Rigorous and Explicit Determination of Reserves and Hyperbolic Exponents in Gas-Well Decline Analysis

Stumpf, Thomas Newman; Ayala, Luis F.

doi:10.2118/180909-pa

Cited by 21 publications

(23 citation statements)

References 16 publications

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“…Empirical models are simple, but they also are mere curve fits, whose parameters have little physical meaning and cannot be generalized. In hyperbolic DCA, for example, the exponent b is adjusted to fit production data, notwithstanding several studies that have tried to elucidate its physical meaning [18][19][20]. Another limitation of most empirical models is their inability to capture the two regimes of oil and gas production in shales that are transient-linear flow at early times and boundary-dominated flow at later times on production [21].…”

Section: Introductionmentioning

confidence: 99%

Physical Scaling of Oil Production Rates and Ultimate Recovery from All Horizontal Wells in the Bakken Shale

2020

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A recent study by the Wall Street Journal reveals that the hydrofractured horizontal wells in shales have been producing less than the industrial forecasts with the empirical hyperbolic decline curve analysis (DCA). As an alternative to DCA, we introduce a simple, fast and accurate method of estimating ultimate recovery in oil shales. We adopt a physics-based scaling approach to analyze oil rates and ultimate recovery from 14,888 active horizontal oil wells in the Bakken shale. To predict the Estimated Ultimate Recovery (EUR), we collapse production records from individual horizontal shale oil wells onto two segments of a master curve: (1) We find that cumulative oil production from 4845 wells is still growing linearly with the square root of time; and (2) 6401 wells are already in exponential decline after approximately seven years on production. In addition, 2363 wells have discontinuous production records, because of refracturing or changes in downhole flowing pressure, and are matched with a linear combination of scaling curves superposed in time. The remaining 1279 new wells with less than 12 months on production have too few production records to allow for robust matches. These wells are scaled with the slopes of other comparable wells in the square-root-of-time flow regime. In the end, we predict that total ultimate recovery from all existing horizontal wells in Bakken will be some 4.5 billion barrels of oil. We also find that wells completed in the Middle Bakken formation, in general, produce more oil than those completed in the Upper Three Forks formation. The newly completed longer wells with larger hydrofractures have higher initial production rates, but they decline faster and have EURs similar to the cheaper old wells. There is little correlation among EUR, lateral length, and the number and size of hydrofractures. Therefore, technology may not help much in boosting production of new wells completed in the poor immature areas along the edges of the Williston Basin. Operators and policymakers may use our findings to optimize the possible futures of the Bakken shale and other plays. More importantly, the petroleum industry may adopt our physics-based method as an alternative to the overly optimistic hyperbolic DCA that yields an ‘illusory picture’ of shale oil resources.

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Section: Introductionmentioning

confidence: 99%

Physical Scaling of Oil Production Rates and Ultimate Recovery from All Horizontal Wells in the Bakken Shale

2020

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“…During the transient flow period, prior to BDF, the productivity index is not constant but varies with time. Araya and Ozkan (2002) defined the transient productivity index for a gas reservoir as where the material-balance pseudotime (t a ) is defined as (Palacio et al 1993;Agarwal et al 1999;Raghavan 1993…”

Section: Identification Of the Bdf Periodmentioning

confidence: 99%

A simple approach to dynamic material balance for a dry-gas reservoir

Jongkittinarukorn

Jokhio

Escobar

et al. 2021

J Petrol Explor Prod Technol

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The dynamic material balance methodology can be used to estimate gas initially-in-place using only production and PVT data. With this methodology, reservoir pressure is obtained without requiring the well to be shut in; it is therefore superior to the static material balance method since there is no loss of production. However, the technique requires iterative calculations and numerical integration of gas pseudotime and is quite complex to implement in practice. A simpler and equally accurate methodology is proposed in this study. It requires only production and PVT data and also does not rely on a shut-in pressure survey. In addition, it requires neither iterative calculations nor numerical integration of gas pseudotime. The results of the analysis include gas initially-in-place and gas productivity index, and can easily be extended to production forecasting. Gas initially-in-place is evaluated with a high degree of reliability. The methodology is successfully tested with two simulated cases and one field case, giving high-accuracy results.

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“…Furthermore, its derivation implies the assumption that the bottom hole pressure is constant, so the method may fail to apply to the variable BHP case. Stumpf and Ayala (2016) deduced the analytical expression of decline index n under the constant BHP condition from the Arps' hyperbolic decline model and the relation of the pseudopressure at BHP to the pseudopressure at average reservoir pressure, and proposed a straight-line analysis method for determining reserves by using the production data within the hyperbolic window (or during early BDF). The inconvenient type-curve matching, however, is ineluctable for locating the start and end of the hyperbolic window.…”

Section: Introductionmentioning

confidence: 99%

An Optimization-Based Method for the Explicit Production Data Analysis of Gas Wells

Zhang

Song

et al. 2022

Front. Energy Res.

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This work aims at the exploration of production data analysis (PDA) methods without iterations. It can overcome limitations of the advanced type curve analysis relying on the iterative calculation of material-balance pseudotime and current explicit methods reckoning on specific production schedule assumptions. The dynamic material balance equation (DMBE) is strictly proved by the integral variable substitution based on the gas flow equation under the boundary dominated flow (BDF) condition and the static material balance equation (SMBE) of a gas reservoir. We introduce the pseudopressure level function γ(p) and the recovery factor function R(p) to rewrite the DMBE in terms of observed variable Y and estimated variable Ye; then the PDA can be transformed into an optimization problem of minimizing the error between Y and Ye. An optimization-based method for the explicit production data analysis of gas wells (OBM-EPDA), therefore, is developed in the paper, capable of determining the BDF constant and gas reserves explicitly and accurately for variable rate and/or variable flowing pressure systems. Three stimulated cases demonstrate the applicability and validity of OBM-EPDA with small errors less than 1% for estimated values of both reserves and Y. Not second to previous studies, the field case analysis further proves its practicability. It is shown that the nonlinear relation of γ to R can be represented by a polynomial function merely dependent on the inherent properties of the gas production system even before sorting out the production data. The errors of observed variable Y provided by OBM-EPDA facilitate the data quality control, and the elimination of outliers not subject to the BDF condition improves the reliability of the analysis. For various gas systems producing whether at a constant rate, a constant bottomhole pressure (BHP), or under variable rate and variable BHP conditions, the proposed method gives insights into the well-controlled volume and production capacity of the gas well whether in a low-pressure or high-pressure gas reservoir, where the compressibilities of rock and bound water are considered.

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Rigorous and Explicit Determination of Reserves and Hyperbolic Exponents in Gas-Well Decline Analysis

Cited by 21 publications

References 16 publications

Physical Scaling of Oil Production Rates and Ultimate Recovery from All Horizontal Wells in the Bakken Shale

Physical Scaling of Oil Production Rates and Ultimate Recovery from All Horizontal Wells in the Bakken Shale

A simple approach to dynamic material balance for a dry-gas reservoir

An Optimization-Based Method for the Explicit Production Data Analysis of Gas Wells

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