The recent development of the TOUGH3 code allows for a faster and more reliable fluid flow simulator. At the same time, new versions of FLAC3D are released periodically, allowing for new features and faster execution. In this paper, we present the first implementation of the coupling between TOUGH3 and FLAC3Dv6/7, maintaining parallel computing capabilities for the coupled fluid flow and geomechanical codes. We compare the newly developed version with analytical solutions and with the previous approach, and provide some performance analysis on different meshes and varying the number of running processors. Finally, we present two case studies related to fault reactivation during CO2 sequestration and nuclear waste disposal. The use of parallel computing allows for meshes with a larger number of elements, and hence more detailed understanding of thermo-hydro-mechanical processes occurring at depth.

A key feature of shale reservoirs is their low level of permeability. As a means of producing from these reservoirs, there is a requirement to create hydraulic fractures with highest level of conductivity, but these fractures are subsequently filled with high amounts of fracturing fluid chemicals during hydraulic fracturing and production from shale is impacted by formation damage that results from clay swelling and proppant embedment. The goal of this work is to develop insights into the proppant embedment that results from the mineral composition of the shale following instrumented indentation, Raman spectroscopy technique coupled with modelling approaches. The Caney Shale is an organic-rich, often calcareous mudrock. Many studies have examined the impact that clay has on different kinds of shale productivity but there is currently no data reported on Caney in relation to horizontal drilling. However, there also remains a lack of understanding of the mechanisms involved. While many scholars have investigated the influence that clay has on fracture conductivity, the combination of the use of indentation techniques and Raman spectroscopy coupled with modelling as a means of comprehending shale well production is an area that needs further consideration. Indentation tests were performed on a micro level on drilled rock core specimens as a means of determining the mechanical composition of bulk phases of these multiphase materials. The outcomes of the micro-indentation revealed that the bulk mechanical properties of the shale sample were higher overall. The creep effect impacts the maximum penetration depth and the modulus of elasticity of the shale sample. The variation in mechanical properties can be attributed to the changes in the mineralogical composition and microstructure. We believe that this method can provide an understanding into trends and help connect to field performance that would enable more comprehensive completions and avoid fracture plugging and loss of production.

Injection of CO2 for geologic carbon sequestration (GCS) into deep sedimentary formations involves fluid pressure increases that engage hydromechanical processes that can cause seismicity by activation of existing faults. In this work, we use a coupled multiphase fluid flow and geomechanical simulator to model spatiotemporal fluid pressure and stress changes in order to study the poroelastic effect of CO2 injection on faults in crystalline basement rock below the injection zone. The seismicity rate along features interpreted to be basement faults is modeled using Dieterich’s rate-and-state earthquake nucleation model. The methodology is applied to microseismicity detected during CO2 injection into the Mount Simon formation during the Illinois Basin – Decatur Project. The modeling accurately captures an observed reduction in seismicity rate when the injection in the second well was into a slightly shallower zone above the base of the Mount Simon formation. Moreover, the modeling shows that it is important to consider poroelastic stress changes, in addition to fluid pressure changes for accurately modeling of the observed seismicity rate.

The Brine Availability Test in Salt (BATS) is a field heater test being conducted in the bedded salt formation at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, NM. BATS is focused on exploring brine availability as part of a wider investigation into the disposal of heat-generating radioactive waste in salt. Brine has the potential to transport radionuclides, corrode waste forms and packages, reduce criticality, and pressurize porosity to resist closure through salt creep. In BATS, two identical arrays of horizontal boreholes were constructed in an experimental drift, 650 m below ground at WIPP. In each array, 13 observational boreholes were installed around a central borehole. One of the two array was heated, and the other array was left at ambient temperature. During the first heating phase (January to March 2020), the 750 W heater ran for 4 weeks. The central boreholes included dry nitrogen gas circulation behind a packer. The gas stream removed moisture which flowed into the boreholes. The gas stream was analyzed in-drift for stable water isotopes using a cavity ringdown spectrometer and gas composition using a quadrupole mass spectrometer. The satellite boreholes in each array included numerous thermocouples, electrical resistivity tomography (ERT) electrodes, acoustic emissions (AE) piezoelectric transducers, distributed temperature and strain fiber optics, and a cement seal exposure tests (both sorel and fly-ash base concretes). Cores from the boreholes were X-ray CT imaged for mineralogical and fracture distribution. We present an overview of the first phase of the test, and illustrate key data collected during the first heating cycle. Follow-on tests in the same boreholes will include gas and liquid tracer tests and additional packer-based gas permeability testing. New boreholes for the next round of BATS in 2021 are being planned.