Estimating Reserves in Tight Gas Sands at HP/HT Reservoir Conditions: Use
and Misuse of an Arps Decline Curve Methodology

Rushing, Jay Alan; Perego, Albert Duane; Sullivan, Richard; Blasingame, Thomas Alwin

doi:10.2523/109625-ms

Cited by 25 publications

(6 citation statements)

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“…In equation [1], if 0 < b < 1 the cumulative production is finite and if b ≥ 1 cumulative production is infinite, which is unreasonable 7 . However, many have reported that b > 1 yields the best fit to US shale production data 4 7 10 . For example, Baihly et al .…”

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confidence: 99%

Nanostructural control of methane release in kerogen and its implications to wellbore production decline

Criscenti

Wang

2016

Sci Rep

101

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Despite massive success of shale gas production in the US in the last few decades there are still major concerns with the steep decline in wellbore production and the large uncertainty in a long-term projection of decline curves. A reliable projection must rely on a mechanistic understanding of methane release in shale matrix–a limiting step in shale gas extraction. Using molecular simulations, we here show that methane release in nanoporous kerogen matrix is characterized by fast release of pressurized free gas (accounting for ~30–47% recovery) followed by slow release of adsorbed gas as the gas pressure decreases. The first stage is driven by the gas pressure gradient while the second stage is controlled by gas desorption and diffusion. We further show that diffusion of all methane in nanoporous kerogen behaves differently from the bulk phase, with much smaller diffusion coefficients. The MD simulations also indicate that a significant fraction (3–35%) of methane deposited in kerogen can potentially become trapped in isolated nanopores and thus not recoverable. Our results shed a new light on mechanistic understanding gas release and production decline in unconventional reservoirs. The long-term production decline appears controlled by the second stage of gas release.

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confidence: 99%

Nanostructural control of methane release in kerogen and its implications to wellbore production decline

Criscenti

Wang

2016

Sci Rep

101

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“…An analysis line can be created by using the parameters in equation (4). Modifying the parameters by trial and error tended to be tedious because matching n and D∞ at the same time tends to be time consuming.…”

Section: Fit a Analysis To The Production Datamentioning

confidence: 99%

Application of the Power Law Loss-Ratio Method of Decline Analysis

McNeil¹,

Jeje²,

Renaud³

2009

Canadian International Petroleum Conference

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Decline analysis using Arp's equations is the primary empirical method used in the petroleum industry for estimating future reserve recovery and generating production forecasts. The development of tight gas and in particular shale gas reservoirs as important new sources of gas production has highlighted a concern with the hyperbolic form. That is, the expected ultimate reserve (EUR) is highly dependent on the choice of 'b' value. Recent work by Ilk et al has proposed a new decline formulation called the "power law loss-ratio" that they claim is more general and robust than Arps. Essentially, the power law loss-ratio predicts that 'b' changes over a well's producing life and the 'D' and 'b' values can be replaced with more predictable parameters called 'D ∞ ', 'ˆi D ', and 'n'. The purpose of this paper is to test the applicability of the power law loss-ratio method with readily available public data. Several wells were analyzed using Arps hyperbolic decline and the power law loss-ratio method. The results of each will be presented along with a comparison of the estimates of ultimate recoverable reserves.

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“…This outcome has the significant potential to overestimate reserves if the ultimate extrapolation is not constrained by "splicing" a terminal exponential decline trend at some time in future. In the studies provided by Rushing et al [2007] and Lee and Sidle [2010] these authors showed that the unconstrained use Arps' hyperbolic rate relation (particularly for cases where the b-values are greater than 1) can and almost always does yield significant overestimates of reserves.…”

Section: Introductionmentioning

confidence: 99%

Decline Curve Analysis for Unconventional Reservoir Systems — Variable Pressure Drop Case

Ilk¹,

Blasingame

2013

All Days

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The premise of this work is the development and application of a new methodology to forecast production data in unconventional reservoirs where variable rate and pressure drop data are typically observed throughout production. Decline curve analysis techniques for the estimation of ultimate recovery (EUR) require the constant bottomhole pressure condition during the producing life of the well-whereas it is not regular practice to maintain a constant bottomhole pressure profile throughout production in unconventional reservoirs. Therefore, the applicability of the time-rate decline relations is questionable, and methods to remove pressure variations from rate response are needed for generating future production forecasts. From a conceptual view point, we propose the utilization of the convolution/superposition theory along with the recently developed "empirical" time-rate equations, which are normalized by pressure drop data. In order to avoid non-uniqueness, a workflow is used where model parameters for the "normalized" decline curve equations are identified using diagnostic "qDb" plots. Normalized decline curve equations are then convolved with the pressure drop data to achieve a history match and to forecast production. We provide demonstrative application of this technique using an example from an high pressure high temperature shale gas reservoir. For varying bottomhole pressure cases, we show that our proposed techniques effectively remove pressure variations from the rate history. We present the differences in computed EUR values using decline curve analysis with and without corrections for varying pressures. In addition, forecasts are generated using supplementary plots such as pressure drop normalized rate versus cumulative production.

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Estimating Reserves in Tight Gas Sands at HP/HT Reservoir Conditions: Use and Misuse of an Arps Decline Curve Methodology

Cited by 25 publications

References 0 publications

Nanostructural control of methane release in kerogen and its implications to wellbore production decline

Nanostructural control of methane release in kerogen and its implications to wellbore production decline

Application of the Power Law Loss-Ratio Method of Decline Analysis

Decline Curve Analysis for Unconventional Reservoir Systems — Variable Pressure Drop Case

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