Thermo-Hydraulic Modelling and Experimental Validation of an Electro-Hydraulic Compact Drive

Electro-hydraulic compact drives (ECDs) are an emerging technology for linear actuation in a wide range of applications. Especially within the low power range of 5–10 kW, the plug-and-play capability, good energy efficiency and small space requirements of ECDs render this technology a promising alternative to replace conventional valve-controlled linear drive solutions. In this power range, ECDs generally rely on passive cooling to keep oil and system temperatures within the tolerated range. When expanding the application range to larger power classes, passive cooling may not be sufficient. Research investigating the thermal behaviour of ECDs is limited but indeed required for a successful expansion of the application range. In order to obtain valuable insights into the thermal behaviour of ECDs, thermo-hydraulic simulation is an important tool. This may enable system design engineers to simulate thermal behaviour and thus develop proper thermal designs during the early design phase, especially if such models contain few parameters that can be determined with limited information available. Our paper presents a lumped thermo-hydraulic model derived from the conservation of mass and energy. The derived model was experimentally validated based on experimental data from an ECD prototype. Results show good accuracy between measured and simulated temperatures. Even a simple thermal model containing only a few thermal resistances may be sufficient to predict steady-state and transient temperatures with reasonable accuracy. The presented model may be used for further investigations into the thermal behaviour of ECDs and thus toward proper thermal designs required to expand the application range.publishedVersio

Evaluation of a permeability-porosity relationship in a low permeability creeping material using a single transient test

A method is presented for the evaluation of the permeability-porosity relationship in a low-permeability porous material using the results of a single transient test. This method accounts for both elastic and non-elastic deformations of the sample during the test and is applied to a hardened class G oil well cement paste. An initial hydrostatic undrained loading is applied to the sample. The generated excess pore pressure is then released at one end of the sample while monitoring the pore pressure at the other end and the radial strain in the middle of the sample during the dissipation of the pore pressure. These measurements are back analysed to evaluate the permeability and its evolution with porosity change. The effect of creep of the sample during the test on the measured pore pressure and volume change is taken into account in the analysis. This approach permits to calibrate a power law permeability-porosity relationship for the tested hardened cement paste. The porosity sensitivity exponent of the power-law is evaluated equal to 11 and is shown to be mostly independent of the stress level and of the creep strains

Modeling and experimental evaluation of the effective bulk modulus for a mixture of hydraulic oil and air

The bulk modulus of pure hydraulic oil and its dependency on pressure and temperature has been studied extensively over the past years. A comprehensive review of some of the more common definitions of fluid bulk modulus is conducted and comments on some of the confusion over definitions and different methods of measuring the fluid bulk modulus are presented in this thesis. In practice, it is known that there is always some form of air present in hydraulic systems which substantially decreases the oil bulk modulus. The term effective bulk modulus is used to account for the effect of air and/or the compliance of transmission lines. A summary from the literature of the effective bulk modulus models for a mixture of hydraulic oil and air is presented. Based on the reviews, these models are divided into two groups: “compression only” models and “compression and dissolve” models. A comparison of various “compression only” models, where only the volumetric compression of air is considered, shows that the models do not match each other at the same operating conditions. The reason for this difference is explained and after applying some modifications to the models, a theoretical model of the “compression only” model is suggested. The “compression and dissolve” models, obtained from the literature review, include the effects of the volumetric compression of air and the volumetric reduction of air due to the dissolving of air into the oil. It is found that the existing “compression and dissolve” models have a discontinuity at some critical pressure and as a result do not match the experimental results very well. The reason for the discontinuity is discussed and a new “compression and dissolve” model is proposed by introducing some new parameters to the theoretical model. A new critical pressure (PC) definition is presented based on the saturation limit of oil. In the new definition, the air stops dissolving into the oil after this critical pressure is reached and any remaining air will be only compressed afterwards. An experimental procedure is successfully designed and fabricated to verify the new proposed models and to reproduce the operating conditions that underlie the model assumptions. The pressure range is 0 to 6.9 MPa and the temperature is kept constant at °C. Air is added to the oil in different forms and the amount of air varies from about 1 to 5%. Experiments are conducted in three different phases: baseline (without adding air to the oil), lumped air (air added as a pocket of air to the top of the oil column) and distributed air (air is distributed in the oil in the form of small air bubbles). The effect of different forms and amounts of air and various volume change rates are investigated experimentally and it is shown that the value of PC is strongly affected by the volume change rate, the form, and the amount of air. It is also shown that the new model can represent the experimental data with great accuracy. The new proposed “compression and dissolve” model can be considered as a general model of the effective bulk modulus of a mixture of oil and air where it is applicable to any form of a mixture of hydraulic oil and air. However, it is required to identify model parameters using experimental measurements. A method of identifying the model parameters is introduced and the modeling errors are evaluated. An attempt is also made to verify independently the value of some of the parameters. The new proposed model can be used in analyzing pressure variations and improving the accuracy of the simulations in low pressure hydraulic systems. The new method of modeling the air dissolving into the oil can be also used to improve the modeling of cavitation phenomena in hydraulic systems

An Artificial Neural Network Approach to Predicting Formation Stress in Multi-Stage Fractured Marcellus Shale Horizontal Wells Based on Drilling Operations Data

The distribution of the anisotropic minimum horizontal stress, both in horizontal and vertical directions, is necessary for effective hydraulic fracture treatment design in Marcellus Shale horizontal wells. Typically, the minimum horizontal stress can be estimated sonic logs. However, sonic log data is not commonly available for the horizontal Marcellus shale wells due to the complexity and cost. The objective of this research is to predict the anisotropic minimum horizontal stress by utilizing drilling parameters including depth, weight-on-bit (WOB), revolution per minute (RPM), standpipe pressure, torque, pump flow rate, and the rate of penetration (ROP). More specifically, artificial neural network (ANN) models will be developed to predict the anisotropic minimum horizontal stress for a horizontal Marcellus shale well from the drilling and well log data. Artificial neural networks are particularly useful to identify complex relationships to predict the properties of unconventional formations. The available data from a Marcellus Shale horizontal well was collected and filtered to prepare data sets for ANN training, testing, and validation purposes. Two networks, for the vertical and lateral sections of the well, were developed. The preliminary results indicated that inclusion of lithology, gamma-ray, and bulk density well log data as inputs can improve the predictability of the networks. Finally, the networks were used to predict the anisotropic minimum horizontal stress in a different Marcellus shale horizontal well with the available sonic log data. To evaluate the applicability of the ANN models, the predicted stresses by the networks were compared against those estimated from the sonic logs. The predictions by both networks (vertical and horizontal) were found to be in close agreement with those estimated from the sonic logs. The results of this research can be utilized as a predictive tool to help fill in the need for an accurate estimation of static geomechanical properties including the minimum horizontal stress in Marcellus Shale horizontal wells and to improve the fracturing treatment design

Fracture detection with azimuthal seismic data, rock physics, and geomechanics

Significant progress has been made for fracture detection in unconventional plays using advanced geophysical techniques such as the use of P-wave AVO algorithms in multi-azimuth data. In the past decade, it has been recognised that major amplitude distortions in anisotropic media occur, for wide-azimuth data, and that these might potentially be related to fracture distribution in the layered media. However, inversion of the azimuthally varying P-wave AVO gradient for the crack density is non-unique without additional information. Aims This research work aims to better understand the seismic anisotropy of shale rocks to improve future exploration by using fracture modelling and azimuthal AVO/AVA for fracture detection, and rock physics to develop a thorough understanding of the reservoir and quantify fracture anisotropy quantitatively and qualitatively. This is a potentially important unconventional oil and gas reservoir of the Late Jurassic age. Specifically, the project aims to improve future oil exploration by using AVAz variations for fracture detection and fracture models in effective media. Scope The scope of this research is to model fractures of the effective medium to see the impact on seismic amplitudes distortions in different azimuthal directions and determine the type of AVO present in the models to compare them with real data in shale-type rocks. Implementation is presented of a new methodology to estimate anisotropic brittleness, the azimuthal TOC and stress field and its comparison with hydraulic treatment pressure data, calculated from inverted volumes with good quality azimuthal seismic data. Rock physics and fluid replacement in fracture models in shale rocks approaches will be tested for (brine/oil/gas) to better understand the fluid substitution in azimuthal synthetic models and the AVAz curves. Motivation The motivation for this work is to develop a better understanding of the anisotropy within the Pimienta Formation, which will help understand the shale-type rock fabric through fracture modelling, azimuthal data for better reservoir characterization in unconventional reservoirs. Methods Based on the effective media theory of fracture models addressed by other researchers, codes were developed and tested to obtain an azimuthal seismic image depending on the type of fracture arrangement (e.g., Hudson, and Linear slip). Within the methodology, in the substitution of fluids, the Linear slip model was tested to verify the synthetic azimuthal response with three cases (Brine/Oil/dry). Azimuthal seismic information provided by PEMEX was used to perform AVO Azimuthal analysis within the Pimienta Formation in order to identify possible fracture swarms and be able to determine the direction of the fast velocity (V_fast) that is related to the direction of fractures and possible current stress. Then rock physics modelling of elastic moduli in an anisotropic way was estimated by developing codes to obtain brittleness, these elastic moduli (e.g., Young´s Modulus and Poisson's Ratio) were used to estimate the stresses in a sub-area in the study area using inverted volumes. Differential Effective Medium (DEM) and Effective Field Method (EFM) have been tested in the study area to estimate the elastic moduli. Results The Pimienta Formation in rock physics template analysis fit much better using friable-sand model instead of friable shale model, different values in anisotropy within Pimienta Formation were found according to the significant amplitude distortions seen in each fracture model which may explain the intrinsic anisotropy of the Pimienta Formation. The azimuthal AVO demonstrated the possible existence of fractures within the Pimienta Formation in the study area according to the differences in the fast velocity (V_fast) and slow velocity (V_slow) and the Thomsen’s parameters, the fluid-filled fracture models through fluid substitution analysis in shale rocks demonstrated amplitude changes depending on the azimuth direction. The elastic properties (e.g., Young´s Modulus and Poisson´s Ratio) were estimated in VTI/HTI modes using the inverted data and finally the stress field using hydraulic treatment pressure information. Conclusions In this research work, two main contributions can be addressed that may help other geoscientists for a better understanding of the anisotropy in shale rock type and can be widely applied for reservoir characterization on unconventional resources in other projects around the world and maybe applied naturally fractured carbonates. 1. A new equation for estimation of the TOC in different azimuths named “upscaled azimuthal TOC “using inverted data from azimuthal seismic data contributed to the novel implementation of the calculation of this attribute which had been experimentally tested on core analysis in different azimuths. 2. A novel approach for the estimation of anisotropic brittleness has contributed to the field of anisotropy on shale rock types by using vertical transverse isotropy (VTI) and horizontal transverse isotropy (HTI) using azimuthal sectors of inverted seismic information. 3. For this research project, applications were developed in the field of geophysics that addressed fractured models (e.g., Hudson, and Linear slip), anisotropic rock physics for the calculation of elastic properties in two main directions 0° (VTI) and 90° (HTI) for the calculation of anisotropic brittleness compared with other researchers in this field. Such applications can help the geoscientific community to model fractures in effective media in a versatile and easy to use way since most software does not handle this type of modelling. 4. These new contributions in geophysics applied to the oil industry were focused on the study of the Pimienta Formation; however, these contributions can be widely used in the development, understanding and characterization of unconventional and carbonate reservoirs around the world. Finally, these contributions and all the analysis carried out in this research work will contribute to more efficient stages design for hydraulic treatment in horizontal wells in unconventional reservoirs, in order to reduce operating costs and the number of wells with the objective of obtaining the highest possible commercial production of hydrocarbon without ignoring the environmental impact and concerns

Hydrates in sediments : their role in wellbore/casing integrity and CO2 sequestration

Gas hydrates have attracted much interest among researchers recently because of their wide range of applications. The impact of natural gas hydrates in subsea sediments on the development of conventional hydrocarbon reservoirs in deep offshore and the potential role of CO2 hydrates as a secondary safety factor in subsurface storage of CO2 are the key areas in this thesis. Several experiments were conducted on synthetic samples containing methane hydrate with different hydrate saturations to measure their geophysical properties, mechanical properties and understand their mechanical behaviour at realistic conditions. A numerical model was also developed with ABAQUS (a finite element package) to investigate the casing stability of the wellbore drilled in gas hydrate bearing sediments in deep offshore environments using the measured properties of gas hydrate bearing sediments under different scenarios. The role of hydrates in subsurface storage of CO2 was studied using a unique experimental set-up by simulating geothermal temperature gradient. The objective was to investigate whether CO2 leaked from subsurface storage sites can be converted into hydrates, providing a secondary seal against further CO2 leakage to ocean/atmosphere.Engineering and Physical Sciences Research Council (EPSRC

Study About Petrophysical And Geomechanical Properties Of Bakken Formation

The objectives of this research are to measure the petrophysical and geomechanical properties of the Bakken Formation in North Dakota Williston Basin in to increase the success rate of horizontal drilling and hydraulic fracturing so as to improve the ultimate recovery of this unconventional crude oil resource from the current 3% to a higher level. Horizontal drilling with hydraulic fracturing is a required well completion technique for economic exploitation of crude oil from Bakken Formation in the North Dakota Williston Basin due to its low porosity and low permeability. The success of horizontal drilling and hydraulic fracturing depends on knowing the petrophysical and geomechanical properties of the rocks. A dataset of geomechanical and petrophyscial properties of the Bakken Formation rocks in the studied areas is generated, after petrophysical properties (including Density, Velocity, Porosity, and Permeability) and geomechanical properties (including uniaxial compressive strength, Young’s modulus, Poisson’s ratio, and Biot’s coefficience) were measured. To obtain those parameters, we not only used regular methods but also proposed some new methods for solving special measurement problems which may also be faced by other tight rock researchers. The results of this research can be used as a guideline and reference to optimize horizontal drilling and fracturing design to increase estimated ultimate recovery (EUR) in unconventional shale oil and gas productions