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Abstract The increase in value of energy resources has generated serious interest in so-called "unconventional energy resource developments", Coal and coal gas recovery schemes have existed for some years, but the application of petroleum technology to the recovery of coal gas on a commercial scale is relatively new. The methane gas produced from coal seams, once considered a menace to coal mining operations, can be recovered and produced using technology currently available. It is the intent of this paper to demonstrate that recovery of this unconventional gas resource is both practical and economic. The generalized design parameters and the important considerations involved in the design of such a system are discussed. In addition, specific references are made to the considerations relevant to the Brookwood, Alabama Coal Degasification Project, a gas production project which is currently demonstrating the viability of this technology. Introduction The emission of methane gas from coal seams has been a persistent safety and economic problem since the beginning of the coal mining industry. In order to operate successfully, sub-surface mines have traditionally been engineered to vent as much methane as possible. While the need for venting increases mine capital and operating cost, this has been viewed as preferential to the alternative of reducing coal extraction rates or, in the extreme, to mine closure. Recent innovations to reduce gas concentrations, via vertical well bores, in advance of active mining operations have created a new method of coal degasification and a new source of a clean fuel. The virtually pure methane gas given off during coal mining operations, if gathered and conserved carefully, can either be used to reduce mine fuel costs, or alternatively, can be sold to gas distribution firms at a profit. The application of conventional petroleum recovery technology to the recovery of the methane gas has proven to be a viable method of not only reducing gas emissions into the mining operation, but also of collecting a valuable product for sale. Coal Gas Technology Methane gas can be found in coal beds either as free gas residing in the coal seam fractures or as a thin layer of gas molecules adsorbed onto the walls of minutely sized pores within the coal structure. The amount of gas stored in a particular coal seam is a function of both the degree of fracturing of the coal and of the properties of the coal seam itself. The amount of gas which can be stored within some selected coal types at varying pressure levels has been reported by Kissell. Figure 1 demonstrates that certain coal seams, if fully saturated at critical seam pressure, will release up to 15 cubic meters of methane gas per tonne (500 cubic feet per ton). This gas volume is in addition to that gas which may be stored in the coal fractures. This figure also demonstrates an interesting natural law regarding gas production rates expected from gas wells drilled into coal seams.
- Materials > Metals & Mining > Coal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Reuse (0.85)
Abstract Production data from coalbed degasification wells characteristically exhibit a negative decline curve. The dynamics of this methane production are complex and interrelated. As production begins, water and free gas are often first- recovered. Continued production lowers pressure and increases permeability to gas, allocating adsorbed gas to flow. permeability to gas, allocating adsorbed gas to flow. This pressure drop within the formation causes sublimation whereby gas, which is absorbed within the coal, forms on the walls of the micropores. Finally, the desorption through production disturbs the chemical and physical equilibrium of the coal, thus enabling the coal to require generation of methane. Introduction Methane from coalbeds has historically viewed gas an explosive nuisance that must be from underground mines in order to prevent disaster. Over the last two decades, however, increasing attention has been given to the production of coalbed pas from single vertical wells. With the infusion of pas from single vertical wells. With the infusion of research support money provided by the Department of Energy, a rise in natural gas prices, and the deregulation of gas produced from coal, this same methane is no longer viewed as a liability, but rather as an asset. As a result, several energy companies have acquired acreage and drilled wells expressly for coalbed methane production. As production figures from coalbeds grow, an unexpected phenomenon has emerged that is apparently characteristic of all coalbed gas wells: a negative decline production curve. EXAMPLES Producing, coalbed degasification wells in the Black Warrior Basin, Alabama and the San Juan Basin, New Mexico all exhibit negative decline production curves. Figure 1 shows gas and water production of the U.S. Steel project in Oak Grove, Alabama. This is 1000 days of production from 17 wells with 4 feet (1.3m) coal at 1000 feet (300m.). Note the inclining gas production curve. Figure 2 is the production curve for the Amoco Production Gahn Gas Commission Number 1 producing from Production Gahn Gas Commission Number 1 producing from 20 feet (20 m.) of coal st 2800 feet (F sq.m.). Again, note the striking incline gas production curve. Another San Juan Basin well (Figure 3) shows five years of inclining gas production. The well is currently averaging 200 MCF per day from 6 feet (2 m.) of coal at 1500 feet (450 m.). Figure 4 is a San Juan Basin well showing a 20-year history of inclining gas production. The gas is produced from 23 feet (7 m.) production. The gas is produced from 23 feet (7 m.) of coal in 160 feet (48 m.) meter open hole completion at 3200 feet (970 m.). These wells are located in different basins and are completed Jr. coals of widely varyings thickness, rank, depth, and geologic age. The spacing of the wells varies from a single degasification well to wells on 22 acre spacing. The characteristic common to all of these coalbed degasification wells is the negative decline production curve. DYNAMICS The dynamics of methane production from coal is complex and interrelated. Four distinct processes occur throughout the life of a degasification well. First, gas is held in coals as both free gas in the fractures and as gas that is adsorbed or held to the wells of the coal micropores in many coalbeds the production of the free gas is Inhibited by water production of the free gas is Inhibited by water saturation. once dewatering has occurred the permeability to gas increases, causing the initial incline permeability to gas increases, causing the initial incline curve of Figures 1 and 2. In the water-free wells of Figures 3 and 4 dewatering does not take place and free gas flows immediately. Secondly, this initial production lowers the pressure within the fractures causing gas molecules, pressure within the fractures causing gas molecules, which are adsorbed to the walls of the micropores, to break free and move to the fractures. Movement of the gas through the coal erodes the coal matrix which improves the communication between the fractures and the micropores. This erosion is evidenced by increased coal fines recovery during periods of peek production. production. P. 403
- Water & Waste Management > Water Management > Lifecycle > Reuse (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- North America > United States > Texas > Permian Basin > Gill Field > Pennsylvanian Formation > Pennsylvanian 6900 Formation (0.99)
- North America > United States > New Mexico > San Juan Basin (0.99)
- North America > United States > Colorado > San Juan Basin (0.99)
- (2 more...)
Abstract Steam-assisted methods for in-situ recovery in Canada typically operate at steam to oil ratios of approximately 3 to 1 and generate in the order of 2 to 5 barrels of produced water per barrel of production. To raise the large quantities of steam required for reservoir stimulation, once-through type steam generators are most commonly used. They are typically designed to produce about 80 per cent quality steam from soft, oil-free feedwater. Suncor Inc operates a cyclic steam injection pilot project near Fort Kent, Alberta. In the early 19805, Suncor planned an expansion of the 180 m/d (1,130 bbl/d) facility to 800 m/d (1,130 bbl/d). The expansion necessitated the development of a reliable water supply. Preliminary investigations into the feasibility of reusing produced water as the sale source of supply for the project expansion revealed this to be a costly and technically high risk option, given the specific produced water characteristics. As a result, an innovative alternative was developed to use a blend of produced water and municipal effluent from a nearby town as the water supply. This paper presents the rationale for the selection of this unique water supply and the process design considerations/or the resulting water treatment system. Background Several operators of in-situ recovery projects are interested in reusing produced water for steam generation in their commercial or semi-commercial projects. This interest has been stimulated by the often scarce supplies of fresh water available in the principal oil-producing regions of western Canada, and environmental pressures to explore alternatives to produced water disposal by injection. Suncor's planned expansion of their pilot project near Fort Kent, Alberta was forecast to require a water supply of 3,700 m/d (20,000 bbl/d) for steam generation. CH2M HILL was retained to investigate the feasibility of reusing produced water as the steam generator feedwater supply. Feedwater Quality Requirements The once-through steam generators used in the expansion operate at a pressure of 13.8 MPa and produce 80 per cent quality steam. Typical manufacturer-specified feedwater quality requirements for these units are listed in Table 1. The maximum concentrations are based primarily on past operating experience rather than solubility considerations. Higher concentrations than those listed reduce the performance and service life of the steam generators. High concentrations of oil and hardness lead to coking and scaling respectively. Localized hot spots in the fouled region contribute to tube burnout. Oxygen leads to tube corrosion and a reduced service life. Iron is believed to attack the protective magnetite layer on the tubes. Uncertainties exist as to the maximum TDS and silica concentrations that can be tolerated in once-through steam generators. Operation with higher silica and TDS concentrations than those listed has recently been reported and successful operation could result in an increase in the maximum limits by the manufacturers. However, at the time of design there was insufficient experience at high pressure (14 MPa) and 80 per cent steam quality to justify exceeding the manufacturer's recommended feedwater quality criteria as the design basis for a project of this size.
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Reuse (0.73)
- Water & Waste Management > Water Management > Lifecycle > Treatment (0.58)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.58)
The paper was presented at the SPE/DOE Unconventional Gas Recovery Symposium of the Society of Petroleum Engineers held in Pittsburgh, PA, May 16-18, 1982. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write 6200 N. Central Expwy., Dallas, TX 75206. Abstract The upper Pottsville Formation in the Warrior Coal Field of Alabama has seven recognized groups of bituminous coal seams. Three of these groups, the Pratt, Mary Lee, and Black Creek consist of seams Pratt, Mary Lee, and Black Creek consist of seams containing commercially significant quantities of methane. Each group has several seams within a vertical interval that, in may areas, can be collectively stimulated. In parts of the Warrior Coal Field, where all three groups can be penetrated in one vertical borehole, the potential production from multiple zone completion wells can result in commercially profitable wells. Various open hole and profitable wells. Various open hole and through the casing completion procedures are being applied resulting in successful methane production from these multiple zone coal gas wells. Introduction The Pratt, Mary Lee, and Black groups of the Warrior Basin can be quite gaseous and all can often be penetrated by a single well. Several communities, companies, and agencies are investigating the commercial feasibility of completing and producing from two or more coal beds in a single well. This paper describes the drilling and completion methods used to date, and generally itemizes the associated costs incurred. Insufficient data exists for determining the most appropriate and cost effective method. BASIN GEOLOGY The Warrior Basin of Northern Alabama and Mississippi is an elongate body of predominately detrital rocks derived from Carboniferous aged sediments resting on a floor of older Paleozoic deposits. These carboniferous rocks, comprising the greatest thickness of detrital deposits in Northern Alabama, are essentially a wedge shaped prism which thins rapidly from southwest to the northern part of the basin. The Warrior Basin has been primary source of energy resource production in northern Alabama yielding hydrocarbons from Mississippian aged rocks and, since the mid 1800's, bituminous coal from Pennsylvanian aged rocks. Pennsylvanian aged rocks. Pennsylvanian aged rocks in the Warrior Basin of Northern Alabama comprise the Pottsville Formation, the major coal bearing unit in the state. The Pottsville Formation, commonly further divided into Pottsville Formation, commonly further divided into upper and lower parts, has been interpreted as the product of deltaic progradation with barrier islands product of deltaic progradation with barrier islands on the delta margin advancing northward as a delta system prograded from a southern or southwestern source. The lower Pottsville Formation is represented by barrier and offshore bar orthoquartzites, delta front sandstones, and back barrier lagoonal shales, and discontinuous coal seams. The upper Pottsville Formation consists of rocks deposited in Pottsville Formation consists of rocks deposited in the upper and lower Pottsville. Lithologies in the upper Pottsville are characterized by sequences of sandstones, siltstones, shales and clays decreasing downward in grain size and separated by groups of coal seams. The coal-bearing rocks of the upper Pottsville Formation make up the Warrior Coal Field, the region from which the great majority of coal in Alabama has been and is presently being produced. The other bituminous coal fields are the Cahaba, Plateau, and the Coosa, (Figure 1). The Warrior Coal Field accounts for over 90% of Alabama's coal production and covers more that 3500 square miles in Northwestern Alabama. The traditional limits of the Warrior Coal Field are defined to the north by outcrop of the Black Creek coal seam, the major seam in the stratigraphically lowest and oldest coal group in the upper Pottsville, and to the east by the Oppossum Valley Pottsville, and to the east by the Oppossum Valley Fault Zone. The southern and western limits of the field have not been established due to their being overlapped by Cenozoic and Mesozoic Coastal Plain deposits. It is speculated that the coal bearing rocks may extend into Mississippi.
- North America > United States > Alabama (1.00)
- North America > United States > Pennsylvania > Allegheny County > Pittsburgh (0.34)
- North America > United States > Texas > Dallas County > Dallas (0.24)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.45)
- Materials > Metals & Mining > Coal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Reuse (0.41)
- North America > United States > Colorado > Piceance Basin > Plateau Field > Williams Fork Formation (0.99)
- North America > United States > Colorado > Piceance Basin > Plateau Field > Iles Formation (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Green Canyon > Block 563 > Warrior Field > Warrior Well (0.97)
Summary A vertical borehole drilled into a friable* coal seam was stimulated by using 53,000 gal (200.6 m,) of foam. Proppant materials were omitted from the treatment fluids and colored, fluorescent pigments were included. The borehole produced 6.6 MMcf (0. 187 x 106 MI 1 of methane at an average rate of 49 Mcf/D (1390 m /d) during its 4.5-month lifetime. After the wellbore was mined through, both vertical and horizontal fracture surfaces were found decorated with fluorescent material. No significant penetration of the fluid into the overlying strata was found. Introduction Foam hydraulic stimulation treatments have been used to increase methane production from vertical degasification boreholes at U.S. Steel's Oak Grove mine, near Birmingham, AL. Fifteen boreholes, in an area approximately 2 miles (3.2 km) northeast of the active workings, have been stimulated using approximately 50,000 gal (190 m3) of sand-laden foam fluid. Despite very low daily gas output from two of these holes, the average production has been more than 70 Mcf/D (2000 m3/d) for the past 11 months. Cumulatively, more than 450 MMcf (1.07 × 10(6) m3) of methane have been removed from these degasification holes. Before foam-stimulated degasification holes can be accepted as part of the standard sequence for development of gassy mines, two major problems must be solved. The most important of these is the potential detrimental influence of the stimulation treatment on the integrity of the strata overlying the coal. In this regard, previous experiences at Oak Grove have not been encouraging. Cracks were observed in the mine roof immediately above the coal-seam portions of the fracture around two boreholes that had been stimulated with small treatments [~20,000 gal (76 m3)]. Although no serious problems have been encountered to date, mine personnel are concerned that these cracks may present difficulties during pillar extraction. The second problem is the excessive operating expenses experienced for boreholes stimulated with sand-laden foam treatments. Sand flow-back into the wellbore has resulted in premature degradation of the dewatering equipment, abundant downtime, and repetitive cleanout procedures. Each of these occurrences could jeopardize the cost effectiveness of this treatment design. Proppant and Injection-Rate Criteria Sand, or an alternative proppant, traditionally has been blended into the stimulation fluid to prevent ground stresses of the formation from closing the induced fracture after the fluid pressure has been released. Production characteristics of the boreholes at Oak Grove, however, suggest that the closure stresses in the Blue Creek coal seam are significantly less than those encountered in the strata for which stimulation treatments traditionally have been designed. It is, therefore, conceptually possible that a treatment conducted without proppant might provide gas productions comparable with those recorded on the existing sand-propped boreholes. Obviously, such a treatment would eliminate the sand-related operating problems that have been encountered. JPT P. 2227^
- Water & Waste Management > Water Management > Lifecycle > Reuse (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract This paper presents an analysis of the coalbed degasification process. The theoretical and experimental basis of the degasification process are discussed and a simulation model which incorporates all aspects of this process is described. The simulator is demonstrated using actual field data developed by a joint industry/government demonstration project funded by the DOE and U. S. Steel. The basic reservoir description is discussed in detail, including variations of important description parameters with location. Initial and boundary conditions are demonstrated and analyzed. Initially, the coalbed was saturated with water. With water production, reservoir pressure is lowered, causing gas to desorb from the coal creating a mobile gas saturation. Subsequently, interwell interference effects are demonstrated and the need for such effects explained. Finally, the long term gas deliverability of the pattern is forecast. This forecast shows that about pattern is forecast. This forecast shows that about 45% of the gas within the pattern can be removed if the pattern is in operation six years ahead of mining. Introduction During the process of coalification, considerable quantities of gases are evolved from the indigenous carbonaceous material. These gases include methane and heavier hydrocarbons, carbon dioxide, nitrogen, oxygen, hydrogen, and helium. The primary constituents are methane and carbon dioxide, and these gases have been observed in coal mines since the inception of the industry. Quantities of methane and air in proper proportions (5 to 15 percent methane) result in proportions (5 to 15 percent methane) result in explosive mixtures. It is these mixtures that when ignited cause the disastrous explosions in coal mines. For many years, the only method of controlling the accumulations of explosive mixtures was a combination of increasing the ventilation and decreasing the extraction rate. These activities are costly and reduce productivity. With the advent of the energy shortage, productivity. With the advent of the energy shortage, the waste of the valuable gas resource makes the practice even more undesirable. practice even more undesirable. GAS CONTENT OF COALBEDS Gas can be contained in coal either as free gas in the joints and fractures or as an adsorbed layer on the internal surfaces of the coal. It is important to understand that the free gas contained in the fracture system will behave according to Boyles and Charles Laws just as gas accumulations in any reservoir rock. On the other hand, the gas which is adsorbed onto the internal surfaces does not behave according to Boyles and Charles Law, but in a very distinctive manner. It is common knowledge that carbonaceous substances such as charcoal, coke, and coal can adsorb gases preferentially, and this is what gives these substances their filtration properties. It is this same mechanism that stores methane and other gases in coal. In the adsorbed state, the gas molecules are "tightly packed and closely held" to the walls of the minute sized pores in the structure of the coal. The packing is thought to be only one molecule thick and its density increases with pressure. The large surface area available because of the very fine pore structure of the coal makes it possible to hold pore structure of the coal makes it possible to hold large quantities of gas. Fig. 1 is a plot that shows the relationship of the volume of gas that can be retained as a function of pressure for several U. S. coals. This plot is shown as volume in cm3/g of coal as a function of pressure shown in atmospheres and is known as the equilibrium sorption isotherm. At low pressures, the volume adsorbed increases rapidly and pressures, the volume adsorbed increases rapidly and almost linearly. At higher pressure when the adsorbed layer becomes more crowded, the adsorption slows and finally, at extremely high pressures, it nearly stops. P. 355
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Reuse (0.81)