Slim Hole Research Articles

Multi-Offset Vertical Seismic Profiles: Fracture and Fault Identification for Appalachian Basin Reservoirs--Two Case Examples: ABSTRACT

Many Appalachian basin reservoirs occur in older rocks that are commonly fractured and faulted. These fractures and faults very often act as the reservoir trapping mechanism, especially in lithologies with no log-detectable matrix porosity. Traditional logging techniques, although possibly showing fault or fracture presence in the well bore, seldom provide clues to the extent of fracturing or location of nearby faults. Surface seismic data should show faults and perhaps even fracturing, but showing these features is often not possible in rugged terrain or in areas with thick coverings of unconsolidated surface material. Traditional seismic also has resolutions lower than that needed to detect small faults (less than 70 ft). Two case examples are shown from the northern Appalachian basin. The first example utilizes Schlumberger's slim hole seismic tool in cased holes in an area of thick unconsolidated glacial material along the Bass Island trend of western New York. The second example utilizes Schlumberger's SAT tool in an open-hole environment in an area of northwestern Pennsylvania with disturbed surface bedding and poor conventional surface seismic returns. The slim hole tool provides good data but with only slightly greater resolution than surface Vibroseis data. The SAT tool provides excellent resolution (down tomore » 25 ft) in highly disturbed bedding.« less

HYDROCARBON SOURCE POTENTIAL OF THE GOLDWYER FORMATION, BARBWIRE TERRACE, CANNING BASIN, WESTERN AUSTRALIA

The Goldwyer Formation is widely known from the subsurface Canning Basin, Western Australia. Microfossils of acritarchs, chitinozoans, and conodonts, and macrofossil remains, indicate it was deposited in a normal marine environment in late Early to Middle Ordovician times (Late Arenig to Llanvirn). In Exploration Permit areas 143 and 225, the Formation is subdivided into four lithologic members, informally designated Units 1 to 4 in ascending stratigraphic order. Horizons within Unit 4, immediately underlying the prospective reservoir dolostones of the Nita Formation, are organic rich with between 0.5 and 6 per cent total organic carbon. Generative potential of these horizons, determined by Rock-Eval, averages 13 litres of hydrocarbon per tonne. A conservative estimate of the cumulative thickness of source rock with hydrogen index (HI) values of 300-900, using whole core fluorescence intensity, is 10 m. Thus, under optimum maturation conditions there is potential for generation of an estimated 61 × 109 barrels of liquids from Unit 4 within EP 143 and EP 225. These figures are based on an integrated analysis of 44 core samples from four fully cored 'slim holes' and cores from one conventional oil well. Kero-gen types and measures of organic maturity cannot be determined accurately from the standard Rock-Eval HI/Tmax crossplot. The dominant oil-prone kerogen in Unit 4 is Gloeocapsamorpha prisca Zalessky 1917 and palynological and gas chromatographic/mass spectrometric studies correlate it with Ordovician kerogens from the Baltic Basin, Michigan and Illinois basins, and Amadeus Basin. Gas chromatographic/mass spectrometric source rock-oil correlations show that oils from the Williston Basin (USA), Canning Basin, and Amadeus Basin are derived predominantly from G. prisca. Palaeogeographic reconstructions suggest that these areas lay within 5° north and south of an Ordovician equator and so provide data for further prediction of possible rich hydrocarbon source areas.

Present status of Fang geothermal project, Thailand

Geothermal exploration work in Fang area began in 1977 when the BRGM and Geowatt of France and EGAT agreed to collaborate on a feasibility study of electric energy production in Fang geothermal area. Twelve exploration wells (FGTE series) and eight slim holes (BH series) have been drilled and produce hot water at 105°C, 0.4 bars at a discharge rate of up to 14 l/s. Exploration well testing and the economic study is to be conducted as part of the next cooperation programme of AFME and EGAT during late 1985 - early 1986. The first 100–300 kWe demonstration plant is planned to be installed by the end of Fiscal Year 1986. The future of the development programme depends on the success of this demonstration plant.

Deep Drilling Into Khuff Formation

Deep Drilling Into Khuff Formation

Slim Hole Logging and Analysis for Uranium Exploration

Significant improvements have been made in uranium logging equipment and analysis techniques. Logging systems now provide geological, geophysical, and geochemical data from routine measurements. Through computer analysis, these systems also can determine porosity, density, permeability, lithology, formation-water resistivity, and thermal and mechanical properties. Introduction Deeper targets for uranium exploration warrant more complete logging systems than those used previously. Such systems can produce adequate data for a geologic understanding of the ore deposition processes with fewer drill holes. As the formation depth increases, data extrapolated from surface outcrops become less reliable and make log-derived data more important. An alternative to a complete logging package is extensive coring of ore-bearing and related formations, but this is expensive and time consuming. We are using reasonably sophisticated logging systems that provide data for geologic models, which are used to understand the sedimentary environment, groundwater, and other physical and chemical properties of uranium deposition. These models, based largely on log-derived data, are important when designing infill drilling for exploration, evaluation, or production. Uranium log interpretation is simplified somewhat by short drilling times that restrict invasion and by lack of hydrocarbons that complicate fluid properties. However, less-sophisticated small-diameter downhole tools can have the opposite effect. Logging System The digital logging systems that we use have been designed for relatively simple operation. Analog records are produced during logging to verify equipment operation and allow operator adjustments if necessary. For most logging tools, digital data are generated uphole from a depth encoder, two count-rate meters, and four 4.5-digit volt meters. Signals are recorded from all of these devices at operator-selectable digitization intervals. Recordings are made with cassette tape decks using a 1,200-baud transfer rate. With this recording rate, logging speed is limited by the downhole instruments themselves. Up to 2,000 ft (600 m) of multiplexed logs can be recorded on one side of a cassette. Each truck is designed to run at least 12 separate downhole tools with minimal operator intervention. At present, three sondes are used routinely and several others are used on an experimental basis. These include a gamma-ray log that uses a 0.75×1.25 in. (1.91×3.18 cm) Nal crystal with downhole scaling in areas where count rates are high. This tool also generates 16- and 64-in. (41- and 163-cm) normal calibrated resistivity curves. A single-point resistivity curve can be recorded for correlation with older uranium logs. Also, a spontaneous potential (SP) curve is measured but is difficult to interpret in mineral logging since this potential is the sum of several variable potentials including chemical, membrane, and filtration.

On geological and technological aspects of oriented n-size core diamond drilling

A device has been developed to obtain N-size oriented bore cores in diamond drilling operations in both the Southern and Newcastle Coalfields of the Sydney Basin, New South Wales, and the Bowen Basin, Queensland. Use of this orientation device in Permian and Triassic sedimentary rocks in both basins proved to be successful in obtaining suitable samples for tectonophysical studies. The overburden of the Coal Measures and the interseam sedimentary sequences which are horizontally deposited consist of conglomerates, sandstones, shales, mudstones and claystones. Cyclic sedimentation patterns are present. Well developed sedimentary planes and prominent sedimentary vectorial features create mechanical anisotropies. Distinct joint patterns exist in these rocks. The geometric and kinematic analysis of these features using petrofabric analysis methods is of importance in the efficient planning of colliery development particularly regarding directional mining and strata control. Slim hole diamond drilling is the main exploration tool used in most economic mineral environments and as non-oriented cores are limited in the information they provide, the orientation device described in this paper has been developed.

The Diamond Drill in Exploration for Oil and Gas

Abstract Most wildcat wells are drilled with conventional oil well rigs. To reducecost of non-productive holes there is an increasing trend toward slim holes forexploration. It is suggested that a step further in this direction may be useof diamond drills. In remote areas where cost of transportation is high; when targets, forexample pinnacle reefs, are relatively small and hard to pinpoint; whencontinuous core is an asset, the diamond drill may make economic sense. Onceproductive targets are encountered, conventional rigs become practical. The advantages, disadvantages, limitations, and possible further adaptationof this normally "hard rock" tool in a "soft rock" environment arediscussed. Introduction The purpose of this presentation is to suggest avenues where the diamonddrill might be useful in exploration for oil and natural gas. The diamond drillis primarily a "hard-rock" tool and the problems of a "soft rock" environmentare different from those normally encountered by hard rock drillers.Nevertheless, under certain geological and geographical conditions the diamonddrill offers advantages which can be of economic interest to those engaged inthe search for oil and gas. This is particularly the case for stratigraphictests in remote areas. Exploration for petroleum and natural gas and exploration for metals isconducted along the same general lines though the details vary widely. Photointerpretation, geophysics, and geological investigations indicate targetareas. Testing of these targets ultimately requires the use of drills. Wildcat wells are drilled with essentially the same drill rigs as areproduction wells. Due to the high cost of wildcatting, considerable effort hasbeen expended to effect economies. One approach has been toward slim holedrilling. Realizing fully the limitations, it is suggested that a further stepin this direction might be through use of the diamond drill. Diamond drillshave been used successfully for stratigraphic tests in some areas and withsavings in cost of as much as 50 percent. Features of diamond drills throughwhich economies may be affected, compared to rotary rigs, include lower capitalcost, smaller crews, and lighter overall and unit weights.

Relating Slim-Hole Drilling Performance to South Louisiana Drilling Problems

Abstract Slim-hole drilling has been utilized in many areas of the world to reduce drilling costs. It has been used successfully in exploratory as well as in development drilling, and many published articles have pointed to the savings made possible with slim-hole drilling. Until the present, however, very little slim-hole drilling has been attempted in South Louisiana, principally because of the deep drilling depths and the complex hole problems encountered. Deeper drilling and complex hole problems mean higher costs which may make certain exploratory drilling prospects unattractive or may preclude further development of oil or gas discoveries. This paper recounts some of the advantages of slim-hole drilling and suggests how proper application of slim-hole drilling techniques could appreciably reduce exploratory and development drilling costs in South Louisiana. Introduction The uses of slim-hole drilling are listed in Table 1. It is significant to note that the slim hole is not intended to replace the conventional-size hole. The smaller diameter hole imposes restrictions on formation evaluation tools, fishing tools and completion tools, and these limitations should be recognized when planning slim-hole drilling. However, these limitations can be tolerated if the wells fall within the categories listed in Table 1. Certainly there are many opportunities for drilling cost reductions through slim-hole drilling in South Louisiana. However, recognition of limitations and careful planning to operate within these limitations are essential to any slim-hole drilling operation. Drill Tubing Increases Rig Depth Capacity Probably the most significant contribution to the success of slim-hole drilling has been the use of drill tubing or thin-walled drill pipe. In addition to reducing the weight of the drill string, the use of drill tubing has resulted in a more efficient hydraulic system in drilling slim holes.

Slim Hole Drilling Decreases Carter's Development Costs

Abstract Rising development costs are recognized as one of the major problems facing the oil industry today. To combat this situation, several new concepts designed to improve drilling techniques have been advanced within recent years. Among the ideas proving most effective is slim hole drilling. Carter's slim hole experience has been in both exploration and pool development wells. In addition, slim hole practices have been successfully applied to water injection wells. In comparison with standard operations, both penetration rate and bit life decreased using slim hole methods. No difficulty was encountered in coring, logging and testing in reduced diameter holes. Actual slim hole costs indicated a significant economic advantage over conventional practices. Savings in dry hole costs ranged up to 25 per cent, primarily from reductions in footage and day work rates. Additional savings accrued in producing wells from economy in tubular goods. Slim hole methods may not always be applicable, as consideration should be given to specific drilling problems and objectives. In many cases, however, slim hole drilling provides significant economic advantages over conventional practices. Introduction Increasing development costs are widely recognized as one of the major problems facing the oil industry today. Inflationary effects are firmly evident in all of the principal components of drilling costs, including labor, transportation, steel products and chemicals. Furthermore, deeper drilling is necessitated to offset depletion of shallow reserves. During recent years the concept of slim hole drilling has been experimentally applied within industry to evaluate its significance as a cost reduction measure. In most cases, slim hole results are reported to be proving effective. The purpose of this discussion is to review experience of The Carter Oil Co. in drilling 108 slim holes which have resulted in estimated savings of $162,000 below the cost which would have been incurred with conventional sized holes.

Slim Hole Technology - An Economic Key to Future Drilling Developments

Introduction "Based on present allowables, probably more than half the wells in Texas today could be produced through 1.5-in. tubing", stated Philip L. McLaughlin, president of The McLaughlin Co., Dallas, at a recent meeting of the Mid-Continent Section Study Group in Tulsa, Okla. McLaughlin, who was very closely associated with slim hole drilling and completion techniques and equipment while employed by the Cardwell Manufacturing Co., spoke to the Mid-Continent Section Study Group on the economics of slim hole drilling and completions. McLaughlin, owner of a firm which specializes in product market research and "assistance programs" for oil companies, opened his discussion by warning the group that since the oil industry is in a period of dynamic transition; oil companies, drilling contractors, service companies and equipment manufacturers must continually make themselves stronger as an industry and more alert to opportunity if they expect to continue their past progress. Oil Industry Needs New Ideas for Economic Survival "If oil is to economically survive in our lifetime, it must show a greater willingness to seek out, test, develop and adopt new ideas and new methods. Many research departments are thinking too small to create big deeds. There is a dire need of a freer exchange of information at all levels of each segment of our industry." Much of our present day equipment has outlived its economic usefulness-demanding an engineering revolution similar to the one the auto industry experienced in the late thirties. To cope with this transition which is resulting from keener competition, poorer economic conditions, higher dry hole ratios and fewer reserves found for each well drilled, coupled with technical and management complacency, he advised that the oil industry must either develop methods of economizing, change "fixed idea" and "ivory tower thinking", or receive a much lower return on investments. "If 15 per cent depletion allowance is passed, I expect a great engineering and economy revolution that must come, will develop in a hurry or the oil industry is likely to wake up some day and find itself, joining the railroad industry, as the second biggest ‘sleeping giant’ in U. S. history.

Developments in Eastern Canada in 1956

During 1956 both exploratory and development drilling increased 10% in southwestern Ontario over the previous year. Production of oil amounted to 593,400 bbls., an increase of 13% over 1955, while gas production showed a marked increase of 21% over 1955 for a total of 13,120,000 MCF. One of the more significant discoveries in southwestern Ontario was located in Huron County where sizeable quantities of gas were found in a Guelph reef. In the St. Lawrence Lowlands an increase of exploratory activity in the form of wildcat wells and slim hole drilling highlighted this area, and a small gas discovery was made in the Trenton rocks of Ordovician age in the L'Assomption area north of the city of Montreal. An interesting showing of gas was also located in the Silurian ? rocks in the Gaspe area.

Slim-hole Drilling on the Gulf Coast

The cost of drilling in the past few years of proration and ever decreasingallowables has received increasing thought and study. It seems to parallel thestrides made with respect to pumping problems in 1932 and 1933. Low profitmargins stimulate the search for economies. Any discussion of slim-hole drilling involves a multitude of abstract values, and the problem can be attacked only by a study of records and rationalthinking. In a measure, traditional methods must be studied with a questioningattitude. The words "slim hole" may be somewhat misleading, as the term isentirely relative. For that reason I wish to define it as used in thisdiscussion. On the Gulf Coast, I would define a normal hole as one in which 103/4-in. surface casing has been set and below which a 9 7/8-in. hole is dug.With this as a datum, holes of larger diameter below surface would be called"large holes," with 12 1/4 in. as the "extra large" class andholes of smaller diameter classed in the slim-hole range, 6 1/4-in.representing about the minimum size. The optimum size has not been definitelydetermined, but the preference is for a program that would call for setting 85/8-in. surface casing and digging a 7 3/4-in. hole. Different sections of thecountry might very properly deviate from this practice because of differencesin depth, formations, regulations, or other factors. This paper will be confined to a discussion of the drilling of exploratorywells, as the drilling of this class of wells is quite a different problem fromthat of drilling a proven field, although many of the same considerations applyin both cases, as will be apparent. Although for many years shallow slim-hole and core-test holes of small diameterhad been dug, it was not, I believe, until the fall of 1937 that seriousconsideration was given to its application in drilling wells 7000 ft., 8000 ft.and 9000 ft. deep on the Gulf Coast. This does not mean that nearly all suchwells drilled on the Gulf Coast now are of the slim-hole variety, but only thatefforts have been aimed in that direction with very encouraging results andthere has been a very definite trend to reduce the size of holes, a trend thatprobably will continue. As to exploration policy, there appear to be two distinct and opposite views.The one usually followed in the past was more or less designed to "shootthe works" on one well. Generally on the Gulf Coast, the depth at whichproduction might be obtained is limited by the drilling equipment andeconomics. With this thought in mind, wildcat wells are often planned with theidea of carrying the depth to 10,000 ft., or even 15,000 ft. All of thepossible hazards are anticipated and the general drilling and casing programsare so predicated. Such wells contemplate the drilling of large-diameter holes;the setting of at least one protective string of casing and an extensive coringpolicy, all of which finally adds up to an expensive well. T.P. 1305