URTeC: 1928491 Dynamic Characterization of Unconventional Gas Reservoirs. Field Cases Arévalo-Villagrán J.A., SPE, PEMEX E&P, Castellanos-Páez F., SPE, Martínez-Romero N., SPE, CNH, and Pumar-Martínez F., SPE, CBM. Copyright 2014, Unconventional Resources Technology Conference (URTeC) This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Denver, Colorado, USA, 25-27 August 2014. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper without the written consent of URTeC is prohibited. Abstract Due to the complexity of unconventional gas reservoirs (shale, tight, and coalbed methane), various analytical models have been developed to estimate formation parameters. This paper presents the results of the modification and application of some analytical production data models. These analytical models were developed by Arévalo and Bello. Additionally, dynamic characterization results are presented using a new model that considers the effects of gas adsorbed in the formation and ultimately improve well production analysis and the evaluation of some formation parameters. For this study, production data were taken from wells located in the Eagle Ford formation in northeastern Mexico. The data were softened in order to utilize the Arévalo models for homogenous-isotropic and low permeability heterogeneous-anisotropic formations. To identify the flow models and formation parameters, the flow diagnostic plot [m(p i ) – m(p wf )] /q g vs t and the specialized plot [(m(p i ) – m(p wf )] /q g vs √t were used. Afterwards, the Bello model was applied to analyze double porosity formations and horizontal wells with multiple fracturing stages. Using the flow diagnostic and specialized plots, four flow regimes were identified (early linear in the fracture system, bilinear in the matrix-fracture system, linear in the matrix, and boundary-dominated) and the reservoir parameters were calculated for constant flowing bottomhole pressure. Finally, from these models, an analytical model was developed that takes into account the effects of gas adsorbed in the formation. This analytical model derives from the Bump model to consider changes in gas compressibility ( c g ) and the King model to consider changes in the gas compressibility factor (z). It also considers Langmuir isotherms, which characterize gas desorption in the reservoir due to pressure drops. With these models, the dynamic characterization of the unconventional gas reservoirs was improved, allowing for a more accurate estimation of the reservoir parameters and subsequently the optimal development and exploitation of these fields. Introduction The United States isn’t the only place in the world with large resources in shale oil and gas. In June 2013, the U.S. Energy Information Administration (EIA) estimated technically recoverable international shale gas across 137 formations in 41 countries (excluding the U.S.) at 6,634 tcf, or nearly ten times the 665 tcf it estimated for the United States. This is 10% higher than the EIA’s earlier estimates of 5,760 tcf in 2011. The international total amount excludes some countries in the Middle East, which still have significant conventional natural gas reserves still in place 1 . Shale test wells have already been fracture-stimulated in Argentina, Australia, the United Kingdom, Poland, China, and Mexico. Some important shale hydrocarbon basins have been identified in Mexico such as La Pimienta-La Casita and Eagle Ford formations in which we estimate combined Technically Recoverable Resources (TRR) of 545 trillion cubic feet (tcf) of gas, which represents 27% of North American shale gas reserves and 7.5% of shale gas reserves worldwide. Mexico began exploring its shale basins in 2011. These basins, similar to others, have geological formations ranging from low permeability (less than 0.1 md) to extremely low permeability (nano-
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Dynamic Characterization of Unconventional Gas Reservoirs. Field Cases
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URTeC: 1928491
Dynamic Characterization of Unconventional Gas Reservoirs. Field Cases Arévalo-Villagrán J.A., SPE, PEMEX E&P, Castellanos-Páez F., SPE, Martínez-Romero N., SPE, CNH, and Pumar-Martínez F., SPE, CBM. Copyright 2014, Unconventional Resources Technology Conference (URTeC)
This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Denver, Colorado, USA, 25-27 August 2014.
The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper
have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is
subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not
necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper without the written consent of URTeC is prohibited.
Abstract
Due to the complexity of unconventional gas reservoirs (shale, tight, and coalbed methane), various analytical
models have been developed to estimate formation parameters. This paper presents the results of the modification
and application of some analytical production data models. These analytical models were developed by Arévalo and
Bello. Additionally, dynamic characterization results are presented using a new model that considers the effects of
gas adsorbed in the formation and ultimately improve well production analysis and the evaluation of some formation
parameters. For this study, production data were taken from wells located in the Eagle Ford formation in
northeastern Mexico. The data were softened in order to utilize the Arévalo models for homogenous-isotropic and
low permeability heterogeneous-anisotropic formations. To identify the flow models and formation parameters, the
flow diagnostic plot [m(pi) – m(pwf)] /qg vs t and the specialized plot [(m(pi) – m(pwf)] /qg vs √t were used.
Afterwards, the Bello model was applied to analyze double porosity formations and horizontal wells with multiple
fracturing stages. Using the flow diagnostic and specialized plots, four flow regimes were identified (early linear in
the fracture system, bilinear in the matrix-fracture system, linear in the matrix, and boundary-dominated) and the
reservoir parameters were calculated for constant flowing bottomhole pressure. Finally, from these models, an
analytical model was developed that takes into account the effects of gas adsorbed in the formation. This analytical
model derives from the Bump model to consider changes in gas compressibility (cg) and the King model to consider
changes in the gas compressibility factor (z). It also considers Langmuir isotherms, which characterize gas
desorption in the reservoir due to pressure drops. With these models, the dynamic characterization of the
unconventional gas reservoirs was improved, allowing for a more accurate estimation of the reservoir parameters
and subsequently the optimal development and exploitation of these fields.
Introduction
The United States isn’t the only place in the world with large resources in shale oil and gas. In June 2013, the U.S.
Energy Information Administration (EIA) estimated technically recoverable international shale gas across 137
formations in 41 countries (excluding the U.S.) at 6,634 tcf, or nearly ten times the 665 tcf it estimated for the
United States. This is 10% higher than the EIA’s earlier estimates of 5,760 tcf in 2011. The international total
amount excludes some countries in the Middle East, which still have significant conventional natural gas reserves
still in place1.
Shale test wells have already been fracture-stimulated in Argentina, Australia, the United Kingdom, Poland, China,
and Mexico. Some important shale hydrocarbon basins have been identified in Mexico such as La Pimienta-La
Casita and Eagle Ford formations in which we estimate combined Technically Recoverable Resources (TRR) of 545
trillion cubic feet (tcf) of gas, which represents 27% of North American shale gas reserves and 7.5% of shale gas
reserves worldwide. Mexico began exploring its shale basins in 2011. These basins, similar to others, have
geological formations ranging from low permeability (less than 0.1 md) to extremely low permeability (nano-