This paper presents a simplified method for predicting the performance of a gas well. A method for determining the deliverability of an unfractured gas well by use of a single-point flow test and a dimensionless Vogel-type inflow performance curve was proposed by Mishra and Caudle. Their procedure necessitates the calculation of real-gas pseudopressures for shut-in and flowing bottomhole pressures (BHP) obtained from pressure-buildup and stabilized-flow tests, respectively. This paper offers a simplification of this technique in which a range of pressure values is defined over which pressure-squared terms can be substituted for pseudopressures. A comparison is made between results obtained from analysis of well-test data on several gas wells made with conventional multipoint test methods, with the Mishra-Caudle technique, and with the simplified method presented in this paper. The simplified method offers the engineer who might not have access to a pseudopressure computer program or pseudopressure tables a method for estimating gas-well deliverabilities. The method of Mishra and Caudle and the simplified method were both observed to yield slightly conservative estimates of gas-well deliverabilities compared with the deliverabilities calculated from multipoint flow-test analyses. The simplified technique was found to be useful for predicting the performance of fractured gas wells as well as unfractured wells.

Chase and Alkandari developed dimensionless inflow performance (IPR) curves for predicting the stabilized deliverability of hydraulically fractured gas wells using just a single-point test, namely a pressure build-up or draw-down test. Unfractured wells can also be analysed by converting the apparent skin factor to an equivalent ratio of Xe/Xf. Results obtained from the dimensionless IPR curve model can be used to generate values of n and C for the equation of stabilized deliverability. This research describes the process used to evaluate the effectiveness of the single-point model using data from 25 Canadian well tests and nine simulated well tests. The tests were analysed using fourpoint test methods, the dimensionless IPR curve method, and by assuming that the exponent of the stabilized deliverability equation was equal to one. The mean absolute value of error between the AOF predicted using multi-point deliverability test analysis methods and the dimensionless IPR curve method for the 25 Canadian wells was 9.2%, with a standard deviation of 8.7%. The mean absolute value of error between the AOF predicted using multi-point deliverability test analysis methods and the dimensionless IPR curve method for the nine simulated wells was 5.6% with a standard deviation of 4.3%. The mean absolute value of error between the AOF predicted using multi-point test methods and by assuming that the exponent of the stabilized deliverability equation was equal to one for the 25 Canadian wells was 30.5% with a standard deviation of 25.2%. The dimensionless IPR curve model appears to offer a conservative, easonably accurate, and economical method for predicting current and future gas well inflow performance from a single-point transient pressure test. Introduction The deliverability or inflow performance of a gas well is usually predicted by utilizing one of three well testing methods: the conventional backpressure test(1); the isochronal test(2); or the modified isochronal test(3). All three methods normally require that four flow tests be performed on a well, including one to stabilization, to accurately predict stabilized deliverability. Industry practice sometimes shortcuts these methods utilizing just three, two and sometimes just one flow test. In the latter case, the exponent, n, of the stabilized deliverability equation, given by Equation (1) is frequently assumed to be equal to one in order to estimate deliverability. Equation (1) Available In Full Paper. Chase and Alkandari(4) developed a single-point test method that uses dimensionless IPR curves for predicting the inflow performance of fractured gas wells producing under stabilized or pseudosteady state flow conditions. The model was developed in an attempt to better estimate gas well deliverability when just a one-point test, namely a drawdown or build-up test, is conducted. The model was based on concepts proposed by Vogel(5) and Standing(6) for oil wells, and Mishra and Caudle(7) for unfractured gas wells. The following equation serves as the basis for the single-point dimensionless IPR curve method. Equation (2) Available In Full Paper. The SPE paper by Chase and Alkandari describes how a Monte Carlo simulation was used to develop the model and generate values for the coefficient M and exponent N as a function of Xe/Xf.

Predicting the deliverability of a gas well is normally accomplished by conducting a four-point backpressure test, an isochronal test or a modified isochronal test. All of these methods require testing a well at a minimum of four flow rates. Several researchers have worked to advance the theory of predicting gas well deliverability using a one-point test. Their research focused on the development of dimensionless IPR curves for gas wells similar to Vogel's curve for oil wells. This paper describes a method for predicting the deliverability of a gas well that requires only pressure build-up or draw-down test data. The method utilizes new dimensionless IPR curves that were developed specifically for hydraulically fractured gas wells. The curves may also be applied to unfractured wells by converting the apparent skin factor obtained from a pressure transient test to an equivalent ratio of external drainage radius to fracture half-length (xe/xf) using the apparent wellbore radius concept. Using the new curves or their general equation, an IPR curve can be constructed. In its simplest application, the new method allows an engineer to predict the AOF of a gas well which, when plotted on log-log paper along with the single stabilized point obtained from the pressure build-up or draw-down test, permits the construction of the stabilized deliverability curve and the determination of its equation.

Chase and Alkandari developed dimensionless inflow performance (IPR) curves for predicting the stabilized deliverability of hydraulically fractured gas wells using just a single-point test, namely a pressure build-up or draw-down test. Unfractured wells can also be analyzed by converting the apparent skin factor to an equivalent ratio of X e /X f . Results obtained from the dimensionless IPR curve model can be used to generate values of n and C for the equation of stabilized deliverability. This research describes the process used to evaluate the effectiveness of the single-point model using data from twenty-five Canadian well tests and nine simulated well tests. The tests were analyzed using four-point test methods, the dimensionless IPR curve method, and by assuming that the exponent of the stabilized deliverability equation was equal to one. The absolute value of error between the AOF predicted using multi-point deliverability test analysis methods and the dimensionless IPR curve method for the twenty-five Canadian wells was 9.2 %, with a standard deviation of 8.7 %. The absolute value of error between the AOF predicted using multipoint deliverability test analysis methods and the dimensionless IPR curve method for the nine simulated wells was 5.1 % with a standard deviation of 4.7 %. The absolute value of error between the AOF predicted using multi-point test methods and by assuming that the exponent of the stabilized deliverability equation was equal to one for the twenty-five wells was 30.5 % with a standard deviation of 25.2 %.

The estimated 4 trillion tons of coal which lie buried beneath the U.S. at depths of less than 3,000 feet are thought to contain nearly 300 trillion cubic feet of pipeline-quality natural gas. The mechanism by which this gas is released is believed to result from the diffusion of adsorbed gas through the microporous bulk matrix into the natural fractures where mass transport is governed by the principles of Darcy flow. This two-step process may ultimately be controlled by conditions of critical flow, or choke flow, in the micropores adjacent to the fractures. Several techniques have been developed to determine the gas content of a coal seam based primarily on the analysis of exploratory cores. Such methods generally yield quite different results when applied to the same core sample. A new technique which relies upon the analysis of decline curves constructed from gas desorption data obtained from a core, appears to give the most reliable results, and indirectly indicates that the Darcy flow mechanism controls the desorption process. Introduction Several authors have noted the existence of vast amounts of methane, or natural gas, in coal seams. The reserves of natural gas in coal, estimated at nearly 300 trillion cubic feet, exceed current proved recoverable gas reserves in the U.S., and proved recoverable gas reserves in the U.S., and represent a possible supplement to dwindling supplies. Methane is viewed exclusively as a hazard in mining operations and is treated as an undesirable by-product of the mining process. Each day over 200 million cubic feet of gas are vented to the atmosphere through ventilation systems in U.S. coal mines. Ventilation systems dilute the methane emitted from mine workings with large volumes of air, thereby reducing the concentration of methane in air to 1 percent by volume, well below the minimum explosive percent by volume, well below the minimum explosive limit of 5 percent methane-in-air. The cost of maintaining an explosion-free mining environment using a ventilation system is estimated to increase the cost of coal extraction by as much as $0.50 per ton. Since the size and cost of a ventilation system is directly proportional to the volume of natural gas associated with a coal seam, an accurate estimation of its gas content is warranted. Overestimating the gas content will result in overdesigned ventilation systems and increased capital expenditures. Conversely, inadequate ventilation figures in creating an unsafe mining environment resulting in decreased productivity and mine shut-downs. productivity and mine shut-downs. Degasification of coal seams in advance of, or during mining operations represents an alternative, or supplement, to mine ventilation. Current technology has demonstrated the feasibility of using vertical, deviated, or horizontal borehole systems to recover natural gas from both mineable and unmineable coalbeds. Feasibility, however, has been overshadowed by less than favorable economics resulting from the low, regulated market price of natural gas. Ultimately, decontrol of the price of natural gas may provide oil, gas, and coal companies with the incentive necessary to exploit the coal-gas reserves of the U.S. COAL RESERVES The coal resources of the Unites States remaining in the ground as of January 1, 1974, have been estimated by Averitt to be in the neighborhood of 3,968 billion tons. This figure represents approximately 25 percent of the identified coal resources in the world. Of this total resource, 91 percent is coal found at a depth of less than 1,000 feet, 43 percent is bituminous coal, and 33 percent is present in what are considered to be percent is present in what are considered to be thick beds. Coal-bearing rocks are present in 37 states underlying approximately 13 percent of the land area of the 50 United States. Coal deposits in the lower 48 states are depicted in Figure 1 according to rank (a measure of fixed carbon content and heat content) of the deposits.