1727 4. DRILLING AND MECHANICAL FEASIBILITY STUDY Because horizontal wells in salars remain relatively new and lack extensive operational precedent, geomechanical and drilling engineering analysis are essential to determine whether proposed well designs, lateral lengths, and completion strategies can be executed safely and consistently across different salar settings. The major challenges of drilling horizontal wells in salars are related to the shallow TVD (80 to 100 m TVD) of the reservoir target and the soft nature of the rock. The shallow TVD and the soft nature of the rock limit the build rate, with a dogleg higher than 10°/30 m significantly increasing the risk of completion (screen) deployment failure. To overcome these challenges the horizontal wells will combine technologies from the lithium brine industry, oil and gas industry (extended-reach drilling) (ERD), and the horizontal directional drilling (HDD) and prioritize the use of locally available equipment, materials, and services in Argentina The well-designed engineering combines the construction of a mechanical earth model (MEM) and a standard drilling engineering analysis. A MEM is a numerical representation of the state of stresses, pore pressure and rock mechanical properties and contains all the relevant geomechanics information (Plumb et al., 2000). The MEM estimates the safe drilling Mud Weight to avoid wellbore collapse and losses. The drilling engineering analysis focus on evaluating the torque, drag, buckling, hydraulics, hole cleaning, ECD, and surge and swab effects associated with drilling, tripping, and casing/liner installation. The objective of the study is to determine whether the wells can be drilled, cased, and cemented within the mechanical and hydraulic limits of the selected rig, tubulars, and anticipated subsurface conditions. 5. DYNAMIC SIMULATIONS DLE production and reinjection scenarios will be dynamically simulated for two development configurations: (i) multiple vertical wells (ii) multiple horizontal wells The dynamic simulation results for scenarios 1 and 2 above were both derived using the static model described in the Model Building section. The static model pore volume was initialized using a constant 500 mg/l lithium concentration together with a 300,000 mg/l salinity enumerated throughout its entirety. The surface temperature at the topmost static model layer – representative of the salar surface - was set at 10°C with a 4.0°C / 100-meter temperature gradient. This surface temperature and subsurface temperature gradient are common to those encountered at high elevations. From the surface temperature, surface pressure, subsurface temperature gradient, and brine salinity, the brine thermophysical properties such as density, viscosity and formation volume factor were established with depth and initialized into the static model. Brine saturation was set equal to 100% throughout the static model. With all static model fluid properties initialized, development cases were constructed employing an equal number of injection and abstraction wells. In each development case a guide rate balance was established setting the total daily injection rate equal to and a function of the total daily brine abstraction rate. A DLE effluent was created as an external fluid containing 50 mg/l of lithium – representing a 90% recovery factor at the DLE plant - which was reinjected into the reservoir to replace the abstracted brine. Well lift rates were constrained to the fluid levels above the ESP intake ports required to maintain reliable motor and impeller / diffuser operation. The first development case assessed a staggered line pattern-type vertical well configuration initially spaced 2-kilometers apart. Both vertical production and abstraction wells have their production casing cemented at the base of the Fractured Formation and were screened across the entirety of the good permeability Target Sands. Well spacing between vertical injection and abstraction wells was then increased until there was no DLE plant effluent breakthrough from the injection wells into the abstraction wells over a 40-year brine mining operation lifespan.
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