Individual Coal Seams Research Articles

REGIONAL AND LOCAL SYSTEMS OF METHANE GAS DISTRIBUTION IN THE COAL-BEARING MASSIFS OF THE DONETS BASIN

Determining the regional and local peculiarities of methane gas distribution in the coal-bearing massifs of the Donets basin will help solve several important problems at once: creating safe conditions for mining operations, using methane as an alternative fuel, and improving the environmental situation in technologically loaded regions. Local gas-saturated systems of coal-rock massifs combining individual coal seams and their host rocks are primarily the result of accumulation and minimal impact of the following geodynamic processes. Important characteristics of rocks and coal as natural gas reservoirs are porosity and gas permeability. Changes in the initial indicators of coal substance indicate a deep transformation that coal seams undergo under fluid dynamic impact, which is determined by regional and local changes in the coal-bearing massifs of the basin.
 Gas content and gas migration in different strata of coal-bearing massifs are related by age and quality characteristics. The qualitative characteristics of the gas mixture of coal deposits are constantly changing along the section and dip of the seam and are particularly distinct in tectonically disturbed areas of coal massifs. All components of the gas mixture of coal seams are controlled by a mosaic of physical parameters of its various parts, both in the undisturbed and in the mined massif. Structural, shielded deposits are often found in relatively undisturbed mine massifs and can be developed as a local gas field. Depending on the condition of the coal and gas reservoir, the gas component can vary widely. During active maximum gas recovery, a large amount of heavy and unsaturated hydrocarbons rise in the workings, which can provoke gas-dynamic phenomena.
 On the basis of isotopic and geochemical studies of gas mixtures of coal-rock massifs, the polygenetic composition of natural gas in coal-bearing strata of the Ukrainian coal basins is substantiated and proved.

Distribution of Upper Paleozoic Coal Seams in the Southeastern Ordos Basin

The Ordos Basin contains abundant coal resources in the Upper Paleozoic strata. They are shallowly buried or exposed in the periphery of the basin, forming recoverable coal mines and coalbed methane resources. For the deeply buried coal seams of the basin, however, due to complex changes and difficult mining, less attention was paid before. In recent years, with the exploitation of tight gas related to coal source rocks, a large amount of drilling and seismic data has been accumulated in the southeastern Ordos Basin, which makes it possible to study the distribution change and factors controlling Upper Paleozoic coal seams. Delineation of deep coal development and distribution is an important basis for coal, coalbed methane and related tight gas resources in the Upper Paleozoic. We use core, logging and seismic data to analyze the coal geophysics, thickness variation, paleotopography and sedimentary facies in the southeastern Ordos Basin. The lower part of the Shanxi Formation (Fm.) and the upper part of the Taiyuan Fm. in the southeastern part of the basin are characterized by low natural gamma ray, low density, high resistivity and high sonic logging values. As the coal velocity is very low and alternates with the high-velocity Taiyuan Fm. and Ordovician limestones, the two sets of coals below and above the Taiyuan limestones form an extremely strong-amplitude reflection in the seismic profile. The two sets of coals are cumulatively 1–10 m thick, averaging 2.4 m, and 4 m is the maximum induvial thickness. The individual coal seams thicker than 2 m cover an area of approximately 2500 km2, and the burial depths of the coal seam range from 2500 to 3000 m. The thick coal seams of the Taiyuan Fm. are mainly distributed proximally in the Ordovician paleokarst depression, while the Ordovician paleokarst depression without incised origin was deposited by distal coeval limestone rocks. There is a complementary relationship between the coal seams and the thickened zone of distributary channel sandstone in the Shanxi Fm.

Petrographic and geochemical characteristics of selected coal seams from the Late Cretaceous-Paleocene Guaduas Formation, Eastern Cordillera Basin, Colombia

Petrographic, geochemical and carbon isotopic determinations were conducted on five samples from four seams within the Late Cretaceous-Paleocene of the Guaduas Formation in Colombia. The individual coal seams are thin, ranging from 0.59 to 1.2 m, and occur over a 157 m interval. The average weighted ash yield is 13.7% (dry basis), although one sample presented values >35%. Vitrinite reflectance increases from 1.33% in the stratigraphically uppermost seam (La Cuarta) to 1.44% in the lower most coal seam (Cisquera), indicating their rank to be medium volatile bituminous.The studied sequence of the Guaduas Formation represents a peat environment influenced by shifting depositional settings, particularly in relation to the proximity of marine/brackish water environments as indicated by Sr/Ba values, sulfur, pyrite, δ13C and the proportion of telinite. A decrease in inertinite indicates that the peat mires were becoming relatively ‘wetter’ stratigraphically upwards. This trend, unlike that of Sr/Ba and telinite, may be driven by climatic shifts rather than only changes in depositional environment.Both trace and rare earth elements, plus yttrium (REY) are related to the inorganic fraction of the coal. All rare earth elements are depleted relative to average worldwide hard coals (for trace elements) and average upper continental crust (for REY) with the notable exception of Li and Sb for the high ash yield sample (the La Cuarta lower coal seam). The abundance of some REY elements (i.e. Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) may be more influenced by the presence of illite rather than just the quantity of total ash yield. Based on the relationship between SiO2 and Nb/Y, the provenance of the inorganics changed from a rhyolitic source at the lowest seam (Cisquera) to a dacite source in the middle layer (El Tesoro) to an andesite source in the stratigraphically uppermost seams (La Gemela and La Cuarta).

ПРО ВПЛИВ МІНЕРАЛЬНИХ ДОМІШОК НА ВИЯВЛЕННЯ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ВУГІЛЬНИХ ШАХТОПЛАСТІВ

Purpose: to establish a possible correspondence between metamorphic processes with artificial thermal destruction of coals and their ashing in order to identify the components of mineral impurities that can affect the manifestation of the hazardous properties of coal mine seams. Methodology is based on a comparison of metamorphic processes that took place at a certain temperature mode in the bowels of the Earth and the production of artificial coals and their ashing. Results: The research made it possible to reveal the important role of mineral impurities in the formation of the hazardous properties of coal seams. This is due to both the significant possible content of mineral impurities in fossil coals, and the simultaneous presence of the main components that determine the hazardous properties of coal seams (carbon, hydrogen, sulfur, oxygen and moisture), both in the organic and in the mineral parts of fossil coals. To improve the regulatory framework for the safe conduct of mining operations, it is necessary to take into account features of the properties of fossil coals due to the presence of mineral impurities in them. In modern regulatory documents on the safe conduct of mining operations, in general, several indicators are used without proper scientific justification: the mass yield of volatiles during the thermal decomposition of coal, the volumetric yield of volatile substances, the thickness of the plastic layer and the logarithm of the electrical resistivity of anthracites. Their values are related to the dry ash-free mass of organic matter only. This excludes consideration of the influence of mineral impurities on the manifestation of the hazardous properties of coal mine seams during mining operations. In many cases, the content of moisture and sulfur is a criterion for the manifestation of hazardous properties of coal seams. They belong to the integral components of both organic and mineral constituents of fossil coals. The share of mineral impurities in the coals of individual coal seams can be more than 40%. The presence of oxygen, hydrogen, sulfur and moisture in mineral impurities significantly affects the manifestation of the hazardous properties of coal seams during mining. The content of mineral impurities in fossil coals in engineering calculations can be determined on the basis of the ash content of coals according to known empirical relationships, corrected for the content of total sulfur and, in some cases, carbon dioxide. Scientific novelty: the significant influence of mineral impurities in fossil coals on the manifestation of hazardous properties of coal seams during mining operations has been proved. Practical value: the results obtained allow substantiating the methodology for the combined use of the composition of organic and mineral components of fossil coals for a reliable forecast of the manifestation of hazardous properties of coal seams and improving the regulatory framework for their safe mining.

Modeling the Contribution of Individual Coal Seams on Commingled Gas Production

SummaryIn coal-seam-gas (CSG) fields, where single wells tap multiple seams, it is likely that some of the individual seams hardly contribute to gas recovery. This study aims to examine the contribution of individual seams to the total gas and water production considering that each seam can have different properties and dimensions. A sensitivity analysis using reservoir simulation investigates the effects of individual seam properties on production profiles.A radial model simulates the production of a single CSG well consisting of a stack of two seams with a range of properties for permeability, thickness, seam extent, initial reservoir pressure, coal compressibility and porosity. The stress dependency of permeability obeys the Palmer and Mansoori (1998) model. A time coefficient (α) relates seam radius, viscosity, porosity, fracture compressibility, and permeability. It is used to aid interpretation of the sensitivity study. Finally, two hypothetical simulation scenarios with five seams of different thicknesses and depths obtained from producing wells are explored. The range in properties represents conditions found in the Walloon Coal Measures (WCM) of the Surat Basin, relevant to the Australian CSG industry.Each seam in the stack achieves its peak production rate at different times, and this can be estimated using α. Seams with lower α reach the peak gas rate earlier than those with higher α-coefficient. The distinct behavior of gas-production profiles depends on the combination of individual seam properties and multiseam interaction. At a αratio > 1 (i.e., αtop/αbottom > 1), the bottom seam peaks first but achieves lower gas recovery than the top seam. An increasing αratio is associated with the inhibition of less-permeable seams and reduced overall well productivity. For αratio < 1, the top seam experiences fast depletion and total gas-production rates decrease drastically. This outcome is confirmed by a more realistic scenario with a higher number of coal layers. Poor combination of seams leads to severe production inhibition of some coal reservoirs and possible wellbore crossflow. The contrast of the seam-lateral extent in the stack and fracture compressibility play an important role in well productivity in the commingled operation of a stack of coal seams. Unfortunately, the lateral extent of individual coal seams is difficult to estimate and poorly known and, therefore, represents a major uncertainty in gas-production prognosis. The αratio analysis is a useful tool to gain understanding of modeled well productivity from commingled CSG reservoirs.

Coal seam development characteristics and distribution predictions in marginal sea basins: Oligocene Yacheng Formation coal measures, Qiongdongnan Basin, northern region of the South China Sea

Coal measures located in marginal sea basins are important hydrocarbon source rocks. For the purpose of effectively guiding future oil and gas exploration, the characteristics and distribution patterns of coal seams in coal measures of a marginal sea basin are systematically outlined. Coal measures in marginal sea basins can have large thicknesses, but the individual coal seams can be very thin and lack lateral continuity. In the study area, the organic micro-components of the coal are dominated by vitrinite, with very low amounts of inertinite and liptinite. The amount of inorganic microscopic components is large, but with limited drilling results, few cores and thin coal seams, which are easily overlooked during logging activities, a comprehensive analysis of the logging data may improve efficiency in coal-seam identification and thickness determination. The development and distribution of coal seams in marginal sea basins are controlled by various factors, including (1) paleoclimatic and paleobotanic conditions, which could fundamentally limit coal formation, (2) coal-forming sedimentary environmental conditions that may limit the scope of coal-seam development from a macroscopic perspective, and (3) paleotectonic and paleotopographic conditions that define the coal-forming structures. Therefore, the descending and rising cycles of base-levels, along with changes in the growth rates of the accommodation spaces, can be used to determine the horizons that are potentially favourable for coal formation and can also indicate the migration trends of coal-forming environments on the structural plane. Seismic wave impedance inversion methods could be utilised for semi-quantitative assistance for prediction of coal seams. In summary, for models of coal-seam development in marginal sea basins, the grades should be divided according to reliability, and the different reliability levels should be predicted separately.The characteristics of coal seams developed in marginal sea basins are described.The macerals of coals developed in marginal sea basins have been ascertained.A development model and distribution prediction method for coal seams are assessed according to the control factors.A model for the prediction of coal-seam distribution is presented.

Flora and dispersed cuticles from the coal seams in the Jan pit of the Šverma coal mine in Žacléř (Bashkirian, Intrasudetic Basin, Czech Republic)

The Lampertice Member in the Žacleř coalfield represents the long-term coal-bearing deposition of nearly all Upper Bashkitian (Namurian to Ducmantian). Nearly the whole thickness, more than 600 m was revealed during the construction of the Jan pit of the Jan Sverma coal mine during 1958–1962. Z. Rieger collected stratigraphically determined plant remains for later evaluation and he also sampled individual coal seams. The plant material was evaluated again and four coal samples were macerated for cuticles to expand our knowledge of Žacleř flora. The following local biozones are valid for the Lampertice Member. The Namutian (Yeadonian) Mariopteris glabra Zone lasts from the basal coal-barren rocks till lower coal seam 17 (there are 24 lower coal seams). The Langsettian is crowed by the LAD of Neuralethopteris schlehanii (Stur) Laveine at upper coal seam 20 (there are 32 upper coal seams). The Langsettian can be divided into the upper and lower parts by FAD of Lonchopteris Brongniart at about lower coal seam 8. The Upper Duckmantian is defined by the FAD of Linopteris neuropteroides Gutbier forma major Potonie from about upper coal seam 11 upwards. The results of cuticular analysis are as follows: Undeterminable cuticles with polygonal or tetragonal, randomly or parallel oriented cells dominate. Such cuticles predominantly belong to seeds. Cordaitalean cuticles are common in three of four samples. They are assigned to the genera Cordaites Unger, Cordaadaxicutis Simůnek et Florjan, and Cordaabaxicutis Simůnek et Florjan. Pteridosperm cuticles are very rare—Silesiacutis prosenchymatica Roselt et Schneider and undetermined cuticles with probably neuropterid cyclopterid affinity.

Determining Coalbed Methane Production and Composition from Individual Stacked Coal Seams in a Multi-Zone Completed Gas Well

This work proposes a novel and cost-effective approach to determine coalbed methane (CBM) production and composition from individual coal seams in a multi-zone completed CBM well. The novel method uses water to cover individual coal seams in a low pressure CBM well followed by an Echometer fluid level survey to determine the water level. Corresponding gas flow measurements and natural gas chromatography analysis are used to determine gas production and composition from unique zones. A field test using this technology is conducted in Central Appalachia for a multi-zone CBM well containing 18 coal seams. Test results show that the shallow coal seams contribute the majority of the total CBM production in this multi-zone well, and the deeper coal seams contain more heavy hydrocarbons like ethane and propane.

Determination of in-situ stress direction from cleat orientation mapping for coal bed methane exploration in south-eastern part of Jharia coalfield, India

Abstract Accurate prediction of in-situ stress directions plays a key role in any Coal Bed Methane (CBM) exploration and exploitation project in order to estimate the production potential of the CBM reservoirs. Permeability is one of the most important factors for determination of CBM productivity. The coal seams in Jharia coalfield generally show low permeability in the range of 0.5 md to 3 md. To estimate the in-situ stress direction in the study area, an attempt has been made to undertake the cleat orientation mapping of four regional coal seams of two underground coal mines located at south-eastern part of Jharia coalfield, India. Cleat orientation mapping is critical to determine the maximum principal compressive horizontal stress (S H ) direction for CBM exploration and exploitation, which in turn controls the direction of maximum gas or water flow though coal beds. From the field study it is found that the average face and butt cleat azimuths are towards N15°W and N75°E respectively. Average permeability of the four above-mentioned major coal seams has been calculated from well logs of nine CBM wells distributing over an area of 7.5 km 2 , adjacent to the underground mines. The cleat orientations are congruous with the regional lineament pattern and fits well with the average permeability contour map of the study area to infer the orientation of in-situ maximum horizontal stress. Goodness of fit for the exponential regressions between vertical stress and permeability for individual coal seams varies between 0.6 and 0.84. The cleat orientation is further validated from the previous fracture analysis using FMI well log in Parbatpur area located southern part of the Jharia coalfield. The major coal seams under the study area exhibit directional permeability, with the maximum permeability, oriented parallel to the direction of face cleat orientation.

Maximizing Energy at Coalface for Coalbed-Methane Fracturing

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 114974, "Maximizing Energy at Coalface for Coalbed-Methane- Fracturing Operations," by Abbas Mahdi, SPE, Schlumberger; Mike Yu, SPE, EnCana; Doug Pipchuk, SPE, Craig Wasson, SPE, Jim Nguy, SPE, and Nathan Kathol, Schlumberger, originally prepared for the 2008 CIPC/ SPE Gas Technology Symposium Joint Conference, Calgary, 16–19 June. The paper has not been peer reviewed. Nitrogen coiled-tubing (CT) fracturing is the predominant method for completing and stimulating dry-coalbed-methane (CBM) formations, such as the Horseshoe Canyon in the west-ern Canadian sedimentary basin. Currently, energy that can be delivered to the coalface of these dry-CBM wells has been limited by the frictional pressure loss through CT. The full-length paper discusses the development of a technique that releases a large-volume pressure pulse downhole during the fracturing process to create an order-of-magnitude change in available energy at the fracture face. Introduction The Horseshoe Canyon dry-coal formations have been exploited commercially since late 2000. The Horseshoe Canyon CBM play is a unique CBM play, in that it consists of a dry underpressured coal, which does not require dewatering before production. The coal consists of multiple thin seams, ranging from 10 to 30 seams per well, that are treated individually. Coal-seam thick-ness ranges from 0.1 to 2.5 m. The production rates from these CBM wells dictate that an efficient drilling and completion model be adopted to be economic. The wells are drilled with CT drilling rigs, cased, and cemented. Wireline perforating crews perforate the zones of interest in a rigless operation. The individual coal seams then are stimulated by injection of dry nitrogen at high rates through a CT reel equipped with a fracturing isolation tool. The dry coal has not responded well to any other form of stimulation. To optimize the completion process, high-rate nitrogen-pumping units were developed to reduce the footprint and cost and to increase efficiency of the operation to the point where one and a half to two wells can be stimulated per day. Since the introduction of that change, various optimization initiatives have been attempted. The optimization of nitrogen-pumping rates and pumped volumes has been the focus of these attempts. High rates have been limited by the inside diameter of the CT string. Several CT sizes have been used for this application. Economics and logistics have limited the CT size for CT fracturing to 2 7/8 in. for deeper wells and 3 1/4 in. for shallow wells. The migration to bigger pipe did pro-vide some reduction in frictional pressure loss, but effective pressure at the coalface still was not transported from the surface efficiently.

Trace Element Geochemistry of Jurassic Coals from Eastern Black Sea Region, NE-Turkey

The majority of coal deposits in the world are of Carboniferous and Tertiary age but Jurassic coals are seldom present. They are also exposed in northern Turkey and occur both at the lower and upper sections of the Liassic-Dogger volcanic- and volcani-clastic series. The coals at the base of the Jurassic units are characterized by higher Ba, Th, Zr, and Cr-Ni and lower S values than those at the top of the units, indicating, in general, laterally consistent trace element contents. The vertical distribution of trace elements in individual coal seams is also rather consistent. The B contents of coals from the Gödül and Norşun areas vary from 1.5 to 4.3 ppm whereas those from the Alansa area are in the range of 95 to 138 ppm. This suggests that the coals in the Gödül and Norşun areas were deposited in a swamp environment inundated by the sea from time to time, whereas coals of the Alansa were deposited in a saline environment.

Metals and polyaromatic hydrocarbons in the drinking water of the Sydney Basin, Nova Scotia, Canada: a preliminary assessment of their source

Twenty-five drinking water samples collected from the household property and from the Sydney Regional Municipality well bores and lakes were analyzed to evaluate the various inorganic parameters, level of concentrations of the priority elements and polyaromatic hydrocarbons (PAHs). The pH of the majority of the water samples was below the guidelines adopted by Health and Welfare Canada (1996), although the drinking waters supplied by the Sydney Regional Municipality were within the guidelines. Only three water samples (13 and 14: Point Aconi area and 16: Port Morien fish plant) have elevated concentrations of various PAHs compared to the detection limit. Eight samples have higher concentrations of manganese and two samples (number 7: Sydney Airport and number 1: RCMP Office; Reserve Mines) have higher concentrations of priority elements (especially lead) than the recommended guidelines (>0.05 mg/l). These priority elements and the PAHs in the drinking water samples may have originated from the leaching of the individual coal seams within that part of the Sydney Basin. Other potential sources of these elements and PAHs (Power Plant disposal, Sydney Tar Pond, metalliferous rocks, hydrocarbon reservoir rocks) are not located close enough to the sampling sites of the water samples. Therefore, they are not considered the source of these elements and PAHs.

Organic Petrology, Thermal Maturity, Geology, and Petroleum Source Rock Potential of Lower Permian Coal, Karoo Supersystem, Zambia

Abstract Data concerning organic petrology and thermal maturity of Lower Karoo coal measures (Lower Permian) are of considerable importance in determining the hydrocarbon potential of sediments in the rift-valley and half-graben complexes of the Luangwa and Zambezi valleys of eastern and southern Zambia, respectively, and in the extensive sedimentary basin developed on relatively stable Precambrian basement in western Zambia, a total area in excess of 3000 km2. Samples from seven outcrop and subsurface localities situated in the northeast (northern Luangwa Valley), east (mid-Luangwa Valley), south (mid-Zambezi Valley), and the Western Province of Zambia were studied. The coal measures are from 9 to 280 m thick, but individual coal seams are generally less than 6 m. The coal macerals contain an average of 60% vitrinite and 9 % liptinite, enough to have potential to generate hydrocarbon. A few samples contain twice this amount of liptinite. Reflected-light microscopy and the thermal alteration index of spor...

Geophysical logs and the search for opencast coal reserves

Abstract The application of down-hole wireline logging techniques in the exploration for, and evaluation of, opencast coal reserves is described. The paper concentrates on the nuclear geophysical suite, in particular gamma and gamma-gamma logging which, to date, provide the most accurate geophysical means of identifying coal seams and estimating their thickness. The use of such logs in the identification of partings in coal seams, abandoned underground workings, sandstones, marine bands, ironstones and water levels is also described. The way in which such logs can be used in the correlation of individual coal seams is demonstrated, together with their use in the interpretation of geological structures in complex structural terrains. The advantages gained by the geophysical logging of boreholes far outweigh the increased costs incurred during exploration.

Multiple-Coal-Seam Well Completions in the Deerlick Creek Field

Summary The multiple-coal-seam completion work conducted during 1982–85 at theDeerlick Creek field entailed a large number of different completion methodsatleast six major design stages. The overall result suggests that there is nosingle "best" or "worst" design, but probably many of each. Motivation to change completions came not from unsatisfactory production butfrom a strong desire to reduce costs. Such reductions were production but froma strong desire to reduce costs. Such reductions were attributed primarily tothe successful application of less expensive, conventional methods. Introduction Multiple-seam well-completion work began in the Deerlick Creek field in Nov.1982 and ended in Nov. 1985. Well completions initially reflected contemporarytechnical concepts of the emerging coalbed-methane-gas industry. During thisperiod, multiple-seam wells were completed openhole. Later attempts to improveon multizone work involved a change to cased-hole, slotted completions. AtDeerlick, slotted-casing completions provided little improvement and in factintroduced additional complications. A basic change in the approach tocompletion design began in Feb. 1984. This new approach emphasized simpler, more cost-effective field operations, not the view that coal completionsnecessitate a unique set of completion criteria. During this period, completionoperational costs were the lowest recorded for the project. The last stage ofwell-completion development at Deerlick can be characterized by a generatedeffort to tailor completion designs to individual coal groups. Typicalcompletions included perforation designs geared specifically to perforationdesigns geared specifically to closely spaced, thick coal seams or to severalfar-spaced, thin coals. Baffle fracturing operations were introduced to allowcompletion designs to be individualized for each of the three coal groups. Overall results indicate that many different completion types produce gaseffectively and that conventional methods can be used successfully to reducecoalbed-methane well-completion costs. From 1982 until 1985, mostcoalbed-methane wells in the eastern U.S. were completed in a single coal bedwith some type of openhole technique. Although this completion could notrecover gas from all the coal seams in a well, single-seam work was simple andcost-effective. The technical risks associated with multizone completions werenot understood at that time, and few operators had attempted to develop themultiple-completion technology. In Nov. 1982, TRW Inc. began to develop theDeerlick Creek field (Fig. 1). In 1986, Taurus Exploration Inc., based inBirmingham, AL, assumed operating responsibility for the project. The coal bedsat Deerlick Creek project. The coal beds at Deerlick Creek field are not deepenough to make mining worthwhile. Three coal groups occur at depths greatenough to contain gas in commercial quantities: the Pratt, Mary Lee, and BlackCreek. In this field, five to eight individual coal seams are completed withineach well (Fig. 2). The developed area is structurally complex, containingnumerous northwest- to southeast-trending normal faults traversed bynorth-northeast-trending "linear" features. Regional dip is to thesouthwest, but local dip can be strongly to the southeast within individualfault blocks. Early Completions In Nov. 1982, multiple-seam well completions at Deerlick reflectedcontemporary technical concepts in this new facet of the coalbed-methaneindustry. By necessity, operations were patterned after unrefined and untestedfield techniques available to the project through other operators' experiences.project through other operators' experiences. This passive approach towell-completion design dominated field development through Jan. 1984. Duringthis period, multiple-seam wells were completed either by openhole techniquesor by jet cutting vertical slots through casing. Openhole Techniques. Wells were completed openhole by isolating each zone(containing one to three individual coal seams) with an inflatable packer aboveand a sand plug below the zone and hydraulically plug below the zone andhydraulically stimulating with gel water and sand proppant through a tubingstring (Fig. 2). proppant through a tubing string (Fig. 2). Popular practicesincluded overflushing, Popular practices included overflushing, changing from12/40- to 12/20-mesh sand, and jetting the coal face before hydraulicfracturing. The field operations necessary for multiple openhole completions wereextremely difficult and costly; up to 2 weeks were required to complete eachwell. One of the most severe problems encountered involved the use ofinflatable packers, which had to be removed after each treatment. Also, adequate settings frequently could not be achieved because of holeirregularities, which caused leaks around the packer. JPT

Correlation of the Coal Measures

THREE are two quite different aspects of Coal Measure correlation. In the first place, there is the desirability of dividing the thousands of feet of Coal Measure strata into zones or other subdivisions, which can be recognized in different coalfields and can be used in the comparison of sequences in different areas; in the second place, there is the demand of the mining engineer for criteria which will make it possible for him in a given area to identify individual coal seams or other rock beds. The broad zoning has its economic uses in the exploration of undeveloped areas in known coalfields and in the interpretation of deep borings into concealed coalfields. In these preliminary stages, it is sufficient to know what part of the Coal Measures has been reached, but as mining operations proceed, especially in areas where seams are much disturbed and faulted, there is need for much more precise information than can be gained from a study of zones which may themselves be hundreds of feet thick.