Pressure Plots Research Articles

Reservoir characterization of the Fahliyan Formation in Dorood Oilfield, Persian Gulf

The reservoir characteristics of giant oil fields in the Persian Gulf are poorly described in the geological literature due to their economic importance to host nations. The Berriasian–Early Valanginian, Lower Fahliyan Formation hosts several giant oil fields in the Persian Gulf, Iran, and in this study, sedimentary microfacies (MF), reservoir characteristics, petrophysics, rock types, and electrofacies of one of these fields are presented. Five MFs are defined and interpreted as representing deposition in lagoon, shoal, and mid shelf settings. MFs deposited in high-energy shoal settings have the best reservoir properties and mainly comprise grainstones and packstones; diagenetic alteration of these MFs reduces reservoir quality. MFs from lagoon and mid-outer shelf settings mainly consist of wackestone with poorer reservoir quality.Cluster analysis applied to well-log characteristics to define electrofacies. Electrofacies are then compared to effective porosity and integrated with the capillary pressure plots to define reservoir rock types. The resulting rock types were correlated to electrofacies and MFs. Here, in most cases, high reservoir quality rock types (RT3 and RT4) correlate well to high porosity and permeability electrofacies (EF1 and EF2) and grain-supported sedimentary microfacies (MF3 and MF4) and vice versa, but in some rare cases, the best reservoir rock types do not correlate to depositional facies due to the complex pattern of heterogeneity in pore types and spatial distribution that reveals considerable impact of diagenesis in the reservoir. This study reinforces the importance of accounting for diagenetic effects (particularly destructive digenetic phenomena which impact permeability) in reservoir rock typing.

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

Centrifugal pump impeller wheel inspired acoustic metamaterial for low frequency sound absorption

Addressing low-frequency noise is a significant concern within the realm of acoustics and noise management. Labyrinthine channel based acoustic metamaterials have been proved to control low frequency noise using local resonance effect and thermoviscous dissipations. Drawing inspiration from centrifugal pump impeller wheel, an acoustic metamaterial absorber has been devised. The design incorporates impeller vanes to create a channel with variable widths and a micro-perforate panel through which sound wave propagates to the channels. Numerical simulations using COMSOL Multiphysics and experimental analysis are conducted employing Two microphone impedance tube method. Acoustic pressure and acoustic particle velocity distribution plots from numerical simulation study are used to comprehend the sound absorption mechanism. Sound absorption coefficient results reveal that this design offers a tunable sound absorption peak in low frequency regime. Furthermore, this paper discusses the influence of various geometric parameters such as, number of vanes, panel thickness and micro-hole diameter. The subwavelength dimensions of the design contribute to noise control in machineries with space constraints.

Self-assembly of single species polygons with patchy models in 2D

The goal of this work is to produce single species of polygons in two dimensions using the self-assembly of a simple patchy molecular model. A molecule is defined as a central soft repulsive Weeks Chandler and Anderson (WCA) atom that is decorated with two or four patches, which describe the two models studied in this work. Model I has two Lennard–Jones (LJ) patches inside of its central atom separated by an angle θ that intends to define the number of polygon sides. The attractive potential of these patches, interacting as pairs, is used to bond molecules together to form polygons. Model II, having two additional soft repulsive WCA patches, tangent on the outside, produces single polygon species configurations. An example of Model I with an angle θ = 120 ∘ , forming a mixture of polygons, is included. Model II produces single polygon species with 3-8 sides, depending on the angle θ between the attractive patches. Molecular dynamics simulations in the canonical ensemble are used to calculate thermodynamic properties such as internal energy, percentage of polygons, pressure and contour plots for the percentage of polygons following isochoric processes. Different starting configurations are used to verify the consistency of the equilibrium results.

Numerical Analysis of the Dynamic Properties of Bionic Raster Ceilings.

In this study, a numerical dynamic analysis of ceiling raster panels was performed. The analysis was conducted on panels designed with inspiration from bionics. The purpose of the analysis was to enable optimisation of the location of the holes in the designed slabs in order to achieve the preferred dynamic properties, including the natural frequencies of the slabs and an appropriate airflow to avoid the occurrence of resonance. Three different types of panels were used and a total of fifteen panels were designed in terms of their geometry, with circular, elliptical, and hexagonal perforations, made of different materials: polypropylene PP, wood, and aluminium. Then, using the finite element method and ANSYS 2023 R1 software, the airflow over the ceiling panels and their natural frequencies and vibration modes were analysed. The analysis took into account not only the shape of the openings, but also their percentage area relative to the total panel area and different airflow velocities. In addition, the results were compared in an analytical way with those obtained for a solid slab. The results obtained include findings on the mode shapes and values of the vibration frequencies of the plates, air pressure maps, histograms, and plots of the pressure dependence on the surface area of the plate openings.

Correlating Capillary Pressure and Resistivity Index for Carbonate Reservoir

Capillary pressure is a significant parameter in characterizing and modeling petroleum reservoirs. However, costly laboratory measurements may not be sufficiently available in some cases. The problem amplifies for carbonate reservoirs because relatively enormous capillary pressure curves are required for reservoir study due to heterogeneity. In this work, the laboratory measurements of capillary pressure and formation resistivity index were correlated as both parameters are functions of saturation. Forty-one core samples from an Iraqi carbonate reservoir were used to develop the correlation according to the hydraulic flow units concept. Flow zone indicator (FZI) and Pore Geometry and Structure (PGS) approaches were used to identify the reservoir hydraulic flow units. The experimentally derived correlations can be used to predict capillary pressure from resistivity, which is widely available from well-logs. FZI and PGS rock typing methods were applied to characterize the reservoir rock types. For both methods, the log-log plot of Leverett J-function and capillary pressure versus resistivity index for each rock type represent a power-law model relationship between these parameters. Despite the good permeability-porosity prediction results, the FZI approach did not yield a good correlation between J and I. PGS resulted in a better performance in terms of both permeability-porosity prediction and Pc with I correlation because PGS honors the pore geometry and structure relationship with the mean hydraulic radius more than FZI. This work introduces a new correlating approach that aims to assist in reservoir characterization and simulation.

Unveiling thermal and hemodynamic effects of aneurysm on abdominal aorta using power law model and finite element analysis

The objective of this study is to find causes of aortic diseases and investigating the ways for better treatment. The governing system of equations has been demonstrated to account for characteristics of blood. The governing system of equation has been solved using the finite element method with appropriate boundary conditions. We analyzed into the relationship between flow characteristics via the aneurysmal abdominal aorta and the aneurysm height, aneurysm length, and non-Newtonian behavior. It investigates how thermal and hemodynamics effects change across the abdominal aortic aneurysm. The velocity, pressure, and temperature surface plots of the results are displayed. There have also been graphic displays of line graphs of axial velocity, radial velocity, axial pressure, radial pressure, axial temperature and radial temperature across the aneurysm. The blood flow simulations obtained results show that increasing blood temperature, pressure and intake velocity all contribute to an increase in viscosity. The results indicate that while the temperature varies little to not at all, the blood flow pressure decrease and velocity significantly vary.

Experimental investigation of storm sewer geyser using a large-scale setup

The storm sewer geyser is a process where an air–water mixture violently erupts from a manhole. Despite the low hydrostatic pressure, violent eruptions can achieve a height of tens of meters above the ground. This current study experimentally investigates large-scale violent geysers using a large air pocket inserted from a pressurized air tank. The total length of the pipe system is approximately 88 m with a 0.1572 m diameter pipe. This large-scale experiment facilitates the investigation of spontaneous geyser eruptions. This study identifies the role of air–water volume ratio and coefficient of pressure (ratio of absolute initial static pressure to initial dynamic pressure) on the geyser intensity using eruption images and pressure plots. A total of 116 cases are tested, in which the volume ratio is parametrically increased from 0 to 1.1 under various operating conditions. A geyser score is defined to quantify the geyser eruption nature based on visual observations. The key findings are as follows: first, a sharp transition in geyser intensity is observed at the critical volume ratio of 0.5, and pre-transition and post-transition intensity exhibit a linear relationship with the volume ratio; and second, the critical volume ratio linearly varies with the coefficient of pressure.

Unveiling the Role of Electrostatic Forces on Attraction between Opposing Polyelectrolyte Brushes.

Electrostatic interaction and molecular excluded-volume effects are responsible for a plethora of nonintuitive phenomena in soft-matter systems, including local charge inversion and attraction between similar charges. In the current work, we study the surface forces and swelling behavior of opposing polyelectrolyte brushes using a classical density functional theory that accounts for electrostatic and excluded-volume correlations. We observe that the detachment pressure between similarly charged brushes is sensitive to salt concentration in both the osmotic and salted regimes and can be negative in the presence of multivalent counterions. A comparison of the theoretical results with the mean-field predictions unravels the role of correlation effects in determining the surface forces and brush structure. For systems containing multivalent counterions, the detachment pressure attains negative values at an intermediate brush-brush separation, and the attractive region in the pressure vs distance plot is magnified in terms of both the depth and width of attraction with increasing counterion valency. However, the interbrush attraction vanishes when the size-induced correlations are switched off. We also investigated the role of counterion size and polymer chain length on the detachment pressure. It is found that smaller counterions are more effective in neutralizing the polymer charge than bigger counterions, leading to a reduced interbrush repulsion and, in some cases, attraction between like-charged brushes at intermediate distances. Meanwhile, varying the chain length of the grafted polymers only shifts the location of the attraction basin, with little influence on the interaction strength. The theoretical predictions show qualitative agreement with experimental observations and offer valuable insights into the interaction between similarly charged polymer brushes in the presence of multivalent ions.

TRIAXIAL COMPRESSION STUDY OF CLAY SAMPLES

The paper presents a unique method for studying mudstone samples using an independent triaxial compression unit developed at the Department of Oil and Gas Well Drilling, Samara State Technical University. Drilling directional and horizontal wells has difficulties associated with wellbore stability. Stability is directly determined by the strength and deformation characteristics of the rocks, and also takes into account anisotropy, bottomhole pressure and wellbore configuration. In this regard, there are emergency situations at the rig: scree and collapse of the walls of wells in the intervals of unstable rocks. The purpose of the study is to study the core properties to prevent these complications during the design phase. Analysis of rock compression test methods was performed. The method of study is physical modeling of mountain stress at the plant for triaxial compression. The work presents a phased study plan. Analysis of the problem of microcracking of mudstones was also carried out. Based on the design characteristics of plant classes for independent triaxial loading, the installation of the second class with multi-stop systems was chosen. At this stage, the installation is equipped with software. Experiments were carried out according to the first loading program, that is, first the core sample was uniformly compressed along all three axes in one position, and then in a turned position on the 90º. Pressure versus displacement plots were obtained. After processing the results, you can find the Poisson ratio, Young’s modulus, and shear modulus, as well as determine anisotropy. In the future, it is planned to conduct experiments on core saturation.

Effect of Vascular Lumen Reduction on the Performance and Energy Consumption of an Innovative Implantable LVAD

This paper presents the results of a study on the effect of vascular lumen reduction on the performance of an innovative implantable LVAD (left ventricular assist device). It details the pressures in the individual cardiac chambers as a function of device frequency. In addition, mass flow rates and energy consumption of the device are examined, varying with lumen reduction and operating frequency. While the lumen reduction of the vessels has little effect on energy consumption, the mass flow rates vary considerably, i.e., above 140 cyc/min, the mass flow rate increment is no longer achieved for specified initial conditions. There are also differences regarding the pressures in the heart; namely, it was found that the pressure plots look similar in all cases, leading to the conclusion that the reduction of the vessel lumen does not affect their shape, but does affect the maximum values of the left ventricular and aortic pressures. Importantly, the innovative device in the form of an intra-cardiac balloon assembly for circulatory support is based on a pulsatile flow strategy and is synchronized with the ECG signal. Other advantages of the proposed solution include a minimally invasive method of implantation, which is important for patients with end-stage heart failure. The design of the device is portable and the device itself is battery-powered, allowing for shorter hospitalization times and faster recovery, even in patients with end-stage heart failure associated with mitral regurgitation and pulmonary hypertension.

Numerical and Experimental Investigation of a Volumetric Resistance Blower Performance and Its Optimization for Portable Computing Device Applications

Abstract In this paper, we present our results on a relatively new kind of blower called Volumetric Resistance Blower (VRB) for cooling of portable computing platforms like laptop computers. The VRB performance was modeled numerically and compared to traditional bladed blowers. The sources of noise, dominant in bladed blower, are absent in case of VRB, because it uses a continuous porous disk instead of discrete blades. Thus, even though at iso-rpm, VRB yielded lower flowrate, its iso-acoustic performance could be superior. Hence, further analysis was crucial to quantify the potential benefit. The acoustics experiments for bladed blower and VRB were conducted in a hemi-anechoic chamber in accordance with ECMA-74 and ECMA TR/99 standards. Iso-acoustics pressure versus volume flowrate plot for both bladed blower and VRB are compared. VRB was found to have superior performance as compared to bladed blower. The volume flowrate at open flow condition for bladed blower and VRB are comparable, but as back pressure increased the flowrate yielded by VRB kept increasing and at stagnation condition, VRB showed around 79% higher static pressure. In the second part of the work, the experimentally validated numerical model for VRB was used for numerical optimization using a design of experiments (DOE) approach and varying the geometrical parameters. Rotor distance (minimum distance from the axis of rotation of impeller to the cutwater surface) was found to be the most important parameter, and an optimum value was found. A second DOE elucidated the optimal rotor hub center location in the two-dimensional space inside the casing as when the rotor is tucked back into the casing as much as possible and when the rotor distance is above 20.15 mm. A partial P–Q curve is generated (up to 20 Pa) for optimal geometry configuration. Based on the numerical and experimental evidence, VRB is found to have the potential to replace traditional bladed design in portable computing devices. In addition, due to absence of blades, it creates lower tonal noise, giving a much more comfortable experience to the end user.

The Longitudinal Mean Arterial Pressure among congestive heart failure patients at Felege Hiwot Referral Hospital, Bahir Dar, Ethiopia

BACKGROUND Congestive heart failure could be defined as a condition where there is a performance or structural impairment of the heart. So this study was targeted on the determinants of the longitudinal mean arterial pressure among heart failure patients treated from January 2016 to December 2019 at Felege Hiwot Referral Hospital in Bahir Dar, Ethiopia. METHODS Hospital-based retrospective data were assembled from the medical chart of 218 randomly selected congestive heart failure patients. The linear mixed effects model corresponding to unstructured_ _covariance structure was employed to spot out the determinants of mean arterial pressure among in patients with congestive heart failure. RESULTS Individual profile plot of mean arterial pressure showed the existence of variability among and between those patients. Moreover, the mean profile plot demonstrated a linearly increasing pattern over the follow-up times. The random intercept and slope model corresponding to unstructured covariance structure was the best fit (AIC: 6001.9(χ^2=80.83), P < 0.0001) as compared to the remaining models. The estimates for age, left ventricle ejection fraction, serum sodium concentration, visit times, serum hemoglobin concentration, residence(rural) and New York Heart Association Classes I, II, and III were given as 0.3758(P-value: <0.0001), 0.2933(P-value: <0.0001), 0.1941(P-value: <0.0001), 0.4471(P-value: 0.0059), 0.5501(P-value: 0.0053), -9.9858(P-value: <0.0001), 18.8943(P-value: 0.0001), 10.8833(P-value: <0.0001) and 2.7318(P-value: 0.0001) respectively, and they are statistically associated with the longitudinal mean arterial pressure of congestive heart failure patients. CONCLUSION The linear mixed effects model corresponding to unstructured covariance structure provides an information on the existence of within and between subjects variations and correlations in addition to identifying the significant factors associated with the longitudinal mean arterial pressure of congestive heart failure patients. So, an application of standard models may ignore such a variation among successive measurements. Thus mixed effects model is recommended for such longitudinal data.

FEATURES OF THE STRESS-DEFORMED STATE OF VERTICAL CYLINDRICAL TANKS UNDER EXTERNAL PRESSURE

The paper investigates the features of the stress-deformed state of cylindrical shells under wind pressure, taking into account its actual distribution on cylindrical structures. The purpose of the work is to obtain a qualitative picture of the distribution of stresses and deformations in the cylindrical wall of the tank under wind load, to determine the effect of wind load on both the strength and stability of the tank. Practical significance. It is known that the stresses caused by the action of the wind load, due to their small value, are safe from the point of view of strength, at the same time, obtaining quantitative values of the stress-deformed state main components of the tank under wind load has a certain practical significance. The task is to solve the problem of deformation of the cylindrical shell under external uneven pressure of the wind type. Content of research. The solution of the deformation problem was performed in a linear formulation for cylindrical shells with geometric parameters corresponding to the geometric parameters of vertical tanks with a volume of 1,000…30,000 m3. The solution of the problem was carried out for several loads of the shell with wind pressure of different intensity q = (0,2…1,2) qcrw. Such formulation of the problem made it possible to investigate the features of the stress-deformed state of cylindrical shells under wind pressure both at small values of the external load and at pressure values close to the critical ones, which is important from the standpoint of shell stability. Conclusions. The static calculation of the shells under wind pressure showed that membrane stresses in the annular direction prevail. Membrane stresses in the meridional direction are the second largest. The distribution of these stresses along the perimeter of the shell corresponds to the wind pressure plot. The main feature of the bending stress graphs is their wave character along the perimeter of the shell. Plots of radial displacements w and deformed shells also have a wave character. The size of such wave deviations is insignificant, but their length is close to the length of the waves of the shell protrusion when it loses its stability. Thus, the process of deformation of cylindrical shells under wind pressure is generally stable. The wind load itself is safe from the strength point of view. However, the obtained nature of the deformation, namely the wave deviations of the surface of the shell, can significantly affect the stability of the shell, which requires additional research.

New Mathematical Technique for Step Rate Test Analysis Aids Determination of Fracture Pressure and Overcomes the Uncertainty of Conventional Analysis.

Experience in the oil industry has shown that it is challenging to sustain successful long-term matrix injection, as injection water quality cannot be maintained rigorously due to facility hiccups and membrane clogging. Most oil field operators have resolved this problem of injectivity decline by increasing the surface injection pressure to part the formation and inject just above the fracture gradient with strict offtake management for zonal conformance. This is not an easy task as injection much above fracture opening pressure can lead to water fingering and poor sweep that results in uneconomical waterflood recovery. The operators, thus, strive to inject at a pressure just above the fracture opening pressure so that the fracture opens near the wellbore but does not extend and then maintain the pressure just above the fracture closing pressure. Therefore, determination of the fracture opening pressure and fracture closing pressure has remained critical data for the success of waterflood projects. The most reliable industry approach to estimating fracture opening and fracture closing pressures comes from the step rate test (SRT). This traditional approach of Cartesian analysis of pressure-rate plot fits straight lines through the data in a plot of injection pressure against injection rate and then estimates the fracture pressure from the intersection of these lines having different slopes. The data received often do not exhibit one clear change in slope, thus resulting in multiple possible solutions, making it difficult for the operator to use the data for high CAPEX facilities design. Most past studies indicate the subjectivity of this Cartesian slope fitting technique. Alternative solutions through multirate superposition analysis found limited application in the analysis of SRT data due to considerable sensitivity to the value of initial pressure used for superposition and lack of stability of rate and pressure data. In this article, a new technique of SRT analysis is presented, which provides a unique solution for fracture opening and fracture closing pressures. It helps to overcome the limitations of the traditional technique of arbitrary fitting of straight lines. It uses the mathematical understanding of cumulative derivatives to recognize that the matrix opens when the cumulative growth of the rate of injectivity shows a change. It estimates the derivative of the injection rate with respect to injection pressure at each step. Then, it estimates the fracture pressure from the plot of the cumulative of this derivative against pressure at each step. It helps to overcome the challenge SRT solutions posed by the nonlinear trend of pressure data at each injection step both before fracture and after fracture is initiated. It also overcomes the limitations of the multirate superposition technique, as it is not sensitive to the value of initial pressure used for superposition.

CFD based modeling of OWC device positioned over stepped bottom

This research deals with various parameters associated with the hydrodynamics of an OWC device positioned over the stepped bottom. The problem is solved using the multiphase based CFD technique in “ANSYS Fluent software”. A “piston type wavemaker” and dynamic meshing technique are employed to produce the incident wave inside the numerical wave tank (NWT). Further, “volume of fluid” procedure is implemented to produce the free surface in the NWT. The “free surface elevation” is analyzed in various instant of time. Contour plots of the dynamic pressure, turbulent kinetic energy and turbulent intensity associated with the fluid motion are provided. Further, the variation of the vertex average total pressure and vertex average y− velocity at the orifice on the OWC device’s top wall are analyzed with respect to flowtime.

Gas Evolution Characterization of NiZn Batteries with Residual Gas Analysis

As humanity strives to reduce its impact on the environment, the need for safe, recyclable, and efficient batteries increases. Nickel-Zinc batteries offer a solution to some of the world’s needs with its materials being abundant and recyclable, its ability to discharge at high currents, and its safe and nontoxic materials providing low risk with applications. Nickel-Zinc batteries are rechargeable, have a ZnO anode, a NiOOH cathode, and an aqueous KOH solution as the electrolyte. During cycling, Ni-Zn cells produce and consume H2 and O2 gas. This gassing behavior has not previously been characterized. The goal of this research was to analyze this gassing behavior by measuring the partial pressure vs. time of a cell’s headspace gas during cycling. The headspace gas was leaked into a vacuum chamber and analyzed with an RGA quadrupole mass spectrometer. The primary trend of the H2 gassing was that the cell produced hydrogen during charging and was rapidly consumed at the end of charging, which indicated recombination with oxygen at an internal catalyst coil. The consumption stopped about midway through discharging and began to produce the H2 gas again. The O2 gassing peaked as H2 was consumed and slowly tapered off during the rest of the discharge and charge. The curvature of these partial pressure plots was dependent of the cycle number and charge rate. The eventual goal of this research is to use the gassing data to indicate the different phases of the electrode materials present throughout cycling. Figure 1

EFFECTS OF ROOF SHAPES ON WIND PRESSURE DISTRIBUTION OF MULTI-SPAN LOW-RISE BUILDINGS

The present study demonstrates the numerical investigation to find out the effects of roof shapes on the wind pressure distribution of multi-span low-rise buildings. Most of the wind load standards of various nations are provided with wind load information of isolated low-rise buildings which in turn practically came out to be inapplicable during the designing of low-rise buildings with multi-spans. Also, most of the wind load studies are carried out using boundary layer wind tunnel (BWLT) which is sometimes not available, time taking process, and is expensive. Therefore, in the present research, numerical simulation has been done for the model of a low-rise building. For investigation, the Ansys CFX platform has been used with the k-ε turbulence model for different angles of wind incidence at an interval of 15°. The wind pressure distribution has been investigated for the model low-rise building with a rectangular plan having six spans of different roof forms i.e., cylindrical roof, mono-slope roof, hip roof, and dome roof. The outcomes of the present numerical investigations are presented in the contour plots of wind pressure and coefficients of wind-induced pressure on the different roof forms of low-rise buildings. The outcomes of the study will be so much beneficial to structural design engineers while considering the wind loads calculations on the different roof forms for low-rise buildings.

Estimating formation and fracturing water production using simple diagnostic plots

The main goal of this paper is to evaluate the possibility of distinguishing between formation and fracturing water based on the water-flowback response without analyzing water chemical data. We analyze flowback production data of 100 multi-fractured horizontal oil wells completed in the Montney Formation and 89 oil and gas wells completed in the Duvernay and Horn River formations. We hypothesize that 1) the slope of water-flowback harmonic decline (HD) profiles (mHD) is proportional to the slope of rate-normalized pressure (RNP) plots (mRNP), and 2) both mRNP and mHD are inversely proportional to the amount of water influx from matrix into fractures. To verify our hypothesis, we 1) extend the previous HD and single-phase flowing material balance models by considering the water influx from matrix into fractures, 2) classify the studied wells based on observed trends, 3) construct RNP diagnostic plots of the studied wells, 4) investigate the relationship between mHD and mRNP, 5) analyze log data and estimate average initial water saturation (Swi) for the studied wells, and 6) investigate the relationship between of mHD and Swi. The results show that mHD for all the studied wells ranges from 0.00001 to 0.036 1/ m3 with a mean value of 0.0056 1/ m3. Wells with higher mHD have relatively higher mRNP values. In contrast, wells with very low mHD show no significant decline in water rate through the entire flowback process and relatively low or inconsistent mRNP values on the corresponding plots of RNP versus material balance time (MBT). We also observe a negative correlation between mHD and Swi obtained by analysis of wireline log data. This correlation and the positive correlation between mHD and mRNP indicate that as Swi increases, water influx from matrix to fracture increases, and thus, both mHD and mRNP decrease. Based on our modified models and the observed correlations, we develop a method to approximately differentiate between formation and fracturing water. The applications of our heuristic method on field data shows that 1) fracturing water production dominates the total water recovery for wells with higher mRNP, and 2) formation water production dominates the total water recovery for wells with lower mRNP.

Revisiting the Clausius/Clapeyron Equation and the Cause of Linearity

In general, for an organic compound a plot of the log vapor pressure versus inverse temperature is linear over a wide temperature range. This however can lead to a point of confusion in an undergraduate thermodynamics course. This linear behavior is typically explained using the Clausius/Clapeyron equation. That is, starting with the Clapeyron equation one first assumes (1) that the change in compressibility upon vaporization is approximately 1, or equivalently that the vapor phase may be treated as an ideal gas where the molar volume of the vapor is much greater than that of the liquid, which may be assumed negligible. And second (2), that the enthalpy of vaporization is constant. While the resulting linear behavior is captured, the underlying assumptions are not applicable over the wide range of temperatures of interest. Here we discuss the shortcomings of the conventional explanation of the Clausius/Clapeyron equation. We further demonstrate that a simple solution is to instead assume that the enthalpy of vaporization relative to the change in compressibility upon vaporization is constant. We provide a series of examples and MATLAB code that can be used in an undergraduate thermodynamics course.