The geomechanical and transport properties of rocks are of great importance to geoscience and engineering, as these properties provide responses to external stresses and flow regimes in the subsurface. Typically, experiments conducted on cores from reservoir formations have a degree of uncertainty, due to the heterogeneous characteristics of rock samples. To combat this uncertainty, binder-jet additive manufacturing (3D printing) is an emerging technology to characterize natural porous media in a repeatable fashion. In this study, the 3D printing sandstone analogue involved sand powder and organic binder to mimic silica grains and cement in natural sandstone. The use of compaction rollers and the adjustment of printing parameters allowed one to test how the porosity and strength of 3D-printed samples can replicate the transport and geomechanical properties of natural sandstone. The densities of samples were increased by ~15% and compressive strength by ~65% with the use of the larger roller. This is a promising alternative to experimental testing to calibrate numerical models in geoscience and engineering. The significance of this approach is to allow for customizable porosity, permeability, and strength in rock samples, while preserving scarce natural rock samples.

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Low permeability, naturally fractured reservoirs such as coal seam gas (CSG, coalbed methane or CBM) and shale gas reservoirs generally require well stimulation to achieve economic production rates. Coupling hydraulic fracturing and micro-proppant or graded particle injections (GPI) can be a means to maximise hydrocarbon recovery from these tight, naturally fractured reservoirs, by maintaining or improving cleat or natural fracture conductivity. This paper presents a summary of the National Energy Resources Australia (NERA) project "Converting tight contingent CSG resources: Application of graded particle injection in CSG stimulation" - which assessed the application of micro-proppants, providing guidance on key considerations for GPI application to CSG reservoirs. Over the last decade, laboratory research and modelling have shown the benefits of the application of GPI to keep pre-existing natural fractures and induced fractures open during production of coal reservoirs with pressure dependent permeability (PDP). Laboratory studies, within this study, provide further insight on potential mechanisms and key factors, including proppant size and optimum concentration, which contribute to the success of a micro-proppant placement. Accompanying numerical modelling studies will be presented that describe the likely fluidized behaviour of micro-proppants (e.g., straining models, electrostatic effects, and ‘screen out’ prediction). This paper outlines the necessary reservoir characterization, treatment considerations, and key numerical modelling inputs necessary for the design, execution, and evaluation of GPI treatments, whether performed standalone or in conjunction with hydraulic fracturing treatments. It also provides insight on the practical application of GPI efficiently into fracturing operations, minimizing natural and hydraulic fracturing damage effects, thereby maximizing potential production enhancement for coals, shales and other tight, naturally fractured reservoirs exhibiting pressure-dependent permeability effects.

Natural rocks are highly heterogeneous due to various geological processes that constantly alter their properties. The accumulation, deposition, and cementation of mineral and organic particles continuously modify the spatial characteristics of rock properties. Property variability or anisotropy is commonly observed in most rock types and influences strength, transport, and thermal conductivity behavior. This unpredictability presents a significant challenge for laboratory testing. Binder-jet additive manufacturing (3D printing) has emerged as a valuable technology for characterizing rock properties in geoscience and engineering. This study proposes a methodology to evaluate the variability and repeatability of mechanical properties of 3D-printed sandstones during binder-jet additive manufacturing. The mechanical properties were analyzed statistically for samples located in various parts of the 3D printer build volume. The results showed that the 3D-printed sandstones exhibited significant variations in their strength and stiffness properties when measured from samples produced within the same build volume during binder-jet additive manufacturing. The Uniaxial Compressive Strength (UCS) varied from 23 to 38 MPa, with an average value of 29 MPa. The Young's modulus, on the other hand, ranged from 1.5 to 4.05 GPa, with an average value of 2.33 GPa. The variability of the mechanical properties, quantified by the standard deviation, decreased when the entire population of 3D-printed sandstones was divided into smaller samples situated at different elevations of the build platform.