Production Analysis of Long-Term Linear Flow in Tight Gas Reservoirs: Case Histories

Arevalo-Villagran, J.A.; Wattenbarger, R.A.; Samaniego-Verduzco, Fernando; Pham, Tai

doi:10.2118/71516-ms

Cited by 35 publications

(14 citation statements)

References 36 publications

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“…This well has produced for more than 44 years without having a hydraulic fracture and is the only well in this reservoir (2) . It is estimated that the wellbore flowing pressure is 800 psi absolute.…”

Section: Well a Case Historymentioning

confidence: 99%

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Rate Dependence of Transient Linear Flow in Tight Gas Wells

Ibrahim

Wattenbarger

2006

Journal of Canadian Petroleum Technology

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Many tight gas wells (permeability less than 0.1 mD) exhibit transient linear flow; sometimes for several years. This behaviour differs from radial flow in many ways. This paper reports another import difference between linear flow and radial flow? rate sensitivity. It has been shown and accepted for years that real gas pseudopressure can be used to apply analytical solutions to transient radial flow. However, it has been noticed that analytical solutions can be in serious error when applied to transient linear flow. Specifically, the slope of the √t plot departs from the analytical value as the flow rates or degree of drawdown becomes higher. This paper demonstrates the rate/drawdown sensitivity of transient linear flow. Then a correction factor is presented which corrects the slope of the plot and improves the accuracy of √k Ac and OGIP, as calculated from production/pressure performance. Introduction Many wells in tight gas reservoirs have long-term performance which exhibit only linear flow, not radial flow, during the transient period. Wells have been observed which stay in the transient linear flow regime for several years. Some of these wells have hydraulic fractures and some do not. It is usually not practical to analyze tight gas wells with build-up tests, but long-term production and pressure data can be used for analysis. Previous papers have presented methods of analysis(1–5). The analysis of these wells comes from plotting [m(pi) - m(pwf)]/ Qg vs. √t and observing the slope, mCPL, and the end of the straight line, tesr (end of the transient linear flow period). From these values, √k Ac and OGIP can be calculated. It has long been accepted that radial flow transient solutions can be approximated by analytical solutions, in terms of m(p), regardless of flow rate. Constant rate solutions have been emphasized, but it can also be shown that constant pwf flow can also be approximated by analytical solutions, regardless of the level of drawdown(5). The drawdown/rate dependency linear flow is different than analysis of radial flow. This difference was demonstrated with reservoir simulation in this work. A correction method was developed to improve the accuracy of analysis of transient linear flow for analyzing tight gas wells. Effect of Drawdown on Transient Linear Flow (Constant pwf) A number of transient linear flow cases were run with constant Pwf. It was found that these cases did not have the same slopes as the analytical solution, but varied according to the level of drawdown. In order to demonstrate this effect, a dimensionless drawdown parameter is defined as follows: Equation (Available In Full Paper) Some results are plotted in Figure 1. It can be seen that the slope of these plots is greatly affected by the level of drawdown, DD. As the drawdown value increases, the slope (mCPL) value decreases. Since the analysis equations(5) are based on analytical solutions, the calculations may be wrong when actual data is analyzed.

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Section: Well a Case Historymentioning

confidence: 99%

“…It is usually not practical to analyze tight gas wells with build-up tests, but long-term production and pressure data can be used for analysis. Previous papers have presented methods of analysis (1)(2)(3)(4)(5) .…”

Section: Introductionmentioning

confidence: 99%

Rate Dependence of Transient Linear Flow in Tight Gas Wells

Ibrahim

Wattenbarger

2006

Journal of Canadian Petroleum Technology

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“…The superposition time (Super-t) function has been used as a tool to analyze the variable flow rate 10 Note that initial properties are used in Eq. 3.…”

Section: Introductionmentioning

confidence: 99%

Determination of OGIP for Wells in Pseudosteady-State-Old Techniques, New Approaches

Ibrahim

Wattenbarger

Helmy³

2003

SPE Annual Technical Conference and Exhibition

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn this paper, we investigate the shortcomings of available methods for the analysis of gas well production performance and we propose a new method to more accurately estimate original gas-in-place (OGIP).Several methods are available in the industry to analyze the production performance of gas wells. The most accurate and dependable of them uses superposition time. This method has the advantage of being able to analyze variable-rate and variable-pressure data, which is usually the nature of field data. However, this method has its shortcomings.In this paper, we use simulation and field cases to review and compare the application of superposition method and illustrate its shortcomings. We present a new normalized pseudotime plotting function for use in the superposition method to smooth field data and more accurately calculate OGIP. The use of this normalized pseudotime is particularly important in the analysis of highly depleted reservoirs with high compressibility where the superposition errors are largest.We also present a new tangent method to calculate the OGIP with current reservoir properties for both constant rate and p wf production.

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“…Ultra-tight reservoirs in the low micro-Darcy range and less generally require multiple fractured horizontal wells (MFHW), with as many as fifty hydraulic fracture stages. Both type of reservoirs predominantly show transient fluid flow patterns, often maintaining the linear flow for several years (Arevalo-Villagran et al, 2001). Unless peculiar conditions exist in the reservoirs, such as the presence of high permeability streaks or in a naturally fractured reservoir, boundary dominated pseudo-steady state flow only occurs at late time when most of the recoverable reserves have been produced.…”

Section: Introductionmentioning

confidence: 99%

Efficient Semi-Analytical Engine for Performance Prediction of Unconventional Reservoirs

Olalotiti-Lawal

Friedel²

2015

SPE Eastern Regional Meeting

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Reliable and fast prediction of fractured well performance is vital for asset evaluation and prudent field development decision making in unconventional, low permeability oil and gas reservoirs. Simple low cost techniques such as decline curve analysis are ill suited of properly accounting for extended transient flow regimes. Numerical simulation techniques on the other hand are unrivaled in capturing geological details and high accuracy in fluid flow description. However, they suffer from high computational expense and often too little relevant data is available. Our objective is to develop an efficient semi-analytical solution that combines the advantages of speed and accuracy from both techniques for forecasts on single well, pad and even field level.Contrary to conventional oil and gas reservoirs, the tight reservoir characteristics allow for the application of analytical solutions to predict the behavior of fractured wells. The depth of investigation is small with spatial property variations having limited influence considering the large local pressure gradients. Fluid flow is mainly of transient nature and less dominated by multi-phase flow effects within the reservoir. Moreover, the typical configuration of an individual well with multiple fracture stage, entire pads with multiple wells or even entire assets allow the application of the superposition in space, providing a cheap means for accurate solution for multi-well problems.This paper presents a transient semi-analytical model based on a tri-linear formulation. It accurately captures fluid flow to a single or multiple fractured wells over the entire life cycle of production, from early linear flow to pseudo-steady boundary driven flow. It is applicable to oil or gas reservoirs with permeabilities ranging from nano-Darcies to approximately one milli-Darcy. It is capable of handling both the vertical and horizontal well type, with either single or multiple fracture stages respectively. Well-bore, stage and pad configurations can be freely parametrized. A tubing head pressure boundary condition is incorporated to model production from those wells more realistically. For shale type reservoirs, a desorption process is incorporated.The model is particularly suitable for quantitative evaluation of field development alternatives involving a large number of fractured wells. The accuracy compared to a high resolution numerical simulation model generally exceeds 90% with a computation speedup factor in the order of one hundred or more. Besides conventional benchmarking with a numerical reservoir simulator, actual field production data from the Marcellus and Eagleford shale wells shows the utility of the new solution. Being both fast and accurate, the technique presented in this paper is ideal for supporting high quality, cost efficient decision making which is crucial in the current low oil price environment.

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Production Analysis of Long-Term Linear Flow in Tight Gas Reservoirs: Case Histories

Cited by 35 publications

References 36 publications

Rate Dependence of Transient Linear Flow in Tight Gas Wells

Rate Dependence of Transient Linear Flow in Tight Gas Wells

Determination of OGIP for Wells in Pseudosteady-State-Old Techniques, New Approaches

Efficient Semi-Analytical Engine for Performance Prediction of Unconventional Reservoirs

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