Fines Mobilization Research Articles

Accurate Collisional Cross Section Measurement by Multipass Cyclic Ion Mobility Spectrometry.

Ion mobility-mass spectrometry (IM-MS) is a powerful analytical tool for structural characterization. IM measurement provides collision cross section (CCS) values that facilitate analyte identification. While CCS values can be directly calculated from mobility measurements obtained using drift tube ion mobility spectrometry (DT-IMS), this method has limited mobility resolution due to the practical constraints on the length of the ion drift path. Consequently, DT-IMS cannot differentiate analytes with similar mobilities or resolve fine mobility features of individual ions. Cyclic IMS (cIMS) instruments leverage a cyclic path enabled by traveling wave ion mobility (TWIM) technology and offer increased mobility solution to address this challenge. While TWIM devices must first be calibrated to enable CCS measurements, current calibration strategies are primarily tailored for single-pass analyses. This preference is partly attributed to the challenges associated with multipass calibration methods, which require both calibrants and analytes to experience the same number of passes. Achieving this consistency can be complicated due to factors like peak splitting and diffusion, and may not be feasible for online IM-MS analyses. A recent report employed average ion velocities obtained from multiple measurements under different separation pathlengths as a path length-independent metric for CCS calibration. However, the ability to exploit this averaging approach is limited by observed variation in ion drift time/velocity in these measurements. In this study, we introduce a novel calibration strategy designed for multipass cIMS analyses, directly targeting the root cause for the path length- and mobility-dependent variations in ion drift time. With this method, we demonstrate that CCS values derived from multipass measurements closely align with those obtained from single-pass analyses, with an average deviation of 0.1%. We apply this method to characterize four isomeric trisaccharides. Our approach not only results in excellent agreement between our measured cIMSCCS values and the reported DTCCS values, with an average difference of only 0.5%, but also allows us to effectively identify subtle mobility characteristics of each compound and determine their respective CCS values. This level of detail and accuracy was previously unattainable using DT-IMS or single-pass cIMS measurements. We developed an algorithm for reconstructing arrival time distribution in cases where wrap-around has resulted in peak splitting. Collectively, the new calibration strategy and the reconstruction procedure maintain reproducibility and precision in CCS measurements while largely eliminating the need for meticulous selection of separation times. We expect that our method will empower researchers to harness the high mobility resolution offered by multipass cIMS analyses without compromising the accuracy of CCS measurement, making it appropriate for straightforward use across a wide range of applications.

An integrated modeling approach to predict critical flow rate for fines migration initiation in sandstone reservoirs and water-bearing formations

Fines migration causes formation damage in sandstone reservoirs and water-bearing subsurface formations. Several factors affect fines migration such as composition and salinity of permeating brine, flow rate, and system pH. Electrostatic forces of van der Waals attraction and electric double layer repulsion, gravitational force and hydrodynamic force all contribute to fines detachment and migration under certain conditions. The current research presents a new integrated model of electrostatic, gravitational, and hydrodynamic forces to estimate the critical injection rate of NaCl brine for fines migration initiation in subsurface formations.The DLVO modeling approach was modified by considering electrostatic, hydrodynamic, and gravitational forces. Parameters such as injection brine salinity, average fine particle size, and zeta potential of sand-brine systems were used, and effective forces were quantified. A microscopic force and torque balance approach was applied to model hydrodynamic forces to modify the DLVO model. The developed models were validated with experimental results.The profiles of injection velocity versus fine particle radius were generated and the models predicted critical flow rates of 0.9, 2.6, and 3.8 cc/min for 0.15 M, 0.2 M, and 0.25 M NaCl, respectively. For model validation, the coreflood experiments were performed on Berea sandstone core samples under given salinities and critical flow rates were determined. Comparable experimental results were obtained with critical flow rates of 1, 3, and 4 cc/min for 0.15 M, 0.2 M, and 0.25 M NaCl, respectively. In addition, sensitivity analysis assesses the impact of different forces on the fines migration phenomenon.Formation damage caused by fines migration is a well-documented problem in sandstone reservoirs and water-bearing formations. Regulating the injection/ permeating fluid rate and salinity can avoid fines migration and associated permeability impairment. Our study presents a novel approach incorporating electrostatic, gravitational, and hydrodynamic forces to accurately predict fines mobilization in fine-containing subsurface formations.

In-situ fines migration and grains redistribution induced by mineral reactions – Implications for clogging during water injection in carbonate aquifers

Water injection into an aquifer is generally motivated by one of three objectives: disposal, managed aquifer recharge (MAR), or aquifer storage and recovery (ASR). Any of these would be undermined if an injection well were to become clogged. This paper investigates whether mineral reactions can cause mobilization of fines and rock grains, and if so, how this would affect clogging. Injection experiments are performed on Edwards Brown (dolomite) and Indiana limestone core samples. X-ray Powder Diffraction analysis of the rocks shows that no clays are present. Filtered-deaired deionized water and pure salts are used to prepare the injection fluids. The core samples are subjected to four sequential injections of fluids: at salinities 44,580 mg/L (referred to as “seawater”), 14,860 mg/L, 7,430 mg/L, and 0 mg/L (deionized water). These salinities are selected to represent disposal, and less saline fluids to represent MAR and ASR projects. Pressure difference is recorded across the core sample at each stage and is used to calculate permeability. The effluent samples are collected to characterize produced fines and elements. The increase in the pH of the effluent samples suggest mineral reactions, which is supported by an increase in the concentration of chemical elements in the effluent samples. Scanning Electron Microscopy (SEM) images show pore enlargement due to dissolution and depict pore blockage due to fines migration, grains redistribution, and mineral precipitation. Mineral reactions dissolved the grain's surface and intergranular cement, releasing silicate fines and rock grains, which in turn reduce the permeability of the rock by 68 % to 99.9 %.

Functional outcomes more than 5 years following acetabulum fracture.

Objectives:The purposes of this project were to evaluate functional outcomes more than 5 years after acetabulum fracture and to determine factors related to function.Methods:This retrospective study consisted of 205 adult patients treated for acetabulum fracture who completed the Musculoskeletal Function Assessment (MFA) a minimum of 5 years following injury. The MFA includes survey of daily activities, gross and fine mobility, social and work function, sleeping, and mood. Higher scores indicate worse function.Results:Two hundred five patients with 210 fractures, 69.3% of whom were male, with mean age of 45.7 and mean body mass index 30.1 were included after mean 128 months follow-up. Fracture patterns included OTA/AO 62A (37.1%), 62B (40.5%), or 62C (22.4%), and 80.0% were treated surgically. Late complications were noted in 35.2%, including posttraumatic arthrosis (PTA: 19.5%), osteonecrosis and/or heterotopic ossification. Mean MFA of all patients was 31.4, indicating substantial residual dysfunction. Worse MFA scores were associated with morbid obesity (body mass index >40: 42.3, P>.09), and current tobacco smoking history vs former smoker vs nonsmoker (45.2 vs 36.1 vs 23.0, P < .002). Patients with late complications had worse mean MFA scores (38.7 vs 27.7, P = .001); PTA was the most common late complication, occurring in 19.5%.Conclusions:More than 5 years following acetabulum fracture, substantial residual dysfunction was noted, as demonstrated by mean MFA. Worse outcomes were associated with late complications and tobacco smoking. While fracture pattern was not associated with outcome, those patients who had late complications, mostly PTA, had worse outcomes.

Critical rate analysis for CO2 injection in depleted gas field, Sarawak Basin, offshore East Malaysia

This study aimed to address the challenges and strategies to determine the critical rate of CO2 injection into a carbonate depleted gas field. In this research, the critical rate is the maximum allowable injection rate before formation damage initiation. The cause of formation damage could be due to in-situ mobilization or trapping of migratory fines resulting in plugging the flow path. This study performed a thorough investigation of a different rock-fluid system to evaluate the safe injection limit, as the critical rate is different for each rock-fluid system. The geochemical effect of CO2 injection toward carbonate formation was also investigated in this research. Other than that, the porosity and permeability changes due to CO2-brine-rock multiphase flow characteristics were considered to understand the feasibility of CO2 sequestration into carbonate formation. This research discussed experimental design to mimic the CO2 injection scenario of CO2 into carbonate depleted gas field. Therefore, several core flooding experiments were conducted under reservoir conditions using representative native cores, CO2, and synthetic formation brine. Abrupt changes in differential pressure (ΔP), analysis of effluent collected after CO2 multi-rate flow, and pH reading are the key indicators to consider that the condition has reached a critical rate. The experimental result demonstrated the existence of fines migration, scale formation, and salt precipitation after the core was subjected to supercritical CO2 multi-rate flow. Considering these issues and challenges associated with injectivity, this study recommended a maximum injection rate prior to field scale injection.

Production versus injection induced poroelasticity in porous media incorporating fines migration

Current fines migration models follow a decoupled approach, not incorporating the effects from the poroelastic response of the porous medium on mobilization and straying of fines and the resulting permeability damages. Furthermore, the impact of in-situ fine particles present in the porous matrix, on the poroelastic response of the formation to fluid-induced flow has not been studied. This paper presents a novel coupled numerical model to explain the spatiotemporal geomechanical response of a saturated porous formation that contains fine particles retained on the solid skeleton, under both injection and production induced flow. The coupled effects from the poroelastic response of the target zone as well as those from the fine-migration-induced permeability reduction are integrated into our mathematical formulations, while also incorporating vertical confinement effects using the Winkler model approximation. Results reveal that fine migration and straining notably impacts the induced pore pressures, displacements, and in-situ permeability, specifically at wellbore vicinity. Higher pore pressure alterations (higher increase under injection, and higher drop under production) is detected when incorporating fines migration, which captures field observations in damaged permeability zones. The impact of fine migration and straining is more significant during production versus injection, due to the geomechanical compression generated in the reservoir under production flow. Exitance of fine particles complicate the geomechanical response of a confined formation to flow, enhancing the effects of vertical confinement. Flow induced deviatoric stresses are significantly higher when fine migration effects are incorporated, resulting in early failure; which cannot be captured using conventional poroelasticity models.

Investigation of fines migration for a high-pressure, high-temperature carbonate gas reservoir offshore Malaysia

A high CO2 carbonate gas field offshore Sarawak, Malaysia, is scheduled for development. Fines migration has been identified as a potential risk for a sustained and stable production for this field, triggering this investigation. The reservoir investigated (subdivided in S3, S2, S1 formation) has an average 8% clays, of which over 50% are migratory illites and 15% migratory kaolinite. This paper discusses the laboratory findings and factors contributing to fines migration for this reservoir. We conducted core flood tests to determine critical flow rates for the onset of fines migration of high CO2 hydrocarbon gas and CO2-saturated brine within the production gas zone. In addition, we measured total suspended solids during each incremental rate stage and performed scanning electron microscopy–energy-dispersive X-ray (SEM–EDX) analysis on the effluents collected. We also performed mineralogical analysis of formation rocks to determine clay types, amount, and morphology. Core floods performed with CO2-saturated brine on S3 and S2 cores showed damage at a critical flow rate of 10 ml/min with permeability recovery of 65–75%. This shows that CO2-saturated brine tends to mobilize the fines such as illite and kaolinite. Core floods performed with high CO2 hydrocarbon gas showed permeability recovery of 93–96% at rates up to 10 ml/min. SEM analysis on effluents collected showed presence of silicate and carbonate particles with size of 5–50 μm. A combined salt dropout and fines mobilization core flood showed a higher degree of formation damage due to fines mobilization with 74% permeability recovery compared to baseline permeability compared to core floods with high CO2 hydrocarbon gas. However, the formation damage due to fines mobilization for this experiment was reversible. Overall, the results indicate that a high potential for fines migration in this type of carbonate system exists for CO2-saturated brine flow with significant less potential for dry CO2 flow.

Colloidal release in high temperature porous media with oversaturated fines during supercritical CO2 transport

This paper presents the impacts of supercritical CO2 transport in high temperature porous media with oversaturated fines. The latter phenomenon (indicates oversaturated fines) is in which the lift force of the fine particle over pore surface is greater than the gravitational and electrostatic forces combined, where the fines are released from the pore surfaces and transport along with the permeating fluid as colloidal-suspension flow. During transport, the fines are captured in the pore-throats and thereby deteriorating the permeability and decreasing fluid recovery as well. Therefore, three sets of coreflood tests have been conducted to examine the fines mobilization in porous media during supercritical CO2 transport and the results have been compared with the results obtained from the subcritical CO2 flow. Produced suspension-colloids have been sent for microstructural analysis and its outcomes, supported the experimental results. Statistical modelling and literature data were employed and compared for model validation, which revealed high agreement.

Reservoir formation damage during hydrate dissociation in sand-clay sediment from Qilian Mountain permafrost, China

Permeability is known as a key factor affecting the gas production effectiveness from the natural gas hydrate-bearing reservoir. We studied the permeability behavior of natural clayey sand core samples from a natural hydrate-bearing reservoir in the Qilian Mountain permafrost before and after hydrate formation, as well as after hydrate decomposition. We found a substantially lower permeability after hydrate decomposition and assumed a formation damage process involving fines mobilization, migration and deposition at pore throats. The assumption was proved by SEM analysis of the filter paper separating the sample and the end caps containing the fluid ports. The analysis showed fines trapped in the paper from the outlet side. Fines migration and resulting formation damage is known from enhanced oil recovery by low salinity water flooding, but was unexpected for hydrate decomposition. The underlying mechanism was identified by a series of different permeability tests. The results indicate that fresh water released from the hydrate dissociation causes the fines mobilization, migration and redeposition at pore throats leading to the observed permeability decrease. Obviously the large volume of released methane gas displaces the remaining saline water and separates it from the fresh water released from the hydrate. The fresh water in contact with parts of the grain framework causes the detachment of clay particles by increased electrostatic forces and clay swelling, if swellable clays are present. This is an important mechanism that has to be taken into account in the planning of gas production from low-permeability clayey hydrate-bearing formations.

Technology Focus: Formation Damage (February 2020)

Technology Focus One of the frustrating aspects of well-productivity analysis is identifying the causes of lower-than-expected productivity index (PI) during initial well lifetime. We are presented with a well that has a higher initial skin than expected with concomitant lower PI. Our task is to evaluate the multivariate aspects of well design, drilling and completion fluid design, geological characteristics (e.g., clay mineral type and abundance), permeability variation, net-to-gross ratio, and kh product among many other variables. The data are plotted, and we attempt to identify trends, if any. Out of all of this, we eventually come to the most-likely damaging mechanism (e.g., significant mud losses to the formation because of a poorly designed particle-size distribution or ineffective wellbore cleanup). Alternatively, the completion can be damaged, the most common mechanism of which, in a well completed with screens, is plugging. The key expression here is “likely damaging mechanism,” because we have no actual way of going downhole and identifying at close range the actual damaging mechanisms. Brant Bennion’s definition of formation damage, which I like to quote, aptly summarizes the conundrum when he said that it was “the impairment of the invisible.” A further complication is the situation where two or more damaging mechanisms are operating concurrently. For example, the previous examples of mud losses to the formation combined with screen plugging can contribute in the same well to lower the PI and increase the skin. However, we have no way of identifying which of these is the most significant factor in explaining the observed well productivity or, in fact, if they are contributory factors in the first place. Inference is the only tool we have, and even that is fraught with inaccuracy. Coreflooding can be used to determine the potential causes of formation damage by replicating the fluid sequence used in the damaged well. However, it is nonquantitative with regard to simulation of damaging effects along the production interval, especially if these are not uniformly distributed within a heterogeneous reservoir (i.e., in such cases, a coreflood represents a specific point along the production interval rather than representing the entire length). Reduced well productivity during later well lifetime is generally a result of a different set of damaging mechanisms than those seen in initial production. Damaging mechanisms typical for mid- to late-life wells include fines mobilization, scale, and asphaltene formation. A few years ago, I was involved in a mud-acid stimulation intervention where we were convinced that the explanation for reduced productivity in this well was fines mobilization (kaolinite). Many corefloods had been performed on this particular formation that showed kaolinite could mobilize under scaled-down reservoir flow rates. For the particular candidate well, we pumped diesel to see if we could flush kaolinite from the near wellbore and saw an increase in productivity for a few days before the PI returned to its previous value. Corefloods were performed to qualify mud acid and showed positive results. The intervention was planned thoroughly and executed as expected. However, when the well was started, the PI was the same as before the intervention. Formation damage can be so frustrating. Enjoy the papers I have selected, some of which touch on the comments I have made. Recommended additional reading at OnePetro: www.onepetro.org. SPE 197974 Raising the Bar of Productivity Improvement in an Abnormal and Distinctive Pressure and Temperature Environment: Niger Delta by Oyeintonbra Imbazi, Shell, et al. SPE 189562 Laboratory Preparatory Work of Cased-Hole Cleanup as Part of an Entire Remedy Program in Removing Damage Attributed to Oil-Based Mud by Hideharu Yonebayashi, INPEX, et al. OTC 28666 Completion-Fluids-Induced Formation Damage in High-Temperature Gas Wells: Causes and Mitigation by Bilel Hamzaoui, Saudi Aramco, et al.

Subcritical CO2 effects on kaolinite fines transport in porous limestone media

Carbonate reservoirs account for 60% share in global oil reserves, and CO2-EOR process is employed in these carbonate fields for effective oil recovery and retention as well. Recent research reports that fines migration may lead to reservoir formation damage in oil bearing limestone and dolomite rocks. Although carbonate reservoirs are poor in clay minerals, some mass of clay fines existence in certain carbonate formations will cause severe damage to permeability and well productivity. This paper reports the single-phase flow of subcritical CO2 in porous limestone rock core containing kaolinite clay fines. Fines are natural reservoir minerals (example, quartz) and clay particles such as kaolinite, illite, feldspar, smectite, and montmorillonite. But, this paper explores this CO2-clay fines behavior in limestone rock as a function of kaolinite. So, two sets of core flood experiments were performed in the rock temperatures 120 °C and 160 °C. Initially, kaolinite clay has been injected into the limestone core in the form of suspension and then dried for hours in order to retain the solid fines in the internal pore chambers of the core. After that, the CO2 under subcritical condition has been injected into the porous limestone core for fines mobilization and injected gas recovery. The major observations that are reported from the experimental tests are there is an increase in gas saturation for increasing injection time. Steady rise of heat transfer coefficient and enthalpy was noted for increasing gas saturation and time. Concentration of fines linearly soars with respect to elevating PVI and permeability declines for rising time. Pressure in the limestone core shows abnormal and nonlinear variation. Finally, gas discharge rate declines for increasing injection time. Experimental data are tested against the statistical model (regression), and the outcome indicated good agreement. Overall, this paper has successfully established the CO2 effects on kaolinite clay fines behavior and its impact on oil recovery in carbonate fields.

A multi-scale experimental study of crude oil-brine-rock interactions and wettability alteration during low-salinity waterflooding

In this study we present the results of a multi-scale experimental investigation of the mechanisms responsible for the increased oil recovery by low-salinity waterflooding (LSWF), i.e., low-salinity effect (LSE). Using core- and substrate-flooding experiments as well as imaging techniques at macro, micro, and nanometer scales, we probe the intricate crude oil-brine-rock interactions and the subtle pore-scale displacement events governing recovery enhancement during LSWF. We performed several LSWF and high-salinity waterflooding (HSWF) experiments on macro-scale (1 inch-diameter) reservoir sandstone core plugs while collecting effluent samples for further analysis.LSWF experiments exhibited a prolonged oil recovery response and notably higher oil recovery compared to HSWF. Imaging effluent samples, at sub-nanometer resolutions using transmission electron microscopy, demonstrated significant fines mobilization during LSWF. The occurrence of electric double layer expansion (DLE) as a source of fines mobilization during LSWF was confirmed by examining scanning electron microscopy images of the reservoir rock substrates before and after contacting the low-salinity brine. Moreover, geochemical analysis of the effluent samples showed evidence of proton excahnge and multi-component ion exchange (MIE) during LSWF. The mobilization of fine particles (due to DLE) and the ion exchange processes are believed to result in removal of oil molecules from the rock surfaces leading to an enhancement in oil recovery as well as alteration of wettability toward increased water-wetness. These observations were then linked to our findings from an earlier study during which LSWF and HSWF experiments were conducted on miniature (5 mm-diameter) core samples while the pore space was being imaged at micrometer resolution. In-situ oil/brine contact angles measured during flow tests conducted on the miniature core samples revealed a significant level of wettability alteration from weakly oil-wet toward increased water-wetness during LSWF. Analysis of fluid occupancy maps showed that this change in wettability lowers the threshold water pressure needed for water-displacing-oil events to take place in the pore elements, which in turn enhances displacement efficiency and oil recovery.

Formation damage and cleanup in the vicinity of flooding wells: Multi-fluid suspension flow model and calibration on lab data

Injection of water into a rock formation through the flooding wells is a common practice to maintain reservoir pressure and increase ultimate recovery of hydrocarbons. While flowing through the well from surface to the rock formation, injected water typically transports fine particles, which are introduced either externally (untreated water) or internally (e.g., particles detached from the inner surface of a pipeline due to erosion and abrasion as well as mineral particles detached from pore surface). In the framework of the two-fluid approach, we formulate mathematical model for filtration of a particle-laden suspension in the vicinity of flooding wells. Two mechanisms affecting transport of non-colloidal fines are considered: trapping and mobilization. Trapped particles reduce permeability and porosity of the rock, which leads to the injectivity decline of the well. The model contains minimal set of tuning parameters describing particle trapping and mobilization rates. This is achieved by critical overview of existing models. We calibrate suspension filtration model against existing experimental (laboratory) data on fines mobilization and trapping in porous media. A parametric study of different flooding scenarios is carried out numerically. In particular, we investigate the effectiveness of periodic flooding regime, when the periods of injection are followed by flowback in order to wash out trapped fines from the near-wellbore zone and restore well injectivity. Implications to formation damage and cleanup phenomena peculiar to hydraulic fracturing and drilling are discussed. Practical recommendations are given.

Study of Carbonate Reservoirs Examines Fines Migration in CO2-Saturated-Brine Flow

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 189569, “Fines Migration During CO2-Saturated Brine Flow in Carbonate Reservoirs With Some Migratory Clay Minerals—Malaysian Formations,” by Y. Sazali, Petronas; S. Godeke, SPE, Universiti Brunei Darussalam; W.L. Sazali and J.M. Ibrahim, Petronas; G.M. Graham and S.L. Kidd, Scaled Solutions; and H.A. Ohen, SPE, HPO Global Resources Ventures, prepared for the 2018 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 7–9 February. The paper has not been peer reviewed. A high-carbon-dioxide (CO2) carbonate gas field offshore Sarawak, Malaysia, is scheduled for development. Reservoirs in this region have an average clay content of 8%; more than 50% of this clay content is migratory illite, and 15% is migratory kaolinite. Therefore, fines migration exacerbated by this low-permeability rock becomes a potential production and injection problem. A study was conducted involving rock mineralogy and dynamic flow to evaluate factors contributing to potential fines-migration damage within the production and injection interval. Introduction Migration of fines is associated with oil and gas production in sandstones as well as carbonate reservoirs. Fine particles located on the surface of rock grains are affected by adhesion, drag, and electrostatic and gravitational forces. Drag and lifting forces detach the particle, whereas adhesion, electrostatic, and gravitational forces press the particle to the surface. Generally, the main sources of movable fine particles in sandstone reservoirs are kaolinite and illite clays. Kaolinite particles are flat plates usually stacked in the form of booklets. The surface area of clay minerals, for example, typically is large because of their structure and small size and is more reactive and prone to mobilization and migration. Once mobilized, the fine particles are retained by size exclusion if their size exceeds the pore-throat size of the matrix. Fines damage also occurs when several small fine particles reach a larger pore throat at the same time and compete for passage through the throat with the result of bridging and sedimentation. Usually, in the case of gas/water flow, the fines move with the wetting water phase. However, fines movement taking place before water movement has been observed in a number of gas reservoirs. The in-situ mobilization and migration of fines without a mobile wetting phase is primarily caused by hydrodynamic drag that exceeds the critical rate to mobilize the fines. It has long been realized during corefloods that colloidal controlled release of particles leading to fines migration may be caused by salinity change following flow rate that causes the fines to bridge at the pore throat. Generally, a decrease in salinity or an increased rate of salinity change leads to particle mobilization. This decrease in permeability caused by decreasing salt concentration has been found to be nonmonotonic.

Physical property characteristics of gas hydrate-bearing reservoir and associated seal sediments collected during NGHP-02 in the Krishna-Godavari Basin, in the offshore of India

Abstract India's National Gas Hydrate Program Expedition 02 (NGHP-02) was conducted to better understand geologic controls on gas hydrate occurrence and morphology, targeting coarse-grained sediments along the lower continental slope offshore eastern India. This study combines seismic, logging-while-drilling data, and a petroleum system approach to provide a regional geologic and lithologic context for: 1) gas hydrate morphology and distribution, and 2) effects of fine-grained sediments (clays and other grains smaller than 63 μm) on gas production in NGHP-02 Area B in the Krishna-Godavari Basin. Area B seismic data show a buried anticline/syncline structure with strong reflectors, R1 and R2, that delineate two of the five lithologic units: Unit I (shallowest), II (R1), III, IV (R2) and V (below the bas of gas hydrate stability). Throughout Area B, gas hydrate morphology depends on its placement within these units. Specifically, core- and grain-scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology. Units I, II and III are generally fine-grained. On the anticline crest, these units host primarily grain-displacing gas hydrate veins linked to pore-occupying gas hydrate in thin, localized, coarser-grained deposits. Diatoms in Unit III increase porosity with depth, reaching ∼70% where it contacts Unit IV, the gas hydrate reservoir associated with reflector R2. The Unit III lithology and porosity allow fluid and dissolved-phase methane to escape Unit IV and form gas hydrate in the fine-grained overburden. Within Unit IV, fine-grained layers are interbedded with coarser-grained gas hydrate reservoir sands, and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production. Fluid motion during gas production can mobilize fines, which can then clog pore throats, limiting production rates. Pore-water freshening during gas hydrate dissociation can increase fines mobilization, particularly given the smectite identified in the fine-grained interbeds.

The coupled effect of salt precipitation and fines mobilization on CO2 injectivity in sandstone

AbstractAppreciable CO2 injectivity is required to inject large volumes of CO2 through a minimum number of wells. In situ geochemical CO2‐brine‐rock reactions may dissolve sandstone rock minerals, and consequently release fine particles into the pore fluid. If the fine particles (‘fines’) are mobilized during CO2 injection, well injectivity could be severely impaired. The transport of fines under CO2 injection conditions involves the complex multiphase flow of dry supercritical CO2, saline formation brine, and fine particles. While transported fines could plug narrow pore channels, the saline pore water could be vaporized by supercritical CO2 to precipitate solid salt into the pores. To understand the impact of mineral dissolution on CO2 injectivity, it is important to consider the coupled effect of fine particle mobilization and salt precipitation. We conducted core‐flood experiments and theoretical modelling to investigate the coupled effect of the fines mobilization and salt precipitation on CO2 injectivity. We found that salt precipitation could increase CO2 injectivity impairment induced by the fines mobilization. The deposited salt reduces the flow area, making the pores more susceptible to particle entrapment. Injectivity impairment increased with decreasing initial rock permeability and increasing saturating brine salinity. Irreducible brine saturation and pore size distribution were identified as parameters that strongly determine the contribution of salt precipitation during the transport of fines. Injectivity impairment was also slightly higher when the rock was first exposed to salt precipitation, before the entrapment of fines. The current findings highlight the complexity and uniqueness of fines transportation under CO2 injection conditions and the impact of mineral dissolution on CO2 injectivity. © 2018 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Effects of delayed particle detachment on injectivity decline due to fines migration

Colloidal-suspension flows in porous media occur in numerous areas of environmental, chemical and petroleum engineering. The main processes are capture and detachment of particles, yielding permeability decline. We developed a governing system of transport equations with particle detachment kinetics, where the detachment by high velocities is instant, due to flow incompressibility, and the detachment by decreasing the fluid salinity is delayed, due to micro-scale diffusion. The system allows for a semi-analytical solution for axi-symmetric low-salinity water injection with fines migration. The model exhibits instant fines mobilization at the beginning of injection by drag force, fines release with delay behind the salinity front by electrostatic force, and the interaction of two concentration waves. The model can be used for laboratory-based injectivity decline prediction during injection of water in aquifers and oilfields, where the injected and formation water compositions are different, and also for fines-migration during drilling fluid invasion.

Aortic valve replacement with stentless bioprosthesis «Kemerovo-AB-Neo»

We analyzed 50 aortic valve replacements (AVR) with Kemerovo-AB-Neo stentless bioprostheses. Mean age was 66.75 (54 to78) years, hospital mortality rate accounted for 2%. The peak transprosthetic pressure gradient (PTPG) in patients operated for aortic stenosis came to 19.57 mm Hg. PTPG was shown to be dependent on the implantation technique; it reached 24.57 mm Hg when in order to fix the proximal line, interrupted sutures were used and ran to 175 mm Hg in the case of running sutures (р = 0.03). Helical CT confirmed fine mobility of the cardiac structures after Kemerovo-AB-Neo implantation: the aortic cross-section area varied up to 84% during the cardiac cycle. It should be noted that AVR with Kemerovo-AB-Neo stentless valves gives good clinical and hemodynamic results early after surgery. A free-hand technique of implantation should be preferred. The implantation of stentless bioprostheses retains cardiac structures mobility and natural aortic root dimensions after performing an AVR.

Massive fines detachment induced by moving gas-water interfaces during early stage two-phase flow in coalbed methane reservoirs

Field observations have shown that the concentration of fines produced during the early two-phase flow stage in coalbed methane (CBM) reservoirs is much higher than single-phase water flow, leading to more frequent workover activities. The typical flow pattern in early two-phase flow is bubble-water flow, in which the liquid phase is mostly contained in the form of liquid “plugs”, separated by a series of moving bubbles/gas-water interfaces (GWIs). Here, we quantify the impact of moving bubbles/GWIs on fines detachment, aiming at better understanding of fines mobilization mechanisms in bubble-water flow towards their effective control. First, fines migration tests in the absence and presence of moving bubbles in water flow, including effluent and permeability measurements, were conducted on fractured coal plugs. The experimental flow velocity was less than the critical flow velocity (CFV) for massive fines release. Experimental results showed that both peak effluent concentration and permeability impairment in the presence of moving bubbles were much greater than when absent, indicating that the quantity of fines detached by moving bubbles/GIWs was much larger than simply by water flow. Second, forces and torques acting on coal fines were analyzed to determine the combined effects of extended Derjaguin-Landau-Verwey-Overlook (DLVO), hydrodynamic, surface tension, and frictional forces on fines mobilization. Theoretical results showed that all in-situ fines could be mobilized by moving GWIs, whereas no fines could be released by water flow when the flow velocity is smaller than the CFV, as the surface tension force arising from passing GWIs greatly dominates hydrodynamic forces by 2–4 orders of magnitude. Theoretical results support experimental data, in spite of some errors due to model assumptions, i.e., spherical fines and homogenous surface.

Effects of clay mineral and physico-chemical variables on sandstone rock permeability

In this paper we highlighted the effect of clay mineralogy and the influence of physico-chemical factors on coagulation- dispersion processes and the rate of pore throat bridging by clays. In particular, we describe the effect of different pH (acidic 2.5 and alkaline 9.5) and the effect of salinity (NaCl) on the stability of clay particles in siliciclastic rocks and their influence on the rock permeability which are often ignored in reservoir engineering literature. We conducted the first experiments on powder (0.05-0.1 mm grain size) samples for tracking mineral reactions and core plugs for permeability. X-ray diffraction (XRD) was run for whole-rock and clay fraction by diagnostic treatments to specify types of clay minerals and to calculate the percentage of each type. The composition of starting material is quartz dominant, with carbonates (dolomite, calcite), feldspars (albite, microcline), chlorite, kaolinite, illite, muscovite, with traces of 14 Å smectite and illite/smectite randomly interstratified structure. In strongly acidic solution, according to XRD, smectite is altered (14 Å peak vanishing), chlorite being also partly reduced, while kaolinite is stable. Carbonates are not involved in reactions. In basic solution, smectite was less affected, but chlorite peaks indicate structural transformation. The shape and broadening of 10 Å peak shows changes in illite and illite/smectite interstratified structures. Altogether, mineralogical changes indicate reactions which lead to fines mobilization. Based on experimental work, in the case injection with pH 2.5 and pH 9.5, there has been a rapid and substantial reduction in permeability as an average 38.54% and 73.72% for acidic and basic solutions respectively. The results confirmed that the reason of the reduction in permeability is due to the non- swelling clay minerals which are dispersed and migrated during the changes in pH, salinity and time. Novelty of these experiments is the tracking of changes in mineralogy by Rietveld refinement on XRD, coupled with diagnostic clay mineral investigation.