A Decline Curve Analysis Model Based on Fluid Flow Mechanisms

2005 ◽  
Vol 8 (03) ◽  
pp. 197-204 ◽  
Author(s):  
Kewen Li ◽  
Roland N. Horne
Keyword(s):  
Fluid Flow ◽  
Linear Relationship ◽  
Relative Permeability ◽  
Oil Recovery ◽  
Single Phase ◽  
Oil Production ◽  
Curve Analysis ◽  
Production Data ◽  
Decline Curve Analysis ◽  
Decline Curve

Summary Decline-curve-analysis models are used frequently but still have many limitations. Approaches of decline-curve analysis used for naturally fractured reservoirs developed by waterflooding have been few. To this end, a decline-analysis model derived on the basis of fluid-flow mechanisms was proposed and used to analyze the oil-production data from naturally fractured reservoirs developed by waterflooding. Relative permeability and capillary pressure were included in this model. The model reveals a linear relationship between the oil-production rate and the reciprocal of the oil recovery or the accumulated oil production. We applied the model to the oil-production data from different types of reservoirs and found a linear relationship between the production rate and the reciprocal of the oil recovery as foreseen by the model, especially at the late period of production. The values of maximum oil recovery for the example reservoirs were evaluated with the parameters determined from the linear relationship. An analytical oil-recovery model was also proposed. The results showed that the analytical model could match the oil-production data satisfactorily. We also demonstrated that the frequently used nonlinear type curves could be transformed to linear relationships in a log-log plot. This may facilitate the production-decline analysis. Finally, the analytical model was compared with conventional models. Introduction Estimating reserves and predicting production in reservoirs has been a challenge for many years. Many methods have been developed in the last several decades. One frequently used technique is the decline-curve-analysis approach. There have been a great number of papers on this subject. Most of the existing decline-curve-analysis techniques are based on the empirical Arps equations: exponential, hyperbolic, and harmonic. It is difficult to foresee which equation the reservoir will follow. On the other hand, each approach has some disadvantages. For example, the exponential decline curve tends to underestimate reserves and production rates; the harmonic decline curve has a tendency to overpredict the reservoir performance. In some cases, production-decline data do not follow any model but cross over the entire set of curves. Fetkovich combined the transient rate and the pseudosteady-state decline curves in a single graph. He also related the empirical equations of Arps to the single-phase-flow solutions and attempted to provide a theoretical basis for the Arps equations. This was realized by developing the connection between the material balance and the flow-rate equations on the basis of his previous papers. Many derivations were based on the assumption of single-phase oil flow in closed-boundary systems. These solutions were suitable only for undersaturated(single-phase) oil flow. However, many oil fields are developed by waterflooding. Therefore, two-phase fluid flow (rather than single-phase flow)occurs. In this case, Lefkovits and Matthews derived the exponential decline form for gravity-drainage reservoirs with a free surface by neglecting capillary pressure. Fetkovich et al. included gas/oil relative permeability effects on oil production for solution-gas drive through the pressure-ratio term. This assumes that the oil relative permeability is a function of pressure. It is known that gas/oil relative permeability is a function of fluid saturation, which depends on fluid/rock properties.

Unified Decline Type-Curve Analysis for Natural Gas Wells in Boundary-Dominated Flow

SPE Journal ◽  
2012 ◽  
Vol 18 (01) ◽  
pp. 97-113 ◽  
Author(s):  
Ayala H Luis F. ◽  
Peng Ye
Keyword(s):  
Natural Gas ◽  
Constant Pressure ◽  
Curve Analysis ◽  
Production Data ◽  
Gas Wells ◽  
Production Potential ◽  
Type Curve ◽  
Type Curves ◽  
Decline Curve Analysis ◽  
Decline Curve

Summary Rate-time decline-curve analysis is the technique most extensively used by engineers in the evaluation of well performance, production forecasting, and prediction of original fluids in place. Results from this analysis have key implications for economic decisions surrounding asset acquisition and investment planning in hydrocarbon production. State-of-the-art natural gas decline-curve analysis heavily relies on the use of liquid (oil) type curves combined with the concepts of pseudopressure and pseudotime and/or empirical curve fitting of rate-time production data using the Arps hyperbolic decline model. In this study, we present the analytical decline equation that models production from gas wells producing at constant pressure under boundary-dominated flow (BDF) which neither employs empirical concepts from Arps decline models nor necessitates explicit calculations of pseudofunctions. New-generation analytical decline equations for BDF are presented for gas wells producing at (1) full production potential under true wide-open decline and (2) partial production potential under less than wide-open decline. The proposed analytical model enables the generation of type-curves for the analysis of natural gas reservoirs producing at constant pressure and under BDF for both full and partial production potential. A universal, single-line gas type curve is shown to be straightforwardly derived for any gas well producing at its full potential under radial BDF. The resulting type curves can be used to forecast boundary-dominated performance and predict original gas in place without (1) iterative procedures, (2) prior knowledge of reservoir storage properties or geological data, and (3) pseudopressure or pseudotime transformations of production data obtained in the field.

Quantification of Uncertainty in Reserves Estimation From Decline Curve Analysis of Production Data for Unconventional Reservoirs

2007 ◽  
Author(s):  
Yueming Cheng ◽  
W. John Lee ◽  
Duane A. McVay
Keyword(s):  
Oil And Gas ◽  
Curve Analysis ◽  
Production Data ◽  
Data Sets ◽  
Gas Wells ◽  
Advanced Technique ◽  
Unconventional Resources ◽  
Decline Curve Analysis ◽  
Decline Curve ◽  
Reserve Estimates

Decline curve analysis is the most commonly used technique to estimate reserves from historical production data for evaluation of unconventional resources. Quantifying uncertainty of reserve estimates is an important issue in decline curve analysis, particularly for unconventional resources since forecasting future performance is particularly difficult in analysis of unconventional oil or gas wells. Probabilistic approaches are sometimes used to provide a distribution of reserve estimates with three confidence levels (P10, P50 and P90) and a corresponding 80% confidence interval to quantify uncertainties. Our investigation indicates that uncertainty is commonly underestimated in practice when using traditional statistical analyses. The challenge in probabilistic reserves estimation is not only how to appropriately characterize probabilistic properties of complex production data sets, but also how to determine and then improve the reliability of the uncertainty quantifications. In this paper, we present an advanced technique for probabilistic quantification of reserve estimates using decline curve analysis. We examine the reliability of uncertainty quantification of reserve estimates by analyzing actual oil and gas wells that have produced to near-abandonment conditions, and also show how uncertainty in reserves estimates changes with time as more data become available. We demonstrate that our method provides more reliable probabilistic reserves estimation than other methods proposed in the literature. These results have important impacts on economic risk analysis and on reservoir management.

Decline Curve Analysis Using Type Curves for Two-Porosity Systems

1981 ◽  
Vol 21 (03) ◽  
pp. 354-362 ◽  
Author(s):  
Giovanni Da Prat ◽  
Heber Cinco-Ley ◽  
Henry Ramey
Keyword(s):  
Fluid Flow ◽  
Flow Rate ◽  
Skin Effect ◽  
Curve Analysis ◽  
Fractured Reservoir ◽  
Type Curve ◽  
Decline Curve Analysis ◽  
Decline Curve ◽  
Wellbore Storage ◽  
Naturally Fractured

Abstract Constant producing pressure solutions that define declining production rates with time for a naturally fractured reservoir are presented. The solutions for the dimensionless flow rate are based on a model presented by Warren and Root. The model was extended to include constant producing pressure in both infinite and finite systems. The results obtained for a finite no-flow outer boundary are new and surprising. It was found that the flow rate shows a rapid decline initially, becomes nearly constant for a period, and then a final decline in rat,- takes place.A striking result of the present study is that ignoring the presence of a constant flow rate period in a type-curve match can lead to erroneous estimates of the dimensionless outer radius of a reservoir. An example is presented to illustrate the method of type-curve matching for a naturally fractured system. Introduction Naturally fractured reservoirs consist of heterogeneous porous media where the openings (fissures and fractures) vary considerably in size. Fractures and openings of large size form vugs and interconnected channel, whereas the tine cracks form block systems which are the main body of the reservoir (Fig. 1). The porous blocks store most of the fluid in the reservoir and are often of low permeability, whereas the fractures have a low storage capacity and high permeability. Most of the fluid flow will occur through the fissures with the blocks acting as fluid sources. Even though the volumetric average permeability in a naturally fractured system is low, such systems often exhibit an effective permeability that is higher than the block matrix permeability, and behave differently from ordinary homogeneous media. These systems have been studied extensively in the petroleum literature. One of the first such studies was published by Pirson in 1953. In 1959, Pollard presented one of the first pressure transient models available for interpretation of well test data from two-porosity systems. The most complete analysis of transient flow in two-porosity systems was presented in 1960 by Barenblatt and Zheltov. The Warren and Root study in 1963 is considered the forerunner of modern interpretation of two-porosity systems. Their paper has been the subject of study by many authors. The behavior of fractured systems has long been a topic of controversy Many authors have indicated that the graphical technique proposed by Pollard in 1959 is susceptible to error caused by approximations in the mathematical model. Nevertheless, the Pollard method still is used. The most complete study of two-porosity systems appears to be the Mavor and Cinco-Ley study in 1979. This study considers wellbore storage and skin effect, and also considers production, both at constant rate and at constant pressure. However, little information is presented concerning the effect of the size of the system on pressure buildup behavior.Although decline curve analysis is widely used, methods specific to two-porosity fractured systems do not appear to be available. It is the objective of this paper to produce and study decline curve analysis for a naturally fractured reservoir. The Warren and Root model was chosen as the basis for this work. Partial Differential Equations The basic partial differential equations for fluid flow in a two-porosity system were presented by Warren and Root in 1963. The model was extended by Mavor and Cinco-Ley to include wellbore storage and skin effect. SPEJ P. 354^

Analyzing Well Production Data Using Combined Type Curve and Decline Curve Analysis Concepts

1998 ◽  
Author(s):  
Ram G. Agarwal ◽  
David C. Gardner ◽  
Stanley W. Kleinsteiber ◽  
Del D. Fussell
Keyword(s):  
Curve Analysis ◽  
Production Data ◽  
Type Curve ◽  
Well Production ◽  
Decline Curve Analysis ◽  
Decline Curve

Quantification of Uncertainty in Reserve Estimation From Decline Curve Analysis of Production Data for Unconventional Reservoirs

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Yueming Cheng ◽  
W. John Lee ◽  
Duane A. McVay
Keyword(s):  
Oil And Gas ◽  
Curve Analysis ◽  
Production Data ◽  
Gas Wells ◽  
Reserve Estimation ◽  
Advanced Technique ◽  
Unconventional Resources ◽  
Decline Curve Analysis ◽  
Decline Curve ◽  
Reserve Estimates

Decline curve analysis is the most commonly used technique to estimate reserves from historical production data for the evaluation of unconventional resources. Quantifying the uncertainty of reserve estimates is an important issue in decline curve analysis, particularly for unconventional resources since forecasting future performance is particularly difficult in the analysis of unconventional oil or gas wells. Probabilistic approaches are sometimes used to provide a distribution of reserve estimates with three confidence levels (P10, P50, and P90) and a corresponding 80% confidence interval to quantify uncertainties. Our investigation indicates that uncertainty is commonly underestimated in practice when using traditional statistical analyses. The challenge in probabilistic reserve estimation is not only how to appropriately characterize probabilistic properties of complex production data sets, but also how to determine and then improve the reliability of the uncertainty quantifications. In this paper, we present an advanced technique for the probabilistic quantification of reserve estimates using decline curve analysis. We examine the reliability of the uncertainty quantification of reserve estimates by analyzing actual oil and gas wells that have produced to near-abandonment conditions, and also show how uncertainty in reserve estimates changes with time as more data become available. We demonstrate that our method provides a more reliable probabilistic reserve estimation than other methods proposed in the literature. These results have important impacts on economic risk analysis and on reservoir management.

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