prior to those extinctions, durophagous predators became less active as coastal sea temperatures declined from 41 Ma to the end of the Eocene, ∼33.5 Ma. In response, dense populations of suspension-feeding ophiuroids and crinoids abruptly appeared. Dense aggregations of brachiopods transcended the cooling event with no apparent change in predation pressure, nor were there changes in the frequency of shell-drilling predation on venerid bivalves.Conclusions/SignificanceRapid warming in the Southern Ocean is now removing the physiological barriers to shell-breaking predators, and crabs are returning to the Antarctic Peninsula. Over the coming decades to centuries, we predict a rapid reversal of the Eocene trends. Increasing predation will reduce or eliminate extant dense populations of suspension-feeding echinoderms from nearshore habitats along the Peninsula while brachiopods will continue to form large populations, and the intensity of shell-drilling predation on infaunal bivalves will not change appreciably. In time the ecological effects of global warming could spread to other portions of the Antarctic coast. The differential responses of faunal components will reduce the endemic character of Antarctic subtidal communities, homogenizing them with nearshore communities at lower latitudes.

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.

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 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

Onshore drilling in Texas Railroad Commission District 3 totaled 814 wells in 1988, a 1% decrease from 1987's total of 822 wells. Exploratory drilling increased by 18.0%; development drilling declined 6.8%. Thirty-six new field discoveries resulted from drilling 128 new-field wildcats for a 28.1% success rate. Other exploratory wells (new-pool wildcats, deeper pool tests, shallower pool tests, and outpost-extension wells) had a 56.0% success rate; 100 wells were drilled in this category. The developmental success rate was 69.3% with 586 development wells drilled in 1988. The Eocene trend was the most active with 28.5% of the activity.. The Wilcox and Yegua Formations were the primary targets, receiving 47.6% and 46.2% of the Eocene activity, respectively. Offshore exploratory drilling in District 3 totaled 109 wells, a 70.3% increase from 1987's total of 64. Development drilling totaled 64 wells, a 28.0% increase from 1987 activity. The offshore exploratory success rate was 6.2% for new-field wildcats and 58.3% for other exploratory wells. The developmental success rate was 75.0%.

Oil and Gas Development in Louisiana Gulf Coast Onshore in 1988

Leasing and seismic acquisition, 2 of the 3 principal indicators of oil and gas activity, rose slightly in onshore south Louisiana in 1988 as a result of oil price stabilization in 1987 and 1988. Upstream operations intensified, and there was a proportional increase in new-field wildcat drilling as well as a waxing of exploratory activity in the riskier Eocene and Cretaceous trends. Drilling activity decreased 12% from 792 wells in 1987 to 696 wells in 1988. This drop was largely at the expense of development wells, as a similar number of new-field wildcat and other exploratory tests were drilled during both years. Operators drilled 74 new-field wildcats, 93 other exploratory wells, and 529 development wells in 1988. Overall success rate fell from 59% to 51% due to the decreased emphasis in development drilling. Five out of 7 new-field discoveries were completed in Eocene rocks, perhaps signaling a release of capital monies to exploratory drilling. Twenty-seven significant extensions were drilled in 1988, with 6, 14, 3, and 4 successful tests in Miocene, Oligocene, Eocene, and Cretaceous sediments, respectively. Land acquisition rose (22%) for the first time since 1981 from 260,000 ac leased in 1987 to 336,136 ac leased in 1988. The preferred leasing sites were Vermilion, East Feliciana, Terrebonne, Cameron, and Acadia Parishes. Geophysical prospecting expanded for the first time since 1981, climbing 36% from 281 crew-weeks in 1987 to 436 crew-weeks in 1988. Favored locales were Terrebonne, Calcasieu, Cameron, Lafourche, Plaquemines, and Vermilion Parishes.

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.

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 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 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 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 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.

Developments in Upper Gulf Coast of Texas in 1972

Exploration for oil and gas in the Upper Gulf Coast of Texas remained rather static in 1972 in comparison with the previous year. Exploration wildcats increased 8% over 1971; however, development wells showed a decrease of 8% for the same period. Likewise, there was an increase in the exploratory wildcat success rate which was offset by a decrease in the development success. Seismic activity was off slightly from 1971. However, the sharp downward decline experienced in 1971 appears to have reached bottom in 1972, as there was only a 3% decline in 1972 versus a 20% decline per year since 1969. Exploration drilling emphasis was in the Oligocene and Eocene trends, with a marked increase in Oligocene wildcats in 1972 when compared with 1971. The year's most numerous discoveri s were in the Oligocene.

Developments in South Texas in 1972

Drilling activity was up in South Texas for 1972 to 1,777 wells compared with 1,656 in 1971. Exploratory drilling was 12.6% successful, down from 14.8% in 1971. Development drilling was 76.3% successful also down from 78.5% in 1971. Geophysical activity continued to drop and was 4% below 1971. Oligocene-Miocene and Eocene seismic activity increased but was offset by the drop in the Jurassic-Cretaceous effort. The Paleozoic and offshore trends had no seismic activity. The first economic Paleozoic gas discovery was in the Pennsylvanian and should spur further exploration. The older Paleozoic and Jurassic trends each had 3 deeper dry holes, and the Jurassic had another well drilling at year end. The Cretaceous-trend shallow San Miguel (Upper Cretaceous) play continued with 2 new discoveries. A new Sligo (Lower Cretaceous) limestone discovery continued the exploratory interest in that part of the trend. Wilcox gas discoveries in Duval and Karnes Counties were important in the Eocene trend. A pair of Vicksburg gas discoveries in Hidalgo County and a Frio oil discovery in Nueces County kept up activity in the Oligocene-Miocene.

Development in Upper Gulf Coast of Texas in 1971

Exploration for oil and gas in the Upper Gulf Coast of Texas declined in 1971. Exploratory drilling decreased 28%, successful completions were down 6%, and seismic exploration was down 75 crew weeks from the 1970 totals. Development drilling increased from 492 wells in 1970 to 535 in 1971, thus reversing a 3-year trend. Successful completions were down slightly, from 73 to 72%. Exploratory drilling emphasis shifted from the Oligocene trend to the Eocene trend, whereas geophysical emphasis, after heavy concentration on the Cretaceous trend in 1970, centered in the Oligocene trend in 1971. The year's most numerous discoveries were in the Eocene trend, but the most significant were in the Miocene trend.

Possible Future Petroleum Provinces of United States Western Gulf Basin--Eocene and Paleocene: ABSTRACT

Two new important future petroleum provinces, gas in Texas and oil in Louisiana, are related to the Wilcox Group. The gas province in Texas covers 8,700 sq mi and has 12,000 cu mi of untested sedimentary rock. In Louisiana, the oil province covers 5,800 sq mi and contains, 3,800 cu mi of untested sedimentary rock. Another possible future oil province, which covers 8,000 sq mi in Texas and Louisiana and has 7,000 cu mi of untested sedimentary rock, is predicted for the Claiborne Group. No new province is foreseen for the Jackson and Midway Groups. New provinces for the Wilcox and Claiborne Groups more appropriately might be described as gulfward extensions of existing producing trends. This report, concerned with possible future Paleocene-Eocene provinces of the western Gu f basin, assumes that technologic advances will permit drilling and production of wells to depths of 30,000 ft. Considerable quantities of both oil and gas have been found in the established Eocene trends. Currently, there are 501 gas, 1,048 oil, and 377 oil and gas fields which have produced from Eocene deposits. Cumulative production to January 1, 1969, totals in excess of 4.2 Tcf of gas and 2.8 billion bbl of oil. These figures do not include casinghead gas, natural gas liquids, and gas flared in past years. Large structures are known to be present at shallower depths within the future prospective areas. Structurally, these areas will be similar to the established trends; regional growth faults will predominate. Faultline and salt-related structural traps will be prevalent. To reduce economic risk, it will be important to use all available subsurface information for detection and definition of depositional trends which may project into the provinces. The greatest attraction in the provinces will be from the Wilcox sandstone. Claiborne exploration will be a by-product of the Wilcox wells. It is not expected that the industry will rush into the provinces, but deep exploration will move gradually farther gulfward as more knowledge is accumulated. Three present fields have provided, and will continue to provide, encouragement for gradual movement into the future areas. In Texas, Northeast Thompsonville and North Milton fields, with reserves estimated at 500 Bcf to 1 Tcf of gas, are along the landward edge of the predicted Wilcox gas province. Fordoche field, with Wilcox oil reserves estimated at 70-120 million bbl, also lies on the landward edge of End_Page 1786------------------------------ the predicted oil province in Louisiana. These 3 fields provide significant clues to productive possibilities within the future provinces. End_of_Article - Last_Page 1787------------

Developments in Southeastern States in 1967

Drilling operations in the southeastern states of Alabama, Florida, Georgia, Mississippi, and South Carolina declined from 896 tests in 1966 to 764 tests in 1967, a decrease of 14.7%. Of the total completions, 395 were exploratory tests accounting for 39 discoveries. The Wilcox (Eocene) trend of southwestern Mississippi accounted for most of the drilling activity (65% of all wells drilled) in the southeastern states. The most important developments were in the Jurassic trend of Mississippi and Alabama where drilling activity increased 71% with increases in both exploratory and development drilling. Two of the most significant developments were the discovery of oil in the Norphlet Formation, thus establishing another major objective in the Jurassic, and the discovery of Smackover oil in Alabama for a new oil pay in that state. Several tests were drilled in Florida with no success. No tests were drilled in Georgia or South Carolina. A slight increase in geophysical activity was registered in 1967 which was largely the result of increased activity in the Jurassic trend of Mississippi and Alabama. Continued exploration is expected in Alabama, Florida, and Mississippi in 1968 with the Wilcox and Jurassic trends being the most active.

Developments in South Texas in 1964

Over-all drilling activity in South Texas increased 10 per cent over 1963. Wildcat completions rose 12.5 per cent and had a success ratio of 1:5. Development drilling increased 9 per cent and was 71.2 per cent successful. Production of oil increased 4.1 per cent over 1963, and gas and gas liquids production also showed gains. Industry interest was focused on deep drilling ventures along the Jurassic Smackover Limestone and down-dip Yegua trends. Another center of attention was in Wilson, Gonzales, and Gaudalupe Counties where the discovery of four shallow Poth Sand (Paleocene-Eocene) fields led to large-scale development programs. The Oligocene-Miocene trend continued as South Texas' most active area with 47 per cent more exploratory drilling than in 1963. Deeper drilling highlighted the exploration program, as it did in the other trends. Geophysical activity decreased 24 per cent from 1963; the most severe reduction was in the Lower Eocene trend. Experimental programs were widespread and introduced several new deep investigation techniques.