Experimental and numerical study of ultrasonic monitoring of hydraulic fracture propagation

Hydraulic fracture monitoring is very useful to understand real-time fracture movement to ensure unwanted events. Active seismic monitoring of hydraulic fracture propagation was studied numerically and experimentally. A discrete element method code was used for modelling the interaction of seismic waves with a propagating hydraulic fracture. A true triaxial stress cell was modified to conduct hydraulic fracturing ultrasonic monitoring experiments. Different seismic events were analysed and compared to estimate fracture geometry in real-time

Steps for conducting a valid hydraulic fracturing laboratory test

Several parameters are involved in a hydraulic-fracturing operation, which is a technique used mainly in tight formations to enhance productivity. Formation properties, state of stresses in the field, injecting fluid characteristics, and pumping rate are among several parameters that can influence the process. Numerical analysis is conventionally run to simulate the hydraulic-fracturing process. Before operating the expensive fracturing job in the field, however, it would be useful to understand the effect of various parameters by conducting physical experiments in the lab. Laboratory experiments are also valuable for validating the numerical simulations. Applying the scaling laws, which are to correspond to the field operation with the test performed in the lab, are necessary to draw valid conclusions from the experiments. Dimensionless parameters are introduced through the scaling laws that are used to scale-down different parameters including the hole size, pump rate and fluid viscosity to that of the lab scale. Sample preparation and following a consistent and correct test procedure in the lab, however, are two other important factors that play a substantial role in obtaining valid results. The focus of this peer-reviewed paper is to address the latter aspect; however, a review of different scaling laws proposed and used will be given. The results presented in this study are the lab tests conducted using a true triaxial stress cell (TTSC), which allows simulation of hydraulic-fracturing under true field stress conditions where three independent stresses are applied to a cubic rock sample

Numerical and Experimental Study of Hydraulic Fracture Active Source Monitoring

Hydraulic fracturing is one of the most common operations performed on oil and gas wells. As thehydraulic fracture propagation is so complex, monitoring techniques are used to determine the real-timegeometry of the induced fracture. In this work focus is made on numerical and experimental study ofactive monitoring of hydraulic fracture. Discrete element method is used for numerical simulation ofseismic wave transmission in a block of rock being hydraulically fractured. In this method the rock ismodeled by an assembly of round particles. On the other hand the results of an ultrasonic laboratoryexperiment in which a block of cement is fractured, are reported. Numerical and experimental deliversimilar results which are in agreement with those published in literature. The results show interesting information which can be applied for active monitoring of field hydraulic fractures

Comparative static and dynamic analyses of solvents for removal of asphaltene and wax deposits above- and below-surface at an Iranian carbonate oil field

During production from oil wells, the deposition of asphaltene and wax at surface facilities and porous media is one of the major operational challenges. The crude oil production rate is significantly reduced due to asphaltene deposition inside the reservoir. In addition, the deposition of these solids inside the surface facilities is costly to oil companies. In this study, the efficiency of different solvents in dissolving asphaltene and wax was investigated through static and dynamic tests. The analysis of solid deposits from the surface choke of one of the Iranian carbonate oil fields showed that they consisted of 41.3 wt % asphaltene, and the balance was predominantly wax. In addition, the asphaltenes obtained from the surface choke solid deposits had a more complex structure than that of asphaltenes extracted from the crude oil itself. The static tests showed that xylene, toluene, gasoline, kerosene, and gas condensate had the highest efficiencies in dissolving solid deposits; conversely, diesel had a negative impact on dissolving solid deposits. Static tests on pure asphaltene showed that, among the tested solvents, gas condensate and diesel had a negative effect on the solubility of asphaltene. The dynamic core flooding results showed that asphaltene deposition inside the cores reduced the permeability by 79-91%. Among the tested solvents, xylene, gasoline, and kerosene resulted in the highest efficacy in restoring the damaged permeability, and higher efficiency was obtained with an equivalent solvent injection rate of 1 bbl/min versus 3 bbl/min

Techno‐economic analysis of direct combustion and gasification systems for off‐grid energy supply: A case for organic rankine cycle and dual fluidized‐bed

Biomass is one of the most versatile sustainable energy sources. This versatility allows utilization of different biomass feedstock using a verity of conversion techniques. Often, a biomass-to-bioenergy conversion method is selected depending on the application, end-use product, and the type of feedstock. In many applications such as residential energy supply, it is possible to select amongst various technologies. Although, there exist several challenges such as cost-effectiveness and sustainability that constrains bioenergy development. To this end, this research elaborates on the impacts of different conversion methods on techno-economic performance of bioenergy systems for residential energy supply. In this context, Organic Rankine Cycle based on direct combustion, and Dual Fluidized-Bed technology based on gasification were selected for that purpose. A techno-economic comparative analysis illustrates that the primary product of the system and fuel cost are the two most important factors in feasibility assessment. The negative impact of feedstock price was more severe on the Organic Rankine Cycle. For wood chips prices below 55$/t, Organic Rankine Cycle could be the better option due to lower capital and maintenance costs. In contrast, Dual Fluidized-Bed could better tolerate the variation of feedstock price; offering 8$/t wood chips

Finite Element Simulation of Downhole Stresses in Deep Gas Wells Cements

Deep gas reservoirs are going to play more important roles in meeting growing demand of natural gas throughout the world. Due to extreme conditions of downhole stresses, pressure and temperature that occur in deep gas wells, maintaining cement mechanical integrity and zonal isolation have become critical concerns of industry during drilling, completion, and production of such wells. Cement sheath is expected to provide a flawless annular seal between casing and formation along the wellbore. However; cement failure cases which are being reported regularly show that there is still need for understanding extreme downhole conditions and the behavior of cement sheath experiencing such an environment. Although Uniaxial Compressive Strength (UCS) of cement is commonly regarded as the most important mechanical property of cement, recent theoretical and experimental results show that other mechanical properties of cement can be even more determinative in its failure.In this study, Finite Element Method (FEM), a widely-used robust numerical tool, is used for simulation of the downhole environment by modeling temperature, pressures, stresses, downhole materials and their interactions. Using this approach magnitude, direction and type of induced stresses in casing, cement, and formation have been determined. Furthermore; a series of sensitivity analyses was performed to reveal the effects of variation of various parameters such as casing internal pressure, differential horizontal stress and casing eccentricity, on the induced stresses in the cement sheath.Radial, tangential and von Mises stress profiles in the deep gas wells cements were investigated. Furthermore, the effect of casing internal pressure, differential horizontal stress and casing eccentricity were studied in the model. Results show that deep gas wells’ cements experience extreme amounts of thermal and mechanical stresses and special consideration is required in cement selection

Active monitoring of a hydraulic fracture propagation: Experimental and numerical study

Hydraulic fracturing is known as one of the most common stimulation techniques performed on oil and gas wells for maximising hydrocarbon production. It is a complex procedure due to numerous influencing factors associated with it. As a result, hydraulic fracturing monitoring techniques are used to determine the real-time extent of the induced fracture and to prevent unwanted events. Although the well-known method of monitoring is the microseismic method, active monitoring of a hydraulic fracture has shown capable of providing useful information about the fracture properties in both laboratory conditions and field operations. In this study, the focus is on laboratory experiment of hydraulic fracturing using a true-triaxial stress cell capable of simulating field conditions required for hydraulic fracturing. By injecting high-pressure fluid, a hydraulic fracture was induced inside a 20 cm cube of cement. Using a pair of ultrasonic transducers, transmission data were recorded before and during the test. Both cases of an open and closed hydraulic fracture were investigated. Then, using a discrete element scheme, seismic monitoring of the hydraulic fracture was numerically modelled for a hexagonally packed assembly and compared with the lab results.The results show good agreements with data in the literature. As the hydraulic fracture crosses the transducers line, signal dispersion was observed in the compressional wave data. A decrease was observed in both the amplitude and velocity of the waves. This can be used as an indicator of the hydraulic fracture width. As the fracture closes by reducing fluid pressure, a sensible increase occurred in the amplitude of the transmitted waves while the travel time showed no detectable variations. The numerical model produced similar results. As the modelled hydraulic fracture reached the source-receiver line, both amplitude and velocity of the transmitted waves decreased. This provides hope for the future real-time ability to monitor the growth of induced fractures during the fraccing operation. At present, however, it still needs improvements to be calibrated with experimental results

Evaluation of PFC 2D for Modeling Seismic Monitoring of Hydraulic Fracture

Hydraulic fracture monitoring is a technique used for determining the geometry of the fracture underground. Active methods of fracture monitoring have shown potential in providing useful information which may not be easily obtained by microseismic methods. In this study Particle Flow Code in Two Dimensions (PFC2D), a Discrete Element Method (DEM) based code, is used for modeling seismic monitoring of a hydraulic fracture. PFC capability in modeling wave propagation in arranged particle assemblies is examined against another verified code. Furthermore, a smooth hydraulic fracture is generated by simulating constant fluid pressure source at the center of the sample. Seismic waves are transmitted across the fracture at different instances before and during fracture propagation. The results show that the width and length of the hydraulic fracture considerably influence the travel time and the amplitude of recorded waves even before the fracture reaches the source-receiver line. This is in accordance with published experimental results