Drill Cuttings Research Articles

Infrared spectroscopy as a tool for hydrothermal alteration mineral analysis to support geothermal reservoir characterization at The Geysers, California, USA

Infrared reflectance spectroscopy (IRS), an analytical method for characterizing geologic materials, is becoming more commonly applied to geothermal energy applications. However, few case studies are available in the literature and are restricted to relatively few volcanic/geologic environments. We present an interpretation of reservoir mineralogy using IRS on drill cuttings from an active magmatic-heat-sourced geothermal system hosted in metamorphic rocks known as “The Geysers”, located in northern California and operated by Calpine Corp. Wavelength ranges investigated include the Short Wave Infrared (SWIR; 1000–2500 nm) and the Long Wave Infrared (LWIR; 2.5–20 μm). We apply this technique to a 2848 m-deep geothermal production well in the northwest Geysers, inferred to overlie a Holocene intrusion and zone of partial melt as indicated by geophysics. We utilized this non-destructive technique to analyze every drill-cuttings sample (3000+ measurements collected at ∼3.3 m intervals). We identify a zonation in mineralogy that changes from illite + chlorite ± kaolinite ± smectite ± calcite at shallow depths (0–1000 m), to illite + chlorite ± calcite at intermediate depths (1000–2200 m), to actinolite + biotite + chlorite ± tourmaline at greatest depths (2200–2848 m). We find the change at 2200 m is proximal to the inferred transition from the “normal” temperature reservoir (∼240 °C vapor-dominated convective zone) to the high temperature reservoir (up to 400 °C, conduction-dominated). We identify a possible association between 1900 nm H2O absorptions and current steam entry locations. The results of the SWIR and LWIR analysis are consistent with some caveats with newly collected bulk rock X-Ray Diffraction (XRD) data, and support and compliment previous work at the Geysers utilizing XRD and petrographic analysis.

Elevated arsenic concentrations in groundwater of the Upper Indus Plain of Pakistan across a range of redox conditions

Groundwater of the Ravi River floodplain is particularly elevated in arsenic (As) on both sides of the Pakistan-India border. To understand this pattern, 14 sites were drilled to 12–30 m depth across floodplains and doabs of Pakistan after testing over 20,000 wells. Drill cuttings were collected at 1.5 m intervals, 132 of which were sand overlain by 77 intervals of clay and/or silt. Radiocarbon dating of clay indicates deposition of the aquifer sands tapped by wells 20–30 kyr ago. Most (85 %) of the sand samples were gray in color, indicating partial reduction to Fe(II) oxides, whereas most (92 %) of the clay and/or silt samples were orange. Associations between groundwater electrical conductivity, dissolved Fe, sulfate, and nitrate suggest that wells can be elevated (>10 μg/L) in As in the region due to either reductive dissolution of Fe oxides, evaporative concentration, or alkali desorption. In the Ravi floodplain, 47 % of 6445 wells tested contain >10 μg/L As compared to only 9 % of 14,165 tested wells in other floodplains and doabs. The As content of aquifer sands in the Ravi floodplain of Pakistan averages 4 ± 4 mg/kg (n = 66) and is higher than the average of 2 ± 2 mg/kg (n = 51) for aquifer sands outside the Ravi. Synchrotron spectroscopy and column-based speciation indicate predominance of As(V) over As(III) in both aquifer sands and groundwater. Whereas multiple processes may be responsible for elevated levels of As in groundwater across the region, spatial heterogeneity in groundwater As concentrations in the Ravi floodplain seems linked to variations in As concentrations in aquifer sands. Regulation by the solid phase may limit variations in groundwater As over time in response to natural and human-induced changes in hydrology. This means spatial heterogeneity could be taken advantage of to lower the exposure across the region with more testing and targeted drilling.

The Development of Advanced Fluorescent Tracers Aimed at Drill Cuttings Labelling and Depth Correlation via Injection with Oil-Based Drilling Mud

Fast and precise geo-steering and geo-navigation upon well drilling are the key parameters for improved well targeting, optimal well placement, and maximal hydrocarbon recovery. To advance geo-steering parameters, we propose a new approach to on-site formation evaluation through the use of fluorescent tracers for drill cuttings tagging according to the depth of origin. Cuttings labelling at the drill bit site is followed by near-real-time drilling depth correlation at the well-head via a camera and AI image recognition systems. To suite the drilling process, the engineered tracers should match to the rheology of the utilized drilling mud. This study was performed to comprehensively investigate the effect of fluorescent tracers on the rheological properties of oil-based drilling mud (OBM) and to determine the optimal quantities of the tracers’ addition. We evaluated critical mud characteristics including electrical stability, thixotropic parameters, shear stress, gel strength, plastic viscosity, and yield point as prepared and in the presence of fluorescent tracers at the range of 1 to 20 wt.%. Additionally, the mud’s effects on the long-term stability of the fluorescent tracers were assessed via hot-rolling tests in conditions mimicking downhole conditions, with the aim of determining the tags’ feasibility for drill cuttings labelling applications. The study also examines the recovery potential of the tracers and their reusability in the drilling process. This investigation provides valuable insights into the potential application of fluorescent tracers for downhole drill cuttings depth correlation which will improve geo-steering works.

Life Detection and Microbial Biomarker Profiling with Signs of Life Detector-Life Detector Chip During a Mars Drilling Simulation Campaign in the Hyperarid Core of the Atacama Desert.

The low organic matter content in the hyperarid core of the Atacama Desert, together with abrupt temperature shifts and high ultraviolet radiation at its surface, makes this region one of the best terrestrial analogs of Mars and one of the best scenarios for testing instrumentation devoted to in situ planetary exploration. We have operated remotely and autonomously the SOLID-LDChip (Signs of Life Detector-Life Detector Chip), an antibody microarray-based sensor instrument, as part of a rover payload during the 2019 NASA Atacama Rover Astrobiology Drilling Studies (ARADS) Mars drilling simulation campaign. A robotic arm collected drilled cuttings down to 80 cm depth and loaded SOLID to process and assay them with LDChip for searching for molecular biomarkers. A remote science team received and analyzed telemetry data and LDChip results. The data revealed the presence of microbial markers from Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, Firmicutes, and Cyanobacteria to be relatively more abundant in the middle layer (40-50 cm). In addition, the detection of several proteins from nitrogen metabolism indicates a pivotal role in the system. These findings were corroborated and complemented on "returned samples" to the lab by a comprehensive analysis that included DNA sequencing, metaproteomics, and a metabolic reconstruction of the sampled area. Altogether, the results describe a relatively complex microbial community with members capable of nitrogen fixation and denitrification, sulfur oxidation and reduction, or triggering oxidative stress responses, among other traits. This remote operation demonstrated the high maturity of SOLID-LDChip as a powerful tool for remote in situ life detection for future missions in the Solar System.

A Review of the Settling Law of Drill Cuttings in Drilling Fluids

During the drilling process, cuttings settle under the action of gravity, which easily results in the formation of a cuttings bed, which then results in wellbore cleaning problems. The settling law of cuttings in drilling fluid is essentially a problem of solid–liquid two-phase settling. This study analyzes and summarizes the effects of the wall effect, the rheology of the fluid, particle shape irregularity, and particle concentration on the settling rate of particles and clarifies the problems faced by current research on the settling rate of particles and the development direction. Studies have shown that walls exert additional blocking effects on particles, thus reducing their settling velocity. The shear thinning effect of non-Newtonian fluids such as power-law fluids and Herschel–Bulkley fluids will reduce the viscosity of the liquid, thus increasing the settling velocity of the particles. Compared with spherical particles, irregular particles will obtain higher resistance in the fluid, leading to a decline in the particle settling velocity. The mutual interference between particles will result in an increase in the drag force on the particles and a decline in the settling velocity. However, when the particles are aggregated, the settling velocity will increase. This study can provide theoretical guidance for predicting the migration law of cuttings during the drilling of horizontal wells, and it has important significance for enriching the theory of solid–liquid two-phase flow.

Ultrasonication-flotation-advanced oxidation tertiary treatment of oil-based drilling cuttings

The treatment of oil-based drilling cuttings (OBDCs) with high oil content is difficult. In this study, a tertiary treatment of ultrasonication–flotation–advanced oxidation for treating OBDCs with a high oil content of 20.10 wt% was proposed for the first time. All stages of the treatment processes were optimised. The recommended parameters for ultrasonication at room temperature were a mass ratio of OBDCs to the degreaser of 1:8, an ultrasonication power of 600 W and treatment time of 30 min. After the ultrasonication treatment, the oil content of the OBDCs decreased from 20.10 wt% to 5.00 wt%. Flotation was performed at room temperature with a mass ratio of OBDCs to the degreaser of 1:10, a stirring speed of 400 rpm, an aeration head aperture of 3 μm and airflow rate of 400 mL/min under N2 injection for 60 min. After the flotation treatment, the oil content of the OBDCs decreased from 5.00 wt% to 2.01 wt%. Advanced oxidation was performed at room temperature with a mass ratio of OBDCs to water of 1:10, 3.57 wt% sodium persulphate in water, 4.17 wt% ferrous sulphate heptahydrate in water and ultrasonication power of 1000 W for 100 min. Following the advanced oxidation treatment, the oil content of the OBDCs decreased from 2.01 wt% to 0.58 wt%. The results of this study provide a new method and idea for treating OBDCs with high oil content.

Physico-chemistry of drilling waste processing by SH-synthesis and mechanochemical activation methods

Purpose of research: is to study the physicochemical features of the processes of processing the ultrafine part of drill cuttings into heat-resistant materials with high refractory properties.
 Methods and objects of research: using the methods of self-propagating high-temperature synthesis in combination with preliminary mechanochemical activation of drill cuttings on a high-energy planetary mill AGO-3, which is performed only in those cases when it is necessary to clean drilling waste from oil products, a composite refractory was obtained that is resistant to deformations from 30 to 80 MPa, at temperatures from 1500 to 1660C.
 Main results of research: it is shown that the physical and mechanical properties are provided by the needle-like structure of the mullite-corundum binder.

Air quality impacts from the development of unconventional oil and gas well pads: Air toxics and other volatile organic compounds

Unconventional oil and natural gas development (UOGD) has expanded rapidly across the United States in recent decades and raised concerns about associated air quality impacts. While significant effort has been made to quantify methane emissions, relatively few observations have been made of Volatile Organic Compounds (VOCs), especially during drilling and completion of new wells. Extensive air monitoring during development of several large, multi-well pads in Broomfield, Colorado, in the Denver-Julesburg Basin, provides a novel opportunity to examine changes in local air toxics and other VOC concentrations during well drilling and completions and production. These operations offer an especially useful case to study as several management practices were implemented to reduce emissions (e.g., electrified, grid-powered drill rigs and closed loop fluid handling systems to reduce truck traffic and limit fluid handling on the pad). With simultaneous measurements of methane and 50 VOCs from October 2018 to December 2022 at as many as 19 sites near well pads, in adjacent neighborhoods, and at a more distant reference location, we identify impacts from each phase of well development and production. Use of weekly, time-integrated canisters, a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous photoionization detectors (PID) to trigger canister collection upon detection of VOC-rich plumes, and an instrumented vehicle, provided a powerful suite of measurements to characterize both transient plumes and longer-term changes in air quality. Prior to the start of well development, VOC gradients were small across Broomfield. Once drilling commenced, concentrations of oil and gas (O&G) related VOCs, including alkanes and aromatics, increased around active well pads. Concentration increases were clearly apparent during certain operations, including drilling, coil tubing/millout operations, and production tubing installation. Emissions of C8–C10 n-alkanes during drilling operations highlighted the importance of VOC emissions from synthetic drilling mud chosen to reduce odor impacts. More than 90 samples were collected of transient plumes. Using composition measurements, meteorological data, and information about well pad activities, these plumes were connected with specific UOGD operations including drilling, flowback, and production equipment maintenance. The chemical signatures of these plumes differed by operation type (e.g., C8–C10 n-alkanes constituted a larger fraction of measured VOCs in drilling-related plumes). Concentrations of individual, oil and gas-related VOCs in these plumes were often several orders of magnitude higher than in background air, with maximum ethane and benzene concentrations of 79,600 and 819 ppbv, respectively. Because these plumes typically impact a monitoring site for just several minutes, they are easily missed by slower-responding instruments. Study measurements highlight future emission mitigation opportunities during UOGD operations, including better control of emissions from shakers that separate drill cuttings from drilling mud, production separator maintenance operations, and periodic emptying of sand cans during flowback operations.

Numerical Simulation and Analysis of the Heat and Mass Transfer of Oil-Based Drill Cuttings in a Thermal Desorption Chamber

To reveal the coupled heat and mass transfer process during thermal desorption of oil-based drill cuttings, a numerical model of heat and mass transfer was established, which is divided into four components = evaporation. The C language programming catch-up method was used to solve the discrete equation, and the interactive effects of the oil-based drill cuttings’ particle size, water content, oil content, content of light and heavy components in oil, heating temperature, heating time, and other operating parameters on the mass and heat transfer of the oil-based cutting particles were investigated. Results showed that the time at which the center point temperature of oil-based drill cuttings with radius of 1 mm and 5 mm reached 600 °C was 441 s and 63 s, respectively, and the temperature difference between the center and the surface increased with particle size. The desorption process of water, light components, and heavy components was not completed individually but mixed alternately. The duration of each desorption component was closely related to the temperature at the center of the oil-based drill cuttings. The smaller the particle size was, the lower the water and oil contents were, and the higher the heating temperature and time were. These conditions were beneficial to thermal desorption, mass transfer, and heat transfer.

Influence of drilling mud pulsations on well cleanout efficiency

Purpose. Determination of the influence of the non-stationary flow regime of the drilling mud on the efficiency of cleaning the wellbore in the annulus from drill cuttings. Methodology. The study on the carrying capacity of the drilling mud in a laboratory installation is carried out by simulating the process of its pulsations at different frequencies. The choice of the studied frequencies was made on the basis of previous studies. The evaluation of the influence of factors on the efficiency of rock removal was carried out using Latin experimental plans, which allowed us to evaluate the influence of the selected factors with a minimum number of experiments without losing the quality of the result. Findings. The influence of factors (mud flow rates, eccentric placement of the drill string, plastic viscosity of the drilling mud, pulsation frequency, rotation of the drill string) on the efficiency of cuttings removal along the annular space of the wellbore is analyzed. Three factors with the best interaction were found, which made it possible to build dependencies of their influence on the efficiency of rock removal on the surface. The effect of changing the frequency of pulsations of the drilling mud has been studied, and graphical dependences of their influence on the decrease in the volume of rock particles in the annular space have been obtained. Originality. Based on the results of experimental studies, the effectiveness of the impact of drilling mud pulsations on cleaning the well from rock particles has been proven. Practical value. The effectiveness of the use of drilling mud pulsations for hydrotransportation of cuttings along the horizontal section of the wellbore has been confirmed.

CUTTING ANALYSIS ON HORIZONTAL DRIILING USING CUTTING CARRY INDEX, CUTTING TRANSPORT RATIO AND CUTTING CONCENTRATION IN ANNULUS METHOD ON A WELL G FIELD S

The basic principle of the drilling operation is to grind the rock formations with bits which will later become drill cuttings. In this process, fluid is needed as a conveying medium, commonly known as drilling mud, because the deeper the drilling, the more drill flakes are produced. One of the prominent functions of drilling mud is lifting the drill shale up to surface. The purpose of this analysis is to quantitatively prove whether the cutting has been successfully lifted to the surface or not, and to determine the elements of the fluid’s physical properties and the drilling mud fluid’s rheology. This analysis was carried out using three methods including; the cutting carry index, which the value required is greater than one; the cutting transport ratio, which the value required is greater than 50%; and the cutting concentration in annulus, which the value required is less than 5%. If the value of the quantitative calculation already has a value above the standard, it can be concluded that the drill cuttings can be lifted optimally. The value of the cutting carry index has to be greater than one, because if it is less than one the solid value in the mud is still lacking, causing a low density so it will affect the carrying capacity of cutting in 1 gal of mud. The value of cutting concentration in annulus should not be more than 5, it is feared that if it exceeds this limit, it can affect the rate of penetration and can cause a stuck. As for the value of the cutting transport ratio should not be less than 50% because if it is less than that the hydrostatic pressure below will be large and can cause formation fractures. In this case, we will discuss the analysis of cutting removal on the 8.5 inch route at 4290 to 5174 ft depth, with a slope of 66.29o from the starting point of the borehole.

A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid

Three high-temperature resistant polymeric additives for water-based drilling fluids are designed and developed: weakly cross-linked zwitterionic polymer fluid loss reducer (WCZ), flexible polymer microsphere nano-plugging agent (FPM) and comb-structure polymeric lubricant (CSP). A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid was developed for deep drilling. The WCZ has a good anti-polyelectrolyte effect and exhibits the API fluid loss less than 8 mL after aging in saturated salt environment at 200 °C. The FPM can reduce the fluid loss by improving the quality of the mud cake and has a good plugging effect on nano-scale pores/fractures. The CSP, with a weight average molecular weight of 4804, has multiple polar adsorption sites and exhibits excellent lubricating performance under high temperature and high salt conditions. The developed drilling fluid system with a density of 2.0 g/cm3 has good rheological properties. It shows a fluid loss less than 15 mL at 200 °C and high pressure, a sedimentation factor (SF) smaller than 0.52 after standing at high temperature for 5 d, and a rolling recovery of hydratable drill cuttings similar to oil-based drilling fluid. Besides, it has good plugging and lubricating performance.

Potential of Thermal Desorption Residue of Oil-Based Drilling Cuttings for Use in Subgrade Materials

Potential of Thermal Desorption Residue of Oil-Based Drilling Cuttings for Use in Subgrade Materials

Characteristics of cuttings migration with new cuttings removal device in horizontal well

Cuttings accumulation in horizontal wells has become an important engineering problem. In this research, the influence of normal drill pipe and cuttings removal device on debris migration behavior are studied by using the CFD-DEM (Computational Fluid Dynamics and Discrete Element Method) coupling approach. The efficiency of cuttings removal is evaluated by the cuttings concentration and cuttings removal time. In addition, the experiment is employed to study the cuttings migration law under different rotational speed of drill pipe, fluid inlet velocities and drill string assembly. According to the numerical and experimental results, cuttings concentration and removal time are obviously decreased by improving inlet fluid velocity and drill pipe rotating speed. The cuttings removal time with cuttings removal device is decreased in range of 32.9%–71.8% compared with the normal drill pipe. The reliability of the designed device is validated by results, which provides guidance for cuttings removal in horizontal wells.

Feasibility Study of Drill Cuttings Slip Velocity Estimation using BBO DTM-Pade’ Semi-analytical Technique

The study reviewed the use of DTM-Pade’ approximation method of Basset–Boussinesq–Oseen equation (BBO) in predicting particle slip velocity. A hypothetical example is used in the study with three different diameters, 3,5 and 7mm, of spherical particle assumed to represent wide rang of drill cuttings’ sizes. In addition, the drilling fluid is assumed to be incompressible fluid in stationary mode. The Pade’ approximation (K=20, [8 8]) is used, based on literature, in calculating slip velocities through 2 seconds time span. It is concluded that this technique is a practical mean of particle slip velocity prediction at high Pad’ orders using Matlab for a short period of time, around (o.1 to 0.2 seconds). However, BBO equation application range such as, single particle fall in infinite incompressible fluid, small particle size rang (less than 3mm), low particle to fluid density ratio (higher than 0.38), limits its application in oil well drilling operations. Moreover, the necessity of more factors considerations in simulating drilling operations including Non-Newtonian fluids, wall effect, and wide range of irregular shaped drill cuttings densities and sizes urges for the use of generalized BBO equation. In drilling operations, concisely, drill cuttings are usually mixed in the wellbore annulus and for more reliable predictions the application of more sophisticated techniques such as Machine Learning (MA) and Artificial Intelligence (AI) become indispensable.

Rice husk ash as a sustainable and economical alternative to chemical additives for enhanced rheology in drilling fluids.

Performance evaluation of drilling fluids is essential for a successful drilling project, as they not only remove drill cuttings but also prevent undesired penetration or outflow of formation fluids by sealing off wellbore walls. However, concerns have been raised about the use of chemical additives in drilling fluids due to their toxicity and non-biodegradability. To this end, agricultural waste materials are recognized as a promising alternative as they are cost-effective, environmentally sustainable, and can be used as a substitute for lost circulation materials. Rice husk ash (RHA) has become popular as an additive due to its renewable characteristics, including its large surface area, silica content, and microporous structure. This research article explores the rheological properties of drilling fluid with RHA as a filter control medium. The results showed that increasing concentrations of RHA in the drilling mud significantly improved its rheology, particularly at higher concentrations (15 and 20 wt.%). The addition of RHA modified the filtration and rheological properties of the drilling mud, resulting in improved plastic viscosity, yield point, density, gel strength, and thixotropy. However, filter loss and mud cake thickness increased at elevated RHA concentrations. Furthermore, the pH test revealed that the mud's properties shifted toward the acidic region as the RHA concentration increased. The results indicate that RHA could be used as a sustainable and cost-effective alternative to conventional chemical additives with a positive environmental impact. This study may also provide valuable insights into the use of RHA in water-based bentonite mud and could serve as a guide for future research in the drilling industry.

Continuous thermal structures of the present-day and contact-metamorphic geothermal systems revealed by drill cuttings in the Kakkonda geothermal field, Japan

Assessing the thermal structure of a geothermal reservoir and its history is of critical importance when evaluating the energy potential and heat source of the reservoir. However, the present and past thermal structures of reservoirs are not easily obtained due to temperature perturbations during drilling and/or the sparse sampling of the reservoir in rock cores. We examined drill cuttings collected from Well-20 of the Kakkonda geothermal reservoir that penetrated to a depth of ∼2700 m and into the Quaternary Kakkonda Granite, which is thought to be the heat source of the Kakkonda geothermal reservoir. Here we provide the first comprehensive report on the compositions of minerals from the Kakkonda geothermal reservoir from the Kakkonda Granite into its contact metamorphic aureole. The minimum temperature for each depth obtained by chlorite thermometry systematically changes within a range of 265–369 °C at depths of 1510–2700 m, and the temperatures are consistent with fluid inclusion thermometry and the temperature of the reservoir undisturbed by drilling. Our method provides a rapid, spatially continuous, and simple way of estimating the past or present thermal profile of a reservoir. The maximum temperature for each depth obtained by biotite thermometry shows a continuous thermal profile for the contact metamorphism with temperatures reaching ∼760 °C at the granite/host-rock interface at a depth of ∼2700 m, and gradually decreasing to ∼630 °C at a depth of ∼1700 m. These results suggest that the thermal effect of the Kakkonda Granite on the surrounding lithologies was much larger than estimated previously. Such high contact metamorphic temperatures require effective heat transfer from the Kakkonda Granite, probably enhanced by magma convection in the magma chamber and fluid convection within the supercritical geothermal reservoir.

Scaling Equations for Annular Flow of Yield-Power Law Fluid and Drill Cuttings

Summary Estimation of frictional pressure loss along the wellbore annulus is the key to determining the wellbore equivalent circulating density. Flow loop experiments are commonly used at smaller scales of flow to measure this quantity. However, a complete set of scaling equations between the measured pressure drop gradient along the annulus of a flow loop device and the one occurring in the wellbore is not reported in the literature. This study applies dimensional analysis to make such a connection while accounting for drillpipe rotation and eccentricity, as well as solid cuttings load, in the annular flow of yield-power law drilling fluids. Simultaneous application of geometric, kinematic, dynamic, and rheological similarities allows for developing direct relations between the quantities that govern the laboratory and wellbore scales of flow. For this purpose, a set of dimensionless groups is identified and held equal between the two flow scales. Dimensional analysis shows that scaling the two-phase flow of drilling fluid and drill cuttings entails 10 dimensionless groups. The solution of the obtained scaling equations determines the required volumetric rates of fluid and solid particles, the inner pipe rotation speed, and the fluid rheology in the flow loop device to establish a complete similitude with the wellbore annular flow. The required similarity between the Reynolds numbers of solid particles or drill cuttings at the two scales of flow introduces a constraint on the rheology of the fluid to be used in the laboratory flow loop. This finding indicates that attaining a complete similitude requires the two fluids to be dissimilar. Once all scaling requirements of the considered similitude are applied, the pressure gradient along the wellbore annulus can be obtained directly in terms of the measured pressure drop in the laboratory flow loop.

Estimating hardness and Young's modulus of shale using drill cuttings: Implications for hydraulic fracturing in shale gas reservoir development

Shale formations are widely prevalent in the oil and gas industry as potential hydrocarbon reservoirs. The hardness and Young's modulus of shale significantly impact the success of hydraulic fracturing operations in shale gas reservoir development. The unavailability of standard-sized core samples (length to diameter ratio ∼2.5) makes it challenging to determine the mechanical properties of shale in the laboratory. This study investigates techniques for estimating hardness and Young's modulus using drill cuttings. The microhardness was measured on shale cuttings of ∼1 mm in size using a micro indenter. Young's modulus was measured at the macro-scale using a uniaxial compression test on a 25 mm diameter core sample. The relationship between microhardness and Young's modulus established for Longmaxi (China) and Ice-Box (Western Canada) shales was applied to another shale (e.g., Sembar Shale of Pakistan), for which no core samples were available. The measured mineralogy of the studied shales provides a common base for the comparison of microhardness and Young's modulus using isotropic and anisotropic theoretical models. A positive correlation was observed between Young's modulus and microhardness for the three shales tested in this study. Although the scale of measurement/assessment is different, the theoretical models show an insignificant impact of the scale range (micro (mm) to macro (cm)) on Young's modulus, microhardness, and brittleness.

Effect of Low Gravity Solids on Weak Gel Structure and the Performance of Oil-Based Drilling Fluids.

Drilling cuttings from the rock formation generated during the drilling process are generally smashed to fine particles through hydraulic cutting and grinding using a drilling tool, and then are mixed with the drilling fluid during circulation. However, some of these particles are too small and light to be effectively removed from the drilling fluid via solids-control equipment. These small and light solids are referred to as low gravity solids (LGSs). This work aimed to investigate the effect of LGSs on the performance of oil-based drilling fluid (OBDF), such as the rheological properties, high-temperature and high-pressure filtration loss, emulsion stability, and filter cake quality. The results show that when the content of LGSs reached or even exceeded the solid capacity limit of the OBDF, the rheological parameters including the plastic viscosity, gel strength, and thixotropy of OBDF increased significantly. Furthermore, the filtration of OBDF increases, the filter cake becomes thicker, the friction resistance becomes larger, and the stability of emulsion of OBDF also decreases significantly when the concentration of LGSs reached the solid capacity limit of OBDF (6-9 wt% commonly). It was also found that LGSs with a smaller particle size had a more pronounced negative impact on the drilling fluid performance. This work provides guidance for understanding the impact mechanism of LGSs on drilling fluid performance and regulating the performance of OBDF.