Experimental Evaluation of Variation in Petrophysical Properties during CO2 Injection in Carbonate Rocks: Effective Mechanisms

Core flooding experiments were conducted in this research to evaluate changes in petrophysical properties of a number of carbonate samples (limestone, dolostone and chalk). The experiments involved carbonated brine flooding, CO2 enhanced oil recovery (CO2-EOR), and Water-Alternating Gas (WAG) processes performed under in-situ reservoir conditions

Dual fuzzy logic PID controller based regulating of dc motor speed control with optimization using Harmony Search algorithm

This paper discusses the implementation of a Proportional-Integral-Derivative (PID) controller for regulating the speed of a closed loop four quadrant chopper fed DC motor. The PID controller is combined with a Dual Fuzzy Logic Controller to form a DFPID controller for enhancing the performance of speed control of the DC motor. The DFLC is optimized using a metaheuristic algorithm known as Harmony Search Algorithm (HSA). The major aim of this research is to gain an effective control over the speed of the motor in the closed loop environment. For achieving this, the parameters for the DFPID are selected through time domain analysis which aims to satisfy the requisites such as settling time and peak overshoot. Initially, the fuzzy logic controller in the DFPID controls the coefficients of the PID achievement gain an effective control over the system error and rate of error change. Further, the DFPID is improved by the HAS for obtaining a precise correction. The solutions obtained by tuning the DFPID controller are evaluated from simulation analysis conducted on a MATLAB/SIMULINK platform. The closed loop performance is analyzed in both time and frequency domain analysis and the performance of DFPID is optimized using the HSA algorithm to obtain precise value of the control process. As observed from the Simulation analysis, the DFPID-HSA generates optimized control signals to the DC motor for controlling the speed. The performance of the intended speed control approach is analyzed in terms of different evaluation metrics such as motor speed, torque and armature current. Experimental outcomes show that the proposed approach achieves better control performance and faster speed of DC motor compared to conventional PID controllers and SMC controller

CO2 saturated brine injected into fractured shale: An X-ray micro-tomography in-situ analysis at reservoir conditions

Fracture morphology and permeability are key factors in enhanced gas recovery (EOR) and Carbon Geo-storage (CCS) in shale gas reservoirs as they determine production and injection rates. However, the exact effect of CO2-saturated (live) brine on shale fracture morphology, and how the permeability changes during live brine injection and exposure is only poorly understood. We thus imaged fractured shale samples before and after live brine injection in-situ at high resolution in 3D via X-ray micro-computed tomography. Clearly, the fractures’ aperture and connectivity increased after live brine injection

PID Controller for A Bearing Angle Control in Self-Driving Vehicles

The enhancement of self-driving vehicles has the potential to disrupt traditional transportation systems, Utilizing progress in secure and intelligent mobility. However, control of movement in self-driving vehicles is still difficult to carry out driving duties in a constantly changing road environment. The regulation of bearing angle is an essential component in self-driving vehicles navigation systems, facilitating the secure and efficient operation of vehicles across a range of environments, including urban streets, highways, and off-road terrain. It employs algorithms and sensor fusion to perceive surroundings, compute trajectories, and execute precise steering commands. The bearing angle represents the angle between the vehicle's current and desired directions. By consistently monitoring this angle and implementing appropriate steering inputs, the self-driving vehicle can accurately stay on track and proactively adapt to obstacles or adhere to a designated route. In this context, we explore the advancements in bearing angle control methods for self-driving vehicles. By conducting simulations of a simplified block diagram for a self-guiding vehicle's bearing angle control techniques, the efficacy of the steering system of self-driving cars has been briefly examined. We provide various methods of control, which are considered approaches for controlling the angle of bearings through lag lead compensation and PID auto-tuned controllers. The results show that the auto-tuned PID controller outperforms all other controllers in terms of transient and steady-state responses

Dissolution behaviour in carbonate reservoirs during WAG injection: A preliminary experimental study

In this study, a core flooding experiment using a water-alternating-gas (WAG) injection was conducted to evaluate its impact on the petrophysical properties of an initially oil-saturated heterogeneous carbonate core sample. Carbon dioxide (CO2) and synthetic formation brine were injected (0.5 pore volume CO2 alternating with 0.5 pore volume brine) alternately following establishment of waterflooding residual oil saturation under reservoir conditions. Gas porosity, gas permeability, NMR (nuclear magnetic resonance) T2 measurements, and X-ray CT scanning were conducted preand post-core flooding. The results show that CO2-WAG injection resulted in substantial additional oil recovery (~30 %) under the applied experimental conditions. The results also show an increase in the permeability of the tested sample from 1.5 to 16 mD, which could be attributed to mineral dissolution. X-ray CT imaging shows signs of excessive mineral dissolution and formation of wormhole structures. It is believed that dissolution within the tested core plug caused the WAG fluids to follow the newly wormhole (causing them to enlarge further), and consequently bypassing many parts of the sample. Therefore, despite a significant increase in oil recovery, a large amount of oil is still left behind

An experimental study for carbonate reservoirs on the impact of CO2-EOR on petrophysics and oil recovery

The injection of CO2into deep geological structures for the purpose of CO2storage and/or enhanced oil recovery (CO2-EOR) may trigger a series of consecutive chemical reactions (e.g. mineral dissolution and asphaltene precipitation) and physical effects (e.g. mechanical compaction and permeability variation). These reactions can significantly impact carbonate reservoirs, due to the presence of highly reactive minerals (e.g. dolomite and calcite), as well as the solvent/precipitation effects of supercritical CO2on complex crude oil mixtures potentially containing heavy fractions such as wax and asphaltene. A core flooding study has been carried out to evaluate changes in the petrophysical properties of a number of heterogeneous carbonate samples (i.e. limestone and dolostone) after undergoing EOR activities under in situ reservoir conditions. In this study, a number of different measurement techniques are conducted to obtain a comprehensive view of the role that mineral dissolution, mechanical compaction and asphaltene precipitation plays during CO2-EOR in carbonate reservoirs. The results show that CO2injection results in higher oil recovery in all the samples evaluated as part of this study. However, early water breakthrough was observed for most samples suggesting a high degree of heterogeneity in the carbonate core samples. In all samples, a decrease in permeability was observed presumably due to asphaltene/resin precipitation and mineral dissolution/precipitation. Chemical analyses of the produced crude oil and scanning electron microscopy images confirmed the precipitation of asphaltene and mineral dissolution that caused permeability reduction. Furthermore, as CO2concentration in the oil/CO2mixture increased more asphaltene/resin precipitation was observed. More asphaltene precipitation was observed in higher permeability and more vuggy core samples than in those with intermediate or low permeabilities. This observation can be possibly attributed to relaxation of fluids as they enter the relatively large vugs (with large surface area) from the pore-throats resulting in the flocculation and/or precipitation of asphaltenes. A slight reduction in porosity and pore size was observed in most samples presumably caused by a combination of mineral/asphaltene precipitation and physical compaction. Overall, the results obtained in this study further highlight the complexities associated with the application of CO2-EOR in underground oil reservoirs where both the crude oil and the rock formation may be expected to interact with the injected fluids. Further research into the underling mechanisms is required

Experimental evaluation of carbonated brine-limestone interactions under reservoir conditions-emphasis on the effect of core scale heterogeneities

CO 2 injection into deep geological structures is very often accompanied by chemical interactions between the host rock and injected fluids and/or the in-situ created solute (i.e. carbonated brine). In fact, the in-situ reactions are considered one way through which the injected CO 2 may be trapped for perpetuity. Depending on the nature and mineralogy of the host rock formation, such reactions may eventually result in a degree of change in the petrophysical properties of the rock. Carbonate formations, due to the presence of highly reactive minerals in their composition, are expected to be more prone to such changes than their sandstone counterparts. This manuscript presents the results of an experimental study conducted to evaluate possible changes in the petrophysical properties of five heterogeneous limestone samples (calcite concentration > 91 wt%). The study includes five reservoir condition core-flood experiments (i.e. one per each rock sample) complemented by other laboratory measurements/analyses including porosity-permeability measurements, X-ray CT (X-ray Computed Tomography) and SEM (Scanning Electron Microscopy) imaging. The results show a significant increase in the post-flood permeability of 80% of the samples caused by the dissolution and removal of carbonate minerals. The X-ray CT images reveal signs of significant mineral dissolution and establishment of flow paths through the initial larger pores in the samples leading, eventually, to the formation of wormhole features along the length of the samples. On the contrary, reduction in permeability is observed in one sample which was a relatively long (15.8 cm) composite sample consisting of two core segments placed one after the other in series. The other four samples were shorter with a nominal length of 6.4 cm. This reduction in permeability is observed predominantly in the outlet segment. This change is thought to have been primarily caused by possible migration of carbonate fines released by mineral dissolution in the inlet plug of the long composite core and to a lesser extent by the precipitation of minerals dissolved and transported from the inlet plug. This hypothesis finds further support in the pre- and post-flood dry weight measurements as well as a post-flood SEM image of the plug which reveals signs of fines migration and mineral precipitation. Slight reductions in the porosity and pore sizes are observed in most of the samples. This is likely to have been caused by the combined effect of fines migration, possible mineral precipitation and physical compaction mechanisms. Mechanical compaction is further evident from the reductions in the physical dimensions of the samples. Overall, the results obtained show that the nature and degree of any change in the petrophysical properties of the rock samples vary to some degree from one sample to the next. This variation is found to depend on the significance and degree of dominance of the three mechanisms of mineral dissolution, mineral precipitation and mechanical compaction if they occur during the flooding process. The migration of carbonate fines also seems to be an important factor in shaping the post-flood sample properties. The presence of any initial core scale heterogeneity in the pre-flood samples is also believed to be a critical factor controlling the eventual outcome

Experimental investigation of changes in petrophysical properties during CO2 injection into dolomite-rich rocks

Carbon dioxide may be injected into an underground geological structure for mere geo-sequestration purposes or as a means of enhanced hydrocarbon recovery. During such an operation, CO2 is expected to dissolve in the in-situ fluids (primarily consisting of brine) generating a reactive in-situ solute (i.e. carbonated brine). Subsequently, a series of consecutive chemical reactions may occur between the solute and the host rock. While these reactions are generally known from a qualitative perspective, to what extent they may impact on the host formation's petrophysical properties requires extensive evaluation on a case by case basis. Due to the presence of highly reactive minerals in their composition, carbonate rocks (e.g. dolostone) present a more complex system to evaluate in terms of the above mentioned chemical reactions. This experimental study has been carried out to evaluate changes in the petrophysical properties of a number of heterogeneous dolostone samples after undergoing carbonated brine flooding under in-situ reservoir conditions. In this study, the core-flood experiments are complemented by pre- and post-flood porosity, permeability and NMR (nuclear magnetic resonance) measurements, X-ray CT scanning and X-ray Diffraction (XRD) and Energy-Dispersive X-ray (EDX) analysis. Overall, a slight increase in the porosity was observed in most samples, most likely, caused by the dissolution of dolomite (CaMg(CO3)2), calcite (CaCO3) and/or anhydrite (CaSO4). The results also show an increase in the permeability of some samples which again could be attributed to dissolution of the minerals. The X-ray CT images show signs of excessive dissolution of minerals and the creation of dissolution patterns (i.e. wormholes). On the other hand, reductions in permeability and porosity by 57% and 12%, respectively, were also observed in a sample. This is believed to be due to the combined effects of the mineral precipitation and mechanical compaction mechanisms dominating over the mineral dissolution. A small shift in the pore size distribution of the samples towards smaller pore sizes was also observed which is believed to have been caused by mechanical compaction