Clay Cake Research Articles

ВЗАИМОСВЯЗЬ НЕЛИНЕЙНЫХ МАТЕМАТИЧЕСКИХ МОДЕЛЕЙ ОБРАЗОВАНИЯ ГЛИНИСТОЙ КОРКИ В РАДИАЛЬНОЙ И ЛИНЕЙНОЙ ГЕОМЕТРИИ

A quasi-stationary model for the formation of a clay filter during well drilling in depth intervals with permeable rocks is proposed, on the basis of which the physical parameters of the media, reservoir and well are established, which determine the dependence of its radial dimensions on time. It is assumed that the filtration pressure fields are described by stationary piezoconductivity equations. The dependence of pressure, mudcake thickness, radius of the zone of pressure disturbances in the permeable rock during drilling and other parameters on time is parametric. Such a dependence arises from an additional equation that relates the amount of fluid absorbed by the formation and the filtration rate at the inlet to the porous medium. The general formulation of the problem, which includes the stationary piezoconductivity equations for the mudcake and reservoir, boundary conditions, and an additional equation, is non-linear, since the boundaries of the perturbation zone in the reservoir and the mudcake are mobile. An analytical solution of the problem was constructed, on the basis of which studies were carried out on the influence of the physical parameters of the medium, wells, etc. on the process of formation of a clay cake in real conditions. Integrals of motion of a nonlinear problem are found, which represent invariant complexes of parameters that do not change during the formation of a mud cake. The presence of such integrals made it possible to establish the relationship between the solutions of problems presented in radial and linear geometries. It is shown that in the particular case of a thin mud filter, the obtained expressions for the radial geometry coincide with the known ones, when the geometric factor of the drilling fluid filtrate corresponds to a flat flow. New possibilities for estimating the physical parameters of reservoirs based on caliper logging have been identified. The solution of this problem is especially important for horizontal wells, in which the intervals of clay cake have a significant length, and its formation occurs under conditions of a wide range of reservoir properties of the formation. The considered problem is of practical importance, since the zone of penetration of the drilling fluid filtrate into the formation has a screening effect on the use of geophysical methods to determine the saturation of the formations. The obtained solutions can be used both to improve the interpretation of geophysical methods and the development of drilling technology.

The Effect of Micro and Nona Silica Addition on the Filtration and Mud Cake of Drilling Fluid

The selection of suitable materials as components of the drilling fluid remains the primary concern of the mud engineer. Micro and nanomaterials represent dense and effective complementary additives to the drilling fluid. In this paper, both micro silica and Nano silica were used in order to find the effect of each on the properties of drilling fluid in general and filtration in particular. Where the results showed that each of them has an effective and different role in improving the properties of drilling fluids in general and filtration in particular. although they are one material, but nanotechnology has contributed to making Nano-silica more efficient and effective than micro-silica. Both materials reduce the permeability of the mud cake and reduce the volume of the filtrate, as well as increase the viscosity, yield point and gel strength. As for density and acidity, fine silica had the biggest effect. Where it can be used as a heavy material, as well as the effect of adding micro silica on the PH value has been studied, as the results prove that the proportion is direct. As for Nano silica, it did not have a significant effect on the density or the pH. The results showed that Nano-silica is the most efficient for reducing filtration, followed by CMC, then PAC, then micro-silica It was found that if the percentage of addition was 25%, the filter volume value is as follows: 0.5 cc for Nano silica, 1.9 cc for CMC, 2 cc for PAC and 3 cc for micro silica. The addition of Nano-silica gave a cohesive clay cake with a permeability of 1.84, five times lower than what was provided by PAC for a 25% addition ratio.

Enhancing of spacer fluids compositions for well cementing

Currently, almost all researchers believe that turbulent flow is the most preferred displacement mode. However, when it comes to cementing, where practical limitations prevent obtaining turbulent flow, opinions begin to differ. In general, either «very slow» flow or «very fast» flow is recommended for all wells in the annulus. There are mainly two types of buffer liquids used – «wash» and «space». The first buffer liquid is «wash», which washes away and removes the remnants of drilling fluid, clay cake, etc., and the second is «space», a thicker system, entering the cavities, cleans them and also pulls out all the remnants of the first buffer liquid to the surface. The first buffer fluid is «wash», basically a thinner, of the drilling fluid, which may contain surfactants - surfactants or liquid-restraining agents, the preferred mode of motion is turbulent. The second buffer liquid – «space», can mainly contain polymeric materials, weighting agents, the preferred mode of movement is laminar (cork). The choice of these fluids is determined by their chemical compatibility with drilling and cement slurries, their effectiveness in removing the drilling fluid. Very important postulates adopted by almost all leading oil firms are given. A new and very affordable composition of the buffer liquid of the following composition has been proposed: «wash» - FLS - 4%, diesel fuel - 2%, the rest is water - 9%; «space» - carboxymethylcellulose (CMC) - 0.5%, bentonite solution with a density of 1030 kg/m3 - 99.5%. If necessary, these buffer fluids can be weighted, for example, with barite, to an average density between the densities of drilling and cement slurries in a given well.. Keywords: buffer fluid; drilling fluid; cement mortar;turbulent flow; mode of motion; mud cake; centralizer; casing string.

DEVICE AND TECHNOLOGY OF CONTINUOUS WELL FLUSHING

Link for citation: Tretyak A.Ya., Litkevich Yu.F., Kruglova T.N. Device and technology of continuous well flushing. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.181-188. In Rus. The relevance research is due to the fact that at present a large number of accidents occur due to the stoppage of the rotation of the drill string and the cessation of flushing during the build-up of the drill string. Staying the wellbore for some time at rest, and then creating flushing fluid pressure pulses accompanying the start and stop of mud pumps, can lead to undesirable phenomena and complications in the form of sticking. Sticking can be mechanical, due to the complex geometry of the wellbore, falls into the rocks from the walls of the well, the formation of cuttings at the bottom of the well due to insufficient flushing of the well. The percentage of such accidents can reach 20. Up to 80 % of differential sticking is due to the pressure difference – hydrostatic, formed in the wellbore due to the density of the drilling fluid, and reservoir, formed in the well formation. Due to these processes, water infiltration from the drilling fluid into the formation occurs, and a thick polymer clay cake is formed on the well walls, which contributes to the formation of differential sticking, that is, the sticking of the drill string to the well walls. The purpose: to develop a device and technology for continuous flushing of wells when building a drilling tool. Objects: device and technology for continuous well flushing. Methods. A device for continuous flushing of the well, consisting of synchronously overlapping on-off valves that provide continuous flushing of the well when building up the drilling tool is proposed for manufacturing. A mobile crane switching synchronizer is described, its design and principle of operation are given. Technological methods are proposed that realize the possibility of the device operation. Results. The solution of the task set made it possible to develop the design of the device and the technology of continuous flushing of wells.

USE OF A SPECIAL LOG COMPLEX FOR STUDYING THE PROPERTIES OF RESERVOIR FLUIDS AND ROCKS OF THE SEDIMENTS OF THE CRETACEOUS AND JURASSIC AGES OF THE ARYSTANOVSKOYE FIELD

The properties of formation fluids and reservoir rocks of the Cretaceous and Jurassic periods deposits of the Arystanovskoye field are given in the article. In the A-418 well drilled within a new poorly explored area, the special well logging methods have been used to assess the prospects of the area and identify possible watering out: multi-frequency electromagnetic propagation logging (MEPL) Dielectric Scanner and high resolution nuclear magnetic logging (NML) CMR-Plus. Properties of formation fluids and reservoir rocks of the Cretaceous and Jurassic deposits of the Arystanovskoye field were determined using these methods. The qualitative characters of reservoirs were used for reservoir quality discrimination such as: decreased values of natural radioactivity, volume density and hydrogen content, clay cake availability, availability of radial penetration profile by electrical resistivity diagrams. The results of the research can be used during the selection of development targets, the selection of methods for hydrocarbons recovery. The relevance of this study is confirmed by the fact that the Arystanovskoye field is currently under development. The research of reservoir rocks in the new A-418 well within the 801–3095m interval will help to perform the reserves update and choose the production method.

DEVELOPMENT OF OPTIMAL COMPOSITION OF DRILLING FLUID FILLER FOR OPEN HOLE WELL COMPLETION

Experimental studies were carried out to determine the effect of inert fillers on the filtration properties of clay cakes during their formation. The sequence of experiments corresponds to the sequence of stages: formation of the main structure of the filter cake (simulation of the opening process by drilling), treatment of the bottomhole zone to restore the initial permeability (for example, during chemical destruction of the filter cakes) and washing out of process fluid filtrates from the bottomhole zone into the well. The solid phase in the drilling fluid can be represented by both structure-forming clay particles and fillers (barite, crushed cuttings, bridging agents, etc.). Moreover, fillers can have individual particles of a size of a colloidal degree of dispersion and significantly affect the filtration performance of drilling suspensions. It is especially important to evaluate the influence of the composition of the solid phase of the clay suspension on the filtration properties at the stage of formation of the main structure of the filter cake. This stage is characterized by a non-stationary filtration process. In essence, the bulk of the studies of filtration processes is carried out in this mode. In our case, it is necessary to determine the dependence of the filtration index of solutions Пр on the composition of the solid phase. In the course of experimental studies, it was confirmed that subsequent filtration through the cakes formed at stage 1 equally depends on the magnitude and nature of the drawdown application, as in stage 1, as well as on the permeability of the filter cake and the clogging zone. Therefore, the research methodology at stage 2 required supplementing experiments with the formation and modification of filter cakes during filtration through permeable sand packs.

Improving energy efficiency in well construction through the use of hydrocarbon-based muds and muds with improved lubricating properties

During the construction of directional wells in spatially curved sections of the barrel, large contact loads and huge resistance to the movement of the drill string during lifting can occur, which leads to increased wear of the drill pipes and high energy costs. One of the directions for increasing the energy efficiency of drilling such wells was the reduction of friction at the metal-metal, metal-rock, and metal-filter cake boundaries. This result can be achieved by introducing special lubricating additives or by switching to a hydrocarbon solution during drilling. The article presents the study of drilling fluids with the introduction of lubricating additives on a lubricity tester Fann EP / Lubricity Tester Model 212, a device for determining the coefficient of clay cake KTK-2, a rotary viscometer Fann 35SA, pH meter Crison GLP 21 to reduce the coefficient of friction of a pair “metal – metal” in a clay solution, which amounted to 70-75%, in an aqueous solution - up to 65%. The optimal concentration of the additive according to the study in different drilling fluids was about 1.5-2%. The results of a study of the effect of the speed and time of mixing a hydrocarbon-based solution during its preparation on the electrostability of the emulsion obtained are carried out on a BVD device, which showed a significant increase in the stability of the washing liquid to 24%, which leads to a decrease in the number of complications associated with pipe wear and a decrease torque when rotating the column.

Tuning the chemistry of seawater with activated clay: an application in SmartWater enrichment for enhanced oil recovery

Studies on the interaction between crude oil, brine, and rock systems showed that the composition of water injected into the oil reservoir influences the amount of oil recovered from such a reservoir. Therefore, researchers are now emphasizing the use of SmartWater for enhanced oil recovery (EOR). In this research, the capability of activated clay to be used for tuning the chemistry of seawater for subsequent production of SmartWater was investigated. Filter cakes were formed using bentonite and its blends with raw clay and activated clay (which was produced in-house using locally obtained clay samples). The capability of the cakes to control the transport properties of permeating seawater was evaluated in terms of ion rejection. The average rejection for the raw clay cake for Na+, K+, Mg2+, and Ca2+ is 4.45, 49.64, 53.33, and 94.43%, respectively. The rejection results for the mixed-matrix cake containing the activated clay were 6.38, 51.34, 86.19, and 78.09 for Na+, K+, Mg2+, and Ca2+, respectively. It was observed that the selectivity of the filter cake for Mg2+ and Ca2+ was reversed due to the addition of the activated clay. Thus, activated clay possesses some potentials for SmartWater production for an EOR application.

Development of spacer fluids and cement slurries compositions for lining of wells at high temperatures

Article is devoted to creation of new compositions of process solutions for lining of directional wells at high temperatures. Developed compositions provide high durability characteristics of cement stone. It is shown that with an increase in packing density of cementing slurry components durability characteristics increase and porosity and permeability of cement stone decrease, whereas an increase in temperature and pressure leads to a significant increase in compressive and bending durability, which is associated with presence of quartz in them.
 It has been established that introduction of special structure-forming additives to the composition of developed cementing solutions allows formation of sedimentation-resistant cement systems that can provide an increase in durability characteristics of cement stone and, in general, quality lining of directional wells. Study of rheological properties of developed cementing compositions showed that the systems have high yield strength at increased temperatures and pressures.
 Developed compositions of water-based spacer fluids increase the cleansing degree for both casing and rocks surfaces from mud and clay cake residues, which improves the cementing quality of oil and gas wells.
 Mechanism for increasing the washing ability of spacer fluids and durability characteristics of cement stone, depending on composition and properties of their constituent components, is disclosed.

Microstructure of clay fabric in electrokinetic dewatering of phosphatic clay dispersions

Abstract Electrokinetic dewatering is considered a promising method for separation of water from clay dispersions in the mining industry. Numerous studies over the past few decades have been conducted on electrokinetic dewatering process in order to identify potential performance improvements. However, little is known about the impact of process on clay microstructure that determines its water content. Here, for the first time, scanning electron microscopy (SEM) was utilized to study the impact of electrokinetic dewatering process on clay fabric microstructure. The studies were conducted on three experimental platforms including 1) a gravity settling experiment to determine the clay structure in the absence of an electric field, 2) a cylindrical tank in which a static electrokinetic separation process was conducted under an electric field applied along the tank height and 3) a continuous dewatering system in which electrokinetic separation took place in two stages along a conveyer belt. The studies suggested that formation of honeycomb microstructures was responsible for poor settling and an acidic environment promoted a more voluminous honeycomb with a higher water content. Under an electric field, a less-ordered structure than a honeycomb was formed during the electrophoresis separation process near the region where the pH was above the point of zero charge. The less-ordered structure was later compressed (i.e. the structure partially collapses) in the 2nd stage of the continuous system in which an already formed clay cake was dewatered through the electro-osmotic process. The insight provided in this study can help improve the performance of electrokinetic separation process.

(Invited) Electrokinetic Separations to Increase the Percent Solids of the Effluent from a Phosphate Mine

Phosphate mining operations create a waste product, consisting of a dilute clay/sand/phosphate suspension that, due to the properties of the suspended solids (primarily clay), requires 25 to 50 years to densify via hindered settling and self-weight consolidation. The objective of this research was to develop and apply an effective electrokinetic separation process to phosphatic clay suspensions, generated during the beneficiation of phosphate ore, a major component of fertilizer. The use of an electric field to separate the water from the solids is attractive because the inherent stability of the clay suspension is due, in part, to the surface charges residing on the platelets.Previous work by others has demonstrated the feasibility of batch-wise electrokinetic separation of phosphatic clay suspensions, but the process is widely regarded as uneconomical. The present research is predicated on the assumption that an economically feasible separation requires a continuous, electrokinetic separation procedure.Solid-liquid separation represents a significant problem for the phosphate mining industry The waste suspensions, initially containing 3-5 wt% solids, are pumped to large impoundment areas termed clay settling ponds. When incorporated, the addition of flocculating agents produce a rapid, but partial, separation, to approximately 10 wt% solids. A further increase in solids content proceeds very slowly. Hindered settling, followed by self-weight consolidation, requires as much as 25 years to reach a solids content of 40 wt%. This is an important target value, because its shear strength will then allow the addition of a surcharge (typically a sand cap) to increase the consolidation rate and magnitude. Through a systematic development of prototypes, from batch to semi-continuous with emphasis on water clarification to semi-continuous with emphasis on solids extraction, our team has developed a fully continuous electrokinetic dewatering prototype. The system takes advantage of the charged nature of the suspended solids. When subjected to an applied electric field, the solids are attracted to the anode and clarified water is collected at the cathode. The process is capable of generating a 40 wt% clay cake and clarified water with turbidity levels below 1 NTU within hours rather than years. Optimization of the design was possible by developing a constitutive relationship between the final solids content, the applied electric field, and the residence time. Successful implementation of a continuous electrokinetic separation process will reduce the vast amount of water consumed by industry. While the process was developed for phosphatic clay suspensions, it is anticipated that electrokinetic dewatering may be applicable to other mining operations such as those associated with the oil sand tar tailings in Canada. This presentation will describe the current state of development, including energy and power requirements.

The effects of pre-existing discontinuities on the surface expression of normal faults: Insights from wet-clay analog modeling

We use wet-clay analog models to investigate how pre-existing discontinuities (i.e. structures inherited from previous tectonic phases) affect the evolution of a normal fault at the Earth's surface. To this end we first perform a series of three reference experiments driven by a 45° dipping master fault unaffected by pre-existing discontinuities to generate a mechanically isotropic learning set of models. We then replicate the experiment six times introducing a 60°-dipping precut in the clay cake, each time with a different attitude and orientation with respect to an initially-blind, 45°-dipping, master normal fault. In all experiments the precut intersects the vertical projection of the master fault halfway between the center and the right-hand lateral tip. All other conditions are identical for all seven models. By comparing the results obtained from the mechanically isotropic experiments with results from experiments with precuts we find that the surface evolution of the normal fault varies depending on the precut orientation. In most cases the parameters of newly-forming faults are strongly influenced. The largest influence is exerted by synthetic and antithetic discontinuities trending respectively at 30° and 45° from the strike of the master fault, whereas a synthetic discontinuity at 60° and an antithetic discontinuity at 30° show moderate influence. Little influence is exerted by a synthetic discontinuity at 45° and an antithetic discontinuity at 60° from the strike of the master fault. We provide a ranking chart to assess fault-to-discontinuity interactions with respect to essential surface fault descriptors, such as segmentation, vertical-displacement profile, maximum displacement, and length, often used as proxies to infer fault properties at depth. Considering a single descriptor, the amount of deviation induced by different precuts varies from case to case in a rather unpredictable fashion. Multiple observables should be taken into consideration when analyzing normal faults evolving next to pre-existing discontinuities.

Development of Electrokinetic Dewatering for Phosphate Mine Tailings

Solid-liquid separation represents a significant problem for the phosphate mining industry. A dilute suspension of phosphatic clays is a waste product of the phosphate ore beneficiation (mineral processing). The suspensions, containing initially 3-5 wt% solids, are pumped to large impoundment areas termed clay settling areas. Addition of flocculating agents causes a rapid but partial separation, resulting in a suspension containing roughly 10 wt% solids. Further increase in solids content, however, proceeds very slowly. Hindered settling and self-consolidation of clay requires as much as 25 years to reach a solids content of 40 wt%. In central Florida, clay settling areas cover over 150 square miles, representing 30% of the mined land.Discovery of new exploitable phosphate ore deposits in Florida, coupled with increased environmental awareness as reflected by regulatory agencies, has motivated a search for a technology that can achieve rapid and economic separation of solids from water. The use of an applied electric field for dewatering was explored in the late 1990s. Electrokinetic separation was found to be promising, but the technology was not considered economical.Under funding from Mosaic, a major phosphate mining company, our group produced bench-top results similar to those reported in the literature. Using a large number of experimental results, we then identified constitutive relations among the increase in solids content, the electric field, and the elapsed time. The analysis showed that for short times, an increase in solids content could be achieved at any electric field, but the maximum increase depended on the strength of the electric field. The constitutive relation was used in boundary element simulations for application of electrokinetic separation to an existing clay settling area. The energy costs were found to be acceptable, but the power requirement was prohibitive.We turned then to development of a fully continuous electrokinetic separation device that could be used as a process unit for a beneficiation plant. This development was stepwise. A semi-continuous system was designed for continuous removal of supernatant water. Under pseudo-steady-state operation, low-turbidity water (<10 NTU) was separated from a clay solids suspension by a combination of electrokinetic dewatering and gravity settling.A second semi-continuous system, which introduced a rotating belt between electrodes to facilitate removal of clay sludge, was designed and tested. A series of small-scale batch experiments were used to identify the optimal belt properties. A constitutive relation similar to that developed for batch operations showed that this system had greater efficiency. This equipment produced thickened clay cake with a solids content greater than 33 wt%. The information obtained from the semi-continuous prototypes was used to design a fully continuous system which provides both clear water and thickened clay.The academic team working on the development includes chemical, mechanical, and civil engineers. The approach taken can be characterized as application of fundamental engineering science to a practical problem of great societal importance.

Evolutionary Development for Electrokinetic Dewatering of Phosphate Mine Tailings

The processing and storage of phosphatic clay suspensions (or mine tailings) which result as a waste product from phosphate mining industry represent an important economic and environmental problem. A very long time is required to allow gravity-driven settling of clay suspensions with an initial 2-3 wt% solids content, and decades may be required to reach 25-30 wt% solids content. The associated impoundments occupy over 100 square miles of land in Florida alone.A combination of experimental and modeling approaches were used to explore the use of imposed electric fields to achieve electrokinetic separation. Batch experiments were used to guide the development of a constitutive relationship describing the changes in solids content with time (t) and applied electric field (E)1,2. A linear behavior between final solids content and Et was found in at short times, and the upper limit of separation was controlled by the value of electric field only.Subsequently, a semi-continuous system was designed for continuous removal of supernatant water. This system allowed measurement of supernatant turbidity, pH, and changes in solids content as functions of applied electric field, flow rate, and settling time. Under pseudo-steady-state operation, low-turbidity water was separated from a clay solids suspension by a combination of electrokinetic dewatering and free settling. A semi-continuous system, which introduced a rotating belt between electrodes to facilitate removing clay sludge, was designed and tested. The batch experiment set up was used to optimize fabric selection. This equipment was able to continuously producing thickened clay cake with a solids content of up to 33 wt%. Evaluation of parameters including electrode spacing, electric field, and residence time provided an understanding of the path for optimization. A similiar constitutive relationship as in batch experiment was also estanblished which correlates final solids content to electric field and residence time.All the systems were also evaluated from an econonic perspective. The energy requirement of the semi-continuous operation that facilitated sludge removal had a lower energy requirement value at a given electric field as compared with the result from batch experiments and the previous semi-continuous operation. All systems followed the trend that high electric fields have a high energy requirement. References J.P. McKinney, M.E. Orazem, A constitutive relationship for electrokinetic dewatering of phosphatic clay slurries, Miner. Metall. Process. 28 (2011) 49.J.P. McKinney, M.E. Orazem, Electrokinetic dewatering phosphatic clay settling areas: numerical simulation and economic assessment, Miner. Metall. Process. 28 (2011) 71.

Influence of initial fabric on fractures developed in shear zones in clay

We examine the influence of initial fabric on the development of fractures in experiments in which clay cakes are sheared over two horizontal base plates that move past each other in wrench-fault motion. An anisotropic fabric in the kaolinite was produced during the preparation of the clay cakes for these experiments. To produce the fabric, the clay was either screeded perpendicular to the underlying fault, screeded parallel to the underlying fault, or molded to develop a cake-parallel fabric that is isotropic in the horizontal plane. The influence of the initial fabric is striking. With cake-parallel fabric, both Riedel (R) and conjugate Riedel (R′) shears develop, the former being much more pronounced than the latter. With a fault-parallel fabric, only R shears developed, while with a cake- and fault-perpendicular fabric, only closely spaced high-angle shears developed initially, with more widely spaced R shears forming later. There is a difference in the orientation of the R shears in the three types of fabric, with the angle being smallest for a fault-parallel fabric (mean of initial fractures of 15°) and largest for a fault-perpendicular fabric (mean of initial fractures of 25°). The high-angle shears have an initial average angle of 80° for cake-parallel fabric and 100° for fault-perpendicular fabric. Only in the case of the high-angle fractures for a fault-perpendicular fabric is there significant rotation after formation. It is likely that the difference in fracture orientation attributed to anisotropy of the initial fabric of the clay also has its counterpart in nature and is not confined to fractures formed in shear zones.

Virus removal efficiency of ceramic water filters: effects of bentonite turbidity

Ceramic water filters (CWFs) are utilized in many developing countries as point-of-use (POU) water treatment devices, to reduce waterborne pathogens in potable water. Virus removal efficiencies of several CWFs are investigated under various influent conditions using MS2 (ATCC: 15597-B1) as a surrogate phage for human enteric viruses. The addition of bentonite turbidity (6–8 NTU) in the influent source water showed increased viral removal efficiency of CWFs by 0.1–0.2 log compared to tests involving clear (&amp;lt;1 NTU) influents. Trials employing an applied clay cake layer, formed using highly turbid influent source water (100 NTU) and no cleaning regime between trials, resulted in viral removal efficiency values of 1.5–2.5 log, compared to 0.2–0.5 log during non-obstructed trials.

Controls of listric normal fault styles in the northern Gulf of Mexico: Insights from experimental models

Passive margins such as the Gulf of Mexico are characterized by two distinct styles of faulting. Homogenous sand/shale packages in offshore Texas mostly display basinward-dipping listric normal faults with associated rollover structures cut by synthetic and antithetic faults. The fault traces are generally long and show a linear trend. Stratigraphic packages with a ductile substratum (salt) in offshore Louisiana are characterized by basinward and landward-dipping, short arcuate faults detaching within the salt. The structures consist of a series of half-grabens, with the movement of salt from the front to the back of each fault block. Clay experimental models are used to study the controls of fault geometries in the two structural styles and their interaction to form complex transfer zones. The surface of the clay cake is laser-scanned to enable 3D visualization and accurate measurements of structures. The results suggest that within homogeneous sand-shale packages, the dips of the faults and their locations are primarily dependent on the direction of the drop down of the basal detachment along pre-existing discontinuities, with the slope of the basal discontinuity and the direction of extension providing secondary controls. On the other hand, the dips of fault systems in packages underlain by a ductile substratum are primarily controlled by the slope of the basal detachment. Therefore, the more common regional Roho systems typically form above salt sheets with initial basinward slopes, whereas counter-regional fault systems form above salt sheets with initial landward slopes. The direction of extension and the presence of small pre-existing discontinuities impart only secondary controls when ductile basal units are involved. The faults initiate at the head of ductile layer and propagate downslope. Complex transfer zones develop at the boundary of the ductile substratum due to interference between the two fault styles.

A New Centrifugal Testing Method: Descending Gravity Test

Abstract This paper presents a new centrifugal testing method that has been developed to observe the effects of void ratio and overconsolidation ratio on the generation of undrained shear strength in cohesive soils. This new method provides soil profiles of constant overconsolidation ratio and varying void ratio throughout the sample profile. Combinations of this method with various in situ shear strength tests such as the cone penetration test and the vane shear test constitutes a new methodology which is named the “descending gravity test” (DGT). When DGT is repeated for different acceleration levels during centrifuge testing, it provides the void ratio-undrained shear strength relationship for various magnitudes of overconsolidation ratio. Therefore it renders the observation of the uncoupled effects of void ratio and overconsolidation ratio on the generation of shear strength feasible. Additionally the method requires the unloading of the clay cake, and since swelling of a sample is more rapid than its consolidation the test takes a relatively short time, hence the method is efficient.

Modification of clay cake permeability by adsorption of protein

During tangential filtration of solid-liquid suspensions, cake formation occurs at membrane surface, a major consequence of which is a decline of flux to, at best, a limit value. In order to show the influence of the composition and properties of the fluid on cake formation, experiments have been performed with a colloidal suspension of clay in the absence or in the presence of protein. We have studied the effects of solution characteristics (ionic strength and pH) on physico-chemical properties of the suspension, such as mean diameter and zeta potential and on separation performances such as ultrafiltration limiting flux. By taking into account electrostatic interactions, it has been possible to explain (i) the evolution in the adsorption isotherms of the protein on the clay with the physico-chemical conditions (ii) the consequences of this adsorption on the limiting flux.

Impoundment Liner Repair by Electrophoresis of Clay

Electrophoresis of clay particles from dilute suspensions is an innovative technology to seal leaks in operating surface impoundments that does not require removal of impoundment contents, exposure of workers to contaminants, or prior knowledge of the leak locations. A suspension of clay particles is added to the impoundment liquid. A cathode (negative electrode) is placed inside and an anode (positive electrode) is placed outside the leaking impoundment. A direct current (DC) electric field is imposed externally across the geomembrane liner through the leaks. The clay particles migrate to the leaks under the influence of the imposed electric field to form a clay cake seal. The results of laboratory experiments to evaluate the use of a DC electric field to direct migration of clay particles into a leak and the hydraulic integrity of the resulting seal are presented in this paper. The effects of clay type, clay particle concentration in suspension, size of leak, and electric field strength on the migration of clay particles and process of cake formation are evaluated. The sealing effectiveness and internal structure of the resulting clay cakes are examined by hydraulic conductivity measurements and nuclear magnetic resonance imaging. Electrophoretic mobilities of bentonite particles in different chemical environments were also measured to evaluate the feasibility of the technology in practical situations.