Study of Sustainable Gas Exploitation Reveals Benefits of CO2 Fracturing

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 4213943, “Benefits of CO2 Fracturing: Analysis for Sustainable Shale Gas Exploitation in Mexico,” by Carlos Felipe Silva-Escalante, SPE, National Autonomous University of Mexico (UNAM) and the Mexican Petroleum Institute (IMP), and Rodolfo G. Camacho-Velázquez, SPE, and Ana P. Gómora-Figueroa, IMP, et al. The paper has not been peer-reviewed.

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The growing environmental concerns related to water usage in unconventional hydrocarbon extraction necessitate the development of alternative fracturing methods. This work evaluates CO2-based fracturing as a sustainable development approach for shale gas reservoirs in the Burgos Basin of Mexico. The results demonstrate that CO2 fracturing represents both an environmentally sustainable and economically viable alternative to conventional methods for shale reservoir development in water-stressed regions.

Introduction

The Burgos Basin represents Mexico’s most significant gas resource, with estimated reserves of 421 Tscf of wet gas and 348 Tscf of dry gas. To date, 27 wells have been drilled for unconventional resources in the basin, with estimated initial production rates of 6 MMscf/D and prolonged production decline curves. The typical well configurations include horizontal geometry, slickwater fracturing fluid, white sand 20/40 proppant at concentrations of 1–5 ppg, and between 10–18 fracturing stages. Investment costs range from $5–14 million per well, depending on complexity.

A critical challenge facing development in this region is water scarcity in northeastern Mexico, which necessitates waterless fracturing approaches for sustainable exploitation of shale reservoirs. Numerous researchers have explored waterless fracturing alternatives, with CO2 fracturing emerging as a particularly promising option. Beyond addressing water scarcity concerns, CO2 fracturing offers the additional environmental benefit of reducing CO2 emissions through beneficial usage of captured carbon.

This study provides an analysis of fracturing propagation and post-closure effectiveness for gas production in a representative Burgos Basin shale reservoir using pure CO2 and industrial CO2 with impurities (CO2-imp) compared with conventional slickwater. Effective geometry and conductive properties of fractures after closure (following flowback) are examined to identify performance-affecting properties and develop production scenarios with reservoir modeling.

CO2 fracturing is evaluated as a waterless option for the Burgos Basin based on the proximity of fixed CO2 sources to development zones. Technoeconomic aspects also are examined to determine the viability of CO2 fracturing as an appropriate option for unconventional reservoir exploitation.

Methodology

Representative well and reservoir models were designed to simulate fracture propagation and post-closure fracture properties and to generate performance and production scenarios using compositional simulators. The simulations compare pure CO2, CO2-imp, and conventional slickwater as fracturing fluids.

The CO2-imp composition consists of 95%-mol CO2 with 4% mol N₂ and 1% H₂O, approximating CO2 obtained from post-combustion technology while satisfying desired transportation criteria. This industrial fluid also contains solid impurities from the post-combustion process, which are incorporated into the fracture simulation as spherical proppant with a diameter of 10 μm and an overestimated concentration of 1 ppg for analysis purposes.