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Hugoton field in Kansas is the largest gas field in North America, with cumulative production over 23 Tcf. Infill and deep drilling activity over the last 10 yr have made it possible to build an extensive database of modern wireline log and core data. Such data formed the basis for a wide-ranging reservoir characterization done to obtain critical information for optimum reservoir management of the field. Reservoir heterogeneity and formation-evaluation problems made it difficult to characterize fluid distribution, estimate gas in place, and determine permeability from wireline log data, but few of the problems in this reservoir characterization study are unique to Hugoton. The techniques described here may be applicable to other reservoirs. Technologies employed to solve the formation-evaluation and lateral-variability problems included artificial neural networks, resistivity modeling, geostatistics, and three-dimensional grid manipulation. ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received April 29, 1996; revised manuscript received October 21, 1996; final acceptance June 10, 1997. 2Amoco Production Co., 1670 Broadway, Denver, Colorado 80202. 3Amoco Production Co., 501 WestLake Park Blvd., Houston, Texas 77253. Current address: Altura Energy Ltd., P.O. Box 4294, Houston, Texas 77210. 4Amoco Production Co., 501 WestLake Park Blvd., Houston, Texas 77253. 5Amoco Production Co., 4502 E. 41st St., Tulsa, Oklahoma 74102. 6Amoco Production Co., 501 WestLake Park Blvd., Houston, Texas 77253. Current address: PGS Reservoir, 10550 Richmond Ave., Houston, Texas 77042. 7Amoco Production Co., 1670 Broadway, Denver, Colorado 80202. Current address: Rocky Mountain Petrophysics, P.O. Box 470337, Aurora, Colorado 80047. We thank the Hugoton JOMT of Amoco Production Company for permission to publish this study. We are grateful to Mobil Exploration and Production, U.S., especially W. H. Jamieson, Jr., for permission to use and publish additional core and log data. We also thank David Reese from Amoco (Denver) for his work on equations relating water saturation to permeability, porosity, and height in the gas column. 3-D seismic interpretation by Mike Bahorich (formerly with Amoco, currently with Apache) is appreciated. Thanks go to Amoco operations and reservoir engineers too numerous to mention for teamwork and testing of the ideas herein. Ann Pettit and Stefan Nowina provided invaluable technical support. This paper benefited from constructive reviews by Robert Raynolds, Joyce Budai, N. C. Wardlaw, Salman Bloch, and Virginia Riggert.*Tcf = trillion cubic feet; Gcf = billion cubic feet.

Computer modeling of gravity profiles of the Rome trough in eastern Kentucky, using data from deep wells in the area as constraints, has provided a general subsurface picture of the area, delineated several major basement features which may be of economic significance, and provided information concerning the areal extent of the trough. As shown in earlier studies, the trough is bounded on the north by the Kentucky River fault zone and its eastward subsurface extension; it is bounded on the south by several uplifts and basins. Older faulting associated with a large gravity high forms the western boundary of the Rome trough; to the east, the trough deepens as it enters West Virginia. The tectonic history of the region is complex and several episodes of rifting are suggested which include the formation of the Rome trough itself. However, a tectonic model to account for the specifics of the formation of the trough cannot be presently formulated because of lack of information in adjacent areas.

Total exploratory drilling in Mississippi, Alabama, Florida, and Georgia increased 8.9% from 1978. A total of 342 tests was drilled compared with 314 in 1978 and new-field discoveries increased from 35 to 44. New-field success rate was 14.2% compared with 11.4% in 1978. Mississippi was the most active state with 235 exploratory tests and 24 of the new-field discoveries. Overall exploratory and development drilling was 780 versus 674 in 1978, a 15.7% increase. The Wilcox trend of southwestern Mississippi led in drilling with 35% of the exploratory tests. Exploratory activity increased over 1978 in the Jurassic trend which had 24% of the tests. The shallow Paleozoic trend accounted for 22% of the exploratory wells and was the leader in new-field discoveries with 18. Activity was constant with 1978 in the Lower Cretaceous trend where 13% of the tests were drilled, and the Upper Cretaceous was the least drilled trend with 6% of the tests. Total exploratory drilling activity will probably increase in 1980 with most in the shallower Wilcox and Paleozoic trends. Acreage for leasing will still be scarce and deep drilling rigs may be in short supply. As usual, most of the exploratory drilling will be conducted by independents and smaller companies.

An increase in drilling activity and further development of secondary-recovery projects resulted in an increase of approximately 2 million barrels of oil and 2,500,000 MCF of gas above the totals of the previous year. New discoveries included 33 new pools, 46 extensions of old pools, and 18 new pays in known producing areas. The amount of deep drilling remained approximately the same.

Four new oil fields to which 45,500,000 barrels of oil reserves have been assigned were discovered in California during 1939; extensions or revisions of existing fields added 257 million barrels of estimated ultimate production; total 302,500,000 barrels of new oil. The 1939 production in the state was 224,354,048 barrels. Estimated reserves were increased by 78,146,000 barrels of oil for a total of 3,178,500,000 barrels as of January 1, 1940. Of more interest to petroleum geologists than merely 1939 statistical data might be a summary of geological endeavors and results in California during the past 20 years and a prophecy for the future. Geological employment and geophysical activity from 1920 to 1939 inclusive are summarized and are correlated with results: namely, new fields discovered, producing wells completed, reserves proved, dry holes drilled, et cetera. Progress of geological thought and changing exploration methods are traced and new developments made possible by deep drilling are outlined. It is concluded that more geological man-years than in the past will be necessary to discover and develop a unit quantity of California's new future oil and gas production.

Again in 1955 operations in the Louisiana Gulf Coast were higher than in the last 5 years. In all, 1, 994 tests were drilled, 769 of which were exploratory tests (31% successful) and 1,225 development wells (87% successful). Oil production showed an increased of 10% during 1955 and gas production an increase of 26%. The 57 new-field discoveries in 1955 showed an increase of 68% over the 34 fields found in 1954. Eugene Island Block 128, Grand Island Block 47, and West Delta Block 59 are three of the more important offshore discoveries, and South Bosco, Bayou Wikoff, Palmetto Bayou Villars fields are the most important onshore discoveries. There were also 110 new pools and 69 extensions to known fields discoveries in 1955. Seismic activity during 1955 showed an increased of 12% over 1954. Reflection seismograph was used in the discovery of 56 of the 57 fields in the Louisiana Gulf Coast. Gravity activity continues to show a slight decrease in 1955. Miocene objectives constituted the majority of exploratory efforts; the Oligocene trend was second. A new world's depth record of 22,559 feet was established in 1955 in the Louisiana Gulf Coast. The average depth of successful new-field wildcats was 12,149 feet. Lease bonuses set an all-time high, one 5,000-acre tract bringing approximately $10,500,000. A high level of leasing activity and the deep drilling trend are expected to continue in 1956.

Deep drilling in the exploration for oil during the past few years has revealed the northern Montana Paleozoic section in the plains of southern Alberta. Records of the Paleozoic of the deep wells in the Kevin-Sunburst field, especially the Adams No. 1, on the Potlatch lease, are compared with those of southern Alberta. Distance from exposures and type localities impose difficulties on correlations, because great lithologic changes occur in the intervals. Most notable are those strata assigned to the Three Forks, composed mostly of a thick massive anhydrite zone. The thin widespread sheet of black shale is chosen as the upper member of the Three Forks formation.

Drilling operations in the southeastern states of Alabama, Florida, Georgia, and Mississippi declined slightly from 764 wells in 1967 to 726 wells in 1968, a decrease of 5%. Of the total completions 410 were exploratory tests which resulted in 28 discoveries. Development drilling maintained a moderate pace with 161 successful wells out of a total of 316 drilled. Deep drilling in the Jurassic trend of Mississippi and Alabama continued to increase sharply in 1968. The most significant developments were a rich gas-condensate discovery from the Norphlet Formation in Escambia County, Alabama, extending Jurassic production 90 mi southeast, and the discovery of several excellent Smackover fields in Clarke and Wayne Counties, Mississippi. The Eocene Wilcox trend of southwestern Mississippi continued to dominate the drilling statistics with 66% of all the wells drilled in the southeastern states. A notable increase in geophysical activity was registered in 1968 resulting largely from a sharp increase in seismic work in the Alabama portion of the Jurassic trend. Exploration is expected to continue at an active pace in the southeastern states in 1969 with the Jurassic and Wilcox trends being the most active.

During 1960, exploration in Pennsylvania resulted in the discovery of 1 new gas field, 8 new gas pools, and 1 deeper pool. It also extended several gas-producing areas, and established a new producing depth record in the state. After drilling a dry hole to the Gatesburg formation (Upper Cambrian) in each of its 2 offshore blocks, the New York State Natural Gas Corporation surrendered its acreage. The new producing-depth record was established by the Robert I. Snyder well No. 1 in Somerset County when gas was found in the Oriskany at 8,574 ft. The well had an initial open-flow after fracturing of 1,572 MCF of gas at a rock pressure of 3,293 psi in 44 hrs. Deep exploration (Middle Devonian or older) found all of the new pools and the one new field. Of the unsuccessful wildcats, 12 were new-field wildcats and 6 were new-pool wildcats. Three deeper pool tests were unsuccessful as were 10 outposts. One new-field wildcat, 8 new-pool wildcats, 1 deeper-pool test, and 3 outposts were successful. There were 61 development gas wells completed and 21 dry holes. The greatest density of deep drilling occurred in Clearfield County. There were 126 deep wells completed in Pennsylvania in 1960 with a total footage of 851,347 ft. Of the 126 wells, 74 were gas wells and 52 were dry holes. Secondary-recovery projects in the Bradford field and the development drilling in the gas fields dominated the shallow-sand drilling activity during 1960. No new shallow-sand oil or gas discoveries were made. In all, 745 shallow-sand wells were completed. Of these, 175 were gas wells, 24 were oil wells, 47 were dry holes, 2 were drilled for underground gas storage, and 497 were drilled in connection with secondary-recovery operations. In addition to the 745 wells, 42 shallow-sand wells were deepened. The total footage of the new and deepened wells was 1,578,933 ft. Oil production increased from 5,760,000 bbls. in 1959 to 5,942,000 bbls. in 1960. Proved oil reserves were estimated at 108,028,000 bbls. on December 31, 1960. Gas production increased from 118,862,000 MCF in 1959 to 119,671,000 MCF in 1960. Gas reserves were estimated at 1,192,132,000 MCF at the end of the year. Distillate produced in 1960 amounted to 67,000 bbls. The total footage drilled, both shallow and deep, was 2,430,280 ft.

Oil production in Kentucky amounted to 21,146,950 bbls., showing a decline of more than 6,000,000 bbls., directly attributable to the drop in Green County. Gas production reached a new peak of 73,896,526 MCF, western Kentucky accounting for 1,872,009 MCF. Deep tests were completed by United Fuel Gas Company in Bell and Elliot counties, and Ralph Thomas drilled a basement test in Lewis County. Interest in Knox production continued to stimulate deep drilling in eastern and central Kentucky. The new oil and gas law which went into effect in June was the greatest forward step Kentucky has taken in its entire history of oil and gas production.

A strong increase in exploratory drilling and success was experienced in 1969. Development drilling was also up. Geophysical activity declined markedly, and land activity remained at about the same level as last year. The Anadarko basin continued to receive major emphasis in all of the above categories as the deep drilling campaign continued along with a high level of shelf and hinge line drilling.

The Lusk Strawn field straddles the Lea and Eddy county line, approximately 30 mi northeast of Carlsbad, New Mexico. It is a northwest-southeast-trending anticline with more than 650 ft of structural relief. The productive unit is primarily a biostrome at approximately 11,300 ft in depth. This biostrome is in the Middle Pennsylvanian Strawn Group. Bioherms grew on the west and north flanks of the feature. Porosity of the pay unit is intercrystalline and vuggy. The pay unit is extremely fractured, and these fractures have been important in the creation of porosity and permeability. To August 1, 1966, the field had produced 12,449,426 bbl of oil and 31,585,786 Mcf of gas from 61 wells draining approximately 10,400 surface acres. Because Lusk was developed on 160-acre spacin , allowables are high and payout is rapid. The discovery of this major field has stimulated deep drilling in the province in search of more Lusk-type production.

Several types of Foothills structures and their relationship to Rocky Mountain structure are illustrated by cross sections, maps, and selected photographs. The types selected are, for the most part, located south of Bow River, and are such structures as have been tested by deep drilling and mapped in detail. The preponderance of overthrust sheets underlain by low-angle sole faults, some of which may be warped or folded, is established. Major underthrust faults, overturned anticlines, underfolded uplifts with major overthrust faults are described. Brief mention is made of minor structures such as high-angle and discoidal faults, sharp and broad-crested anticlines, and other types. Metamorphism, carbon ratios, salients and recesses, and other topics are also discussed.

Since 1948, when gas was discovered in commercial quantity in Buchanan County, 180 wells have been completed in southwestern Virginia. Much of the area under development lies within the boundaries of the Cumberland overthrust block and 38 of the deeper wells have penetrated a zone of shearing near the base of the Devonian shale. This zone, which is very definitely indicated by strong gas blow-outs when drilled, is regarded as the sole of the Cumberland overthrust block.

Drilling operations in the southeastern states of Alabama, Florida, Georgia, and Mississippi declined from 786 wells in 1969 to 668 wells in 1970, a decrease of 15%. The decrease is due primarily to the subnormal number of wells drilled in the Wilcox area of Mississippi. Of the total completions, 311 were exploratory tests which resulted in 42 discoveries. Development drilling during 1970 included 357 completions netting 204 oil wells and 17 gas wells. Deep drilling in the Jurassic trend of Mississippi and Alabama continues to highlight the drilling activity and registered a 20.4% success in exploratory drilling and 68.8% success in development drilling. Probably the most significant discovery during 1970 was the Smackover oil discovery at Jay field in Santa Rosa County, Florida, thus establishing the first Jurassic oil production in Florida. The discovery of Cotton Valley and Hosston oil production in Leflore County, Mississippi, extended production from these formations 47 mi north. Drilling in the Eocene Wilcox trend of southwestern Mississippi declined from 468 wells in 1969 to 263 wells in 1970. An increase in geophysical activity was registered in 1970 resulting largely from an increase in seismic work in Mississippi and Florida. Exploration is expected to continue at an active pace in the southeastern states in 1971 with the greatest emphasis in the Jurassic trend.

In 1963, there were 3,992 wells drilled in the Permian Basin. This represents a 14% decrease from 1962. Exploratory tests averaged 32% and development drilling 88% as being successful. Exploratory success gained 4% while development remained the same compared to the previous year. Of the 359 successful exploratory tests drilled during 1963, 61 were considered significant based on reserves, potential productive area and geological significance. Geophysical activity increased 6% in crew-weeks for seismic; while gravity decreased 57%. The Delaware basin led the province in seismic activity. The Central Basin platform was the most active geologic feature in drilling activity while having several promising discoveries. San Andres, Wolfcamp, and Pennsylvanian activity in the north part of the Northwestern shelf resulted in establishing interesting new reserves. Deep Pennsylvanian gas exploratory drilling continues in western Eddy with discoveries stimulating interest. Two promising oil discoveries were completed on the Ozona platform indicating a sizable reserve. Encouraging discoveries were plentiful in the Midland basin from new-field wildcats and drilling deeper in shallow pay fields. Deep drilling is increasing in the southeastern part of Delaware basin where major gas reserves are indicated. The Val Verde basin continues to increase its gas reserve through deep explora ory drilling. Pecos County led the Permian Basin area in number of discoveries, and now has the world's deepest production. Leasing was active in basin areas. A Strawn oil discovery in central Crockett County stimulated leasing there and into Sutton County. The 47th Texas University Land Auction brought the University $2,950,000 for 50,621 acres. Leasing in western Eddy County, New Mexico, was active based on Pennsylvanian gas discoveries.

Drilling operations in the southeastern states of Alabama, Florida, Georgia, and Mississippi increased from 726 wells in 1968 to 786 wells in 1969, an increase of 7.7%. Of the total completions, 418 were exploratory tests which resulted in 38 discoveries. Development drilling during 1969 included 368 completions netting 177 oil wells and 18 gas wells. Deep drilling in the Jurassic trend of Mississippi and Alabama continued to increase, registering a 21% success in exploratory drilling and a 77% success in development drilling. The most significant developments were a Smackover gas-condensate discovery in Holmes County, Mississippi, which extended Jurassic production 36 mi northwest, and a deep H2S-rich gas-condensate discovery in Rankin County, Mississippi. The Eocene Wilcox trend of southwestern Mississippi remained the most active drilling area in the southeastern states with 59.5% of all completions. An increase in geophysical activity was registered in 1969 resulting largely from an increase in seismic work in Alabama and Florida. Exploration is expected to continue at an active pace in the southeastern states in 1970 with the Jurassic and Wilcox trends being the most active. Also, an increase in activity is expected in the Black Warrior basin in 1970 following a major lease play in 1969.

Future major oil and gas deposits in the S. Arkansas and N. Louisiana region will come from deep drilling in one of the following sequences: 1) The Eagle Mills red beds [Permian], which occupy an asymmetrical trough N. of a structural high along the Arkansas-Louisiana state line. These are not considered potential reservoirs. 2) The Stanley-Jackfork-Atoka [Carboniferous] beds underlie the Eagle Mills and extend much further N. These may contain gas deposits but will be difficult and expensive to explore. 3) The Morehouse Formation, S. of the Arkansas-Louisiana state line high, presents the best possibilities for future deep production and deserves further investigation.

Minor variations in production in Israel in 1977, from fields discovered more than 20 years ago, resulted in a 20% decline to 585 BOPD and a 5% increase to 5.9 MMCFGD. Geophysical activity declined, and 1 crew was released at midyear. Deep drilling was undertaken at 2 locations. Fourteen wells were drilled on shallow gas prospects with negative results. The National Energy Authority and the newly created Ministry of Energy began functioning.

Drilling operations in the southeastern states of Alabama, Florida, Georgia, and Mississippi increased slightly during 1972, as 642 wells were drilled, compared with 637 in 1971. There was a notable increase in the Jurassic trend activity in both exploratory and development drilling. In the Upper Cretaceous trend drilling activity declined because of less development drilling at Baxterville and Heidelberg fields. Drilling in the other trends remained very near the 1971 level. Of the total completions, 387 were exploratory tests which resulted in 40 discoveries. Development drilling included 255 completions netting 140 oil wells and 13 gas wells. Deep drilling in the Jurassic trend of Mississippi, Alabama, and Florida continues to highlight the drilling activity with 41% of the total wells drilled. Jay field dominated the development drilling with 57 completions. At year end production from this field was nearing 2 million bbl of oil per month, which was more than half of the total Jurassic production in the 3-state area. Significant exploratory successes in this trend were Big Escambia Creek field in Escambia County, Alabama; Blackjack Creek field in Santa Rosa County, Florida; and Lake Como field in Jasper County, Mississippi. Drilling in the Black Warrior basin increased from 41 wells in 1971 to 48 wells in 1972 and recorded 8 exploratory successes. The most significant of these is the Corinne field discovery in Monroe County, Mississippi. Geophysical activity shows a decrease from the previous year in Alabama and Florida and an increase in Mississippi. Exploration is expected to continue at an active pace in the southeastern states in 1973 with the greatest emphasis again in the Jurassic trend. Also, a continued increase in activity is expected in the Black Warrior basin.

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.

The largest producing pool in Tennessee is in Scott county, oil being obtained at a depth of 1250 feet from the St. Louis limestone. Probably the oldest oil pool is the Spurrier-Riverton pool, in Overton, Pickett and Fentress counties. Several wells have come in recently getting oil from the Ordovician, 160 to 275 feet below the Chattanooga "black" shale. A pool has recently been developed in Sumner and Macon counties, where oil is being obtained 30 to 125 feet below the Chattanooga in wells with an average depth of about 300 feet. Western Tennessee is being prospected in the vicinity of Reelfoot Lake. Shows of gas have been encountered in the top of the Cretaceous at a depth of about 1700 feet, along the Kentucky-Tennessee line. Drilling is now in progress on a plunging anticline at Huntingdon, Carroll county. Prospects for additional pools in the Silurian and Ordovician rocks underlying the Highland Rim of Tennessee are very favorable, while deep drilling in the western part of Tennessee into the Cretaceous sands is worthy of considration. End_of_Article - Last_Page 99

Exploratory activity in the Panhandle District during 1959 was up 22.8% over 1958, although the exploratory success rate was down 1.2%. There were 106 completions and 218 dry holes. A large majority of the discoveries were in Pennsylvanian reservoirs in the Anadarko basin; however, deep drilling in the Panhandle and Hugoton fields accounted for many discoveries. Leasing and geophysical activity decreased and are expected to remain down during 1960.

The Bryan Heights salt dome is located in southern Brazoria County, Texas, near the mouth of Brazos River and nearly due south of Houston. It is marked topographically by a low mound which rises about 25 feet above sea-level. The top of the salt is encountered at an average depth of about 1,100 feet. Formations of Quarternary and later Tertiary age overlie the dome, and as in the case of other Gulf Coast domes there are more or less steeply inclined Tertiary rocks surrounding the salt core. A sulphur-bearing cap rock is of chief economic importance, sulphur being mined by the Frasch hot-water process from depths of about 700 to 900 feet below the surface. Some deep drilling, to dephts of more than 3,500 feet, has been undertaken on the flanks of the dome, but no commercia oil or gas has been encountered.

In all, 2,727 wells were drilled for oil and gas in Illinois and Indiana in 1947 as compared with 2,870 in 1946, a decrease of 5 per cent. Total oil production decreased 11 per cent from 82,128,000 barrels in 1946 to 72,900,000 barrels in 1947. Wildcat drilling increased from 760 completions in 1946 to 792 completions in 1947. Forty-four new pools and approximately 76 extensions were discovered in the two states in 1947 as a result of wildcat drilling. The new production found in 1947 was almost entirely from Mississippian strata. Little deep drilling was done, and no major amounts of oil were produced from strata below the Mississippian. A "Trenton" pool, Woburn South, was discovered in Bond County, Illinois, which had six producing wells at the end of the year. Drilling is expected to continue in 1948 at nearly the same rate as in 1947.