Gas-Production-Data Analysis of Variable-Pressure-Drawdown/Variable-Rate Systems: A Density-Based Approach

2014 ◽  
Vol 17 (04) ◽  
pp. 520-529 ◽  
Author(s):  
Miao Zhang ◽  
Luis F. Ayala H.
Keyword(s):  
Data Analysis ◽  
Material Balance ◽  
Gas Production ◽  
Variable Pressure ◽  
Production Data ◽  
Variable Rate ◽  
Well Performance ◽  
Gas Well ◽  
Type Curves ◽  
Performance Forecasting

Summary This study demonstrates that production-data analysis of variable-bottomhole-flowing-pressure/variable-rate gas wells under boundary-dominated flow (BDF) is possible by use of a density-based approach. In this approach, governing equations are expressed in terms of density variables and dimensionless viscosity/compressibility ratios. Previously, the methodology was successfully used to derive rescaled exponential models for gas-rate-decline analysis of wells primarily producing at constant bottomhole pressure (Ayala and Ye 2013a, b; Ayala and Zhang 2013; Ye and Ayala 2013; Zhang and Ayala 2014). For the case of natural-gas systems experiencing BDF, gas-well-performance analysis has been made largely possible by invoking the concepts of pseudotime, normalized pseudotime, or material-balance pseudotime. The density-based methodology rigorously derived in this study, however, does not use any type of pseudotime calculations, even for variable-rate/variable-pressure-drawdown cases. The methodology enables straightforward original-gas-in-place calculations and gas-well-performance forecasting by means of type curves or straight-line analysis. A number of field and numerical case studies are presented to showcase the capabilities of the proposed approach.

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

2022 ◽  
Vol 9 ◽  
Author(s):  
Lixia Zhang ◽  
Yong Li ◽  
Xinmin Song ◽  
Mingxian Wang ◽  
Yang Yu ◽  
...  
Keyword(s):  
Data Analysis ◽  
Balance Equation ◽  
Gas Flow ◽  
Material Balance ◽  
Gas Production ◽  
Production Data ◽  
Variable Rate ◽  
Material Balance Equation ◽  
Gas Wells ◽  
Gas Reservoir

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.

scholarly journals An Analytical Method for Parameter Interpretation of Fracture Networks in Shale Gas Reservoirs considering Uneven Support of Fractures

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Shijun Huang ◽  
Jiaojiao Zhang ◽  
Sidong Fang ◽  
Xifeng Wang
Keyword(s):  
Data Analysis ◽  
Shale Gas ◽  
Analytical Method ◽  
Material Balance ◽  
Gas Production ◽  
Production Data ◽  
Analysis Method ◽  
Gas Reservoirs ◽  
Data Analysis Method ◽  
Parameter Interpretation

In shale gas reservoirs, the production data analysis method is widely used to invert reservoir and fracture parameter, and productivity prediction. Compared with numerical models and semianalytical models, which have high computational cost, the analytical model is mostly used in the production data analysis method to characterize the complex fracture network formed after fracturing. However, most of the current calculation models ignore the uneven support of fractures, and most of them use a single supported fracture model to describe the flow characteristics, which magnifies the role of supported fracture to a certain extent. Therefore, in this study, firstly, the fractures are divided into supported fractures and unsupported fractures. According to the near-well supported fractures and far-well unsupported fractures, the SRV zone is divided into outer SRV and inner SRV. The four areas are characterized by different seepage models, and the analytical solutions of the models are obtained by Laplace transform and inverse transform. Secondly, the material balance pseudotime is introduced to process the production data under the conditions of variable production and variable pressure. The double logarithmic curves of normalized production rate, rate integration, the derivative of the integration, and material balance pseudotime are established, and the parameters are interpreted by fitting the theoretical curve to the measured data. Then, the accuracy of the method is verified by comparison the parameter interpretation results with well test results, and the influence of parameters such as the half-length and permeability of supported and unsupported fractures on gas production is analyzed. Finally, the proposed method is applied to four field cases in southwest China. This paper mainly establishes an analytical method for parameter interpretation after hydraulic fracturing based on the production data analysis method considering the uneven support of fractures, which is of great significance for understanding the mechanism of fracturing stimulation, optimization of fracturing parameters, and gas production forecast.

Gas-Rate Forecasting in Boundary-Dominated Flow: Constant-Bottomhole-Pressure Decline Analysis by Use of Rescaled Exponential Models

SPE Journal ◽  
2013 ◽  
Vol 19 (03) ◽  
pp. 410-417 ◽  
Author(s):  
M.. Zhang ◽  
L.F.. F. Ayala H.
Keyword(s):  
Material Balance ◽  
Exponential Model ◽  
Equation Modeling ◽  
Well Performance ◽  
Time Data ◽  
Gas Well ◽  
Exponential Models ◽  
Fluid Parameter ◽  
Performance Forecasting ◽  
Bottomhole Pressure

Summary Gas-well performance forecasting during boundary-dominated flow (BDF) is largely based on the application of pseudopressure, pseudotime, and material-balance-pseudotime concepts to rate, pressure, and time data. Recently, Ayala H. and Ye (2012; 2013) and Ye and Ayala H. (2013) demonstrated the convenience and importance of a rescaled exponential model that successfully forecasted gas-well decline in BDF by use of density-based dimensionless parameters in place of pseudovariables. In this study, the interdependability and interchangeability of these methodologies is formally demonstrated with a rigorous derivation for rescaled exponential models on the basis of fundamental physical principles applicable to BDF conditions. The rescaled exponential equation is demonstrated to be a rigorous rate/time equation modeling gas-rate decline in wells produced against a constant-bottomhole-pressure specification. The proposed BDF decline equation is shown to be able to be expressed in terms of a dimensionless fluid parameter (B¯) that quantifies the μgcg dependency on density for the depletion process of interest, which has been directly tied to the hyperbolic decline coefficient experienced by a declining gas well. Case studies are presented to demonstrate the capabilities of the rescaled exponential model for gas-rate forecasting for wells producing at a constant bottomhole pressure, and its performance is compared with all other available models in the literature.

The Use of Rate-Transient-Analysis Modeling To Quantify Uncertainties in Commingled Tight Gas Production-Forecasting and Decline-Analysis Parameters in the Alberta Deep Basin

2014 ◽  
Vol 17 (02) ◽  
pp. 209-219 ◽  
Author(s):  
H.. Luo ◽  
G.F.. F. Mahiya ◽  
S.. Pannett ◽  
P.. Benham
Keyword(s):  
Transient Analysis ◽  
Early Time ◽  
Gas Production ◽  
Tight Gas ◽  
Well Performance ◽  
Deep Basin ◽  
Type Curves ◽  
Production Forecasting ◽  
Rate Transient Analysis ◽  
Production History

Summary The evaluation of expected ultimate recovery (EUR) for tight gas wells has generally relied upon the Arps equation for decline-curve analysis (DCA) as a popular approach. However, it is typical in tight gas reservoirs to have limited production history that has yet to reach boundary-dominated flow because of the low permeability of such systems. Commingled production makes the situation even more complicated with multiboundary behavior. When suitable analogs are not available, rate-transient analysis (RTA) can play an important role to justify DCA assumptions for production forecasting. The Deep-basin East field has been developed with hydraulically fractured vertical wells through commingled production from multiple formations since 2002. To evaluate potential of this field, DCA type curves for various areas were established according to well performance and geological trending. Multiple-segment DCA methodology demonstrated reasonable forecasts, in which one Arps equation is used to describe the rapidly decreasing transient period in early time and another equation is used for boundary-dominated flow. However, a limitation of this approach is the uncertainty of the forecast in the absence of extended production data because the EUR can be sensitive to adjustments in some assumed DCA parameters of the second segment. In this paper, we used RTA to assess reservoir and fracture properties in multiple layers and built RTA-type well models around which uncertainty analyses were performed. The distributions of the model properties were then used in Monte Carlo analysis to forecast production and define uncertainty ranges for EUR and DCA parameters. The resulting forecasts and EUR distribution from RTA modeling generally support the DCA assumptions used for the type curves for corresponding areas of the field. The study also showed how the contribution from the various commingled layers changes with time. The proposed workflow provides a fit-for-purpose way to quantify uncertainties in tight gas production forecasting, especially for cases when production history is limited and field-level numerical simulation is not practicable.

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