Seismic Work Research Articles

Developments in Western Canada in 1961

Over-all exploration activities (as reflected by expenditures) in Western Canada during 1961 continued to decline from the peak year of 1957, with most of the reduction due to decreased wildcat drilling in Saskatchewan and the Territories, and lower Crown land bonuses in Alberta. Seismic work increased slightly (principally in northeastern British Columbia) for the first time since 1953, and surface mapping declined for the second consecutive year. Alberta continued to lead other provinces by a substantial margin in all phases except surface mapping. The Arctic Islands, which began drilling its first wildcat, showed a sharp increase in exploration. Comparisons below are with 1960. I. DRILLING. Exploratory tests down 49 (6%) to 769 Discoveries--oil 50 (down 4). Gas 77 (down 10) Extensions--oil 76 (up 28). Gas 82 (up 22) Development wells up 15 (1%) to 1,689 Main areas--Beaverhill Lake and Cardium oil fields, Mississippian oil and gas fields of Alberta; Mississippian and Viking oil fields of Saskatchewan; and Triassic oil and gas fields of British Columbia II. EXPLORATORY METHODS. Expenditures down $30 million (10%) to $260 MM Seismic up 45 mos. (8%) to 613 mos. Gravity up 13 mos. (130%) to 23 mos. Surface Mapping down 30 mos. (10%) to 260 mos. III. PRODUCTION. Crude up 89 MBPD (17%) to 611 MBPD Liquids up 100 MBPD (18%) to 640 MBPD Gas Sales up 315 MMCFPD (27%) to 1,509 MMCFPD Sulphur up 260 long tons/day (23%) to 1,370 long tons/day EXPORTS. Crude up 66 MPBD (60%) to 180 MBPD Gas up 169 MMCFPD (55%) to 476 MMCFPD IV. RESERVES (Proved remaining). Crude up 496 MM bbls. (14%) to 4,166 MM bbls. N.G.L.'s up 37 MM bbls. (7%) to 576 MM bbls. Gas up 2.9 TCF (9%) to 33.3 TCF Sulphur up 2.8 MM long tons (5%) to 58 MM long tons V. LAND. Holdings down 2 MM acres (1%) to 255 MM acres Sales down $10 MM (16%) to $57 MM

GEO PHYSICAL INVESTIGATIONS IN TREMADOC BAY, NORTH WALES

The results of a gravity survey of North Wales ( Powell 1956 ) suggested that Tremadoc Bay, off North Wales, might be a Triassic basin, the eastern boundary being a major fault coinciding in part with the coastline, but nowhere exposed. To test these ideas a seismic refraction survey has been made of Tremadoe Bay, consisting of a long traverse and some short lines, these being supplemented by a number of shorter profiles across the coastal flats of Morfa Dyffryn. A survey of the bay with a proton magnetometer was also undertaken and some closely spaced gravity and magnetic measurements have been made on Morfa Dyffryn. The results of the seismic work indicate the presence of three layers. The top layer has a maximum thickness of about 1800 feet and a velocity of 6500 feet/sec., thins westwards and ultimately dies out. It is considered to be late Mesozoic or Tertiary in age. All the evidence indicates the eastern boundary of this layer to be a major fault or a scarp. The middle layer has a maximum thickness of 6000 feet and a velocity of 13,000 feet/sec. The form and magnitude of the gravity anomaly in the area, after allowing for the effect of the top layer, make it most unlikely that this second layer has a low enough density to be Mesozoic. It is probably Ordovician. The third and lowest layer identified is thought to be Cambrian. The form of the regional gravity low over Cardigan Bay points to a structural origin for the bay, though the alternative theory that the anomaly is due to a major granitic intrusion is considered possible.

Edwards Gas Trend in South Texas: ABSTRACT

Drilling since 1954 across a wide area in South Texas has established a new and deeper trend of production which may be an important reserve of oil and gas. It extends from the Mexican border on the Rio Grande northeastward across Webb, LaSalle, McMullen, Atascosa, Karnes, DeWitt, and Lavaca counties, a distance of 200 miles, and has reached a width of 13 miles in McMullen County. Several factors held back the early development of the play: it is deeper than most operators in the district usually drill; the gas encountered was sour; and the geology is more complex than anticipated. These factors are now fading into the background and additional development is expected. The large size of some of the reservoirs and their capability makes this a profitable operation. The new development ranges in depth from 9,000 to below 14,000 feet, with the latter figure expected to be increased. Production is established in various structural features The Edwards limestone (Fredericksburg group of the middle Albian Cretaceous) is the main producing zone to date although additional drilling should prove other Cretaceous formations to be productive. Structural patterns proved to date include piercement-type and deep-seated salt domes, folding along both down-to-the-coast and upthrown fault blocks, and possibly simple reef development in the limestone. Across central Atascosa County is a series of up-to-the-coast fault blocks which have been tested and yielded several profitable oil and gas fields at depths of 7,000-8,000 feet in the Edwards limestone. This trend is now almost completely explored, and is not considered part of the new development area. Seismic work has been largely responsible for most discoveries though some fields were mapped as surface structures as early as 1932. An unconformity at the top of the Cretaceous in some areas makes shallow subsurface misleading and the seismic interpretation difficult. Additional sample work is needed to determine newly found stratigraphic changes. Well expenses have been reduced as contractors solve their local problems. A dry hole will range from $100,000 to $125,000, though some of the deeper tests have been extremely expensive. Completion costs are high due to the need of high-pressure connections and the sulphur content which makes corrosion-proof tubing and fittings necessary. The gas must be cleaned before sale and additional expensive plants will be required. It is too early to estimate gross reserves for the district, but development to date indicates a major figure. The first opinions on the trends assumed that gas would be the only product, as the first ten fields yielded only minor condensate production. The discovery of the Persons field in Karnes County in 1959 changed that idea. One oil well was also completed on the north end of the Fashing field in Karnes County, with accumulation caused by a stratigraphic or permeability trap, within the gas reservoir. End_of_Article - Last_Page 126------------

Developments in Colorado and Western Nebraska in 1960

Total wells drilled (906) in Nebraska during 1960 represented a 5% decrease from 1959, although exploratory drilling increased 6.1%. Success ratio for wildcat wells was 10.4%. Most significant were 6 new fields discovered on the west flank of the Cambridge arch, where in addition to Lansing-Kansas City production, Reagan sand (Cambrian (?)) was found productive at Sleepy Hollow. Total production in western Nebraska for 1960 was 23,921,487 bbls., an increase of 5.9% over the 22,584,096 bbls. produced in 1959. The Denver basin production increase amounted to only 2.6%, whereas Cambridge arch production increased over 806%. Drilling in Colorado totaled 703 wells, a decline of 16.1% from 1959. Exploratory drilling in eastern Colorado decreased 76.7%, while wildcat wells in western Colorado increased 11.8% over 1959. Success ratios for the two areas were 11.9% and 16.7%, respectively. Foremost in importance was the discovery of gas and condensate from the Mississippian and Devonian rocks at Southeast Lisbon in the Colorado part of the Paradox basin. Six gas fields and two oil fields were found in northwest Colorado, including a significant Weber (Pennsylvanian) discovery on the Danforth Hills anticline and several Cretaceous Mancos-Mesaverde transition zone gas discoveries. Total production in Colorado for 1960 was 47,427,297 bbls., a 2.1% increase of 973,885 bbls. over the 46,453,412 bbls. produced in 195 . Geophysical activity increased sharply on the Cambridge arch, south-central Nebraska, and in the Paradox basin of southwest Colorado, the latter area accounting for 54% of total seismic work in Colorado and Nebraska. These same areas provided the most active regions, leasing and trading-wise. The decline in Denver basin Cretaceous exploration, which was sharply down in 1960, is expected to continue during 1961. However, this will undoubtedly be offset by continued increased activity in western Colorado and on the Cambridge arch of south-central Nebraska. Changes during 1960 in the Mineral Leasing Act involving increased annual rentals of Federal lands will probably cause a more rapid evaluation of such lands during 1961.

NOMOGRAMS TO SPEED UP SEISMIC REFRACTION COMPUTATIONS

Nomographic solutions of a number of equations commonly employed in seismic refraction work are presented. The equations solved are: 1. Depth to a second layer, by means of the critical distance formula. 2. The critical angle and offset distance formulas. 3. True velocity of bedrock from the apparent up‐ and down‐dip velocities. 4. Depth to a second layer by means of the intercept‐time formula. This last solution is also applied to (a) finding the throw of a fault and (b) depth to an irregular second layer at each seismometer beyond the critical distance. Geometry of each of the nomograms is explained. Procedure for using each of the nomograms is described.

GEOPHYSICAL CASE HISTORY OF THE HORSE CREEK FIELD, LARAMIE COUNTY, WYOMING

The Horse Creek field located in Laramie County, Wyoming, was discovered and developed by the General Petroleum Corporation following a reconnaissance gravity survey and preliminary and detail seismic surveys. The gravity survey, made during 1940, delineated a strong maximum gravity anomaly having a magnitude of about 5 mg. Limited seismic work was then conducted in the area during 1941 and 1942 and mapped a prominent anticline having some 2,000 ft of closure. In September, 1942, General Petroleum Corporation spudded in their No. 78-31-G well, located on the apex of the structure. This well was completed as the discovery for the field, producing from the lower Cretaceous‐Lakota sand. The second well, No. 74-6-P, was completed in April, 1943, as the lower Cretaceous‐Muddy sand discovery for the field. Further seismic work was done during 1944 and 1945 to detail and refine the structural picture. Subsequent drilling developed the Muddy sand as the primary producing zone in this field. A total of 32 producing wells has been drilled on this structure and to August, 1958, the total cumulative production from the field was 3,519,000 barrels of oil.

Petroleum Developments in Mexico in 1959

Four hundred forty-one wells were drilled in Mexico during 1959 as compared with 379 drilled the preceding year. The average depth per well was increased to 7,035 ft. as compared with an average of 6,958 ft. per well during 1958. During the year of 1959, 133 wells were classified as exploratory holes, of which 82 were new-field wildcats, resulting in the discovery of 11 new gas and oil fields. Other exploratory holes were classified as follows: 9 new-pool wildcats, 9 deeper-pool tests, 8 shallower-pool tests, and 25 extension wells; 31 of these exploratory holes were completed as producers. Of the total number of wells, 298 were successful. The new fields discovered were located as follows: 1 in the Eocene trend in Northeast Mexico, 5 in Cretaceous and Jurassic limestones and calcarenites in the Tampico Embayment, and 5 new fields in Miocene sands in the Isthmus and Tabasco region, one of which is an off-shore prospect. The main exploratory effort, as in previous years, was concentrated along the coastal plain of the Gulf of Mexico where all the producing fields are located; however, seismic work in Baja California and gravity work in the Yucatan Peninsula and Northeastern Chihuahua were continued. One test was drilled to the Cretaceous in Northeast Mexico, and 5 tests were drilled to explore the productivity of the Upper Jurassic and Lower Cretaceous formations in the Tampico Embayment. In the Veracruz Embayment, as in the past year, drilling activities decreased considerably as only 4 wells were drilled in search of oil: 2 were drilled to the Middle Cretaceous, as yet unproductive in this area and 2 to the Eocene and Oligocene. Crude oil and distillate production in 1959 was 105,758,473 bbls., an increase of 9.5% over the previous year. Total gas production was 329,363,504 MCF, an increase of 79.7% over 1958.

Developments in West Texas and Southeastern New Mexico in 1959

The recovery from the 1958 recession is well illustrated in the drilling for and production of crude oil in West Texas and Southeastern New Mexico. In 1959, 7,721 wells of all classes were drilled in this area, being a 23% increase over 1958. The 1,200 exploratory wells made a 9% increase, and the 6,570 development wells made a 27% increase over the previous year. The success ratio decreased slightly as shown by the 23% successful exploratory tests, down 4%, and the 88% success for development wells, down 2%. With comparable allowables and producing days, production for the year was 520,213,777 bbls. of oil, a 19% increase. The most important discoveries were the Forest Oil Corporation and Pan American Petroleum Corporation's Harris No. 1 in Dawson County, Hill & Meek r's Trower No. 1 in Loving County, and the Argo Oil Company's Neal No. 1 in Pecos County. The most spectacular discovery was the Turner's Shannon No. 4-BB in Crockett County. Exploratory methods followed the same general pattern as in previous years with increased emphasis on subsurface geological methods. Geophysical activity was down 6% from the 1958 level. The Delaware basin, Sheffield channel, and Val Verde basin areas continued to be the most active from the standpoint of seismic work. Leasing activity continued high in the area with bonus prices increasing and length of primary term decreasing. There was one University Land Sale held with competition less intense than in previous years with the average bonus price decreasing. There appears to be a trend toward more joint ventures and drilling units in both the areas of tightly held acreage and in the more unexplored areas in which the drilling costs are extremely high.

AMMONIUM NITRATE BLASTING AGENTS

I have read with interest the article by Jack Martin and Thomas O. Hall on ammonium nitrate blasting agents in seismic work (GEOPHYSICS, v. 24, p. 155–163).

Geology of North Tejon Field: ABSTRACT

The North Tejon field is approximately 25 miles south of Bakersfield, 2½ miles north of the Tejon-Grapevine field, in the southern end of the San Joaquin Valley. The discovery well was the Reserve Oil and Gas Company's Butler-Wehr No. 67-18, completed in March, 1957, from the interval 11,850-12,200 feet. Production is from the Vedder sand of lower Miocene (Zemorrian) age. This discovery was the result of a combined geological-geophysical effort. Initial regional subsurface geologic studies indicated the possible presence of a structural bowing in the area, and subsequent seismic work substantiated this hypothesis. Shortly after the discovery, the Standard Oil Company of California obtained a 50% interest in approximately 2,000 acres surrounding the No. 67-18. Since that time, Standard and Reserve, with Reserve as operator, have drilled and completed 5 additional wells in the Vedder. Development by Reserve Oil and Gas Company is proceeding with three drilling strings. The field is at present divided into two areas; the Main area, site of the original discovery, and the Highway area, a westerly extension discovered in April, 1958, by Richfield Oil Corporation. Indications at present point to a probable joining of the two areas as drilling continues. The structure of the field is interpreted as a northeast plunging nose, complicated to a small degree by faulting. The fault appears to control accumulation to some degree. The main controlling factor appears to be an updip permeability barrier. Stratigraphically the area is fairly simple, the only really anomalous unit being the basalt section, which varies in thickness from 2,000 feet in the Main area to 50 feet or less in the Highway area. Production in both of the areas is from the Vedder sands. These sands are found at depths ranging from 8,700 feet in the Highway area to 12,000 in the Main area, indicating an oil column of 3,300 feet. End_Page 252------------------------------ Average gross thickness of the producing interval is between 400 and 500 feet. Dependent on structural position and permeability, a well may produce from one to as many as six identifiable zones in the Vedder section. Present Vedder production in the field is approximately 3,000 B/D of 32-35° gravity crude. After completion the wells are restricted to varying rates dependent on their individual characteristics. Only the western limit of production has been established to date. End_of_Article - Last_Page 253------------

Petroleum Developments in Mexico in 1958

Three hundred seventy-nine wells were completed in Mexico during 1958, as compared with 389 drilled during the previous year. However, the average depth per well increased from 6,463 ft. to 6,958 ft. for a total footage of 2,636,900 ft., an increase of 122,735 ft. over the total footage drilled during 1957. Seventy-six wells were classified as exploratory holes, 17 of which were successful (22%). Fifty-five new-field wildcats were drilled and new reserves were added through the discovery of 4 new oil and/or gas fields, 12 new pools, and 1 extension to a previously producing field. Of the total number of wells, 285 were successful (75%). Two new gas fields were located in the Eocene and Oligocene trends of Northeastern Mexico, one oil field was found in the Poza Rica district, and a fourth oil field was found in central Tabasco in southern Mexico. The bulk of the exploratory effort was concentrated in the coastal plain of the Gulf of Mexico, where all the producing fields are located; however, gravity and seismic work continued in the Baja California and Yucatan peninsulas and in Chihuahua in north-central Mexico. In northeastern Chihuahua an unsuccessful deep exploratory test was completed during this year. Several tests were drilled to the Cretaceous and Jurassic in Northeastern Mexico, and in the Tampico Embayment most exploratory wells penetrated the Upper Jurassic formations which produce in the Constituciones and San Andres fields. In the Veracruz Embayment drilling activity decreased considerably and will be followed by a campaign of deeper wells to test the Middle and Lower Cretaceous sediments, as yet unproductive in this area. Production in the Isthmus and Tabasco region increased 7,000 bbls. per day during the year. This increase being due to the development of the La Venta and Ogarrio fields and the completion of the absorption plant in the Macuspana district. Crude oil and distillate production for 1958 was 100,641,405 bbls. Total gas production was 262,626,152 MCF. This means an increase of 8.5 million bbls. of oil and about 100 millions MCF of gas.

Developments in West Texas and Southeastern New Mexico in 1958

The 1958 recession curtailed operations in West Texas and Southeast New Mexico to the extent that both exploratory tests and total wells drilled were 13% below the 1957 high. This is the first decline in exploratory tests since 1954. 6,280 wells of all classes were drilled in the area. With reduced allowables, production for the year was 438,705,749 bbls., or 20% below the 1957 record year. Success ratio for all exploratory wells was 27%; the ratio for development wells was 90%. The most important discoveries were the Brown-Bassett field of Terrell County, Texas; the Dunigan, Happy, Red Loflin, and Teas fields in northern Borden and southwestern Garza counties, Texas; the Good, SE. field in southern Borden County, Texas; the Block 9 field in Andrews County, Texas; the I.A B. (5070 Penn) field in Coke County, Texas; the Little Lucky Lake field in southern Chaves County, New Mexico; and the South Vacuum field, Lea County, New Mexico. Exploratory methods followed the same pattern as in previous years. Subsurface methods accounted for 38 discoveries, seismic 14, seismic and subsurface methods combined accounted for 15 successful wells, and 7 were drilled by non-technical or unknown methods. From the statistics it appears that more emphasis is being placed on detailed subsurface geological studies. Geophysical activity was 25% below the 1957 level. The Delaware basin continued to be the most active area from the standpoint of seismic work. The concentration of interest in the Val Verde basin, northeast part of the Midland basin, Northwestern shelf, and parts of the Eastern shelf, accounted for a majority of lease acquisitions in the area. The state conducted only one University Land Sale but the bonus prices remained high. It is anticipated that more joint ventures and drilling units will result, in view of the unavailability of land in favorable areas. Acreage is being dropped in areas considered least promising.

GETTING THE MOST OUT OF PRESENT SEISMIC INSTRUMENTS

Much of the present seismic work is being carried out in areas where results are difficult to obtain. The paper outlines the requirements for seismic instruments for these operations. The particular characteristics desired for specific problems are illustrated, and the instrument factors that affect these characteristics are outlined. Examples of the effect of instrument adjustment are shown. The attainment of optimum results with present equipment under diversified field conditions may require modifications according to area, in shooting techniques, geophones, amplifiers, galvanometers, recording, and record presentation. The discussion of the advantages of magnetic recording assumes that the best field techniques have been applied.

SEISMIC SURVEY OF SINAI AND THE GULF OF SUEZ

Severe obstacles are present to increase the difficulty of seismic operations in the Gulf of Suez area. A program combining land seismic work, semi‐marine exploration over a reef zone, and rapid offshore reconnaissance is described. The results of each are illustrated, and the value of a rapid marine survey in guiding more detailed work on land is emphasized.

Geology of McAlester-Arkansas Coal Basin: ABSTRACT

The McAlester-Arkansas Coal basin is an elongate arcuate basin in southeastern Oklahoma and northwestern Arkansas. It is bounded by the following: Mississippi embayment on the east, Ozark uplift on the north, Ouachita Mountains on the south, and Arbuckle Mountains on the west. The stratigraphic sequence ranges from Cambrian through Pennsylvanian age with aggregate thicknesses of 2,000 feet of sediment along the northern rim of the basin to probably in excess of 25,000 feet in the southern part of the area. Paleozoic rocks of late Pennsylvanian age crop out over most of the area. The depositional axis has not been determined by drilling as yet. Geophysical methods may define the basin and clarify the relationship between the Arbuckle-Ozark type rocks and the Ouachita rocks. Surface structures generally strike east-west and were formed by compressional forces from the south (Ouachita area) against the Ozark positive area on the north beginning in early Pennsylvanian time, and extending into the late Pennsylvanian. The effect of these forces is reflected by the amount of structural relief present; highly faulted structures occur south of the Choctaw fault, well defined structures north of the Choctaw fault, and gentler folds along the Arkansas River. The basin has been the scene of exploratory work for many years with the greatest and best organized effort being carried out presently. Surface, subsurface, aerial photo interpretation, and geophysical mapping methods have been attempted. Monotonous sequences of sands and shales crop out, making surface work difficult. Rough terrane, poor accessibility, and hard drilling make seismic work expensive. Subsurface work will become increasingly important as more deep wells are drilled. Gas prospects in Atoka and Morrow rocks are numerous, but a great volume of sediments both Pennsylvanian and pre-Pennsylvanian in age have not been evaluated. End_of_Article - Last_Page 212------------

Developments in Wyoming and Idaho in 1956

There were 1,026 wells drilled in Wyoming in 1956. The 339 exploratory wells represent the greatest number drilled in any year. There was more development drilling than last year, but less than the peak year of 1954. There were 36 discoveries, of which 80% were Cretaceous. The Powder River basin led in activity, with 34% of the exploratory wells, accounting for 30% of the discoveries. The Green River basin had 12% of the wells, for 30% of the discoveries. The Bighorn and Wind River basins each had about 20% of the exploratory tests and 20% of the discoveries. There were no discoveries in the Hanna, Laramie, and Julesburg basins in the southeast part of the state. Stratigraphic exploration was more extensive than seismic structural work. Discoveries appear disappointing but evaluation of stratigraphic discoveries requires years. Very encouraging development drilling in 1956 at two insignificant discoveries of 1951 and 1953 has established two major stratigraphic oil fields. Stratigraphic plays in the Mesaverde, Phosphoria, and Muddy formations commanded most attention. Several tests of complicated thrust-fault seismic prospects were drilled. Five exploratory wells were drilled in Idaho. No oil or gas was found.

Oil and Gas Developments in Utah and Nevada in 1956

Drilling activity in Utah reached a record high with 77% more wells drilled in 1956 than in 1955. In Nevada drilling was about equal to that in 1955. Important new oil and gas reserves were discovered in San Juan County, Utah. Wells drilled in that county alone accounted for 39% of the Utah tests. Thirty-eight approved U.S.G.S. units were in effect at the end of the year. The Navajo Indian land sale resulted in selective bids exceeding $3,000 per acre. Leasing in Utah greatly increased, whereas in Nevada large blocks were being surrendered. Geophysical exploration was greatly increased in 1956. Over 800 crew-weeks of seismic work were reported as compared with approximately 400 in 1955. Plans for pipeline outlets to California or the Gulf Coast supplied stimulus to Four Corners exploration. The principal trends expected in 1957 are: decreased drilling and exploration activity in Nevada; rapid development of indicated reserves in San Juan County, Utah; increased exploration activity in the northwestern part of the Paradox basin; and steady exploration effort in the Uinta basin and on the Uncompahgre uplift.

Developments in East Texas in 1955

Statistically, 1955 developments were comparable with the previous year, except for the increased exploratory drilling. The discovery ratio remained approximately the same. No major reserves were indicated from these new discoveries, but reserves increased substantially from extensions and new pays. Development drilling decreased 6% in 1955. Exploration drilling increased 19%, reflecting the faith operators have that new substantial reserves will be found. In all, 627 wells were completed as producers. Major reserve increases came from extensions of old fields rather than new fields. Of the important new discoveries, 10 were new fields, 9 deeper pools, and 2 shallow pools. Twenty-seven of the new producers were in the Lower Cretaceous, 7 in the Upper Cretaceous, and 2 in the Jurassic. Geophysical activity decreased 4% from the previous year. Seismic, gravity-meter, magnetometer, and core-drill work amounted to 1,341 crew-weeks.

ON SURFACE‐WAVES IN LOOSE MATERIALS OF THE SOIL*

ABSTRACTFor the first time a method of observing the effects of hammering and of small blasts has been applied in a series of experiments on various soils, using a three component set of small mechanical leaf spring seismographs. The seismograms have been subjected to a thorough harmonic analysis. By means of these experiments, the theoretical concept of Rayleigh waves generated in a layer overlying a semi infinite medium has been confirmed. The dispersion curves resulting from different experiments correspond well with theoretical dispersion curves.It may be. concluded that every seismic pulse generates a specific Rayleigh wave mechanism in loose layers. The depth of penetration of the Rayleigh wave mechanism and its frequency spectrum depend upon the delivery of energy and upon the consistence of the particular soil.Most of the energy delivered is transformed into surface‐waves, and it is obvious that the direct reading of pulses in seismograms effects mainly group velocities of the Rayleigh wave mechanism. Thus, all endeavours to procure information about near surface layers of loose soils by refraction seismic work, as the present investigations show, meet with far more difficulties than has been assumed in the past.With regard to the determination of the critical frequencies of the generated surface waves, the method of harmonic analysis of seismograms is superior to the usual dynamic method of soil mechanics, since rotating weights do not give the characteristic phase velocities and transversal wave velocities necessary for judging the consistency of loose soils.Finally, a method of determining the absorption of surface waves is discussed.

Developments in East Texas in 1954

Exploratory drilling increased 12% and field well drilling increased by 27% during 1954. The increase in field well drilling was due to the rapid development of several important discoveries made during 1953. Twenty-three discoveries were made: 14 of these were new-field wildcats, 3 shallower-pool, and 6 deeper-pool. Of this total, 14 were completed as oil wells and 9 as gas wells. New production was limited to the Cretaceous section. New-pool discoveries were made in the Neches, Cornersville, Red Lake, Elkhart, Kildare, Willow Springs, Ham-Gossett, South Dome-Buffalo, and East Texas fields. Geophysical exploration decreased by 2% over the previous year. Seismic, gravity, magnetometer, and core-drill work accounted for 1,398 crew-weeks.