Abstract
Conventionally, high-pressure water-based fluids have been injected for hydraulic stimulation of unconventional petroleum resources such as tight gas reservoirs. Apart from improving productivity, water-based frac-fluids have caused environmental and technical issues. As a result, much of the interest has shifted towards alternative frac-fluids. In this regard, n-heptane, as an alternative frac-fluid, is proposed. It necessitates the development of a multi-phase and multi-component (MM) numerical simulator for hydraulic fracturing. Therefore fracture, MM fluid flow, and proppant transport models are implemented in a thermo-hydro-mechanical (THM) coupled FLAC3D-TMVOCMP framework. After verification, the model is applied to a real field case study for optimization of wellbore x in a tight gas reservoir using n-heptane as the frac-fluid. Sensitivity analysis is carried out to investigate the effect of important parameters, such as fluid viscosity, injection rate, reservoir permeability etc., on fracture geometry with the proposed fluid. The quicker fracture closure and flowback of n-heptane compared to water-based fluid is advantageous for better proppant placement, especially in the upper half of the fracture and the early start of natural gas production in tight reservoirs. Finally, fracture designs with a minimum dimensionless conductivity of 30 are proposed.
Highlights
Continued development of new technologies has resulted in better exploitation of unconventional reservoirs, leading to efficient and expeditious production of petroleum resources
Sensitivity analysis was performed for hydraulic stimulation with n-heptane and the effect of different parameters, such as fluid viscosity, injection rate and reservoir permeability, were analyzed
With attributes of quick fracture closure, better propped fracture height, minimizing phase trapping and quick flowback, the proposed fluid is recommended for hydraulic fracturing operations in tight and ultra-tight gas reservoirs
Summary
Continued development of new technologies has resulted in better exploitation of unconventional reservoirs, leading to efficient and expeditious production of petroleum resources. Billions of liters of water have been utilized in these operations yearly because most of the treatments utilize water-based fluids with water as the main component [3,12,13]. Such high volumes of water create issues of water shortages, quality degradation, surface handling, and disposal [3,13,14,15]. Alternative fluids for hydraulic fracturing, such as foam-based, acid-based, alcohol-based, and gas-based, have been proposed These fluids have their own limitations, such as surface handling, difficult rheological characterization, lower fracture conductivities, proppant placement issues, higher surface injection pressure requirements, and higher costs [18,23,24,25]
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