Investigation of Water Composition on Formation Damage and Related Energy Recovery from Geothermal Reservoirs: Geochemical and Geomechanics Insights

The main challenge in extracting geothermal energy is to overcome issues relating to geothermal reservoirs such as the formation damage and formation fracturing. The objective of this study is to develop an integrated framework that considers the geochemical and geomechanics aspects of a reservoir and characterizes various formation damages such as impairment of formation porosity and permeability, hydraulic fracturing, lowering of formation breakdown pressure, and the associated heat recovery. In this research study, various shallow, deep and high temperature geothermal reservoirs with different formation water compositions were simulated to predict the severity/challenges during water injection in hot geothermal reservoirs. The developed model solves various geochemical reactions and processes that take place during water injection in geothermal reservoirs. The results obtained were then used to investigate the geomechanics aspect of cold-water injection. Our findings presented that the formation temperature, injected water temperature, the concentration of sulfate in the injected water, and its dilution have a noticeable impact on rock dissolution and precipitation. In addition, anhydrite precipitation has a controlling effect on permeability impairment in the investigated case study. It was observed that the dilution of water could decrease formation of scale while the injection of sulfate rich water could intensify scale precipitation. Thus, the reservoir permeability could decrease to a critical level, where the production of hot water reduces and the generation of geothermal energy no longer remains economical. It evident that injection of incompatible water would decrease the formation porosity. Thus, the geomechanics investigation was performed to determine the effect of porosity decrease. It was found that for the 50% porosity reduction case, the initial formation breakdown pressure reduced from 2588 psi to 2586 psi, and for the 75% porosity reduction case it decreased to 2584 psi. Thus, geochemical based formation damage is significant but geomechanics based formation fracturing is insignificant in the selected case study. We propose that water composition should be designed to minimize damage and that high water injection pressures in shallow reservoirs should be avoided.

The Effect of Firing Temperature on the Composition and Microstructure of a Geocement-Based Binder of Sodium Water-Glass

The fire performance of a geocement-based binder was investigated with a combination of analytical techniques, in terms of changes in composition and microstructure. Geocement, formulated as Na2O∙Al2O3∙6SiO2∙20H2O, was prepared using metakaolin, sodium water-glass, rotten stone and sodium hydroxide. The mixture was homogenized by passing through a hydrodynamic cavitator. Cubes of 20 mm were prepared, hardened at laboratory conditions for 28 days, and subsequently burnt at 600, 800 and 1200 °C in a laboratory furnace. Cavitation treatment resulted in a highly amorphous binder; amorphous fraction decreased upon firing up to 800 °C due to crystallization, and increased above 1000 °C because of melt formation. Porosity increased with firing temperature and pores larger than 1 mm in diameter prevailed at 1200 °C. The material remained stable up to 1200 °C. The results indicate the adequacy of this geocement-based binder for preparing fire-protecting materials.

Effect of Sintering Temperature on Biphasic Calcium Phosphate (BCP) Biocomposite

The present report aims to fabricate biphasic calcium phosphate (BCP) biocomposite in order to study the effects of sintering temperature on the sintered BCP biocomposite characteristics (phase’s formation, porosity and hardness properties). These effects were quantified using design of experiment (DOE) to develop mathematical models. BCP biocomposite pellets (60 wt% HA) were fabricated using mixing, pressing and sintered at two different temperatures (1100°C and 1250°C). The experiment was run by following the run order suggested by DOE software (Minitab 16) through randomization stage. Results show that sintering temperature will affect the formation of α-tricalcium phosphate (α-TCP) and the porosity of the samples. The formation of α-TCP phases will reduce the hardness value of BCP biocomposite.

The Effect of Sand Production on Formation Porosity in Unconsolidated Oil Field

Formation porosity near the wellbore can be changed by massive sand production, so it is impractical to use the initial formation porosity in downhole operation design in unconsolidated sand reservoir. The numerical method for sand prediction is limited for its complicated calculation procedures. An analytical model for porosity variation calculation is developed by coupling the material balance equation with the critical fluid drag force. With the result of sand production simulated test, the model can quantify the relation between sand production rate and formation porosity variation. Application of the model in oil field shows that it is simple and practicable for field engineering design.