Damaged Formation Research Articles

Adjacent rock mass damage in influence zones of stopes with rock bolt support and shotcrete lining

Heading and stoping in mines change the stress–strain behavior of adjacent rock mass, which can lead to adverse consequences, including the limiting state of rocks and formation of damaged zones. The damaged zones appear not instantly but are associated with mining operations. The parameters of the damaged rock zones depend on geotechnical conditions of stoping, on mechanical properties of rocks and on the stoping impact. Natural structural discontinuities in rock mass even more complicate calculations. Traditionally, the size of the damaged zones is controlled via mine support installation. However, in hard rocks, efficiency of mine support systems is not so high. This article presents an analytical solution on the support design and conditions to ensure that no damaged zones arise in adjacent rock mass. The analysis of the physical, mechanical and structural properties of rock mass, typical of mines of Apatit’s Kirovsk Branch of allowed reliable numerical modeling and comparison of sizes of damaged rock zones in various stopes without support and with rock bolting and shotcrete lining. The damaged zone pattern in adjacent rock mass around an arched stope is analyzed as a case-study of mines of Apatit’s Kirovsk Branch, and the effect of the rock bolt support and shotcrete lining on the size of this zone is determined. The calculations show that in the discussed geological conditions, the use of mine support reduces the size of the damaged zone by 7–20 %, which helps optimize the support design and expands its application field but fails to totally eliminate damaged zone formation. The mechanical properties and structural discontinuities in rock mass have a serious effect and should be in spotlight of the analysis.

Component deformation-based collapse evaluation of RC frameunder different collapse criteria

Developments in performance-based earthquake engineering have emphasized the importance of evaluation of structural collapse resistance. Several collapse criteria were proposed to define structural collapse in various perspective. In this paper, collapse resistant capacity of ductile reinforced concrete (RC) frame was evaluated using different collapse criteria. Since most of the criteria focus on overall structural response, a component deformation-based method was adopted to describe the damage in component level. Incremental dynamic analysis (IDA) of a 6-story ductile RC frame conforms to current codes was conducted in OpenSEES. The collapse resistant capacity under different collapse criteria was compared. Moreover, relationship between overall structural response and the distribution of damaged components were discussed through the component deformation-based method. It was indicated that the story of maximum inter-story drift ratio is neither consistent with the one which is most seriously damaged nor with the story of maximum residual inter-story drift ratio. Furthermore, the component deformation-based method can depict structural damaged state and formation of collapse mechanism more reasonably. The analysis result evidences that structure conforms to current code have the good ductility and hardly reaches physical collapse under rare earthquake, however, the structure is more likely to be demolished due to unacceptable residual deformation.

Evaluation of residual defects created by plasma exposure of Si substrates using vertical and lateral pn junctions

Defect creation in both the vertical and lateral directions of Si substrates during plasma processing has become a critical problem in the fabrication of three-dimensional structural devices. In this study, the authors present pn junction structures that can be used to evaluate defects in both the vertical and lateral directions of a Si substrate. Samples with these pn junction structures were exposed to fluorocarbon plasma; after plasma exposure, a chemical dry etching process was employed to determine the influence of residual species on damaged layer formation, and capacitance–voltage measurements were conducted to detect the formation of defects in the Si substrate. The results confirmed that defects created by plasma exposure act as carrier trapping sites. Spectroscopic ellipsometry and time-of-flight secondary ion mass spectrometry revealed that the damaged layers were tens of nanometers thick, and cathodoluminescence analysis identified the presence of “latent” defects in the damaged layer even after furnace annealing. Moreover, current–voltage measurements of devices with different pn junction distances revealed that leakage current in both the vertical and lateral directions increased with decreasing pn junction distance. The experimental results of this study demonstrate that plasma-induced damage (PID) creates defects in both the vertical and lateral directions; lateral defects are assumed to be caused by the stochastic straggling of incident ions, which has been predicted by molecular dynamic simulations. The implementation of devices with lateral pn junctions is essential in improving the understanding of PID mechanisms and designing future electronic devices that are sensitive to latent defects.

Approach-to-magnetic saturation of Fe nanoparticle/nanorod encapsulated multi-walled carbon nanotubes under heavy ion irradiation

Effects of irradiation with swift heavy ions at different fluences on the structural and magnetic properties of multi-walled carbon nanotubes filled with Fe nanorods and nanoparticles (Fe-MWCNTs) are investigated. An up-shift in the ‘G’- band of the Raman spectra with the increasing fluence designates the development of stresses in Fe-MWCNTs. During the ion-irradiation, the disorder parameter that signifies the defect concentration initially decreases at lower fluence and then picks-up with a further rise in fluence. Structural characterization by electron microscopy reveals damaged walls and formation of defects in Fe-MWCNTs irradiated at the highest fluence. The average diameter of Fe-MWCNTs inferred from high-resolution TEM shows a reduction from 56 (±2) nm to 36 (±2) nm upon increasing the irradiation fluence from 5 × 1012 to 1 × 1014 ions/cm2. The ferromagnetic character of Fe nanoparticles/nanorods embedded in the MWCNTs swamps the diamagnetic nature of bare MWCNTs and hence a saturation behaviour in magnetization is seen for the Fe-MWCNTs. A significant reduction in the saturation magnetization (≈20%) is observed in the ‘irradiated’ Fe-MWCNTs when compared to their ‘as-prepared (pristine)’ counterparts and is attributed to the increase in surface disorder and weakening of exchange interactions upon irradiation. The coercive field follows a monotonous thermal decline in both ‘pristine’ and ‘irradiated’ Fe-MWCNTs. Contrary to the expectation, the coercivity of the ‘irradiated’ Fe-MWCNTs is less than nearly half the value for ‘pristine’ samples, in the entire temperature range 2 K–300 K.

Indústria cultural e semiformação: democracia e educação sob ataque nos países ibero-americanos à luz da teoria crítica

This essay aims to reflect, based on the foundations of the Critical Theory of Society, about cultural industry and semi-formation (Halbbildung) in the context of Ibero-American countries. The concept of cultural industry not only remains relevant, but it is fundamental to understanding semi-formation or damaged formation. The reflection is anchored in M. Horkheimer, T. W. Adorno and H. Marcuse, first generation thinkers of the Frankfurt School. Formation (Bildung), as assumed by these authors, can provide the necessary substrates for the praxis of resistance to the process that prevents the flourishing of autonomous individuality, in which democracy has been attacked.

Isocostunolide inhibited glioma stem cell by suppression proliferation and inducing caspase dependent apoptosis

Glioblastoma multiform (GBM) is a highly aggressive brain tumor with poor life expectancy, and glioma stem cells (GSCs) are a small population of tumor cells existed in GBM, in which GSCs response to drive GBM recurrence, invasion and contribute to the anti-cancer resistance. GSCs have been identified and developed as a therapeutic target for GBM and can be used in drugs screening. Isocostunolide is a natural sesquiterpenoid and contained abundant resource in medicinal plants, but the anti-cancer efficacies of it against GSCs are still unexplored. In this investigation, the anti-tumor activity of isocostunolide against GSCs was investigated and the result demonstrated that it inhibited the growth of GSCs (GSC-3#, GSC-12#, GSC-18#) significantly with an IC50 value of 2.80μg/ml, 2.61μg/ml, 1.07μg/ml, respectively. In further mechanism study, isocostunolide inhibited GSCs cell proliferation, induced GSCs apoptosis significantly, as well as increased the proportion of the cleavage of caspase-3. The result suggested that isocostunolide induced GSCs apoptosis via the caspase dependent apoptotic pathway. Moreover, isocostunolide damaged GSCs colony formation capacity significantly and exhibited the anti-cancer efficacy against GSCs in vitro.

No-Damage Stimulation By Use of Residual-Free Diverting Fluids

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 177495, “No-Damage Stimulation Based on Residual-Free Diverting Fluid for Carbonate Reservoir,” by Y. Shi, X. Yang, F. Zhou, Y. Gao, S. Lian, X. Li, and X. Han, Research Institute of Petroleum Exploration and Development, CNPC, prepared for the 2015 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 9–12 November. The paper has not been peer reviewed. Horizontal wells and acid stimulation are essential technologies for the development of complex carbonate reservoirs. However, conducting effective stimulation in horizontal wells with long intervals is extremely difficult because traditional acid systems can flow only into the high-permeability formations, leaving the damaged formation untreated. This paper studied three residual-free fluid systems for acid treatments and fracturing in order to develop no-damage or reduced-damage and highly effective stimulation techniques for long-interval wells. Introduction Horizontal wells are essential for the development of carbonate reservoirs in China. However, horizontal wells always have long intervals, so they are extremely difficult to stimulate. The fluid systems used are a critical aspect of high-efficiency stimulation. Traditional acid systems, which do not have diverting capabilities, can flow only into the high-permeability formations, leaving the damaged formation untreated. That is why long-interval wells with high heterogeneity need to be treated by a diverting acid system. A new diverting acid system should have the following characteristics: The capability to reduce the acid/rock reaction rate; a diverting performance to achieve uniform stimulation in a carbonate reservoir with high heterogeneity; and use of clean chemical additives to eliminate or limit damage. This paper analyzes three clean fluid systems for acid treatment and fracturing. The no-damage stimulation systems considered are a temperature-controlled deep-diverting acid system (TCA), a pH-controlled self-diverting acid system (DCA), and a fracture-reorientation technology using degradable fiber (RDF). TCA Diverting Mechanism of TCA. The TCA system is similar to ordinary gelled acid during pumping. The gelling agent can dissolve in water in a short time, reducing the frictional resistance of the system dramatically and making it easy to prepare and pump. At formation temperature, the system has a high viscosity to ensure diverting and retarding performance. After the acid fracturing treatment, the viscosity of the spent acid decreases in order to flow back easily and leave no damage in the formation.

Integrated Experimental and Analytical Wellbore Strengthening Solutions by Mud Plastering Effects

Wellbore stability has plagued oil industry for decades. Inclusion of the mud in drilling and the effect of mud cake build up incorporate very complex chemical, thermal, mechanical, and physical phenomena. It is very difficult to quantify all these phenomena in one model. The after effects of mud cake buildup, its permeability and variation in thickness with time alter the actual stress profile of the formation. To see the impact of the whole mechanism, a combination of laboratory studies and numerical modeling is needed. This paper includes the procedure and results on stress profiles in near wellbore region based on laboratory studies of mud cake buildup in high pressure and high temperature environment using permeability plug apparatus (PPA). The damaged formation zone is very susceptible to drilling fluid and results in alteration of existing pore pressure and fracture pressure. This paper presents integrated experimental and analytical solutions for wellbore strengthening due to mud cake plastering. Conducting experiments on rock core disks has provided more realistic results which can resemble to field conditions. The experimental work here provides an insight to effect of mud cake build up at high pressure and high temperature conditions using a heterogeneous filtration medium prepared from different sandstone cores. Results were used in the analytical model to see the effect of stresses in the formation. The primary objective is to investigate the wellbore hoop stress changes due to formation of filter cake by mud plastering using the analytical models built upon the laboratory results. The models developed in this work provide insights to quantify on wellbore plastering effects by mud cake build up.

Improvement of Minority Carrier Lifetime by HCN Treatments

We have developed a method of improving minority carrier lifetime by use of HCN treatments. Metal contaminants, Fe, Ni, and Cu, are introduced during slicing Si ingots to produce Si wafers, and also during alkaline etching processes for removal of a damaged layer and formation of mat-textured surfaces. The concentrations of metal contaminants are greatly decreased by cleaning with HCN solutions having pH of 12, while they are decreased only slightly by pH 9 HCN solutions. Two kinds of metal contaminants, i.e., contaminants present deeply in saw damaged regions and on the surface due to re-adsorption during alkaline etching, can be removed by pH 12 HCN solutions while only the latter can be by pH 9 HCN solutions. The minority carrier lifetime is increased by removal of a damaged layer by alkaline etching but decreased below that of as-sliced wafers after formation of mat-textured surfaces. The lifetime is increased by the HCN treatment and it is attributed to i) removal of metal contaminants and ii) passivation of interface states by the formation of Si-CN bonds from Si dangling bonds.

Modeling of plasma-induced damage and its impacts on parameter variations in advanced electronic devices

A comprehensive model predicting the effects of plasma-induced damage (PID) on parameter variations in advanced metal–oxide–semiconductor field-effect transistors (MOSFETs) is proposed. The model focuses on the silicon recess structure (Si loss) in the source/drain extension region formed by high-energy ion bombardment during plasma etching. The model includes the following mechanisms: (1) damaged layer formation by ion impact and penetration, (2) Si recess structure formation by a subsequent wet etch, (3) MOSFET performance degradation, and (4) MOSFET parameter variation. Based on a range theory for plasma-etch damage, the thickness of the damaged layer exhibits a power-law dependence on the energy of the ion incident on the surface of Si substrate. Assuming that the damaged layer was formed during a gate or an offset spacer etch process, the depth of Si recess (dR) is a function of the depth profile of the created defect site (ndam), the wet-etch stripping time (tw), and the energy of the incident ion. It was found that dR also showed a power-law dependence on the average ion energy E−ion estimated from applied self-dc-bias voltage for various tw. As for MOSFET performance degradation, the threshold voltage (Vth) shifted and the shift (ΔVth) increased with an increase in E−ion and a decrease in gate length. This induces an increase in subthreshold leakage current (Ioff) for MOSFET. Technology computer-aided-design simulations were performed to confirm these results. By integrating the presented PID models, parameter variations could be predicted: Using a Monte Carlo method, it was demonstrated that PID increases parameter variations such as Vth and Ioff. It also was found that the variation in E−ion induces Vth and Ioff variations, comparable to that induced by other process parameter fluctuations such as dopant fluctuation and gate length. In summary, considering the effects of PID on parameter variations is vital for designing future ultralarge-scale-integrated circuits with billions of built-in MOSFETs.

Random Sequential Adsorption Model of Damage and Crack Accumulation: Exact One-Dimensional Results

The random sequential adsorption (RSA) model is modified to describe damage and crack accumulation. The exclusion for object deposition (for damaged region formation) is not for the whole object, as in the standard RSA, but only for the initial point (or higher-dimensional defect) from which the damaged region or crack initiates. The one-dimensional variant of the model is solved exactly.

649. Effects of GIT1on Human Neuronal (NT2N) Cells

Top of pageAbstract Mature mammalian neurons, except for olfactory neurons, are incapable of cell division. Promoting the regeneration of degenerated adult neurons is a major goal in neurological science. The human teratocarcinoma cell line (NTera 2 or NT2) is capable of neuronal differentiation following treatment with retinoic acid. These neurons (NT2N cells) have a stable neuronal phenotype. The effect of GIT1 overexpression in human NT2N cells was evaluated using an adenoviral vector. A recombinant GIT1 and GFP adenoviral vector (AdEGFP-GIT1) was constructed. The biologic activities of GIT1 were assessed according to the induction of neuronal spine formation, cell migration, and the amounts of GAP-43 and active Cdc42. Cells treated with AdEGFP-GIT1 were compared to untreated cells and to cells treated with AdEGFP. NT2N cells in the AdEGFP-GIT1 group demonstrated more spine formation and higher numbers of migrating cells than that either cells treated with AdEGFP or untreated NT2N cells. GAP-43 and active Cdc42 were quantified by dot ELISA method. The results showed that the amount of GAP-43 and active Cdc42 in the AdEGFP-GIT1 group was much higher than in AdEGFP and untreated NT2N groups. In conclusion, GIT1 overexpression promotes spine formation, migration, and expression of the growth factor GAP-43 and active Cdc42. The GIT1/|[beta]|-PIX/Cdc42/PAK pathway may play an important role in the biological activities of neurons. GIT1 also stimulates GAP-43 expression which may help promote regeneration of damaged axons and formation of new synapses. Therefore, GIT1 may have potential in the treatment of nerve injury.

Optical effects of metallic mirror surface modification

Abstract The optical effects of radiation damage on metal mirrors of MeV- and keV-range ions have been examined. Al, Cu and Cr ion beams of 1–3 MeV energy were used to bombard Al, Cu and stainless steel mirrors respectively with doses spanning 10–25 dpa. The effects following long-term sputtering with keV-range ions of hydrogen plasma (or deuterium) on mirror reflectivity R in the UV and visible spectral regions were investigated. The modifications of two stainless steel mirrors' optical properties induced by the deposition of different thicknesses of B layers have also been studied. The ex situ ellipsometric data for multiple angles of incidence (within the interval from 64 to 80°) were recorded at a wavelength of λ =632.8 nm, before both ion irradiation and boronization and after the treatment. It was found that even short keV-range ion bombardment of Al mirrors drastically changed their reflectivity at any given wavelength, in contrast to a stainless steel mirror. The boronization resulted in noticeable changes of the optical constants in the UV. The optical constants of the boron film on the stainless steel substrate ( n =2.53, k ≈0), with thicknesses d ( d =7.3 and 16.6 nm), were calculated from the ellipsometric data. The IR ellipsometric measurements within the frequency range 400–5000 cm −1 were performed for stainless steel mirrors pre-irradiated by Cr ions and then coated by B to clarify the damaged layer formation mechanism. The ellipsometric changes have been attributed to both modification of the metallic mirrors' surface mirror relief and the formation of a skin layer with better conductivity after ion treatment.

Structural damage accumulation and stable postcritical deformation of composite materials

The macroscopic failure of composite materials is preceded by complex multilevel processes accompanied by accumulation and localization of damaged centers and formation of a failure cluster. Therefore, the study of these mechanisms is one of the basic problems for the mechanics of modern composite materials used in aerospace engineering. The formation of a theory of the stable postcritical deformation of the work-softening media is considered. The pseudo-plastic deformation affected by structural damage of granular composites is investigated within the framework of the considered two-level structurally phenomenological model of heterogeneous media. The stable evolution of the interconnected processes is accompanied by stress redistributions, partial or complete unloading, and strain or damage localization that are one of the main causes of implementation of the postcritical deformation stage. The numerical calculation results of inelastic deformation and failure of the periodic unidirectional fiber-reinforced composites are presented under conditions of the displacement-controlled transverse proportional loading mode. The main mechanisms of the work-softening behavior for the indicated type of materials are described in the macro-homogeneous stress-strain states. Macroscopically, the failure of heterogeneous media as a result of postcritical deformation and the loss of stability of damage accumulation depends on the stiffness of the loading system. When a deformable body is fixed on the closed surface with sufficiently but not infinitely large coefficients of stiffness, it is possible to observe the equilibrium development of the localized volumes of work-softening and damage. The constitutive equations for the work-softening isotropic, transverse isotropic, and orthotropic media are presented. The effect of the loading system on the stability of deformation, damage accumulation, and failure under monotone and nonmonotone triaxial loading was studied. The growth of failure strains with increase in stiffness of the loading system and unequal resistance of heterogeneous body are registered and investigated. A preventive unloading method is offered for the mathematical modeling of the damage accumulation during the testing of the materials on the servo-controlled systems. The displacement-controlled mode is simulated by a series of soft loading and unloading cycles. The detected phenomenon of failure where the unloading leads to stress-strain diagrams with a negative slope of the descending branch was not found either in the displacement or stress-controlled monotone loading mode.

Forecasting of rock trencher performance using a fuzzy logic approach

During geotechnical and geomechanical activities, boreholes are often drilled to investigate the detailed properties of underground formations. Some of the formation parameters, particularly transport properties such as hydraulic conductivity and storativity, are then determined by carrying out hydraulic testing in the boreholes. Conventional methods for interpretation of such borehole tests usually assume uniform formation properties, i.e. the formation is homogeneous and parameters do not change with space and time. This is often not appropriate: the formation may be damaged because of stress-induced compression, drilling breakage, drilling solids invasion, changes in saturation or wettability, fracture filling wash-out, and so on. Such processes usually result in alteration of parameters, therefore borehole test analysis results will not reflect true (far-field) formation characterization. Spurious results can affect other hydrogeological and geomechanical analyses such as underground water flow prediction, pore pressure propagation, borehole stability analysis, and slope stability. A new method is presented for damaged formation characterization based on a new constant-head hydraulic solution which considers formation alteration effects. The new solution simulates alteration effects by considering a gradual variation of permeability with radius in the form of a power relationship which contains two parameters, one to describe the alteration degree, the other to describe alteration zone size. Procedures for estimation of formation alteration characteristics by evaluating these two parameters quantitatively from constant-head test data are presented.

Evaluation of formation damage from a constant-head borehole test

Abstract During geotechnical and geomechanical activities, boreholes are often drilled to investigate the detailed properties of underground formations. Some of the formation parameters, particularly transport properties such as hydraulic conductivity and storativity, are then determined by carrying out hydraulic testing in the boreholes. Conventional methods for interpretation of such borehole tests usually assume uniform formation properties, i.e. the formation is homogeneous and parameters do not change with space and time. This is often not appropriate: the formation may be damaged because of stress-induced compression, drilling breakage, drilling solids invasion, changes in saturation or wettability, fracture filling wash-out, and so on. Such processes usually result in alteration of parameters, therefore borehole test analysis results will not reflect true (far-field) formation characterization. Spurious results can affect other hydrogeological and geomechanical analyses such as underground water flow prediction, pore pressure propagation, borehole stability analysis, and slope stability. A new method is presented for damaged formation characterization based on a new constant-head hydraulic solution which considers formation alteration effects. The new solution simulates alteration effects by considering a gradual variation of permeability with radius in the form of a power relationship which contains two parameters, one to describe the alteration degree, the other to describe alteration zone size. Procedures for estimation of formation alteration characteristics by evaluating these two parameters quantitatively from constant-head test data are presented.

Effects of Heterogeneity and Anisotropy on Probe Measured Permeabilities

Abstract Numerical simulations and laboratory experiments were used to study effects of heterogeneity and anisotropy on probe measured permeabilities. Simulation results show that the geometric factors for unsteady-state flow measurements are not different from the ones obtained for steady-state. Effects of a nearby flow barrier on probe measured permeability are studied experimentally and numerically, and it is concluded that the effect of a local flow barrier is negligible when the barrier is located farther than one-half of a probe-tip diameter from the probe. Probe measured permeability on a damaged formation is profoundly affected by the damaged zone thickness. Working with geometric factors, a methodology to obtain undamaged and damaged zone permeabilities, and damaged zone thickness is developed. To obtain such information uniquely three measurements with three different probe tip sizes are required. The effects of anisotropy on probe measured permeability are also investigated by introducing tensorial permeability for probe measurements. Several simulation runs were performed for different anisotropy ratios at various cross-bedding angles. Results are presented in the form of dimensionless parameters that can be used to determine depositional dip angle and permeabilities in the principal directions.

Neural transplantation and recovery of cognitive function

AbstractCognitive deficits were produced in rats by different methods of damaging the brain: chronic ingestion of alcohol, causing widespread damage to diffuse cholinergic and aminergic projection systems; lesions (by local injection of the excitotoxins, ibotenate, quisqualate, and AMPA) of the nuclei of origin of the forebrain cholinergic projection system (FCPS), which innervates the neocortex and hippocampal formation; transient cerebral ischaemia, producing focal damage especially in the CA1 pyramidal cells of the dorsal hippocampus; and lesions (by local injection of the neurotoxin, colchicine) of the granule cells of the dentate gyrus. Following chronic alcohol or lesions of the FCPS, transplants of cholinergically rich fetal brain tissue into the terminal areas (neocortex and/or hippocampus) restored performance almost to control levels, with a time course consistent with growth of the transplants and integration with host tissue; transplants of cholinergically poor fetal tissue (hippocampus) were without effect, as were transplants of cholinergically rich tissue into the region containing the nuclei of origin of the FCPS. Grafts of primary cells enriched in glia and cultured neuroblastoma cells into the terminal areas of the FCPS were equally effective, suggesting that there are multiple mechanisms by which neural transplants can restore cognitive function following diffuse cholinergic damage. In contrast, after ischaemia- or neurotoxin-induced damage to CA1 or dentate granule cells respectively, cholinergically rich fetal transplants into the damaged hippocampal formation were ineffective in restoring performance. After ischaemic damage, however, performance was restored by suspension grafts of CA1 cells but not by transplants containing CA3 pyramidal cells or granule cells; and after colchicine damage it was restored by solid grafts containing granule but not CA1 pyramidal cells. Furthermore, electrophysiological evidence has demonstrated functional, graft type-specific host-graft functional neuronal connectivity. Thus, restoration of cognitive function by neural transplants is possible after damage to either diffuse (cholinergic) or point-to-point (intrahippocampal) forebrain systems, but the transplant must be appropriate to the damage to be repaired. Because the different types of brain damage studied provide analogues of human alcoholic dementia, Alzheimer's disease, and heart attack, these results are encouraging with regard to the eventual application of neural transplant surgery to the treatment of cognitive deficits in humans.

Damage Caused By Clay-based And Clay-free Inhibitive Fluids In Sandstone Formations

Abstract This paper describes the results of a research project on the extent of damage caused by clay-based and clay-free inhibitive fluids in two consolidated sandstones of permeability ranges 0.008-0.013 µm2 (D) and 2.2-2.6 µm3 (D) under simulated borehole conditions using a closed loop circulating facility. The fluids, containing K +, Mg + +, or Ca + + ions as well as clays, solid bridging materials and different polymers, can be used either as drilling fluids or as workover, fracture and gravel pack fluids. The damage was studied on the basis of two factors, viz. damage ratio (DR) (percentage of original permeability lost after encountering the fluids) and sectional damage ratio (SDR) (determined by cutting the damaged core into several segments and then determining the damage ratio of each segment relative to the original permeability of the core). The sectional damage ratio is used to determine the radius and extent of damage in the formation. The dynamic filtration characteristics and the rheological properties of the used fluids were also evaluated. The effect of increasing the temperature and differential pressure on formation damage and filtration characteristics of the sed fluids were also investigated. The effect of the presence of formation pore bridging materials (viz. chalk) in decreasing the extent of damage is also demonstrated here. Introduction During the short phase of "mud spurt." a mud loss occurs in "overbalanced" drilling as a result of the positive differential pressure Δp. The mud spurt continues as long as free faces of the fommtion are available. After the building of the inner and/or outer "filter cake" only the filtrate can dissipate into the formation. In the mud spurt phase, the introduction of the solids into the formation, the changed conditions of fluid saturation in formation pores. solubilization of some of the materials from the rock matrix into [he filtrate and transportation of finer solids into the formation to a wide distance contribute to the reduction of formation permeability and hence well productivity; thus, the formation is deemed damaged. In addition to drilling, filtrate invasion and solid transport can occur during other well operations, such as well cleaning, fracturing and gravel Packing, which result in formation damage. This paper reports on the results of investigations into the extent of damage caused by some clay-based and clay-free inhibitive fluids containing cations and formation pore bridging materials in two consolidated sandstones. The effect of temperature and differential pressure as damage influencing factors were also investigated. The damage was evaluated using mostly 1–5% KCI-solution saturated cores and in some cases, oil saturated cores. Theoretical Background The reduction in the productivity of a well through contamination by drilling and treating fluids has been defined as formation damage. The productivity of a damaged formation is given by Muskat(6) as: Equation (Available In Full Paper) This equation shows that the productivity of a particular well in a formation depends upon two factor, viz. kd (permeability of the damaged formation) and rd (radius of the damaged zone).

A Novel Procedure to Increase Well Response to Matrix Acidising Treatments

ABSTRACT Matrix acid treatment design in clastic formations has traditionally been based on field experience or core-flushing tests. The choice of stimulation fluid compositions has frequently been limited to full-strength (12% HCl/3% HF) or half-strength (6% HCl 1.5% HF) mud acid. These practical rules of thumb have given good results but have not always ensured an optimum acid/rock reaction, i.e. the maximum net dissolution of the rock minerals and impairment coupled with a minimum of secondary precipitate formation. This paper shows how mathematical modelling of the chemical equilibria using a thermodynamic simulator can identify the ideal acid formulation, even when cores are not available. The input for the simulator is the mineralogical composition of the formation (from cuttings, sidewall samples or cores), the nature of the inorganic damage and the rock's porosity-permeability relationship. Chemical equilibria are calculated for different acid compositions taking into account the dynamic nature of the acidising process: the drop in acid strength during reaction with the damaged formation, and the changing rock composition due to attack by the acid. The results are translated via the porosity-permeability relationships into a theoretical well-productivity improvement factor. The acid composition which gives the highest productivity improvement is the optimum or Specially Formulated Mud Acid (SFMA) composition. It is important to note that the SFMA concept is not limited to HCl or HCl/HF acid formulations, but can also deal with other types such as Buffer Regulated HydroFluoric Acid (BRHFA). It will be shown that different rock compositions lead to very different SFMA formulations. SFMA recipes have been tested in core-flushing experiments, and have been found to give better performance than standard mud-acid recipes. The procedure was further validated by analysing the spent fluids regained by back production after field treatment. Field case histories in which improved production results were achieved using the SFMA approach are described.