A Laboratory Study to Better Understand the Formation Damage Using Colored and Fluorescent Particles

Formation damage is still a controversial subject within the industry especially when it takes place during Produced Water Re-Injection (PWRI). However, there is a consensus that formation damage results from a complex interaction between water quality, petro-physical and rock mechanical properties of the reservoir as well as the well architecture and completion. A lot of experimental work has been made in these last decades to understand and quantify the main mechanisms, parameters governing formation damage due to PWRI and the literature in this domain is plentiful. Nevertheless, a lot of questions are left unanswered particularly when it is a question of unconsolidated sands. This paper describes a core-flooding program performed with sand packs at different permeabilities, variable water qualities and injection conditions. Experiments were performed by injecting well-characterized system that contains either solid particles, mono-sized oil droplets or both of them at various sizes and proportions. It was shown that for mixture of solid and oil particles, the damage approach based on flow of solid suspensions alone doesn't apply and solid particles-oil droplets interaction is to be considered. This paper also details the role of each of the produced water components, their interaction and deposition within the core as well as the subsequent damage they induce. More generally, answer to some practical questions would be provided like: Do solid particles act by their size or concentration? Is oil in water content a key factor? How and where solids and oil deposit? Is there a critical concentration of solid particles and/or oil allowing injecting always in matrix regime and avoid fracturing unconsolidated reservoirs which often lie at shallow depths and in which fracturing can induce cap rock integrity and injection confinement issues? Would it be possible to control formation damage by controlling the injection conditions (flow rate, water salinity, etc…)? The answers provided here would give practical rules to help in adequately designing and optimizing PWRI projects.

Recently it has been shown that the presence of residual oil in a formation can have a considerable influence on the trapping mechanisms for particles present in re-injected produced water (Ali 2007, Ali et al 2005, 2007, 2009). This article reports on a further set of extensive coreflow experiments which confirm and extend these results. The tests were conducted in a CT-scanner, allowing direct observation of the build-up of particle deposition along the core. These experiments are relevant to operational issues associated with PWRI (Produced Water Re-Injection). In many cases, produced water is injected into formations containing oil, so reduced oil saturation is achieved rapidly in the area around the well. Even if the well is outside the oil zone, trapped oil droplets are always present in produced water, and a residual oil zone will gradually build-up around the well. Major differences are found between the deposition profiles for fully water saturated cores and the cores having residual oil saturation. In particular, particles penetrate deeper into the core with residual oil saturation and considerably more particles pass completely through the core without being trapped. The X-ray technique allows direct observation during the experiment of the deposition process inside the core, eliminating the complicating effect of any external filter cake. As a result, an analysis can be performed of the deposition parameters relevant inside the core, using Deep-bed Filtration Theory, and the results of this analysis are presented. In particular, it is shown that the values of the filtration function determined from the CT-scan (X-ray) data are consistent with those obtained from analysis of the effluent concentration. Moreover, both methods of analysis find quite clearly that the filtration coefficient increases with decreasing flowrate. The results indicate that formation damage near a wellbore during water injection will be reduced by the presence of residual oil, and that particles will penetrate deeper into the formation. The result is also relevant to injection under fracturing conditions, since particle deposition in the wall of the fracture (where residual oil may be present) is one of the mechanisms governing fracture growth.

Evaluation and comparison of different models for asphaltene particle deposition in flow streams

Water injection under fracturing conditions is an important method to overcome the production decline caused by the injectivity loss in reservoirs with strong formation damage. Also, the modeling of injectivity loss and fracturing processes is subject of several studies, and the effects of the reservoir properties over the model performance become significant. Quantification of these effects, by means of technical and economical performance indicators is important for the injection project dimensioning and to determine the efficacy and viability of the injection process to be implemented. The objective of this work is to quantify the effects of directional permeability anisotropy, using Sweep Efficiency and Net Present Value (NPV) as study parameters, on the production performance during a waterflooding under fracturing conditions, in which the injectivity loss is represented by an analytical decline equation, and a virtual horizontal well is used to represent the fracture growth. The results show the applicability of water injection under fracturing conditions. Also, it can be established the importance of reservoir properties into the injectivity loss and fracture propagation models, and the significance of the Recovery Factor (RF) and NPV in the determination of these effects. Finally, is showed the relation between the permeability anisotropy degree and production parameter, and its importance in the waterflooding behavior. Introduction Water injection under fracturing conditions allows overcoming the effects of the injectivity loss due to formation damage in reservoirs. Besides, it is the most common method for additional oil recovery used worldwide and its use represents about 80% of all recovery methods. Sigh (1982) states that water injection involves different variables that influence the flood performance, the facilities dimensioning, and the economic performance of a waterflooding project. The injectivity loss phenomenon, mainly due to the formation damage caused by the solid particles deposition, implicates continuously rise the bottom-hole pressure to maintain a constant water rate. Typically, the operational limit for injector bottom-hole pressure is the fracture pressure. Nowadays, an option to combat loss injectivity is to increase the injection pressure above the formation fracturing pressure creating high conductivity channels (fractures). One possible problem related to this procedure is the possibility of the fractures to intercept producing wells yielding high water production and low recovery factors. Due to complexity and number of variables involved in water injection above formation fracturing pressure, the use of simulation tools is important to allow monitoring the growth of the fractures and their effect in the performance of the reservoir during the process of water injection. Besides, recent studies are focused in different aspects as fracture mechanisms, modeling and fracture effects in the reservoir performance (Van den Hoek (2004), Gadde et. al. (2001)). To model those effects, the fracture behavior must be reproduced in the flow simulator and its effects in the behavior of the production during the process of injection of water. It is also necessary to model the injectivity loss.

Injectivity decline during PWRI originates not only from filter-cake build-up, but also from in-depth deposition of oil droplets or solid particles. Physical modelling of particle deposition mechanisms in porous media is thus of key interest for optimizing PWRI operations. The present work brings new insights on oil droplets and solid particle deposition mechanisms in porous media. The experimental conditions were selected such as the ratio between pores and particle sizes is sufficiently large to ensure in-depth propagation. The parameters are: the nature of the particles injected and a Peclet number calculated on the size of the collector grains (Peg), that encompasses in a nondimensional form the impact of both flow rate and particle size. The results are analysed in the frame of the "colloidal approach". For oil droplets and solid particles, the deposition efficiency (n) shows a transition from a behaviour in which nvaries as a power-law of Peg, with exponent values -2/3 (Diffusion Limited Deposition, DLD) to -1 (Reaction Limited Deposition, RLD), characteristic of convection-diffusion regime, to a behaviour characterized by an increase of η versus Peg, characteristic of hydrodynamic deposition regime. In the case of oil droplets (not or slightly charged), the transition occurs at a critical Peg value, Pegcgeom, corresponding to a diffusion layer thickness around the collector grain equal to the droplets diameter. In the case of electro-sterically stabilized solid particles, the transition takes place at Peg<Pegcgeom for small particles and at Peg<Pegcgeom for larger particles.

Although ophthalmic viscosurgical devices are quite important for safe cataract surgery, currently, postoperative residual ophthalmic viscosurgical devices can cause various complications. Previously, we developed a method to visualize residual ophthalmic viscosurgical devices after irrigation/aspiration in vitro and found that the amount of residual ophthalmic viscosurgical device on a single-piece intraocular lens was greater than that on a three-piece intraocular lens. In the present study, we compared the amounts of residual ophthalmic viscosurgical device among various foldable intraocular lenses to investigate the factors that determine the quantity of residual ophthalmic viscosurgical device. Simulated cataract surgery was performed in pig eyes using an ophthalmic viscosurgical device labeled with fluorescent silica particles. After the simulated surgery procedure, the fluorescent silica attached to the intraocular lens was observed and quantified by inductively coupled plasma-atomic emission spectrometry after intraocular lens removal. The amount of residual ophthalmic viscosurgical device was compared among five representative single-piece intraocular lenses and one three-piece intraocular lens. The distribution and amount of the residual ophthalmic viscosurgical device differed for each intraocular lens. The amount of silicon in the lens capsule differed among the intraocular lens types. The postoperative residual tendency of ophthalmic viscosurgical devices differed among various single-piece intraocular lenses. The behavior of the intraocular lenses within the capsule affected the residual tendency. The removal of ophthalmic viscosurgical device in the lens capsule should be tailored for each intraocular lens to improve efficiency.

Novel chromophoric and fluorescent carbonitrile-functionalized poly(vinyl amine) (PVAm) and PVAm/silica particles were synthesized by means of nucleophilic aromatic substitution of 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile (1) with PVAm in water. The water solubility of 1 has been mediated by 2,6-O-β-dimethylcyclodextrin or by pre-adsorption onto silica particles. Furthermore, 1 was converted with isopropylamine into the model compound 1-M. All new compounds were characterized by NMR, FTIR, UV–vis and fluorescence spectroscopy. The solvent-dependent UV–vis absorption and fluorescence emission band positions of the model compound and the carbonitrile-functionalized PVAm were studied and interpreted using the empirical Kamlet–Taft solvent parameters π* (dipolarity/polarizability), α (hydrogen-bond donating capacity) and β (hydrogen-accepting ability) in terms of the linear solvation energy relationship (LSER). The solvent-independent regression coefficients a, b and s were determined using multiple linear correlation analysis. It is shown, that the chains of the polymer have a significant influence on the solvatochromic behavior of 1-P. The structure of the carbonitrile 1-Si bound to polymer-modified silica particles was studied by means of X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) measurements. Fluorescent silica particles were obtained as shown by fluorescence spectroscopy with a diffuse reflectance technique.

We report on a novel approach to synthesize ultrabright fluorescent silica particles capable of producing a large number of complex spectra. The spectra can be excited using a single wavelength which is paramount in quantitative fluorescence imaging, flow cytometry and sensing applications. The approach employs the physical encapsulation of organic fluorescent molecules inside a nanoporous silica matrix with no dye leakage. As was recently demonstrated, such an encapsulation allowed for the encapsulation of very high concentrations of organic dyes without quenching their fluorescent efficiency. As a result, dye molecules are distanced within ∼5 nm from each other; it theoretically allows for efficient exchange of excitation energy via Förster resonance energy transfer (FRET). Here we present the first experimental demonstration of the encapsulation of fluorescent dyes in the FRET sequence. Attaining a FRET sequence of up to five different dyes is presented. The number of distinguishable spectra can be further increased by using different relative concentrations of encapsulated dyes. Combining these approaches allows for creating a large number of ultrabright fluorescent particles with substantially different fluorescence spectra. We also demonstrate the utilization of these particles for potential multiplexing applications. Though fluorescence spectra of the obtained multiplex probes are typically overlapping, they can be distinguished by using standard linear decomposition algorithms.

Cretaceous Bashijiqike ultra-deep tight sandstone, the main pay zone of Keshen gas field in Tarim Basin, has characteristics such as huge buried depth (6500 m ~ 8000 m), ultra-low matrix permeability and well-developed natural fractures. Due to lacking of a thorough research on the formation damage mechanism, there is no corresponding formation damage control method. And that's why this reservoir is suffering from severe formation damage. In this paper, the multi-scale characteristic of the reservoir space and seepage channel was described firstly. Then, a series of experiments were carried out to determine the multi-scale damage mechanisms, including the fluid sensitivity damage of matrix and fracture, the phase trapping damage of matrix and fracture, the loading capacity and the dynamic damage of fracture induced by drilling fluids. Then, the multi-scale formation damage mechanisms were summarized. Results showed the gas reservoir are characterized by typical multi-scale structures, i.e. micro-nano pore-throat and multiscale natural fractures. Severe salt sensitivity damage, alkali sensitivity damage and water phase trapping damage were the main damage mechanism of micro-nano pore-throat. For micro-fracture (aperture ≤ 100 μm), the dynamic damage degree induced by drilling fluids can reach up to 60.01 %. For Mesoscale fracture (aperture > 100 μm), lost circulation induced by inadequate loading capacity of drilling fluids was the main damage mechanism. Then, a complete multi-scale approach for damage control was proposed: ① Using oil-based drilling fluids to inhibit the fluids sensitivity damage and phase trapping damage of micro-nano pore-throat and natural microfracture; ②Optimizing the solid particle size distribution of drill-in fluid to reduce the dynamic damage degree of micro-fracture induced by drilling fluids; ③Adding acid soluble temporary plugging materials while drilling to prevent lost circulation. According to the proposed approach, the total production of the test well was 94 × 104 m3, which is much higher than that of non-test wells. This research provides a detailed case of forming the multi-scale approach for damage control based on the multi-scale formation damage mechanisms. This method is practical and useful, and it has important guiding significance to develop the ultra-deep fractured tight gas reservoirs efficiently.

Water production normally increases as field gets more matured; especially for fields developed via water injection or natural aquifer support. Handling water production is always a challenge from both financial and environmental prospects. The field under study is a giant oil and gas producer in Gulf area. Before embarking on the PWRI project, the routine way to handle the field's water production (~65 Mbbls/d) was to dispose through dedicated wells drilled only for that purpose and completed as open hole in Dammam, Simsima and UER formations. On the other hand, the water injection project sourced by water supply wells drilled and completed with ESP's through the same formations. In 2010, PWRI project was commenced through replacing the aquifer water injection by produced water re-injection in one of the water injection clusters without water treatment. Since then, about 22–29 Mbbls/d of produced water are being injected through four water injection wells. After commencing the project, it was very crucial to assure that, no injectivity impairment due to produced water re-injection in addition to wells' integrity. The water injection performance was closely monitored as WHIP and injection rate and using some techniques like Hall plot to detect any injectivity impact. Pressure fall-off tests (PFO) were frequently performed to detect any formation damage associated with PWRI. Moreover, PLT was performed in one of the wells before and after switching from aquifer water to injection water. The two logs were compared and proved that, there is no change in the injection profile across the horizontal section of that well. Corrosion logs were also utilized showing that, no integrity issues related to PWRI. As of now, some 24 MMbbls of produced water were injected with no impact on wells' injectivity or integrity.

Experimental investigation of formation damage during drilling of ultradeep fractured carbonate reservoir

Fluorescent particles are used for a diverse number of biochemical assays including intracellular imaging, cellular tracking, as well as detection of a variety of biomolecules. They are typically prepared by postpolymerization conjugations of dyes onto preformed particles. Herein we report the synthesis of aminomethyl-functionalized fluorescent particles via the synthesis and application of polymerizable fluorescein monomers. These monomers allowed high and controllable fluorophore loading into the particles, resulting in enhanced fluorescence properties in comparison with more commonly used carboxyfluorescein conjugated particles. Furthermore, the particles were rapidly taken up by cells with enhanced fluorescence. The herein presented results demonstrate the advantages of dye polymerization in contrast with more conventional conjugation strategies for fluorescent particle generation with applications in the life sciences.

In an ongoing effort towards a more sustainable rare-earth element market, there is a high potential for an efficient recycling of rare-earth elements from end-of-life compact fluorescent lamps by physical separation of the individual phosphors. In this study, we investigate the separation of five fluorescent lamp particles by high-gradient magnetic separation in a rotary permanent magnet separator. We thoroughly characterize the phosphors by ICP-MS, laser diffraction analysis, gas displacement pycnometry, surface area analysis, SQUID-VSM, and Time-Resolved Laser-Induced Fluorescence Spectroscopy. We present a fast and reliable quantification method for mixtures of the investigated phosphors, based on a combination of Time-Resolved Laser-Induced Fluorescence Spectroscopy and parallel factor analysis. With this method, we were able to monitor each phosphors’ removal dynamics in the high-gradient magnetic separator and we estimate that the particles’ removal efficiencies are proportional to (d2·χ)1/3. Finally, we have found that the removed phosphors can readily be recovered easily from the separation cell by backwashing with an intermittent air–water flow. This work should contribute to a better understanding of the phosphors’ separability by high-gradient magnetic separation and can simultaneously be considered to be an important preparation for an upscalable separation process with (bio)functionalized superparamagnetic carriers.

Injectivity decline during sea waterflooding or produced water re-injection is widely observed in North Sea, Gulf of Mexico and Campos Basin fields. The formation damage occurs mainly due to the deposition of suspended solids around injectors and the build-up the external filter cakes in the well bores. The ability to predict injectivity decline accurately is of great importance for project designs and water management. A comprehensive model that incorporates a variety of factors influencing the process is desirable for the prediction. In this paper, a new comprehensive approach for predicting injectivity decline during water flooding is proposed. The deep bed filtration is described by novel stochastic random walk equations. The injectivity decline model takes into account the reservoir heterogeneity and the distribution of solid particles by sizes. It also accounts for the later formation of the external filter cake and its erosion. A piece of software SNY is developed with the proposed model. The model is able to capture the behaviors of the injectors in the field: the initial slow injectivity decline due to the deep bed filtration of suspended particles, the later faster decline due to the build-up of the external cake, and the temporary steady state due to the cake erosion. Stronger normal dispersion or median heterogeneity close to the injector leads to farther penetration of the particles and slower impedance increase. Neglecting the particle population heterogeneity may lead to the underestimation of formation damage and predicts late transition to external cake formation. The impedance at the steady state and the starting time are highly influenced by the cake properties. The impedance and the external cake thickness at the steady state are likely to be higher in horizontal wells than those in vertical wells.

The Pekisko formation in the Bigoray field in central Alberta is an oil-bearing dual permeability/porosity dolomite. A portion of the reservoir has permeabilities in the range of 1-2 Darcy and porosities approaching 25-30% while the rest of the reservoir features 10-30 millidarcy average permeabilities, 8-12% porosities and low initial water saturation. It is suspected that both rock types contribute to the flow of oil. Drilling of horizontal wells in the Pekisko formation offers technological challenges in terms of field development and formation impairment. Damage mechanisms for the two rock types are expected to be different yet need to be addressed in one drilling fluid system. Open hole completion/stimulation to repair any formation damage and the avoidance of underlying water adds to the drilling challenges. This paper describes the results of laboratory formation damage studies to both identify damage mechanisms and evaluate which drilling fluid system to be used in the horizontal well section. The higher permeability/porosity dolomite core plugs were damaged by solids plugging while aqueous phase trapping and solids plugging were responsible for damage in the lower quality rock. A total of eight horizontal wells have been drilled in the field as of December 1997. The horizontal wells were drilled with three types of drilling fluids: oil, oil-soluble resin and a carbonate bridging system containing an aqueous phase trap reduction agent. The horizontal wells drilled with the carbonate/aqueous phase trap drilling fluid system had better oil production and less water than the wells drilled with the other drilling fluids. Discussion will also focus on stimulation of those horizontal wells that were damaged in the drilling process. P. 161