Multiple-contact Experiments Research Articles

Improving robotic impedance control performance employing a cascaded controller based on virtual dynamics model

We propose a cascaded impedance control algorithm based on a virtual dynamics model (VDM) to achieve robust and effective mechanical impedance for a robot interacting with unknown environments. This cascaded controller consists of an internal loop of virtual impedance control based on a VDM and an external loop of impedance reference control. The VDM-based virtual impedance control can achieve the same effect as the conventional admittance control; its intermediate output of force/torque serves as the input for the external loop reference impedance control. Therefore, this cascaded controller shows superior performance by combining the advantages of admittance control and impedance control. We evaluate the controller in multiple-contact experiments on a six-degrees of freedom (6-DOF) industrial robot manipulator. The result shows that under various contact situations such as soft and rigid surfaces and free space, the proposed method can rapidly track the target and effectively maintain stability. In the experiments conducted on the robot in contact with various environments, the proposed control method reduced the steady-state error by more than 20% compared with the conventional admittance control.

An Investigation of Recovery Mechanisms for Oil Field Optimization by Three-Phase Core Flood and Simulation Studies

Two potential recovery mechanisms are being considered for a major field which required laboratory measurements to investigate the efficiency of the two scenarios: gas flood followed by water flood and water flood followed by gas flood. Although simply stated, the recovery scenarios involved complex three-phase processes which had to be replicated in the laboratory at reservoir conditions to provide reliable data upon which reservoir development decisions could be made. The first sequence consisted of water displacing oil to residual oil saturation (Sorw), oil displacing water to residual water saturation (Swro) and gas displacing both oil and water to Sor3φ,g and Swr3φ,g. The second sequence consisted of gas displacing oil to residual oil saturation (Sorg), oil displacing gas to trapped gas saturation (Sgto) and water displacing both oil and gas to Sor3φ,w and Sgt3φ,w respectively. Composite cores of four well-matched plugs at Swi were used and all measurements were made at bubble point conditions. A vertical core holder was housed inside a reservoir condition facility equipped with gamma attenuation saturation monitoring (GASM). Temperature stability and the use of GASM were paramount for the accurate measurement of produced fluids, especially trapped gas saturation. Oil, gas and water produced volumes were also measured using a separator housed inside the core flood oven to provide optimum temperature stability. The laboratory results were modelled in a compositional simulator using an equation of state tuned to conventional PVT data and both swelling and multiple contact experiments. The objective was to build a three-phase predictive model from the constituent two-phase relative permeability data. The paper details the experimental methods and presents results for each section of the two sequences. The key conclusions are that Sorg>Sorw> Sor3φ,g> Sor3φ,w and Sgt3φ,w< Sgto.

An integrated study of the dominant mechanism leading to improved oil recovery by carbonated water injection

Abstract Enriching the injection water with CO2 has demonstrated encouraging results to improve oil recovery and securely store CO2 in underground oil reservoirs. However, the mutual interactions taking place between carbonated water and reservoir oils are not fully understood. Assuming that the phase behaviour of free CO2 and oil phase that takes place during conventional CO2 flood will also take place during carbonated water injection (CWI) would be misleading. Recently, it has been visually demonstrated that CO2 transfer from carbonated water into a “live” crude oil would trigger the formation of a new gaseous phase, which would hugely boost the performance of CWI under real reservoir conditions. Therefore, characterization of this new phase would have significant implications for identifying the suitable conditions at which CWI displaces the oil more efficiently. In this study, through a series of multiple-contact tests linked to micromodel and slim tube experiments, it has been aimed to comprehensively investigate; (i) CW–oil phase behaviour, (ii) the characteristic of gaseous new phase, and (iii) its impact on oil recovery by CWI, (iv) CW displacement front propagation inside the reservoir as CW moving far from injection point. We have studied the interactions between CW and live crude oil (crude oil with solution gas) by performing a series of high-pressure high-temperature fluid characterization tests. The live oil was sequentially brought into contact with CW and in each contact, the resultant phases were analysed to track the CO2 transfer between different phases and to determine the composition and characteristics of the new phase. The results revealed that the new phase forms immediately when live oil is brought into contact with the CO2-enriched water and it grows at subsequent contacts. The results of gas chromatography analyses also reveal that the new phase is composed of a multi-component mixture of hydrocarbons starting with CH4 and CO2 at early stages and becoming richer in CO2 towards latter contacts. Alongside the multiple-contact experiment, direct visualisation experiments performed at identical conditions confirm the rapid formation and growth of the new phase for the live oil system. Furthermore, to assess CW–live oil phase behaviour and displacement front propagation over long distances inside the reservoir, two carefully designed slim tube experiments were performed to compare the performance of secondary CWI against the conventional waterflooding in a one-dimensional long porous medium. The results of the slim tube tests showed that CWI led to an average improved oil recovery of 24% compared to conventional water flood. The outcomes of this integrated investigation unravel the characteristic and impact of the new phase formation on improved oil recovery by CWI. This would enable us to identify and target suitable reservoirs for this EOR technique.

Variation of reservoir fluid property during the high pressure air injection process

ABSTRACTThis research aimed at determining the variation of reservoir fluid property during the high-pressure air injection process. For this purpose, the forward multiple contact experiment was employed by pressure–volume–temperature (PVT) system to investigate the physical property variation of the crude oil and the complex oxidation reactions. The results show: under the relative low temperature and pressure condition, instead of carbon dioxide, carbon monoxide dominates the products in the air phase. The gas/oil ratio and volume ratio increased due to the generated gas while the viscosity and density achieved a descending trend. The colloid and bitumen in the oil phase reduced by half but the amount of wax achieved a small increase. The low-temperature oxidation and pyrolysis reactions caused the fluctuated change of the different compounds. The amount of light compounds decreased at the beginning and then increased while that of heavy compounds showed the opposite trend. But at last, due to the H/C ratio, the light compounds increased to more than their initial value.

Characterization of Carbon-Dioxide-Induced Asphaltene Precipitation

Asphaltene precipitation continues to be one of the major problems during the carbon dioxide enhanced oil recovery process. Supercritical carbon dioxide is injected into oil reservoirs to enhance oil recovery in the tertiary phase of production. Development of multiple-contact miscibility is important in the success of a carbon dioxide flood. In this paper, we establish conditions at which solids are formed in carbon dioxide–oil systems and characterize these solids by a variety of analytical techniques. Crude oils containing low and medium amounts of heptane-insoluble asphaltenes were used in the study. A high-pressure thermodynamic system was designed and fabricated, and a number of thermodynamic experiments were performed with dead and live oils. Multiple-contact experiments were first performed by adding a “light–intermediate” cut to the crude oil and later by creating actual multiple contacts. Precipitation onset for dead oils was obtained between 20 and 30 mol % CO2. CO2-induced solids consisted of ...

Computer Controlled Chamber Measurements for Multiple Contacts for Soil-Skin Adherence from Aluminum and Carpet Surfaces

ABSTRACT A computer-controlled mechanical chamber was used to perform multiple contacts between human cadaver skin or cotton sheet samples and soil-laden carpet or aluminum foil to measure mass soil transfer. The amount transferred was measured with an analytical balance. The contact parameters of pressure (10 to 50 kPa) and time (10 to 50 s) were varied for 760 separate multiple contact experiments, where two soil types (play sand and lawn soil) and two soil sizes (< 139.7 and ≥ 139.7 < 381 μm) were used. Through parametric and non-parametric tests, this article specifically looks at the influence and interaction of these experimental parameters on the transfer of soil or sand to human skin during multiple contacts. The relationships between the amount of soil or sand that transfers for a first contact, for a second contact, and overall are also presented. On average, a second contact added an additional 8% of soil or sand to the adherence material (i.e., cloth, skin). The experimental variables of pressure, time, soil size, and soil type had less influence on the magnitude of transfer for the second contact as compared to the first contact.

New Approach in Gas Injection Miscible Processes Modelling in Compositional Simulation

Abstract A number of factors must be considered in the design of miscible displacement processes. This paper discusses a new approach that relates primarily to the laboratory and modelling studies that precede the EOS-based compositional simulation of reservoir performance during the vapourizing/condensing gas drive process. The phase behaviour of a solvent/oil system and determination of miscibility conditions by various special PVT experiments (including the swelling test, RBA, slim tube test, and the continuous multiple-contact experiment) are reviewed along with their importance in building an accurate EOS model to be used in compositional simulation. In addition to experimental PVT data, a special core flow test design for measuring the relative permeabilities to generated fluids by forward/reverse multiple contact experiments is discussed. Based on laboratory PVT and SCAL data, a novel interfacial tension-dependent model of relative permeability and capillary pressure data is presented along with the advantages if incorporated into commercial EOS-based compositional simulation software packages. Introduction Mass transfer between the gas and oil components dominates the displacement characteristics of miscible or near-miscible floods. The overall displacement efficiency of any oil recovery displacement process can be considered conveniently as the product of microscopic and macroscopic displacement efficiencies. In equation form: where E = overall displacement efficiency, ED = microscopic displacement efficiency, and EV = macroscopic (volumetric) displacement efficiency. Microscopic displacement relates to the displacement or mobilization of oil at pore scale. That is, ED is a measure of effectiveness of the displacing fluid in moving (mobilizing) the oil at those places in the rock where the displacing fluid contacts the oil. ED is reflected in the magnitude of the residual oil saturation, Sor, in the regions contacted by the displacing fluid. Macroscopic displacement efficiency relates to the effectiveness of the displacing fluid(s) in contacting the reservoir in a volumetric sense. EV is a measure of how effectively the displacing fluid sweeps out the volume of a reservoir, both areally and vertically, as well as how effectively the displacing fluid moves the displaced oil toward production wells. It is desirable in an Enhanced Oil Recovery (EOR) process that the values of ED and Ev, and consequently E, approach 1. An idealized EOR process would be one in which the displacing fluid removed all oil from the pores contacted by the fluid (Sor →0). Several physical/chemical interactions occur between the displacing fluid and the oil that can lead to efficient microscopic displacement (low Sor). These include miscibility between the fluids, decreasing the interfacial tension (IFT) between the fluids, oil volume expansion, and reducing oil viscosity. The maintenance of a favourable mobility ratio between displaced and displacing fluids also contributes to better microscopic displacement efficiency. EOR processes are thus developed with consideration of these factors. The goal of an acceptable EOR fluid is to maintain favourable interaction(s) as long as possible during the flooding process. In enhanced recovery operations, oil entrapment occurs due to complex interactions between viscous, gravity, and capillary forces.

A general strategy for the NMR observation of half-integer quadrupolar nuclei in dilute environments.

A general strategy for the observation of low gamma half-integer quadrupolar nuclides in biological systems is presented. The methodology combines low-temperature (4-100 K) techniques with cross-polarization (CP) experiments while employing a so-called Carr-Purcell-Meiboom-Gill spin-echo sequence (CPMG). This combined approach is termed CP/QCPMG. Also discussed are data processing issues that are unique to the induced signals that result from the QCPMG pulse sequence. Central to this strategy is the development of a stable low-temperature (4 to 250 K) NMR double-resonance probe. The probe is robust enough to handle multiple contact experiments and long acquisition periods with 1H decoupling. This approach is illustrated with low-temperature solid-state 67Zn and 25Mg NMR CP/QCPMG experiments on model compounds. The conclusion reached is that the strategy affords sufficient sensitivity to examine Zn2+ and/or Mg2+ binding sites in metalloproteins.

Experimental studies and discrete thermodynamic modeling on supercritical CO2 extractions of a hexadecane and crude oil

Continuous multiple-contact experiments using a supercritical CO2 were performed to study the phase equilibrium behavior of the dynamic extractions of a hexadecane and crude oil. The extraction yields increased as CO2 density increased with a pressure rise at constant temperature. The rates of extractions were also greater at higher pressure. The simulated distillation analysis of extracted crude oil samples represented that the earlier extracts contained lighter compounds and the latter extracts contained progressively heavier compounds. These compositional changes occurring during a dynamic extraction were also ascertained by phase-equilibrium flash calculations using the equations of state and a pseudo-component lumping method. Two different equations of state, Soave-Redlich-Kwong and Peng-Robinson, were used to predict the equilibrium compositions of the extract phase that is a supercritical carbonic phase. The results of phase behavior calculations established the nature of the extraction and partitioning process as a function of time. These results also provided reasonable agreement between the experimental data and the calculated values.

Equilibrium Phase Compositions of CO2/Hydrocarbon Mixtures— Part 1: Measurement by a Continuous Multiple-Contact Experiment

AbstractA new experimental technique that simultaneously measures compositions and densities of two phases in equilibrium is described. Because it operates continuously, the experiment can be performed more rapidly than conventional static-equilibrium measurements. Details of the experimental apparatus are reported, and results of test displacements for two simple CO2/hydrocarbon systems are compared with static-equilibrium phase composition measurements for the same systems. A simple analysis of the operation of the experiment is used to assess the experimental error that results from the continuous nature of the experiment and to suggest ways to reduce that error. Application of the experimental technique to a CO2/crude oil system is reported in a companion paper.1

The Effect of Phase Behavior on CO2-Flood Displacement Efficiency

Summary The relationship between phase behavior and displacement efficiency (meaning here, recovery efficiency in the absence of any bypassing) as regards the displacement of Wasson crude oil by CO2 is examined at two different pressures--the lower pressure the one at which three coexisting hydrocarbon phases are encountered. At both pressures, experimental phase behavior data comprising primarily phase volume fractions observed in both single- and multiple-contact experiments are presented. Pseudoternary representations of the phase behavior are incorporated into a simple, one-dimensional, finite-difference simulator to relate the phase behavior to displacement efficiency. At the appropriate dispersion level, displacement efficiencies computed with the model are consistent with high oil-recovery efficiencies obtained experimentally in slim-tube displacements, and indicate that the displacement efficiency of the process (again, in the absence of bypassing) should be high in certain consolidated media as well. Introduction Probably as much research effort has been spent on phase-behavior aspects of CO2 flooding as on any other feature of the process. Undoubtedly the most rigorous way of examining the importance of this factor is by means of a fully compositional simulator containing dispersion terms and employing an equation of state capable of describing in detail phase equilibria related to the process. But modeling the phase behavior of CO2-crude oil mixtures is not easy, particularly in the case of low-temperature (i.e., less than, say, 120 degrees F) systems where three (four, counting precipitate) coexisting hydrocarbon phases are encountered. And even though three-phase single-contact data can be matched, as shown by Fussell, who used a Redlich-Kwong equation of state, it has yet to be demonstrated that an equation of state "tuned" to single-contact data and using pseudocomponents will describe adequately the multiple-contact process that is CO2 flooding. Furthermore, the complexity of the equation-of-state approach presents problems. it often results in black-box usage in the simulations, which inhibits the investigator from obtaining any basic insight into the overall process mechanism. In addition, if one wanted to examine correctly the relationship between phase behavior and recovery efficiency in situations where viscous fingering occurs--by explicitly simulating fingers, for example (not practical in every-day reservoir scale simulations)--it is quite possible that the time and cost of such computations that use an equation of state would be extremely high and possibly prohibitive.Partly because of these problems with the equation of state approach and partly because the experimental data reported here may be of some interest, we present a simpler but much less general alternative approach to examine the importance of phase behavior in CO2 floods involving crude oils. In this approach, single-contact phase equilibrium experiments are augmented by multiple-contact experiments where the composition of the crude is varied in a manner qualitatively similar to what might take place during an actual displacement. Data from both these experiments then are combined to construct a ternary diagram applicable at one specific pressure. (We also advocate the use of multiple-contact data in determining equation-of-state parameters.) JPT P. 2067^