Rock Cuttings Research Articles

Updated Geologic Structures and Stratigraphy of the Darajat Geothermal Field in Indonesia

The main objectives of the evaluation of the geologic structures and stratigraphy of the Darajat geothermal field are to refine and update both the Darajat conceptual and geologic1 models. Re-interpretation of the borehole image logs, additional petrographic analysis of rock cuttings and cores, integration of subsurface data from the wells drilled during 2009-2011, and recent resource observations allowed definition of at least seven (7) lithologic units based on the dominant rock type. The updated stratigraphy of the reservoir was correlated with the surface rocks to develop a volcano-stratigraphy and geochronology of the Darajat geothermal system. The andesite-intrusive complex, which comprises the Darajat geothermal reservoir and the hypothesized sub-volcanic portion of an earlier liquid-dominated geothermal system, belongs to the Kendang Volcanics and makes up subsurface Units A and B. The interpretation of the major volcano-tectonic features and structures at Darajat was refined through the analysis of the Light Detection and Ranging (LIDAR) data/imagery that was acquired in 2014. The LIDAR Digital Elevation Model (DEM) hill-shade map shows several conspicuous volcanic vents in Puncak Cae, Gagak and Kiamis. The prominent Kendang Fault, which extends to the Kamojang Field in the northeast, might be a section of the ring structure of an earlier volcano, herein, called Kendang. Wellbore image data from several wells suggest that the Kendang Fault may dip at 70° eastward. Although needing further substantiation, we hypothesize that the decompression event that preceded the development of the steam-dominated geothermal reservoir at present might be related to the eruption of the Kendang volcano. The Gagak Fault is another prominent surface structure and believed to form during the eruption of the resurgent Gagak volcano after the eruption of the older Kendang volcano.

Petrological, Chemical, and Mineralogical Characterization of Anka (Zamfara State) Manganese Ore

Manganese deposit reserves exist in Nigeria, which have potentials as raw materials for industrial applications such as batteries, steel and electrical appliances. The present level of exploitation of Manganese is very low and, in most cases, appropriate processing would be necessary to attain desirable qualities. This paper provides petrological, chemical and mineralogical characterization of manganese ore in Anka area of Zamfara state, Nigeria. A chip of about 1/8 of an inch and about 1 inch by 1 inch was cut from the lumps of Anka (Zamfara state) manganese sample using rock cutter, after which their surfaces were trimmed and the chip was mounted on a grinding machine to make the surface smooth. The samples were mounted on a slide and viewed using Leica Petrological Microscope. 500 g of the ore was weighed using digital weighing balance. The sample was crushed and ground until 80% passing of 250µm is achieved. The ground ore was blended homogenously before the analysis while for the ore microscopy study, true fraction representative of the manganese ore samples were prepared, polished mounts and characterized using Scanning Electron Microscope-energy dispersed X-ray (SEM/EDX). However, X-ray Fluorescence was used to determine the chemical composition while identification of the associate mineral phase was done using X-ray Diffraction. From the petrological analysis carried out on the crude samples reveals the presence of heavy mineral and segregation distribution of the mineral. The XRF results shows 77.81% MnO, 60.26% Mn, 10.9% Fe2O3, 4% Al2O3 while Spessartine (3MnO.Al2O3, 0.830), Silicon oxide (SiO2, 1.122), Quartz (SiO4, 0.728), Pyrolusite (MnO, 1.543), and Almandine (Fe3Al2SiO12, 1.583) were identified as the major phases in the ore.

Effect of eccentricity and inner pipe motion on flow instability for flow through annulus

Present work implements the Energy gradient method (EGM) to study the effect of variation in eccentricity, radius ratio and inner pipe movement on the fully developed flow of Newtonian fluid through an annulus for the flow instability. The formula for the flow stability parameter has been derived considering the eccentricity and radius ratio of the annulus. Results have been plotted for flow stability parameter (K) for annulus of various eccentricity and radius ratio. Further, the relationships for the critical flow parameter have also been obtained. Flow instability is very crucial parameter in oil well drilling process as turbulent flow is desirable for the transportation of rock cuttings to the surface generated during the process.

Interpretation of gravity data to delineate the subsurface structures and reservoir geometry of the Aluto–Langano geothermal field, Ethiopia

The Aluto–Langano geothermal field is located within the central-southern part of the Main Ethiopian Rift, about 200 km southeast of Addis Ababa. This study analyzes gravity data to define the geometry of the geothermal reservoir and subsurface geological structures controlling the geothermal system. A Bouguer anomaly map of the area was generated using a Bouguer density of 2.49 g/cm3, which was obtained from the gravity dataset using different optimization methods. In order to highlight the structures of interest in the calderic system, a regional-residual separation was conducted. The map produced shows two dominant high Bouguer anomalies underlying Aluto caldera associated with the presence of basaltic rocks and the occurrence of fumarolic activity. Analysis of horizontal gradients of gravity data showed that the area is characterized by the presence of high gradient anomalies associated with geothermal manifestations. A 3-D gravity model for assessing the geothermal heat source architecture within the Aluto caldera area is also presented. The model was constrained using the estimated densities of rock cuttings obtained from drilled wells. The results from 3-D modeling imaged a high-density body at depth surrounded by a less-dense body (∼2.55 g/cm3), which is interpreted to be the geothermal reservoir. The model was then interpreted together with surface manifestations, lithology, and geological structures. The less-dense body found west of the Adonsha fault lineament could be the expression of the second reservoir, which is likely deeper than the productive reservoir found along the NNE–SSW trending structure (i.e., the Artu Jawe Fault Zone) in the central area.

Soil Contamination Assessments from Drilling Fluids and Produced Water Using Combined Field and Laboratory Investigations: A Case Study of Arkansas, USA.

Rotary drilling for oil and natural gas uses drilling fluid for lubrication of the bit, to seal off unstable shale layers, and floating out rock cuttings. Drilling fluid is a water–clay chemical mixture. Produced water is a water–sand chemical mixture. Land farming is a common disposal technique of drilling fluid and produced water. In the land farming process, amendments of fluid are repeatedly applied to the soil surface. Plant growth and soil chemical properties may be altered by additions of drilling fluid, because of alkalinity, salinity, trace elements, and petroleum residue contained in waste. The objective of this study was to determine the change in soil pH, electrical conductivity (EC), total nitrogen and carbon, and extractable nutrient levels following the land application of drilling fluid and produced water. The study was a comparison of three plots with similar soil properties and conditions. The three study plots had various levels of drilling fluid and produced water applications. The data show a major difference from field-to-field for EC, Na, and Cl levels. The EC and salt levels increased with additional applications of drilling fluid and produced water. The percent total nitrogen values and plant available P levels were very low in all fields. High EC and salt values, coupled with low N and P levels, would be detrimental to plant growth and development. To successfully vegetate this land-farm site, application of N and P fertilizer would be required. This study help to give a better understanding of practical ways to land-farm drilling fluid and produced water in a fashion that both minimizes environmental issues and is economically feasible in Arkansas. Thus, this research will provide important information for soil contamination management and contributes on understanding of the responses of soil properties to drilling fluid and produced water in the future.

Heat Moisture Modified Rice Flours as Additive in Drilling Fluids

Drilling mud is a dense, viscous fluid mixture used in oil and gas drilling operations to bring rock cuttings to the earth's surface from the boreholes as well as to lubricate and cool the drill bit. Water-based mud is commonly used due to its relatively inexpensive and easy to dispose of. However, several components and additives in the muds become increasingly cautious and restricted. Starch was introduced as a safe and biodegradable additive into the water-based drilling fluid, in line with an environmental health concern. In this study, the suitability of four local rice flours and their heat moistures derivatives to be incorporated in the formulation of water-based drilling fluid was investigated. They were selected due to their natural amylose contents (waxy, low, intermediate, and high). They were also heat moisture treated to increase their amylose contents. Results showed that the addition of the rice flours into water-based mud significantly reduced the density, viscosity, and filtrate volume. However, the gel strength of the mud was increased. The rice flours, either native or heat moisture treated, could serve as additives to provide a variety of low cost and environmentally friendly drilling fluids to be incorporated and fitted into different drilling activity.

Research on rock breaking mechanism and load characteristics of TBM cutter based on discrete element method

Tunnel boring machine (TBM) is a large-scale tunnel engineering equipment, which has unparalleled advantages in safety and work efficiency. The cutter is subjected to complex and variable random impact loads, resulting in damage to bearings, cutter rings, and cutter shafts. Therefore, based on the discrete element simulation platform and experiment, this paper established the cutter rock simulation model based on the experimental data, and analyzed the rock breaking process, cutter load magnitude, and variation law. The research results show that when the cutter pole diameter decreases from 200 mm, 100 mm, and 0 mm in sequence, the rolling force increases accordingly, and the maximum increase of the rolling force is 56%. Meanwhile the lateral force decreases and the maximum average decrease value is 26%. Moreover, the rolling force showed a downward trend with the increase of the cutter spacing. When the cutter spacing is increased from 80 mm to 120 mm, the average rolling force decreases by 51%, and the maximum value rises slightly, increasing by 2%. And, the lateral force tends to increase, with an increase of 17% and the maximum lateral force value increase was 29%. The results can provide load input reference for TBM cutter layout, cutterhead structure design, and performance evaluation.

Influence of polypropylene beads and sodium carbonate treated nanosilica in water-based muds for cuttings transport

The drilling for hydrocarbons from oil and gas wells requires efficient drilling fluid and cutting-edge drilling technology. Furthermore, the removal of rock cuttings from oil and gas wells while drilling is a vital task of the drilling fluid, particularly in large-angle wells and long-range drillings. The rock cuttings if not transported to the surface effectively can result in severe costly drilling problems of drag and torque, pipe sticking, faster bit damage, etc. This research suggests a new method that applies polypropylene beads (PP) and silica nanoparticle (NS) treated by sodium carbonate (Na2CO3) to enhance the cuttings transport efficiency (CTE) of water-based mud (WBM). Tests were carried out in laboratory-scale cuttings lifting rig simulator equipped with a 20-ft. Long annulus, a 2.75-in. ID outer acrylic pipe, and an inner drill pipe of 1.05-in. OD. Six different 10 ppg weighted mud samples were formulated and coded mud nos. 1–6 using PP beads and Na2CO3 treated NS concentrations. Four cuttings sizes in the range between 0.4 and 4.0 mm at various hole angles (0°, 30°, 60°, and 90°) without pipe rotation were evaluated using a constant flow rate of 5.13 L/s. The results of rheological characterization using Herschel-Buckley model showed that all the mud systems are shear-thinning as the flow behaviour index ranged between 0.50 and 0.60. The fluid consistency parameter of the WBM indicates that the addition of PP beads and NS concentrations decreases the viscosity of the WBM. Also, the viscosity, yield point, gel strength, and filtration parameters of the WBM were decreased when the PP beads and NS concentrations were introduced before and after thermal aging experiments. This interprets the thinning nature of the mud systems. However, when these products were applied to lift cuttings to the surface, the lifted cuttings increased. The optimum mud system using Bingham plastic expression was found at mud no. 6 (BM-PP8-NS1) containing apparent viscosity of 30.5 cP at a shear rate of 1022 s⁻1, plastic viscosity of 13 cP and a yield point of 35 lb/100 ft2 at 78 °F. Cuttings size and hole angles seem to wield significant influence on CTE as the smallest cuttings (0.4–1.4 mm) were easier to be lifted in the vertical hole (0° angle), while the largest ones (2.8–4.0 mm) were the most lifted in the horizontal section (90° angle). The findings of this study can help for a better understanding of the mud performance of PP beads and Na2CO3 dispersed NS mixture for cuttings transport in a wellbore.

The Artabba Fortress (E.P. 364): The Discovery of a Hasmonean-Herodian Fortress on the Northern Border of Judea

The Artabba fortress, a site until recently unknown, is located at the summit of a high hill; its monumental remains were exposed by chance during development work carried out by residents of the nearby village of Deir Abu Mash’al. The remains included fortifications, architectural elements, five huge cisterns, ritual baths and storage pits, as well as various rock cuttings and numerous potsherds from the Hellenistic and Early Roman periods. These finds, especially the fortifications and the impressive water-supply system, are the principal features of sites in the Judean Desert and the settled areas of the country where there were fortresses from the Second Temple period. The archaeological finds, in conjunction with geographical and historical information, make it possible to date the fortress to the time from the reign of Simeon the Hasmonean to the end of Herod’s reign. The discovery of the Artabba fortress sheds light on the history of settlement in northern Judea in the Second Temple period.

Rock Mass Discontinuity Extraction Method Based on Multiresolution Supervoxel Segmentation of Point Cloud

Discontinuity sets play an essential and pivotal role in the deformation monitoring and stability analysis of the rock mass, but there are still many challenges for accurately and rapidly extracting discontinuity. In this study, an extraction and characterization method of discontinuity sets based on point cloud supervoxel segmentation was proposed, which consists of four parts: 1) a multiresolution supervoxel segmentation (MRSS) algorithm was developed to classify unstructured point cloud into multiresolution facets and discrete points; 2) to extract the individual discontinuity, the single supervoxel that having spatial connectivity, similar planarity, and parallelism was clustered; 3) the orientation of individual discontinuity was calculated, respectively, based on the plane fitting parameters; and 4) for comprehensively analyzing the stability of rock mass, the improved K -means clustering algorithm is utilized to constructing the discontinuity sets that having similar orientation information. The novel method has been successfully tested on two practical cases (a rock cut and a side slope point cloud captured by the terrestrial laser scanner). A comparison with existing methods shows that the deviation of the discontinuity orientation for rock cut is less than 1°, and the time efficiency is increased by 2.6 times. In addition, the orientation variation of the seven principle discontinuity in the five temporal side slope point cloud is relatively small, the dip direction and angle are within 2° and 1°, respectively. We can conclude that the proposed method can efficiently obtain the full extent of every individual discontinuity from rock mass surface point cloud and accurately analyze their orientation information.

Deep Learning and Time-Series Analysis for the Early Detection of Lost Circulation Incidents During Drilling Operations

Drilling operations consist of breaking the rock to deepen a wellbore for oil or gas extraction. A drilling fluid, circulating from the surface through the drill pipe and from the annulus to the surface, is used to remove rock cuttings and maintain hydrostatic pressure. Drilling fluid lost circulation incidents (LCIs) are major sources of non-productive time (NPT) in drilling operations. These incidents occur due to preexisting natural fractures (vugs, caverns, etc.) and/or drilling-induced hydraulic fractures. The initiation of an LCI could lead to other hazardous drilling phenomena, such as formation influx or kick/blowout, stuck pipe incidents, among others. LCIs are typically monitored at the rig site by observing drilling fluid levels in the fluid tanks. This manual process incurs missing the occurrence or late detection of LCIs. Machine learning (ML) and deep learning (DL) classification algorithms are powerful in processing time-series data and achieving early detection of such temporal phenomena. In this study, we performed a large-scale analysis of the surface drilling and rheology data obtained from historical wells with LCIs. This analysis includes primary and secondary preprocessing steps including, aggressive sampling, feature engineering, and window normalization to derive generalizable DL models for real-time operations. Focal loss was utilized to account for data class imbalance and train robust and generalizable models. The results obtained from different ML/DL algorithms showed that one-dimensional convolutional neural network models resulted in the best performance with state-of-the-art precision, recall, and F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> scores of 87.34%, 73.40%, and 79.77%, respectively, on unseen test drilling data.

Continental flood basalt magmatism contemporaneous with Deccan traps in the Mannar basin, offshore Sri Lanka

AbstractThe Gulf of Mannar and adjoining Cauvery basin to the north between India and Sri Lanka are associated with a failed rift, which initiated during the late Jurassic to early Cretaceous as a precursor to the breakup of East Gondwana. Despite the occurrence of igneous rocks that can be noted in seismic profiles, offshore, and deep seated occurrence of those have lead only to the limited understanding of igneous activity in the Mannar basin. Rock cuttings recovered in the Barracuda exploratory well in the Mannar basin shows approximately 700 m thick basalt rock sequence interlayered with sediments at a depth of 3500–4200 m below mean sea level. Here, we analyzed samples recovered from the Barracuda well for major and trace element composition. Major and trace element data suggest that the basalts were crystallized from two different degrees of partial melts from a similar source. Chondrite normalized rare earth element (REE) patterns indicate that the basalts are similar to continental flood basalt, though they show a distinct Ba positive anomaly. Importantly, supported with previously available K–Ar data, we decipher that these basalts are contemporaneous with the Deccan traps. Rifting between Seychelles and India which had occurred at ~62 Ma approximately 3.5 Ma after the main Deccan eruption is synchronous with the Barracuda volcanism suggesting coeval rifting between Seychelles–India and India–Sri Lanka. Thus, our data suggest simultaneous rifting between Seychelles–India and India–Sri Lanka. Large plate reorganizations that took place during this time period in the Indian Ocean have likely caused consequent passive rifting in the Mannar basin.

Prediction of Penetration Rate for PDC Bits Using Indices of Rock Drillability, Cuttings Removal, and Bit Wear

SummaryPredicting rate of penetration (ROP) has gained considerable interest in the drilling industry because it is the most-effective way to improve the efficiency of drilling and reduce the operating costs. One way to enhance the drilling performance is to optimize the drilling parameters using real-time data. The optimization of the drilling parameters stands on the fact that drilling parameters are interrelated; that is, corrections in one factor affect all the others, positively or negatively.Analysis of the available models in the literature showed that they did not take into account all factors, and therefore, they might underestimate the ROP. To improve the accuracy of predicting the bit efficiency, a new ROP model is developed to preplan and lower the drilling costs. This approach introduces three parts of the process that were developed to describe the challenge of predicting ROP: aggressiveness or drillability, hole cleaning, and cutters wear, which are interrelated to each other. The approach discusses each process individually, and then the influence of all three factors on ROP is assessed. Taking into account the drilling parameters and formation properties, ROP1 is estimated by use of a new equation. Then, lifting the produced cutting to the surface and evaluating how that affects the bit performance is proposed in the second part of the process (hole cleaning). Finally, wear index is introduced in the third part (wear condition) to predict the reduction of ROP2 caused by cutter/rock friction.The approach serves and could be considered as a baseline to identify all factors that can affect the bit performance. The developed model equations are applied to estimate ROP in three vertical oil wells with different bit sizes and lithology descriptions in Libya. The results indicate that the driven model provides an effective tool to predict the bit performance. The results are found in good agreement with the actual ROP values and achieve an enhancement of approximately 40% as compared to the previous models.

Flow Properties of Fresh Mud (Drilling Fluid) Used in Horizontal Directional Drilling

AbstractFresh mud (uncontaminated by soil or rock cuttings) plays important roles during borehole drilling, and its rheology has been studied for years in the oil and gas drilling industry. However...

Coupling DDA and 4D-LSM through contact theory for rock cutting

In this work, the rock cutting is modelled through coupling of 4D-LSM with DDA. The rock cutter and its 3D motion were simulated by using DDA with triangular surface mesh, and the rock is modelled by using 4D-LSM with multi-body failure criterion. The dynamic contact treatment between the cutter and the rock specimen was further handled by using Dr. Shi’s contact theory where the entrance block of the cutter between spherical particles was used to calculate the contact forces. Then, the 4D-LSM and DDA were coupled through an explicit-implicit mixed solving scheme. Finally, the coupled model is used to model rock cutting problems and compared with exist numerical approach to highlight its advantages.

Using a high-pressure water jet-assisted tunnel boring machine to break rock

The concept of tunnel boring machine (TBM) disc cutter rock breaking coupled with high-pressure water jets has been proposed to overcome the difficulties that occur when TBMs encounter extremely hard rocks. Thus, to meet actual engineering requirements for the TBM construction of tunnels as part of the Wan’anxi water diversion project in Longyan City (Fujian Province, China), experiments were conducted on high-pressure water jet-assisted TBM disc cutter rock breaking. By varying kerf depth and width under different water jet parameters and performing disc cutter rock breaking tests on rock surfaces with no kerf, single kerf, and double kerfs, the effects of different kerf depths on the disc cutter rock breaking process, load, and efficiency were examined. The test results showed that high-pressure water jets can generate the regular kerfs required for the coupled disc cutter rock breaking of granite. Employing the coupled rock breaking method also resulted in a decrease in specific energy and an approximately 40% decrease in the normal force of the disc cutter, thereby significantly improving rock breaking efficiency. These results provide key technical parameters for the design and manufacture of high-pressure water jet-assisted rock-breaking TBMs and serves as a reference for similar processes.

Combined Microbial Consortium Inoculation and Black Locust Planting Is Effective in the Bioremediation of Waste Drill Cuttings.

Waste drill cuttings (WDCs), produced during gas and oil drilling consisting of 80% rock cuttings and 20% drilling muds, are an increasingly potent source of environmental pollution. We studied the efficiency of bioaugmentation and phytoremediation to remediate WDCs in an experiment where WDCs were incubated in a greenhouse for 120 days with and without black locust (Robinia pseudoacacia) plant and with or without bacterial and fungal consortium inoculant. The pollutant removal rates were highest in inoculated and planted treatment, followed by inoculated treatment and planted treatment. The small decrease in contaminant level in the control treatment suggested that indigenous microorganisms in WDCs had little pollutant degradation capability. In the inoculated and planted treatments, after 120 days, the germination rate of red clover seeds was on the same level as in the natural soil, showing a marked decrease in the ecotoxicity of WDC. Both the bacterial and fungal richness and bacterial diversity increased in all the treatments over time, whereas fungal diversity increased only in the not-inoculated treatments. The activity of laccase enzyme played a key role in the bioremediation process. The enzyme activities were mostly governed by inoculated consortium and soil bacterial community, and black locust affected the bioremediation mainly through its effect on N content that further affected bacterial and fungal communities.

A novel NMR surface relaxivity measurements on rock cuttings for conventional and unconventional reservoirs

Surface relaxivity (ρ) is an intrinsic rock property that makes low-field NMR a valuable tool for determining pore size distribution of geological formations. Its value can vary considerably in different rocks depending on the type and distribution of the rock minerals, rock surface wettability and petrophysical properties. Therefore, laboratory measurement of ρ is required on a case by case basis. However, existing NMR methods are expensive, complex, and most often require supplementary and expensive non-NMR measurements. Rock samples are also required to be well consolidated and cylindrical so that experiments can be run at high pressures – a barrier for measurements of unconsolidated and thinly laminated unconventional rocks. This study proposes a new NMR method termed ‘NMR grain sizing method’, that uses different grain sizes of a given rock to generate pores of corresponding sizes. Using a geometric constant, grain specific surfaces are transformed to pore surfaces, and the governing NMR equation is rearranged so that we have a method that measures ρ from only NMR measurements on rock cuttings. This approach is simple, inexpensive, and does not require supplementary measurements. It offers an added advantage for characterizing thinly laminated formations. A proof of concept is demonstrated for three unconventional rocks (Qusaiba shale, Jafurah carbonate mudrock and Eagle Ford) and two conventional rocks (Berea sandstone and Indiana limestone). The ranges of surface relaxivity are 96.9–134.5 μm/s (Qusaiba shale); 62.07–106 μm/s (Jafurah carbonate mudrock); 55.9–68.72 μm/s (Eagle Ford); 35.51–43.2 μm/s (Berea sandstone); and 33.2–40.54 μm/s (Indiana limestone). All ρ measurements are reproducible with 95% confidence interval. The measured values for Indiana limestone and Berea sandstones were validated with micro CT based pore network models and also compare well with literature data. Measurement of Qusaiba shale and Jafurah carbonate source rocks are apparently reported for the first time here.

Breakage mechanism of hard-rock penetration by TBM disc cutter after high pressure water jet precutting

To achieve greater efficiency of TBM driving and lower cutter maintenance costs in hard rock formations, the TBM integrated high pressure water jet system was developed. By examining the working modes of water jets and disc cutters, this paper investigates the mechanical response and failure mechanisms for the simple case in which a water jet is first used to cut, followed by disc cutter rock breaking. As disc cutters use penetration-type rock breaking, laboratory quasi-static penetration tests and numerical simulations were carried out for kerf specimen precutting with a high pressure water jet. The influence of kerf parameters on the mechanical behavior of rock breaking was studied, and the mechanisms of surface and internal cracks and fractures were revealed and discussed. The results show that peak penetration force decreases with the increase of kerf depth, and slightly increases with the increase of kerf spacing. The specific energy decreases significantly with the increase of kerf depth and gradually becomes stable once the kerf depth becomes greater than 18.14 mm. The internal cracks formed in shallower kerf specimens mainly include shallow tensile cracks and deep vertical split cracks. However, the internal cracks of deeper kerf specimens incline and bend, extending towards the bottom of the kerf. The theoretically obtained minimum shear load, optimal failure depth, and fragment area all increase with kerf spacing, but the angle of the shear plane remains approximately 45°. These findings may provide some reference for the design and construction of TBMs integrated with high-pressure water jets.

Microscale approximation of the elastic mechanical properties of randomly oriented rock cuttings

This study examined a method for approximating the transversely isotropic (TI) elastic mechanical properties and bedding plane orientations of randomly oriented rock cuttings. Microindentation testing was conducted on multiple rock cuttings with unknown bedding orientations to obtain their experimental indentation moduli. The measured indentation moduli were assumed to be functions of both the bedding orientations and the intrinsic TI mechanical properties of the rock cuttings. This assumption holds due to the anisotropic stress history and preferred horizontal alignment of the rock fabric along the bedding direction, as well as the presence of plate-like clay particles with intrinsic TI mechanical properties. An anisotropic contact mechanics solution was then utilized to predict both the TI elastic mechanical properties and bedding plane orientations of the cuttings using a constrained inverse algorithm that minimizes the error between the predicted indentation modulus (a function of both the predicted elastic constants and the orientation of the cuttings) and the experimental indentation modulus. Several constraints were imposed on the inverse algorithm to mathematically bound the TI stiffness matrix and optimization results. A Monte Carlo simulation was also incorporated into the inverse algorithm to consider the effects of uncertainties in the experimental results. The results obtained from the proposed indentation–inverse algorithm approach show good agreement with the results obtained using non-invasive ultrasonic pulse velocity measurements on a 2.5 cm cube sample.