Creation Of Wormholes Research Articles

Fines migration poses challenge for reservoir-wide chemical stimulation of geothermal carbonate reservoirs

Fines material, which can compromise the permeability of geothermal reservoirs, is often only considered with regard to existing fines like clay particles that are mobilized. However, fines are also generated due to dissolution. This is a significant risk coming from chemical stimulation techniques in geothermal reservoirs, that try to increase the range of stimulation with retarded acid systems. Deeper in the reservoir, fines cannot be extracted as is done in the near wellbore region after stimulation and the generation of fines has to be prevented. This work investigates the dependence of fines generation on the reaction conditions. Flow-through experiments with citric acid on dolostone were conducted, creating dissolution regimes with a range of different Damköhler numbers. During the stimulation experiments, the creation of wormholes and the widening of existing flow paths could be differentiated by the shape of the differential pressure curves measured across the samples. Fines were always generated and could greatly reduce the permeability of the rock samples. But for very high Damköhler numbers, where the dissolution created large pathways, the fines were transported out of the major pathways as well as dissolved therein, thus not interfering with the increase of permeability due to dissolution.

Creation of wormholes during the cosmological bounce

In this work we demonstrate that wormholes can in principle be naturally created during the cosmological bounce without the need for the exotic matter or any kind of additional modifications of the gravitational sector, apart from the one enabling the cosmological bounce. This result is general and does not depend on the details of the modifications of gravitational equations needed to support the bounce. To study the possible existence of wormholes around the cosmological bounce we introduce general modifications of Einstein’s field equations need to support the bouncing solutions. In this regime we show that it is possible to construct a cosmological wormhole solution supported by matter, radiation and vacuum energy, satisfying the Weak Energy Condition (WEC), which asymptotically approaches the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. However, at a specific cosmological time, which depends on the parameters of the bouncing cosmological model, the WEC describing the matter needed to support such wormholes is spontaneously violated. This means that such wormholes could potentially exist in large numbers during some period around the bounce, significantly changing the causal structure of space-time, and then vanish afterwards.

Three-dimensional simulation of wormhole propagation in fractured-vuggy carbonate rocks during acidization

Acidization is a widely used stimulation technique for carbonate reservoirs aimed at removing formation damage, and if successful, can result in the creation of wormholes of specific lengths and conductivities around the wellbore. The formation of wormholes depends on the injection rate for a particular acid-mineral system and can be predicted through numerical simulations of the reactive phenomenon during acidization. In this paper, the commonly used two-scale continuum model is enhanced to encompass fractured-vuggy porous media. The fractures are characterized by a pseudo-fracture model, while vugs are represented by a cluster of anomalous matrices with high porosity. Moreover, a method for generating random pore-fracture-vuggy models is proposed. The governing equations are discretized by the finite volume method and are solved under three-dimensional linear and radial conditions. Sensitivity analysis of dissolution dynamics with respect to fracture and vug parameters is performed. The simulation results indicate that both fractures and vugs significantly impact wormhole development. Except for fractures perpendicular to the acid flow direction, fractures in other directions play a crucial role in determining the direction of wormhole growth. Cited as: Liu, P., Kong, X., Feng, G., Zhang, K., Sun, S., Yao, J. Three-dimensional simulation of wormhole propagation in fractured-vuggy carbonate rocks during acidization. Advances in Geo-Energy Research, 2023, 7(3): 199-210. https://doi.org/10.46690/ager.2023.03.06

Wormholes effect in carbonate acid enhanced oil recovery methods

Acid enhanced oil recovery has been a focus of interest in the oil industry due to its significant results on improved recovery, especially in carbonate reservoirs. However, in carbonate reservoirs, highly conductive pathways called “wormholes” are created when acidic fluids are injected into carbonate rocks. Wormholes could jeopardize the enhanced oil recovery outcome and sweep efficiency leaving a substantial volume of oil in the reservoir unswept. This phenomenon has not been investigated yet. The main objective of this study is to identify the impact of these wormholes on the overall oil recovery during enhanced oil recovery practices. This was achieved by injecting acidic fluid into Indiana limestone at various injection rates to control the creation of wormholes. The injection rates were selected based on a proposed dimensionless phase space that predicts the wormholes development and dissolution phase. Our results show that wormholes have a significant impact on the enhanced oil recovery performance resulting in a decrease in the overall oil recovery by 9.6% for portions of the reservoir that experience wormholing. In real field applications, it is recommended to avoid creating wormholes over large portions of the reservoir affected by acid injection as it may jeopardize the field development outcome leaving an unspecified amount of oil in virgin regions in the reservoir which results in additional operational complications. Wormholes are only beneficial near the wellbore for wellbore cleanup and matrix treatment purposes thus providing easier access to the reservoir. However, care needs to be taken to constrain wormhole formation to skin factor reduction and avoid far-reaching wormholes in the reservoir. Cited as: Alarji, H., Clark, S., Regenauer-Lieb, K. Wormholes effect in carbonate acid enhanced oil recovery methods. Advances in Geo-Energy Research, 2022, 6(6): 492-501. https://doi.org/10.46690/ager.2022.06.06

Inorganic Acid Optimizes Remediation of Formation Damage in Carbonate Producer

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208185, “Single-Phase Retarded Inorganic Acid Optimizes Remediation of Drilling Formation Damage in High-Temperature Openhole Horizontal Carbonate Producer,” by Ahmed Mohamed Fawzy, Noor Nazri Talib, SPE, and Ruslan Makhiyanov, SPE, ADNOC, et al. The paper has not been peer reviewed. Emulsified acid is one of the preferred choices among retarded-acid options used in Middle East high-temperature carbonate producers. However, it also brings operational complexities. The recent introduction of a single-phase retarded inorganic acid system (SPRIAS) has enabled stimulation with the same benefits as those of emulsified acids while eliminating its drawbacks. A newly drilled oil producer in one of the largest carbonate fields onshore Middle East was selected for pilot implementation of the SPRIAS. The experience gained with this pilot well confirmed the SPRIAS as a reliable option to replace emulsified acids in the region. SPRIAS The SPRIAS has the dissolution capacity of hydrochloric acids (HCl) of similar concentration. It also has a retardation factor equivalent to that of emulsified acid, which allows the creation of wormholes just as deep into the formation. Such a retardation effect was demonstrated through numerous pore-volume-to-breakthrough (PVBT) coreflow experiments at downhole conditions. Fig. 1 shows such a PVBT experiment with 15% HCl, emulsified acid, and a SPRIAS of similar HCl acid concentration on a 1-in.-diameter×6-in.-long, 8-md Indiana limestone core at 250°F. The PVBT of the emulsified acid and SPRIAS are significantly smaller than that of HCl and are statistically similar. Because it is not an emulsion but a single-phase aqueous fluid, the SPRIAS also has a viscosity within the same order of magnitude as HCl. This allows the SPRIAS to be pumped at higher rates than retarded emulsified acid. For the application discussed in this study, the SPRIAS was selected to improve the stimulation of the tighter part of the wellbore because the retarded-acid system can develop deep wormholes at low injection rates.

A Numerical Approach to Investigate the Impact of Acid-Asphaltene Sludge Formation on Wormholing During Carbonate Acidizing

AbstractCarbonate acidization is the process of creating wormholes by injecting acid to increase reservoir permeability and oil production. Nevertheless, some reservoir oils are problematic with low asphaltene stability, which affects the wormholing process. The interactions between acid, rock, and asphaltene lead to acid-asphaltene sludge formation, which reduces oil productivity and acid injectivity. Neglecting this sludge formation leads to over predicting the depth of the wormhole penetration. Therefore, a numerical model was developed in this study to provide a better understanding of acid-asphaltene sludge formation effect on wormhole creation and propagation in carbonates. A one-dimensional radial model was developed by coupling fluid flow equations in porous media with asphaltene deposition and acid-asphaltene reactions. Then, the developed model was validated and utilized to investigate the effects of different parameters on wormholing including asphaltene presence, acid injection volume and concentration, formation temperature and porosity, and asphaltene concentration. Results showed that acid injection in carbonates with asphaltenic oils reduce wormhole penetration from 40% to total pore blockage as opposed to reservoirs without asphaltene deposition. The findings also highlighted that shallow wormhole penetration is more pronounced with a high volume of acid injection, high porous formations, less diluted acid, and a high concentration of asphaltene. In addition, there is an optimum acid injection volume at which wormhole penetration is high and its infiltration is deep into the formation. This is the first work to discuss modeling of acid-asphaltene sludge formation and subsequent wormhole development in carbonates, which is particularly important for problematic crude oils.

Feasibility of limestone reservoirs as a carbon dioxide storage site: An experimental study

Carbon capture and storage technology is a means to permanently store carbon dioxide (CO2) in suitable geologic formations, such as depleted oil and gas reservoirs and saline aquifers. The potential of depleted carbonates reservoirs for being a secure storage site has been assessed in several studies based on the key storage aspects. However, minor attention has been given to rock type and the potential compaction of carbonates at different injection rates when geochemical interactions posed by supercritical CO2 reduces their elastic properties and strength. In this study, limestone samples were tested to investigate changes in their physical and mechanical characteristics once flooded by CO2 at a very low injection rate. The results obtained indicate that an excessive pressure drop might be experienced even under a very low injection rate because of continuous dissolution of carbonates in the presence of CO2 and brine. Creation of wormholes and the dissolution of the matrix were also observed through scanning electron microscope, computerized tomography scan, and nuclear magnetic resonance tests. It was also observed that the elastic parameters and the strength of the limestone samples may significantly decrease after CO2 flooding, which might be linked to calcite dissolution and weakening of the solid skeleton.

Pore volumes to breakthrough estimation in carbonate acidizing with hydrochloric acid by using an analytical derivation method

Acidizing treatment is considered as a significant process in the oil well stimulations to form wormholes in carbonate formation in order to enhance the reservoir fluid production. Obtaining the number of pore volumes to breakthrough is an important objective in matrix acidizing, for it contributes to determining the wormhole characteristics such as type, shape, and size. Finding this number in experimental works requires a considerable amount of time, energy and cost. Therefore, this study aimed to establish an analytical method in which a reasonable result is achieved for the number of pore volumes to breakthrough. This purpose is accomplished by solely implementing acid and formation properties without performing any experimental works. The process of wormhole creation is done through developing a numerical model by utilizing the conservation of mass law method in which the carbonate core is considered as a closed system and the overall mass in the system as constant during the acid injection process. Furthermore, a constant number is added to the mathematical part of the model in order to eliminate the dimensionless Damköhler number which is supposed to be calculated experimentally. The results of the numerical procedure of the model are further compared to four other experimental works, which led to calculating the average accuracy of this model that is shown to be 95.98%. This study puts forward a comprehensive numerical model to estimate the number of pore volumes to breakthrough with an acceptable accuracy rate merely through implementing known acid and core properties.

Application of ultrasonic as a novel technology for removal of inorganic scales (KCl) in hydrocarbon reservoirs: An experimental approach

Inorganic scales are one of the most important causes of formation damage, which causes pressure drops near wellbores; these in turn impair permeability and severely reduce production in oil and gas reservoirs. This paper examines the effectiveness of ultrasonic waves in removing potassium chloride (KCl) scales. Twenty core samples with different permeabilities were exposed to KCl precipitation. After measuring the permeabilities of the saturated core samples, the samples were first subjected to water injection, and then to water injection with ultrasonic wave radiation. At each stage, sample permeabilities were measured and recorded. The results showed that water injection with two pore volumes did not significantly improve permeability, especially in low-permeability core samples. Ultrasonic wave radiation with water could efficiently improve permeability; this result is more obvious for samples with lower permeabilities. SEM images taken from thin sections of the core samples under water injection and water with ultrasonic waves showed that ultrasonic waves distorted the crystal lattice of the KCl scales, causing cracking and delamination. Creation of wormholes in KCl deposits within fractures also resulted from the application of ultrasonic waves. Analysis of chlorine in the output water from core samples in the core-flooding process showed that ultrasonic waves increased the solubility of scales in water, improving the recovery of permeability in the samples. Results of this study show that using ultrasonic waves can be considered a novel and practical method in the removal of inorganic scales in the near-wellbore region of oil and gas reservoirs.

NMR as a Characterization Tool for Wormholes

Summary Acidizing is a common practice that aims to recover the initial skin factor or even decrease it further. Acids tend to create conductive channels (wormholes) through carbonate formations that connect the reservoir to the wellbore and bypass the damaged zones. Optimum wormholes are formed when certain conditions are met, such as optimum acid concentration and optimum injection rate. To thoroughly grasp wormhole creation, several characterization techniques should be performed. Computed-tomography (CT) scan and differential-pressure data are two practices commonly used for characterization of wormholing in laboratories by use of core-plug samples. Differential-pressure data and CT scan can verify the occurrence of acid breakthrough and qualitatively suggest the size and path of a wormhole. Nuclear magnetic resonance (NMR) was introduced in earlier studies as a new characterization tool for wormholes. NMR can detect the changes in micro- and macropores that are caused by acid injection, and it can indicate changes in interconnectivity between different pore systems and detect the materialization of formation damage induced by injected acids. However, the NMR technique cannot detect the new porosity corresponding to the generated wormhole because of an inability to sustain saturation fluids inside the core-plug samples. In this study, the NMR measuring method is further improved by use of a customized polytetrafluoroethylene (PTFE) tube as a container for core-plug samples. Because PTFE material does not interfere with NMR readings, this improvement allows the core-plug samples to maintain full saturation, which enables the detection of the new wormhole porosity. As a result, NMR can indicate different characteristics of the generated porosity, including the size of the wormhole and the changes in diffusion coupling and the distribution of each pore size. This technique can elaborate new aspects of wormhole generation and characteristics in carbonate reservoirs, in addition to assessing the damage caused by the stimulation fluid.

Evaluation of Rock Mechanical Properties Alteration During Matrix Stimulation With Chelating Agents

Well stimulation using acidic solutions is widely used to treat carbonate formations. The acidic fluids remove the near-wellbore damage and create channels around the wellbore by dissolving fraction of the carbonate rocks. Many stimulation fluids have been used such as hydrochloric acid (HCl) acid, organic acids, and chelating agents to stimulate carbonate reservoirs. Wormholes that are created by these fluids are very effective and will yield negative skin values and this will enhance the well productivity. In addition to the wormhole creation, the diffusion of these fluids inside the pores of the rock may create significant and permanent changes in the rock mechanical properties. These changes can eventually lead to weakening the rock strength, which may lead to future formation damage due to the wellbore instability. In this paper, the effect of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) chelating agents on the carbonate rocks elastic properties was investigated. The effect of wormholes created by chelating agent on the rock mechanical properties was investigated. Computed tomography (CT) scan and acoustic measurements were conducted on the core samples before and after matrix stimulation treatments. Experimental results showed that the mechanical properties of strong rocks such as Indiana limestone (IL) cores were not affected when chelating agents were used to stimulate those cores. On the other hand, less strong rocks such as Austin chalk (AC) show significant alteration on the rock elastic properties when chelating agents were used as stimulation fluids.

Tunnelling with wormhole creation

The description of quantum tunnelling in the presence of gravity shows subtleties in some cases. We discuss wormhole production in the context of the spherically symmetric thin-shell approximation. By presenting a fully consistent treatment based on canonical quantization, we solve a controversy present in the literature.

Creation of wormholes by quantum tunnelling in modified gravity theories

We study the process of quantum tunnelling in scalar-tensor theories in which the scalar field is non-minimally coupled to gravity. In these theories gravitational instantons can deviate substantially from sphericity and can in fact develop a neck - a feature prohibited in theories with minimal coupling. Such instantons with necks lead to the materialisation of bubble geometries containing a wormhole region. We clarify the relationship of neck geometries to violations of the null energy condition, and also derive a bound on the size of the neck relative to that of the instanton.

Percolation of CO2‐rich fluids in a limestone sample: Evolution of hydraulic, electrical, chemical, and structural properties

AbstractPercolation of CO2‐rich fluids in limestones causes the dissolution (and eventual reprecipitation) of calcium carbonate minerals, which affect the rock microstructure and change the rock petrophysical properties (i.e., hydraulic, electrical, and elastic properties). In addition, microstructural changes further feed back to affect the chemical reactions. To better understand this coupled problem and to assess the possibility of geophysical monitoring, we performed reactive percolation laboratory experiments on a well‐characterized carbonate sample 35 cm in length and 10 cm in diameter. In a comprehensive study, we present integrated measurements of aqueous chemistry (pH, calcium concentration, and total alkalinity), petrophysical properties (permeability, electrical formation factor, and acoustic velocities), and X‐ray tomography imaging. The measured chemical and electrical parameters allowed rapid detection of the dissolution of calcite in the downstream fluid. After circulating fluids of various salinities at 5mL min−1 for 32 days (about 290 pore sample volumes) at a pCO2 of 1 atm (pH = 4), porosity increased by 7% (from 0.29 to 0.31), permeability increased by 1 order of magnitude (from 0.12 D to 0.97 D), and the electrical formation factor decreased by 15% (from 15.7 to 13.3). X‐ray microtomography revealed the creation of wormholes; these, along with the convex curvature of the permeability‐porosity relationship, are consistent with a transport‐controlled dissolution regime for which advection processes are greater than diffusion processes, confirming results from previous numerical studies. This study shows that nonseismic geophysical techniques (i.e., electrical measurements) are promising for monitoring geochemical changes within the subsurface due to fluid‐rock interactions.

Mitigation of colluding route falsification attacks by insider nodes in mobile ad hoc networks

AbstractColluding malicious insider nodes with no special hardware capability can use packet encapsulation and tunneling to create bogus shortcuts (in‐band wormholes) in routing paths and influence data traffic to flow through them. This is a particularly hard attack using which even a handful of malicious nodes can conduct data traffic analysis of packets or disrupt connections by dropping packets when needed. Simulation analysis shows that a disproportionately large amount of traffic goes through routes with wormholes even when a secure routing protocol (SRP) such as Ariadne is used. To mitigate such attacks and augment existing on demand SRPs, distributed packet filtering techniques based on statistical profiling of control packet propagation speeds are proposed. These techniques do not require network‐wide synchronized clocks or new packet transmissions and need only simple computations by the sources or the destinations of the connections. The proposed packet filters together with Ariadne are implemented in the Glomosim simulator and their effectiveness is evaluated. The simulation results indicate that the proposed packet filters can reduce the in‐band wormhole creation and their usage by a factor of 2‐‐10. Also, the false alarm rates of the proposed techniques are very low and have little impact on normal network throughput, making them practical for mobile ad hoc networks. Copyright © 2008 John Wiley & Sons, Ltd.

An Integrated Experimental Study of Foamy Oil Flow During Solution Gas Drive

Abstract One of the important mechanisms in the primary production of heavy oil reservoirs under solution gas drive is the foamy oil flow effect. This form of flow occurs only under certain combinations of capillary, viscous, and gravity forces. Several studies have been carried out to examine this effect on the recovery process, but it remains poorly understood and difficult to model. The objective of this study was to examine the roles of capillary, viscous, and gravity forces in foamy oil flow. Primary depletion experiments were conducted in a 2 m long sand pack holder to measure the oil and gas production at different depletion rates. The effect of gravitational forces was investigated by comparing the experiments conducted in horizontal and vertical orientations of the 2 m long sand pack. In the vertical orientation, the solution gas drive performance was evaluated with production from the bottom end of the sand pack, as well as with production from the top end. The experimental results are presented in terms of the oil and gas production behaviour affected by the capillary number and gravity forces. The results indicate that the gravity forces do not significantly influence the ultimate oil recovery when the oil is produced under foamy oil flow. Even at the lowest depletion rate used in these tests, when the oil flow and gravity are in the same direction, gravity segregation of gas did not improve the oil recovery significantly. Recovery efficiency and the critical gas saturation at which free gas flow starts are primarily dependent on the capillary number. Introduction Some of the heavy oil reservoirs in the world show anomalous primary production under solution gas drive. Smith(1) was one of the first researchers who presented a detailed analysis of such unusual production behaviour. Since then, it has been the subject of many studies, due to its importance in making reliable projections of future production and optimization of field operations. These studies can be divided into three categories. The first category focuses mainly on the geomechanical aspects(2, 3). It is believed that the production of sand with oil improves the inflow performance by creating wormholes (high permeability channels). Experimental and theoretical studies(3, 4) have shown that the high pressure gradients present during cold production can overcome the cohesive strength of the sand matrix and this leads to the creation of wormholes. However, the mechanics of wormhole network development are not yet clear. The second category focuses on multiphase flow behaviour, and can be further divided into two subcategories. First, there are the conventional two-phase flow models(5, 6), which suggest that solution gas drive, whether in light oils or in heavy oils, is describable by the critical gas saturation and oil-gas relative permeability. In these, the high oil recovery is attributed mainly to low gas mobility. However, a good history match of the field performance is not obtained by using low gas mobility; it also requires enhanced permeability far from the wellbore due to sand production(7).

A geochemical reaction-transport simulator for matrix acidizing analysis and design

A new two-dimensional geochemical simulator, CIRF.A, and its application to matrix acidizing analysis and design are presented. The simulator is based on the solution of the equations of fully coupled fluid flow, species transport and rock/fluid reactions and includes the effects of grain growth/dissolution and the alteration of porosity and permeability due to mineral reactions. Our program has a large built-in thermodynamic and kinetic database. The simulator is tested by laboratory core acidizing results. It is demonstrated that simulation results are in good agreement with experimental observations. Both laboratory and simulation results indicate that an acidizing treatment may induce formation damage due to the precipitation of byproducts from the reactions of acids with rock minerals. A series of simulation runs have been carried out under different conditions to determine the strategy for minimizing the acid induced formation damage. High injection velocity and higher acid concentration are shown to reduce mineral precipitation and formation damage. The simulator is also used to predict permeability and productivity improvements for typical acid treatments of undamaged and damaged wells in sandstone formations. Our simulator is shown to be capable of simulating all the sandstone acidizing procedures that include pre-flush, mud acid treatment, after-flush and back production. In carbonate formations, matrix acidizing may lead to the development of dissolution fingers and the creation of wormholes. It is demonstrated that the simulator can also capture the fingering and wormholing phenomena. We believe this new geochemical simulator is an invaluable tool for matrix acidizing analysis and design.

Carbonate Acidizing: Toward a Quantitative Model of the Wormholing Phenomenon

Summary We present the first quantitative study and complete model of the wormholing phenomenon, leading to a means of predicting and optimizing carbonate acidizing treatments. Laboratory experiments on a gypsum model system and computer simulations show that for a given geometry, wormholes can be quantified by a unique parameter, their equivalent hydraulic length. The behavior of this quantifying parameter vs. all the system parameters is studied and allows the quantitative prediction of the efficiency of an acidizing treatment. This study highlights the fractal nature of the phenomenon, which is accounted for in the equations, and the strong effect of the sample geometry. Three types of etching can be obtained: compact, wormhole type, or homogeneous. The optimum conditions for achieving die best skin decrease correspond to the creation of wormholes and can then be defined in terms of fluid reactivity and injection rate.

Wormhole creation via classical fluctuations and inflating worlds

It is shown that wormhole creation via classical fluctuations, being a necessary condition for an inflating world to appear accidentally, is compatible with global geometry constraints provided this process starts at the initial T +-region of space-time.

Creation of Wormholes by First Order Phase Transition of a Vacuum in the Early Universe

Creation of Wormholes by First Order Phase Transition of a Vacuum in the Early Universe