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Keywords: decline curve analysis

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Proceedings Papers

Prannay Parihar, Russell Warner, James Micikas, Lianne Armpriester, James Anderson, Elizabeth Zuluaga

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE Low Perm Symposium, May 5–6, 2016

Paper Number: SPE-180247-MS

... content and bulk density available in public domain for San Juan Basin to confirm the remaining gas-in-place and need for additional takeaway points in the reservoir.

**Decline****curve****analysis**was used to assess the production performance of more than one hundred infill wells drilled since 2007...
Abstract

The San Juan Basin, located in northwestern New Mexico and southwestern Colorado, is one of the most prolific natural gas producing regions, and one of the largest gas basin in the United States in terms of total estimated gas reserves. More coalbed methane has been produced from the San Juan Basin than the rest of the world combined. This paper analyzes the performance of original and infill wells producing from the Fruitland Coal formation and offsetting Chevron's acreage position in key areas of the North San Juan Basin. Subsurface and production data of these wells available in the public domain formed the basis for the project team to recommend an infill drilling program to maximize the value of the company's current acreage position. The project team developed a comprehensive approach to arrive at a probabilistic production forecast and utilized subsurface data on coal gas content and bulk density available in public domain for San Juan Basin to confirm the remaining gas-in-place and need for additional takeaway points in the reservoir. Decline curve analysis was used to assess the production performance of more than one hundred infill wells drilled since 2007 and to determine the potential impact on the expected ultimate gas recovery of the offset original 160-acre spacing wells. Understanding potential interference risk was critical to justifying the need for downspacing. The project team recommended drilling additional infill wells based on several criteria: no observation of significant interference with the majority of existing producers, considerable remaining gas-in-place that could not be developed at the current well spacing and a positive correlation between performance of Fruitland Coal wells and the thermal maturity of the San Juan Basin. The project team performed data analysis of four different type producing areas (TPAs) delineated within the basin based upon similar reservoir characteristics and production behavior. The data analysis confirmed the opportunity to drill and reduce spacing for improved recovery in areas where underlying geologic parameters like reservoir connectivity and reduced permeability has led to low recovery.

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE Rocky Mountain Regional/Low-Permeability Reservoirs Symposium and Exhibition, March 12–15, 2000

Paper Number: SPE-60284-MS

... hydraulic fracturing reservoir surveillance clough 19 interference fracture field development optimization and planning asset and portfolio management reservoir type upstream oil & gas point bar wellbore

**decline****curve****analysis**production control fetkovich spe annual technical conference...
Abstract

Abstract Effective production-decline analysis is crucial to the successful management of declining oil and gas wells. From analysis of declines caused by reservoir conditions, engineers can generate valuable information such as reserve estimates (useful for property value appraisal) and production forecasts (useful for generating cash-flow forecasts). In short, a production-decline analysis is at the heart of many economic decisions about the future of a well or property. Because decline analysis is so important, engineers are faced with a significant problem when the conventional methods of analysis break down. For example, wells completed in fluvial, meander-belt systems such as those found in the Piceance basin, Colorado often do not follow the conventional production decline patterns established with exponential and hyperbolic equations. Rather, the decline reflects the complex interaction arising from compartmentalized, point-bar reservoirs that are commingled at the wellbore. This paper presents an improved method of analyzing these complex declines using a numerical simulator. Central to this method is the definition of six different reservoir types, each of which can be subjected to different boundary conditions and hydraulic fracture options (i.e., with or without fracture, different fracture orientations, different fracture lengths, etc.). While there are other configurations available in nature, these reservoir types form a sufficient representation for modeling purposes of the compartmentalized reservoirs likely to be encountered and produced. The modeling itself is done in two steps. The first step is to model the individual responses of the reservoir types and superpose the responses in various combinations until a rough match of actual production history is achieved. This best-match combination is then used as a starting point for the second step: modeling the complete system allowing commingling at the wellbore. Further model runs are made until an acceptable match is found. This match is the basis for predicting future performance. Introduction Given the importance of decline curve analysis, it is no surprise that a number of different approaches, from the simple to the complex, have been developed. Some of the most popular methods involve the empirical equations developed by Arps 1 and production type curves. In 1944, Arps presented the equations for exponential, harmonic and hyperbolic decline. Brons and McGarry 2 later detailed the economic application of these equations and presented clear definitions for nominal and effective decline rates. To generate his type curves, Fetkovich 3,4 combined the Arps equations with the analytical constant pressure infinite (transient period for finite systems) solutions developed by Ehlig-Economides and Ramey 5,6 and Uriet and Raghavan 7,8 . These type curves allow engineers to glean information from the infinite-acting period as well as the decline. Because of the versatility of the approach, many production type curves have been developed over the years for specific physical situations, e.g., wells with hydraulic fractures, 9–11 dual porosity systems, 12 two-phase flow, etc. The Fetkovich curves have even been recast in rate integral form 13 and rate derivative form 14 . The two methods described above are relatively easy to apply and are sufficiently accurate for a wide range of wells. Unfortunately, they often do not work well for wells completed in compartmentalized meander-belt systems because of the complex physical setting. These methods are based upon a single layer model. As such, they must lump the collective responses of a commingled, multilayer system with irregular geometry and natural and hydraulic fractures into the response of one "effective" layer.

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE Rocky Mountain Regional/Low-Permeability Reservoirs Symposium, April 5–8, 1998

Paper Number: SPE-39927-MS

... pressure

**decline****curve****analysis**. 39927 - . . Practical Production Data Analysis Society of Petroleum Engineers J. H. Frantz, Jr,, S. A. Holditch & Asswiat6s, Inc., J. P. Spivey, S. A. Holditch & Associates, Inc., and C. W. Hopkins, S. A. Holditch & Associates, Inc. ~ lw( SociatycfPetrch Eilg!s-raarl...
Abstract

Abstract This paper presents several production data analysis case histories. The primary purpose of this work is to illustrate the practical application of advanced production data analysis methods in low permeability gas reservoirs. Production data provide important information about reservoir quality and volume and the stimulation effectiveness. The analysis results can provide estimates for permeability-thickness product, skin factor or fracture half-length, gas in place, and drainage area. Pressure transient information can also be integrated with production data analysis to further characterize the reservoir. Practical applications of production data analysis results include estimating short- and long-term production rates, estimating reserves, designing/evaluating stimulation (and restimulation) treatments, predicting and evaluating production increases from changes in flowing well pressure (plunger-lift and compressor installations), determining infill well potential and optimal well spacing, and identifying natural fracture and/or layered behavior. We will show examples of the above applications using actual field data. New type curves were also used in this work to analyze difficult datasets and to provide a starting point for more sophisticated history-matching methods. The final portion of this paper will include recommendations for field data collection and database utilization. P. 231

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE/DOE Low Permeability Gas Reservoirs Symposium, May 19–22, 1985

Paper Number: SPE-13898-MS

... wells. P. 491 tight gas special case gas well production forecasting straight line equation complex reservoir decline curve

**decline****curve****analysis**tight gas well inverse square-root equation production monitoring exponent decline shape type curve hyperbolic exponent arp equation...
Abstract

SPE Member Abstract Standard decline curve equations can by used outside their normal range of application to give accurate and theoretically valid projections of tight gas well performance. This approach is preferable to the use of the reciprocal square-root of time as a preferable to the use of the reciprocal square-root of time as a tight gas well "type curve". Introduction Low permeability fractured gas wells, when produced without constraint, typically exhibit a characteristic decline curve shape: a steep initial decline followed by a long well life at low producing rates relative to the initial potential. The common producing rates relative to the initial potential. The common methods of forecasting production from these wells vary in complexity and in the amount of detail required. Decline curves and mathematical curve fitting require only monthly production data; no knowledge of reservoir properties is necessary. The problem with these techniques it that, especially at early times, problem with these techniques it that, especially at early times, virtually any curve can give a reasonable fit to monthly data. On the other hand, log-log type curves and mathematical simulation require knowledge of the fracture and reservoir geometries as well as a detailed history of flowing rates and pressures. As a practical matter, this kind of detail is often unavailable practical matter, this kind of detail is often unavailable The utility of decline curves can be enhanced by recognizing the influence of the physics of reservoir fluid flow on the resulting semi-log plot. The characteristic tight gas well decline shape is a predictable result of the flow from a low permeability reservoir into a more conductive fracture. The Arps Equation The Arps equation is the most commonly used ratetime decline relationship: (1) Arps treated the equation as empirical, but noted that the exponent can be influenced by the reservoir flow conditions. The value of b determines the degree of curvature of the semi-log decline, from a straight line (exponential decline) at be = 0.0 to increasing curvature at higher values of b. He stated that the value of b varies between zero and 1.0, with no discussion of the possibility of b greater than 1. There is no theoretical basis for limiting the exponent to values less than 1. Using numerical simulations, Gentry and McCray showed that reservoir heterogeneity (e.g., layered reservoirs) can result in a hyperbolic exponent exceeding 1. A single decline equation with b less than 1 cannot approximate a typical tight gas decline shape as shown in Figure 1. Bailey used mathematical curve fitting to determine the "best fit" hyperbolic equation for wells in three tight has basins. For his representative group of fractured Wattenberg Field wells, the optimized exponent exceeds 1 in all but a few cases, and ranges as high as 3.5 in one case. In practice, many engineers avoid the use of hyperbolic decline curves. Some use a favorite French curve to approximate tight gas well declines. Another common approach is to assume a decline shape composed of a series of straight line segments: for example, 50% exponential decline for two years, then 20% decline for three years, followed by 8% decline to an economic limit. While these methods may give satisfactory results for a group of similar wells, one must ask: Why do these wells follow a decline shape which is apparently arbitrary? The Inverse Square-Root of Time Equation In search of an equation which explains the influence of low permeability and flow geometry on the shape of the decline curve, permeability and flow geometry on the shape of the decline curve, some recent papers and articles have proposed the following equations for use with tight gas well declines: (2) The argument for this equation is based on the physics of linear flow and on observations from log-log type curves for fractured wells. P. 491

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE/DOE Low Permeability Gas Reservoirs Symposium, March 14–16, 1983

Paper Number: SPE-11640-MS

... or short production Predicting rates and reserves based on test data or short production histories is difficult using conventional

**decline****curve****analysis**. The usual approach to predicting reserves by**decline****curve****analysis**, in this type of well, is to arbitrarily assign a high exponential decline rate...
Abstract

Abstract Production decline curves of three representative low permeability gas wells in the Piceance Basin are analyzed. These wells produce from the Mancos "B", Mesaverde and Wasatch formations, respectively. It was found that long term production in these wells could be approximated using linear flow equations. This observation leads to the development of a decline curve method for predicting rate-time behavior based only one or two years of production data. The method is easy to apply and requires only data which is routinely reported to state oil and gas regulatory agencies. This type of data is public information and is readily available in most states. The observed long-term linear flow behavior indicates that fracture lengths are much longer than would be expected from hydraulic fracturing treatments. Possible explanations for this behavior are discussed. The possibility of using short-term test data to define the long-term possibility of using short-term test data to define the long-term production decline curve is also discussed. production decline curve is also discussed Introduction Production histories of fractured low permeability gas wells in the Piceance Basin are characterized by a sharp initial decline followed by a Piceance Basin are characterized by a sharp initial decline followed by a long transition into exponential decline. These two decline periods correspond to linear and pseudo steady-state flow, respectively. Predicting rates and reserves based on test data or short production Predicting rates and reserves based on test data or short production histories is difficult using conventional decline curve analysis. The usual approach to predicting reserves by decline curve analysis, in this type of well, is to arbitrarily assign a high exponential decline rate for the first two or three years, followed by a lower decline. Another approach is to find a hyperbolic decline curve to fit the early tine data and extrapolate to estimate future rates. Both of these approaches can result in large errors in calculated reserves. Early production data of low permeability gas wells should exhibit some linear flow characteristics. The constant pressure solutions for fractured wells presented in the literature predict that linear flow (the half unit slope) ends at tDxf=0.015. For reasonable values of fracture length and reservoir rock properties, linear flow should end in a few days or months, yet actual field data shows apparent linear flow lasting four years or more in some wells. Therefore, if fracture type curves are used to project well rates, based on a match that does not properly describe the linear flow system the predicted rates and reserves may be high. The basic problem, therefore, appears to be one of reservoir description. Long natural fractures, long narrow reservoirs or thin high permeability beds can all result in long term linear flow behavior. permeability beds can all result in long term linear flow behavior. Hydraulic fractures are superimposed on the natural system. Short-term testing may characterize the hydraulic fracture, but long-term production may be controlled by the naturally occurring reservoir properties. This paper proposes a decline curve analysis technique for wells exhibiting paper proposes a decline curve analysis technique for wells exhibiting long-term linear flow characteristics and explores some possible explanations for this phenomenon. Three wells which product from typical low permeability gas reservoirs in the Piceance Basin were selected for analysis. Case I is a Mancos "B" well in the Douglas Arch area, Case II is a Mesaverde well near the DOE MWX site, and Case III is a Wasatch well near Rifle, Colorado. The general well locations are shown on Figure 1. Only readily available information was considered in this analysis. P. 351