Analysis Of Drill Cuttings Research Articles

Fracability Modeling in Shale Hydrocarbon Development Based on Geomechanical Analysis of Well Log and Mineralogy Analysis of Drill Cuttings: A Case Study of the Lower Baong Fm and the Belumai Fm of the NSB-001 Well in the North Sumatra Basin, Indonesia

Abstract The North Sumatra Basin, Indonesia has a very large shale hydrocarbon potential, especially from the Lower Baong Formation and the Belumai Formation. The Belumai and Lower Baong Formations were deposited in the Early Miocene - Middle Miocene, in transgression conditions, when the North Sumatra Basin was in the regional sagging phase. These conditions greatly affect the facies and diagenetic changes of quartz, smectite and kaolinite minerals in rock fracability. The main problem in producing shale hydrocarbons is the very low permeability of unconventional-shale-reservoirs, so that at the production stage of shale hydrocarbon, a fracability model is needed as a basis for planning hydraulic fracking, thus the fractures are connected to each other and can flow the hydrocarbon fluid optimally. From the results of previous studies, it was shown that the shale hydrocarbon fracability value was controlled by lithofacies, and correlated with rock brittleness, brittle mineral content, clay content, and compressive strength. The fracability model is used to determine fracable zone intervals as a candidate for hydraulic fracking, by using geomechanical analysis of well log data and mineralogy analysis of drill cuttings data from the NSB-001 well as a case study. Based on the correlation results of lithology (Mud Log), mineralogy analysis, MBT, and TOC (Drill Cuttings), the sweetpot fracable window (fracable zone interval) can be determined, which is correlated with the presence of fracture barrier.

AN ASSESSMENT OF STEMMING TECHNIQUES AND THE PERFORMANCE OF STEMMING PLUGS IN BENCH BLASTING OPERATIONS IN PAKISTAN

This research article presents a comparative analysis of stemming techniques and the performance of stemming plugs in bench blasting operations, based on a case study carried out in cement quarries of Pakistan. For Image analysis, the Wip-Frag software is utilized in order to demonstrates the benefits of stemming plugs over traditional methods. Real time images captured during blasting at various cement quarries reveal a substantial presence of boulders within the muck pile when using conventional stemming materials such as drill cuttings and clay. This typically requires additional time and costs for secondary drilling and blasting or hydraulic hammering. Blast tests results indicate that stemming plugs improved the throw and shape of the muck pile, and significantly decreased the boulders percentage. This study also compares the results of Wip-Frag software with sieve analysis of drill cuttings, indicating potential limitations in the software's reliability for particle size distribution. These results contribute to improve blasting operations and emphasize the importance of proper stemming techniques. improving blasting efficiency, the use of stemming plugs can potentially minimize the operational costs and improve overall performance.

Ore/waste identification in underground mining through geochemical calibration of drilling data using machine learning techniques

Chemical X-ray fluorescence (XRF) analyses of drill cuttings and measurement-while-drilling (MWD) records were jointly collected in two production levels with different mineralogical characteristics of a narrow vein underground mine. More than 840 chemical samples and 23,000 MWD records with geological and geotechnical accompanying data constitute the database used in this study. A classification methodology and a site-specific model were developed following two approaches: a k-means clustering heuristic algorithm to define rock classes based on their physicochemical features, and a machine learning (ML) ensemble model trained with those classes to distinguish ore and waste as function of drilling parameters. Oversampling and under sampling techniques are required due to the unbalanced size of the rock classes. The prediction success rate (F1 score) is about 70% for the ore when associated with a high content of silica, and about 86% for the waste. When continuous drilling chips sampling is carried out, the operator bias is reduced and the F1 scores exceed 80% for all classes using different ML techniques. The study presents a complete analysis of the correlations between rock mineralogical characteristics and their mechanical response during drilling, highlighting the benefits that MWD-based information can bring to the analysis-while-drilling (AWD) for ore grading.

Jake Seller Draw impact structure, Bighorn Basin, Wyoming, USA: The deepest known buried impact structure on Earth and its possible relation to the Wyoming crater field

We provide evidence demonstrating the impact origin of a structure, here named the Jake Seller Draw impact structure, which is buried below the Jake Seller Draw drainage basin, in the Bighorn Basin of Wyoming, western United States. The 4.3-km-diameter structure was first recognized as a seismic disturbance at a depth of ∼6.5 km in two- and three-dimensional seismic profiles. Microstructural analysis of drill cuttings situated in the center and outside of Jake Seller Draw revealed the presence of multiple sets of planar deformation features and planar fractures in nine quartz grains, thereby confirming the hypervelocity impact origin of the structure. The seismic data show that Jake Seller Draw is a complex impact structure containing a 1-km-wide central uplift. The geologic and seismic data suggest that Jake Seller Draw is the most deeply buried impact structure known on Earth to date. The stratigraphic framework suggests that the crater was formed in a nearshore environment at the Pennsylvanian−Permian boundary, ∼280 m.y. ago. This age coincides with the age of the Wyoming crater field 300 km southeast of Jake Seller Draw and may suggest a common origin.

Automated real-time formation evaluation from cuttings and drilling data analysis: State of the art

Traditional formation evaluation via laboratory testing and wireline logging of horizontal wells and deep formations face challenges due to several reasons and lead to uncertain results. Real-time cuttings and drilling data analysis of horizontal wells is an actively developing alternative approach to formation evaluation that can overcome several challenges faced by laboratory testing and wireline logging in providing improved estimates of formation parameters relevant to reservoir and completion quality. This study presents a state-of-the-art review of the latest methods and technologies in drill cuttings analysis to enable real-time characterization of the entire suite of formation properties, including chemical composition, densities and porosity, permeability, lithology, geomechanical properties, and characterization of fracture patterns. Specifically, the methods/techniques that enable characterizing drill cuttings in real-time and critically reviewed in this study include Raman spectroscopy for chemical composition, nuclear magnetic resonance for densities and porosity, liquid pressure pulse for permeability, deep learning for rock classification, 7 different methods for geomechanical properties, and mud loss signatures for characterization of fracture patterns. Benchmark comparison of drill cuttings analysis with the measurements from the core samples at similar depths is also reviewed. Key learnings are provided in 4 areas: to address the uncertainties in estimates of specific parameters affected by physical deformations due to drill bits, minimum cutting size for reliable nuclear magnetic resonance data, sweet spot identification, and power and network considerations for real-time analysis, respectively. Cited as: Singh, H., Li, C., Cheng, P., Wang, X., Hao, G., Liu, Q. Automated real-time formation evaluation from cuttings and drilling data analysis: State of the art. Advances in Geo-Energy Research, 2023, 8(1): 19-36. https://doi.org/10.46690/ager.2023.04.03

Assessment of Chlorine, Fluorine, and Sulfur Concentrations in Depth Profile of Drill Cuttings from Onshore and Offshore Oil and Gas Exploration Wells

The assessment of chlorine, fluorine, and sulfur concentrations in depth profile of drill cuttings was performed using ion chromatography after sample preparation by pyrohydrolysis. The parameters for pyrohydrolysis were optimized using a Box-Behnken design, and the established conditions were 300 mg of sample, 300 mg of V2O5, temperature of 1000 °C, reaction time of 25 min, and absorbing solution of 50 mmol L-1 NH3 + 150 mmol L-1 H2O2. The accuracy was evaluated by the analysis of certified reference materials and recovery tests, and the results showed a good agreement between determined and certified values and recoveries (89-108%). The precision (relative standard deviation (RSD) < 10%), and the limits of detection (0.5-2.5 mg kg‑1) were suitable for drill cuttings analysis. The concentration of chlorine, fluorine, and sulfur in drill cuttings at different depths was at mg g-1 range, and its variation is related to the mineral composition of the samples.

Digital rock physics: Defining the reservoir properties on drill cuttings

Well drilling with core extraction is one of the most expensive procedures in the oil industry. The potential alternative, which may open opportunities for cost-efficient acquisition of petrophysical data, can be an approach based on digital analysis of drill cuttings. The main purpose of this research was to evaluate the possibility of using digital cuttings analysis and rock physics for reservoir properties evaluation. The carbonate samples of core and cuttings were simultaneously collected from the same intervals during the drilling of deviated wells in the Carboniferous reservoir of the oil deposit in the Republic of Tatarstan, Russia. Based on the core analysis using the optical study of thin sections and XRD, we investigated sedimentological and mineralogical features and classified all lithotypes of well intervals. The standard samples were produced from all defined facies and their reservoir properties were studied in routine tests. The largest cuttings from each well interval were separated and their structures were compared using μCT with core subsamples of the same intervals. We assessed the changes of cuttings structure occurring in the drilling process, which include the colmatation of the pore space with drilling fluid and disintegrated rock particles and the formation of secondary fractures. Detailed analysis of cuttings from one well interval consisting of the border between the facies of high porous grainstones with packstones and dense micrite limestones demonstrated that high porous varieties were eroded in the drilling process. The analysis of chemical composition using XRF-mapping, XRD and SEM with EDS showed that most of the cuttings were constituted by disintegrated rock particles or form elements (e.g. separate fusulinids) cemented by drilling mud. However, more durable cuttings from dense micrite limestones facies were generally retained their dominant calcite composition and original rock structure, with only secondary fractures. Finally, we analyzed pore space properties and performed digital simulations of wave propagation velocities to compare the characteristics of these cuttings and core subsamples from this lithotype, scanned in the same μCT settings. The results demonstrate close characteristics of porosity 0.08–0.6%, dominant pore sizes 1–60 μm and velocities Vp = 6130–6240 m/s, Vs = 3180–3230 m/s. However, the comparison of obtained values with measured on standard samples shows a significant difference, which is caused by deviation from REV. The potential use of cuttings for assessing reservoir and petrophysical properties can be possible in case of provision with the factors of cuttings structure alteration, representativity of samples, as well as optimization for these purposes of the drilling process with cuttings selection.

Low-Field Nuclear Magnetic Resonance Methodology for Analysis of Drill Cuttings from Unconventional Tight Reservoirs

A nuclear magnetic resonance (NMR)-based method was developed to quickly and accurately determine porosities and densities of tight reservoir rocks from drill cuttings. The method combines low-fiel...

Rare earth elements in drill cutting samples from off-shore oil and gas exploration activities in ultradeep waters

Rare earth elements (REEs) are essential in high technology industries and have great economic value. The monitoring of REEs concentrations in rocks from oil well drill cuttings is critical to avoid environmental contamination and evaluate new sources of these elements. However, information is scarce about the REEs concentrations in drill cuttings. In this work, the concentration of REEs in drill cuttings from oil and gas exploration wells in ultradeep coastal water of Brazilian were investigated at different depths. The drill cutting samples were submitted to microwave-assisted acid digestion prior to the determination of concentration by ICP-MS, using Rh as internal standard for calibration. The limits of quantification (LoQ) ranged from 3.3 μg kg−1 for Ho to 198 μg kg−1 for Sm. The accuracy was evaluated by analyzing certified reference materials for rocks. The obtained REEs concentrations agreed with the certified values, reaching 83%–105% agreement. The drill cutting depth profile analysis indicates Ce, La, Nd, Sm, and Eu concentrations up to mg kg−1. The REEs concentrations obtained in drill cutting depth profile was analyzed by principal component analysis (PCA), and hierarchical cluster analysis (HCA) identified tendency and similarity between drill cutting samples. Three groups were formed according to the composition of the REEs. In addition, the concentration of these chemicals elements varied at different depths. The analysis of drill cuttings revealed REEs concentrations up to the mg per kg-range (ppm), potentially making this disposable material an alternative source for REEs extraction, and adding value to this material.

Assessing hydrofacies and hydraulic properties of basaltic aquifers derived from geophysical logging

Abstract Basaltic aquifers are an important source of water supply in many regions worldwide. Because of their cooling process, flood basalts normally have complex internal structures and unpredictable permeable zone distribution. Geophysical profiling is a reliable tool used to identify the vertical variations of physical properties within the flood basalts, mainly to distinguish between low and high permeability intervals. In this study, a detailed analysis of drill cuttings, and geophysical logging of two depth wells helped to identify the typical response of main facies of flood basalts in the Serra Geral aquifer system. The evidence obtained from this work confirms that flood basalts may be classified as multilayer aquifer systems in which a highly permeable top covers a center with low permeability as a result of recurrent floods. In several cases, permeable layers are represented by a weathering horizon developed between two flood events. This study uses an empirical model to estimate the porosity based on acoustic velocity logging. A useful model based on a well-established Kozeny-Carman model was developed to predict the permeability of basaltic rocks using porosity data. The results obtained allow to identify the permeable intervals of basaltic aquifers and to estimate their hydraulic properties.

Transient and steady state analysis of drill cuttings transport phenomena under turbulent conditions

Understanding the intricacies of multiphase flows is paramount to any drilling operation, and this has been under continuing and intensive development for the past decades. A major complexity associated with this operation is the uncertainty in the transport phenomena of generated cuttings as drilling progresses under different attainable configurations and fluid rheological conditions. Increased transport efficiency of drill cuttings in most drilling operations is usually characterised by an increased mud circulation velocity; this creates complex turbulent interactions between the solid and liquid phases. The study of the dispersion of these cuttings, in relation to their axial, tangential and slip velocity profiles in the annulus is carefully investigated in this work under steady and transient conditions. Computational Fluid Dynamics models (Eulerian–Eulerian, Lagrangian–Eulerian/Discrete Element Method) are utilised for this purpose. The implementation of the Eulerian–Eulerian model provides a macroscopic description of the distribution of fundamental flow properties such as pressure, volume fractions and velocities of each phase. Furthermore, a direct description of the particulate flow, inherent transient motion, interparticle and particle-wall collisions are obtained with the particle tracking functionality of the Lagrangian–Eulerian/DEM technique. The results obtained using the Eulerian–Eulerian model reveal that particle slip velocities are lowest at the central regions of the annulus with the effect of asymmetry due to inner pipe rotation being more pronounced along the longitudinal plane. Particle diameter has tremendous effects on the alteration of turbulence properties of the continuous phase with very distinct velocity profiles. Cuttings trajectory analysis show some extra phenomena which have been physically observed in available experimental studies; one of which is the occurrence of ejections of coherent structures at the walls of the flow domain. The difficulty of carrying out transient and steady state experimental measurements of particle velocities is an area where CFD shows great potential. The few available data in literature are well predicted with errors less than 11%. Similarly, fluid axial and tangential velocity predictions carried out, yield reasonably accurate results, thus further validating the CFD approach employed in this work.

Frontier exploration and the North Atlantic Igneous Province: new insights from a 2.6 km offshore volcanic sequence in the NE Faroe–Shetland Basin

The Lagavulin exploration well 217/15-1Z penetrated a c . 2.6 km thick volcanic sequence dominated by extrusive basaltic rocks spanning the Paleocene–Eocene boundary in the NE Faroe–Shetland Basin. The well comprises one of the thickest drilled sequences through the North Atlantic Igneous Province. Integrated analysis of drill cuttings and wireline-log data reveals key volcanic lithofacies: (1) tabular lava flows; (2) compound lava flows; (3) hyaloclastite; (4) volcaniclastic rocks. The volcanic facies reveal two major sub-aqueous to subaerial sequences consistent with lava delta progradation. These sequences are separated by a volcanic hiatus represented by extensive reddened soils, which preceded the re-submergence of the area. Emergence followed by submergence of the first lava delta is interpreted to record an intra-T40 transient uplift event near the Paleocene–Eocene boundary. Basalts from the lower c . 1.3 km have low TiO 2 (<1.5 wt%) and low Zr/Y (2–3), with olivine-phyric picrites towards the base (Mg# 70–82; olivine Fo 85–91 ). The hiatus correlates precisely with a change to high-TiO 2 (2.5–3.2 wt%), high-Zr/Y (>4) compositions, which dominate the upper sequence. The associated change in lava geochemistry, transient uplift and volcanic hiatus appears consistent with a transient pulse of hot buoyant plume material passing beneath the area. Supplementary material: All raw geochemical data and supplementary analyses are available at http://www.geolsoc.org.uk/SUP18888 .

A Complete Petrophysical-Evaluation Method for Tight Formations From Drill Cuttings Only in the Absence of Well Logs

Summary The amount of tight-formation petrophysical work conducted at present in horizontal wells and the examples available in the literature are limited to only those wells that have complete data sets. This is very important. But the reality is that in the vast majority of horizontal wells, the data required for detailed analyses are quite scarce. Petrophysical evaluation in the absence of well logs and cores can now be considered owing to the possibility of measuring both the permeability and porosity of drill cuttings. This is essential because the application of the successive correlations used throughout the paper is based on porosity and permeability data. To try to alleviate the data-scarcity problem, a new method is presented for complete petrophysical evaluation derived from information that can be extracted from drill cuttings in the absence of well logs. The cuttings data include porosity and permeability. The gamma ray and any other logs, if available, can help support the interpretation. However, the methodology is built strictly on data extracted from cuttings and can be used for horizontal, slanted, and vertical wells. The method is illustrated with the use of a tight gas formation in the Deep basin of the western Canada sedimentary basin (WCSB). However, it also has direct application in the case of liquids. The method is shown to be a powerful petrophysical tool because it allows quantitative evaluation of water saturation, pore-throat aperture, capillary pressure, flow units, porosity (or cementation) exponent m, true-formation resistivity, and distance to a water table (if present). Also, the method allows one to distinguish the contributions from viscous and diffusion-like flow in tight gas formations. The method further allows the construction of Pickett plots without previous availability of well logs, and it assumes the existence of intervals at irreducible water saturation, which is the case of many tight formations currently under exploitation. It is concluded that drill cuttings are a powerful direct source of information that allows complete and practical evaluation of tight reservoirs in which well logs are scarce. The uniqueness and practicality of this quantitative procedure originate from the fact that it starts only from the laboratory analysis of drill cuttings—something that has not been performed in the past.

Cuttings Characteristics and Mechanics Behavior in Horizontal Wells of Liaohe Oil Field

Cuttings transport of drilling and washing process in horizontal well is a typical two-phase (liquid-solid) or three-phase (gas-liquid-solid) flow phenomena. In this paper, it analyzes the flow characteristics of Huan 127-Lian H2 horizontal wellbore , then uses experimental method to study the behavior of the particle size distribution and the mechanics. This study provides an important way to master cuttings settling in fluid medium, it can explain how the cuttings bed is generated and cleared, and why the procession of cuttings of migration is stopped. In addition, measurement and analysis of drill cuttings is the basis erosion and abrasion analysis of BHA.

Cenozoic cooling and denudation in the North Pennines (northern England, UK) constrained by apatite fission-track analysis of cuttings from the Eastgate Borehole

The Cenozoic landscape development of Britain remains relatively poorly understood. On the one hand, ‘plumists’ have tried to explain the present-day topography as a consequence of effects of the Iceland mantle plume during the Palaeocene-Eocene British Tertiary Igneous Province (BTIP) magmatism, with little or no subsequent modification. On the other hand, abundant evidence exists from fluvial and marine terraces and superimposed karstic levels for significant vertical crustal motions during the Quaternary, which clearly has nothing to do with any mantle plume. To shed light on this issue, we present the first publication of data that constrain the Cenozoic thermal history of the North Pennine uplands of northern England, from apatite fission-track analysis of drill cuttings from the Eastgate Borehole in Weardale, in the western part of County Durham. Our results indicate ∼650m of regional denudation since the latest Oligocene/Early Miocene, plus the ∼400m of localized entrenchment that has created the modern Weardale valley. Before the latest Oligocene/Early Miocene, but following the BTIP magmatism, the crust in this region experienced significant cooling, mainly due to a decrease in the geothermal gradient from ∼55 to 61°Ckm−1 to the present 38°Ckm−1, along with ∼300±200m of denudation. Although significant BTIP magmatism occurred in northern England, it thus had only a limited net effect; the crust experienced dramatic heating, but cooled back to its original thermal state within, at most, a few tens of millions of years. We suggest that this rapid cooling effect resulted from westward flow of relatively cold material within the mobile lower-crustal layer, driven by the lateral pressure gradient induced by earlier heating effects and effects of surface processes. Whatever topography developed during the Palaeogene, as a direct result of these heating effects, underplating at the base of the crust, and the associated modest denudation, was presumably also short-lived; significant changes to the crustal thickness, and thus to the topography, can be envisaged as a consequence of subsequent lower-crustal flow.

Origin of the Mt Ashmore structural dome, west Bonaparte Basin, Timor Sea

New insights into the 3D structure, composition and origin of the Mt Ashmore dome, west Bonaparte Basin, Timor Sea, are enabled by reprocessed seismic-reflection data and by optical microscopic, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM) analyses of drill cuttings. The structural dome, located below a major pre-Oligocene post-Late Eocene unconformity and above a ∼6 km-deep-seated basement high indicated by marked gravity and magnetic anomalies, displays chaotic deformation at its core and a centripetal kinematic deformation pattern. A study of drill cuttings of Lower Oligocene to Lower Jurassic sedimentary rocks intersected by the Mt Ashmore 1B petroleum-exploration well reveals microbrecciation and extreme comminution and flow-textured fluidisation of altered sedimentary material. The microbreccia is dominated by aggregates of poorly diffracting micrometre to tens of micrometres-scale to sub-millimetre particles, including relic subplanar fractured quartz grains, carbonate, barite, apatite and K-feldspar. A similar assemblage occurs in fragments in basal Oligocene sediments, probably derived from the eroded top section of the dome, which protrudes above the unconformity. SEM coupled with EDS show the micrometre to tens of micrometres-scale particles are characterised by very low totals and non-stoichiometric compositions, including particles dominated by Si, Al–Si, Si–Ca–Al, Si–Al–Ca, Si–Mg, Fe–Mg–Ca, Fe–Mg and carbonate. XRD analysis identifies a high proportion of amorphous poorly diffracting material. TEM indicates internally heterogeneous, fragmented and recrystallised structure of the amorphous grains, which accounts for the low totals in terms of the high-volatile and porous nature of the particles. Another factor for the low totals is the uneven thin-section surfaces which affect the totals. No volcanic material or evaporites were encountered in the drillcore, militating against interpretations of the structure in terms of magmatic intrusion or salt diapirism. Such models are also inconsistent with the strong gravity and magnetic anomalies, which signify a basement high below the dome. An interpretation of the dome in terms of a central rebound uplift of an impact structure can not be proven due to the lack of shock metamorphic effects such as planar deformation features, impact melt or coesite. However, an impact model is consistent with the chaotic structure of the domal core, centripetal sense of deformation, microbrecciation, comminution and fluidisation of the Triassic to Eocene rocks. In this respect, an analogy can be drawn between the Mt Ashmore structural dome and likely but unproven impact structures formed in volatile (H2O, CO2)-rich sediments where shock is attenuated by high volatile pressure, such as Upheaval Dome, Utah. In terms of an impact hypothesis the Mt Ashmore dome is contemporaneous with a Late Eocene impact cluster (Popigai: D = 100 km, 35.7 ± 0.2 Ma; Chesapeake Bay: D = 85 km, 35.3 ± 0.1 Ma).

Pore-scale modelling based on microscopic analysis of drill cuttings

Pore-scale modelling based on microscopic analysis of drill cuttings

Estimation of Rock Aggregates Quality Using Analyses of Drill Cuttings

There is a need for an effective method to estimate the quality of crushed rock aggregates and its usability in the early stages of project planning, e.g., for road and railway constructions and quarry prospecting. The proposed method is based on mineralogical and petrographic analyses of drill cuttings and analysis of the coarse fraction to estimate the homogeneity/heterogeneity of the bedrock. The geological analyses are followed by an estimation of the rock materials’ mechanical properties and their potential technical usability. Development and practical applicability (field and laboratory) of the method have been performed and correlated to three road projects from regions of different geological and climatic zones in Sweden. The study confirms the capability of the proposed method as a surveying tool.

Sources of hydrocarbon pollution in surface sediments of the Campeche Sound, Gulf of Mexico, revealed by biomarker analysis

Surface sediments from the shelf area of the Campeche Sound (Gulf of Mexico) and the adjacent abyssal plain were sampled in the course of environmental monitoring for petroleum pollution as a result of industrial activity in the largest oil field in Mexico. Offshore oil production, refinery activities and heavy ship traffic, as well as natural petroleum seeps, are potential sources of pollution of water and sediment in the area. Gas chromatography–mass spectrometry (GC–MS) analysis of the nonaromatic hydrocarbon fractions of the sediment extracts revealed overlapping hydrocarbon assemblages indicating multiple sources. Samples taken close to known asphalt seeps exhibit biomarker patterns virtually identical to those of reference crude oils, so the asphalts have apparently escaped from petroleum reservoirs with fractured cap rocks. Other sediments, with distributions superimposed on mature fossil hydrocarbons, contain biomarkers typical of neither fossil fuels nor immature organic matter (OM) in marine surface sediments. They obviously derive from drill cuttings recovered during penetration of Tertiary to Cretaceous deposits and disposed of into the shallow sea, as indicated by the comparative analysis of drill cuttings from several wells in the area.

Wellsite, Laboratory, and Mathematical Techniques for Determining Sorbed Gas Content of Coals and Gas Shales Utilizing Well Cuttings

Drill cuttings can be used for desorption analyses but with more uncertainty than desorption analyses done with cores. Drill cuttings are not recommended to take the place of core, but in some circumstances, desorption work with cuttings can provide a timely and economic supplement to that of cores. The mixed lithologic nature of drill cuttings is primarily the source of uncertainty in their analysis for gas content, for it is unclear how to apportion the gas generated from both the coal and the dark-colored shale that is mixed in usually with the coal. In the Western Interior Basin Coal Basin in eastern Kansas (Pennsylvanian-age coals), dark-colored shales with normal (∼100 API units) gamma-ray levels seem to give off minimal amounts of gas on the order of less than five standard cubic feet per ton (scf/ton). In some cuttings analyses this rule of thumb for gas content of the shale is adequate for inferring the gas content of coals, but shales with high-gamma-ray values (>150 API units) may yield several times this amount of gas. The uncertainty in desorption analysis of drill cuttings can be depicted graphically on a diagram identified as a “lithologic component sensitivity analysis diagram.” Comparison of cuttings desorption results from nearby wells on this diagram, can sometimes yield an unique solution for the gas content of both a dark shale and coal mixed in a cuttings sample. A mathematical solution, based on equating the dry, ash-free gas-contents of the admixed coal and dark-colored shale, also yields results that are correlative to data from nearby cores.