Fahad Khan

Deep saline aquifers offer the largest global capacity potential for geologic carbon storage, yet storage performance is frequently constrained by coupled limitations on \COtwo{} dissolution (solubility trapping) and injectivity under high-salinity conditions. Elevated ionic strength suppresses \COtwo{} solubility via ``salting-out'' effects. Meanwhile, near-wellbore dry-out during injection of dry or undersaturated \COtwo{} can concentrate brine and precipitate salts, reducing permeability and injectivity. Mineralogy and \COtwo{}-brine-rock wettability further control multiphase flow topology, interfacial area for dissolution, capillary trapping, and compatibility of additives with reservoir surfaces. This review critically evaluates chemical pre-flush and additive-enabled conditioning strategies intended to (i) increase local aqueous \COtwo{} dissolution capacity, (ii) mitigate or prevent dry-out-driven salt precipitation and near-wellbore formation damage, and (iii) enhance \COtwo{}-brine contact through mobility control. We synthesize and compare evidence for four strategy families: (1) freshwater and engineered low-salinity (LoSal) pre-flush slugs and intermittent re-wetting; (2) chelating agents (e.g., EDTA/GLDA/DTPA) that complex multivalent cations and alter dissolution/precipitation pathways; (3) surfactant-derived \COtwo{} foams, including \COtwo{}-soluble surfactants designed for foam generation at the displacement front with achievable injectivity; and (4) nanoparticle-assisted and hybrid foam systems that extend foam stability under harsh salinity and temperature.

Unconventional hydrocarbon reservoirs are challenging media to exploit and develop for energy due to very low permeability. As such, unconventional means, such as horizontal drilling and hydraulic fracturing, are typically practiced. During hydraulic fracturing, the formation breakdown pressure is of great importance and determines the fluid pumping cost. Less attention has been given to breakdown pressure reduction for a cost-effective and enhanced hydraulic fracturing operation. The objective of this study is to explore the application of thermochemical fluids to induce thermal shock with the purpose of generating microcracks and reducing the breakdown pressure in high-temperature unconventional reservoirs. For this, thermochemical fluids of an endothermic nature (reduces the temperature when mixed) and Kentucky Sandstone and Eagle Ford Shale were utilized. In particular, we investigated the effect of endothermic reactions between ammonium chloride (NH₄Cl) and sodium hydroxide (NaOH) on the strength and breakdown pressure of both samples by applying multiple cycle treatments. The obtained results indicated a significant reduction in both the strength and breakdown pressure of the rocks, with Kentucky Sandstone showing a reduction of 53.07% and Eagle Ford Shale by 34.71% in breakdown pressure. This novel approach not only provides a promising alternative to traditional fracturing methods in high-temperature reservoirs but also could bring a significant reduction in fluid pumping requirements as well as the operational cost of hydraulic fracturing.

Summary: Oilwell cement ensures wellbore stability and isolates zones while bearing casing load and formation pressure. Its properties, crucial in extreme downhole conditions, include compressive strength, fluid loss resistance, and durability. In the present work, bismuth ferrite nanoparticles (BFO NPs) were synthesized using the sol-gel method and used as an additive in oilwell cement. The synthesized BFO NPs were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), and dynamic light scattering (DLS) techniques to analyze the functional groups, crystalline structure, morphological features, and hydrodynamic size distribution. Tests at 70°C and 2,000 psi revealed that 1% by weight of cement (BWOC) BFO NPs increased compressive strength by ~136% and reduced fluid loss to ~64% compared with base cement. It can be conjectured that the exposed facets of BFO NPs containing oxygen act as nucleating sites that promote the ordering of the silicate tetrahedra, thereby increasing the strength and crystallinity and reducing the water loss. The experimental results confirm that the BFO NPs can improve the properties of oilwell cement slurry at high-pressure, high-temperature (HPHT) conditions. This research underscores the potential of BFO NPs as sustainable additives for optimizing oilwell cement performance under challenging HPHT conditions, paving the way for advancements in sustainable construction practices.