Mud Contamination Research Articles

Low-density granite-based geopolymer for well cementing: The role of burnt lime in enhancing early strength

In the pursuit of sustainable solutions within the oil and gas industry, the environmental and mechanical limitations of Ordinary Portland Cement (OPC) have led to the evaluation of more sustainable alternative materials for oilwell cementing applications. Particularly in shallow-depth cementing operations, where low-density slurries are essential to prevent formation breakdown, current solutions fall short in balancing environmental impact with the industry's performance requirements. Geopolymers, known for their reduced carbon footprint and comparable mechanical properties, have been seen as a promising alternative. However, increasing water content to lower the slurry density remains a challenge for geopolymers due to the weakening effect and prolonged reaction. The specific role of burnt lime (CaO) has the potential to enhance the early strength of low-density geopolymers yet remains under-explored for this particular case. This study aims to fill this gap by examining the effects of two different reactivities of CaO on a low-density granite-based geopolymer at low temperatures and investigate the potential of CaO to enhance the early strength of low-density geopolymers, aiming to provide a sustainable alternative to traditional cementing materials in oil well operation. The investigation consists of viscosity measurements, pumpability tests, and compressive strength evaluations. Additionally, isothermal calorimetry, TGA, XRD, and SEM were conducted to gain a deeper understanding of the behavior of each sample. Supplementary tests were conducted to evaluate the effect of varying CaO concentrations and the impact of mud contamination on the performance of low-density geopolymers. The investigation revealed that calcium oxide did not significantly impact the initial viscosity of the slurry however, it affects gelation and rate of the reaction. Short-term strength was shown to be affected by CaO at two different temperatures, yet negligible effects were seen in the long-term period for geopolymers with a high water-to-solid ratio. The findings suggest that CaO can significantly enhance the early strength of geopolymers, which are crucial properties for cementing operations in oil and gas wells. This could contribute to accelerate the possibility of geopolymers as a viable sustainable replacement for Portland cement especially in shallow and low-temperature well-cementing applications.

Drilling mud contamination effect on wellbore cement strength: An experimental investigation

Cementing is an essential downhole operation during the drilling of oil, gas, and geothermal wells, with the primary objective of providing structural support and a seal in the wellbore. It is important to attain adequate cement strength to preserve well integrity, inhibit fluid movement, enhance zonal isolation, and hold the wellbore casing in place. However, a significant challenge arises from the potential contamination of the cement by drilling mud (DM) during the placement process. This study aims to assess the impact of both water-based drilling mud (WBDM) and oil-based drilling mud (OBDM) contamination on the strength of API Class G wellbore cement by comprehensively investigating the underlying causes and the mechanism of strength degradation. Following a systematic methodological approach and the guidelines provided by API and ASTM, cement slurries were prepared and contaminated with DM at 10 %, 20 %, and 30 % concentrations by volume. Subsequently, both neat and contaminated samples were cured for 1, 3, 7, and 14 days, after which a series of uniaxial compressive strength (UCS) tests were conducted, and the results were further reinforced by microstructural and petrophysical property analysis. The results demonstrate that both WBDM and OBDM contamination significantly reduce cement strength, irrespective of curing time. Though the effect of OBDM contamination appears to be more pronounced, the effect of WBDM contamination is also remarkable. After final curing of 14 days, WBDM-contaminated cement samples exhibited an average strength reduction of 45.06 %, while OBDM contamination led to a 66.32 % reduction in strength compared to the neat cement with 30 % contamination. Additionally, for the same curing time and contamination percentage, porosity was found to be increased by 71.18 % and 91.33 %, respectively. The mechanism of neat and contaminated cement hydration is explained with the support of SEM-EDS tests, which confirmed the presence of contamination and revealed how two different drilling muds generate dissimilar pore structures within the cement sheath, affecting the hydration and ultimately contributing to the observed reduction in strength. The findings quantify the negative impact of WBDM and OBDM contamination on wellbore cement, emphasizing the importance of mitigating mud contamination during cementing operations.

Real-time chemostratigraphy at wellsite; removing drilling uncertainties

Real-time chemostratigraphy is a workflow deployed at wellsites to remove stratigraphic uncertainty and support drilling operations. This study presents the chemostratigraphic wellsite workflow which, during drilling operations, support either the placement of casing points (using predefined geochemical markers to target a depth above a specific stratigraphic feature) or aid geosteering. Geosteering is typically employed during the drilling of a horizontal well and is done to keep the drill within a certain zone or horizon to maximise production. Wellsite chemostratigraphy has been effectively deployed to wellsites within multiple basins around the globe and has recently been utilised in the Perth Basin. The wellsite workflow starts before the deployment, with offset wells analysed by inductively coupled plasma (ICP) spectroscopy within a laboratory-based setting. This builds the correlative element-based framework and identifies the trends required to assist with either core placement, casing point, or geosteering. Samples are analysed by energy dispersive x-ray fluorescence units (these data are then used to confirm the zone previously defined) and can be identified at wellsite using the onsite tool, the selected elements of which are those less likely to be affected by drilling mud contamination and loss of circulation material (LCM). However, during drilling operation, there may be instances where LCM must be added to the drilling muds, which may have an effect on the data quality for certain elements. With a dedicated ICP spectrometry elemental database behind the wellsite operation, machine learning tools may be employed to ‘repair’ correlation critical elements.

Corrosion resistance and mechanisms of class C fly ash-based geopolymer in simulated oil well environments: Mud contamination and salt solutions at high temperature

Geopolymer presents great potential in oil well environment. For class G oil well cement (OWC) and class C fly ash-based geopolymer, the comparative experiments under simulated oil well environment were performed. The early age properties of geopolymer were measured. Considering the higher downhole temperature, the high temperature resistance of geopolymer at 60 ℃ and 180 ℃ was investigated. Also, the mud contamination resistance of geopolymer at 60 ℃ was explored. A self-designed percolation pipe was used to simulate the process of fresh geopolymer slurry exposed to three salt solutions (5% Na2SO4, 5% NaHCO3 and 2.5% Na2SO4 + 2.5% NaHCO3). The corrosion resistance to salt solution of geopolymer at 60 ℃ was studied. The results showed that geopolymer had higher early strength and high temperature stability than OWC. Meanwhile, compared with OWC, geopolymer possessed better mud contamination resistance due to the smaller pore diameter and the denser matrix. Additionally, all of three salt solutions decreased the compressive strength of OWC, especially the simultaneous existence of Na2SO4 and NaHCO3 accelerated the deterioration of OWC. By contrast, the porosity and pore diameter of geopolymer declined and the compressive strength increased in Na2SO4 solution. Although the compressive strength of geopolymer decreased in NaHCO3 solution, the deterioration degree was lower than OWC. Overall, geopolymer presented better adaptability and durability than OWC in oil well cementing.

Nanostructured antifouling coatings for galvanized steel food storage and container surfaces to enhance hygiene and corrosion resistance against bacterial, fungal, and mud contamination

Nanostructured antifouling coatings for galvanized steel food storage and container surfaces to enhance hygiene and corrosion resistance against bacterial, fungal, and mud contamination

Experimental investigation of the cementation and tensile properties of cement to formation interface considering surface irregularity and drilling mud residue

Cement sheath is an annular structure situated between casing and formation, which is designed to seal the formation and reinforce the borehole. However, owing to the surface irregularity and drilling mud residue, the interface between the cement sheath and the formation is one of the weakest parts for fluid leakage causing well integrity issues, which would also affect the reliability of the cement bond logs. To evaluate the cementation state and tensile properties of the cement-formation interface, rock-cement composite disc specimens are prepared, considering key factors such as lithology, interface irregularity, treatment of oil-based drilling mud contamination, and flushing fluid washing. Flushing efficiency of the drilling mud contaminated rock surface, interface cementation characteristic, referenced tensile strength, and tensile fracture morphology are acquired and analysed comparatively. Results show that (1) the flushing efficiencies of shale and sandstone are 74.1 ~ 61.9% and 52.4 ~ 28.4%, respectively, decreasing with the increase in surface irregularity. (2) The rock-cement interface gradually becomes poorly cemented as the surface cleanliness decreasing and the irregularity increasing. (3) Under the condition of drilling fluid contamination, there exists a transitional area at the cemented interface, where microcracks and pores are developed. (4) With the influence of drilling mud contamination, the referenced tensile strengths of shale-cement and sandstone-cement interfaces drop from 2.716 to 0.586 MPa and from 2.840 to 0.007 MPa, respectively. The effects of underground temperature and pressure environment are not particularly considered in this study and would be investigated systematically in future research.

Experimental Study on the Compressive and Shear Mechanical Properties of Cement–Formation Interface Considering Surface Roughness and Drilling Mud Contamination

In a casing-cement sheath-formation system, the cement–formation interface is usually weakly cemented for the residual of drilling mud, in which a leakage path would easily form, threatening the safe operation of underground energy exploitation and storage. To evaluate the compressive and shear mechanical behavior of the cement–formation interface, cement–rock composite cylindrical specimens were prepared. Uniaxial and triaxial compression and direct shear tests were implemented. The flushing efficiency of the rock surface, compressive strength, interface incompatible deformation, parameters of shear strength, and morphology of shear failure surface were acquired and analyzed. Results show that the flushing efficiency of shale surface decreases from 76.7% to 64.2% with the surface roughness increasing from 0 to 2 mm. The flushing efficiency of sandstone is only 44.7%, remarkably lower than that of shale. With the stress condition transforming from uniaxial to triaxial compression, the feature of the stress–strain curves changes from elastic-brittle to elastoplastic, and the compressive strength increases from 20.6~60.1 MPa to 110~120 MPa. The cement part presents noteworthy plastic deformation and several micro shear fractures develop. There is incompatible deformation between cement and rock, which induces interface debonding for almost all the composite specimens. The internal friction angle and cohesive strength both decrease with the increase in pollution degree of drilling mud, and increase with the rise in surface roughness. The shear facture surface is not exactly the rock–cement interface, but usually manifests as a shear zone, in which the rock, cement, and interface all contribute to the final shear failure. The above findings would be valuable for the revealing of cement–formation interface failure mechanism.

Reconstruction of geochemical characteristics of original organic matter in drilling cuttings contaminated by oil-based mud

Oil-based drilling mud (OBM) contamination, commonly occurring in cuttings during petroleum exploration, has had been a problem seriously hindered source rock identification and evaluation. To eliminate the effect of contamination on “free” bitumen extracted directly from source rock, “enclosed” and “bound” bitumens were released from the mineral matrix by demineralization and from the kerogen structure using an improved catalytic hydropyrolysis technique, respectively. Geochemical and carbon isotopic compositions of the three types of bitumen were used to reconstruct the geochemical characteristics of original organic matter in their source rocks. Results indicate that “free” and “enclosed” bitumens have similar biomarker distributions and n-alkane δ13C values in non-contaminated cuttings, but the former is more susceptible to OBM contamination. “Enclosed” bitumen can thus be used to characterize the organic geochemistry of source rocks contaminated by OBM. The carbon isotopic compositions of individual n-alkanes in “free” and “enclosed” bitumens differ from those in “bound” bitumen, likely because of the effects of diagenesis and other secondary alteration. “Bound” bitumen is more likely to preserve the molecular carbon isotopic characteristics of original organic matter in source rocks, while the “free” and “enclosed” bitumens more represent the generation products. Based on biomarker characteristics and carbon isotopic compositions of “bound” hydrocarbons, Wenchang (WC) Formation (Fm.) source rocks in the Zhu I Depression of the Pearl River Mouth Basin (PRMB) can be divided into three types in normal medium–deep (WC–I), shore–shallow (WC-II), and special medium–deep (with different algal blooms growth rates; WC-III) lacustrine source rocks. The special medium–deep lacustrine source rocks of Wenchang Fm. are characterized by high ratio of C30 4-methylsteranes to C29 steranes (4-Me/C29 > 0.66) and heavy δ13C values (δ13Ckerogen < −26.1‰), which are obviously different from those of normal medium–deep lacustrine source rocks. The combination of “free”, “enclosed”, and “bound” hydrocarbons geochemical and isotopic compositions thus provides a comprehensive understanding of source rocks.

Inherent Flame-Retardant, Humid Environment Stable and Blue Luminescent Polyamide Elastomer Regulated by Siloxane Moiety.

The rapid development of the polymeric materials market has created an urgent demand for the thermoplastic polyamide elastomer (TPAE) owing to its greater functionality, and ability to be synthesized via a facile and industrial route. In this work, a series of novel silicone-containing polyamides (PA1212/Si12) were successfully synthesized from 1,12-dodecarboxylic acid (LA), 1,12-dodecarbondiamine (DMDA), and 1,3-bis (amino-propyl) tetramethyldisiloxane (BATS), via a one-pot melt polycondensation method in the absence of a catalyst. FTIR, 1H-NMR, GPC and inherent viscosity results cohesively prove that the polymerization of monomers was well conducted, and the chemical structure was in high accordance with the design. As expected, the Si12 unit-content of the copolymers regulate the properties of the series. As the feeding ratio of BATS in the diamines increases from 5 mol% to 40 mol%, the thermal transition temperatures, Tg and Tm, decline steadily before finally stabilizing at ~6 °C and 160 °C, respectively, indicating that the co-polyamides possess improved chain flexibility but restricted crystallization ability. The conspicuous evolution in crystalline morphology of the series was observed by XRD and AFM. The increased PA Si12 phase induces the crystallized PA 1212 phase to transit from a thermally-favorable large and rigid crystal structure (α phase) to a kinetically-favorable small and ductile crystal structure (γ phase). Reflected in their stress–strain behavior, PA1212/Si12 copolymers are successfully tailored from rigid plastic to ductile elastomer. The tensile strength mildly drops from above 40 MPa to ~30 MPa while the reversible elongation increases from ~50% to approximately 350%. Accordingly, the moderate surface tension differences in the monomers facilitate the efficient conduction of the co-polymerization process, and the distributed short siloxane unit in the backbone fulfills the copolymer with desirable elasticity. Interestingly, the novel silicone-containing polyamides also display Si12 unit-content dependent flame retardancy, humidity stability, and unconventional solid-state fluorescence properties. The elastomers exhibit a low bibulous rate and anti-fouling characteristics to dye droplets and mud contamination, pass the V–1 rating (UL 94) with a constantly declining PHRR value, and emit blue luminescence under a 365 nm light source. Herein, we propose a new facile strategy for developing a high-performance and multifunctional silicone-modified polyamide, which bears promising industrialization potential. In addition, this first reported silicone-containing thermoplastic polyamide elastomer, which is self-extinguishing, anti-fouling and blue-luminescent, will further broaden the application potential of thermoplastic polyamide elastomers.

Measured Properties of Annular Cement Compared With Ultrasonic Cement Logs

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204015, “A Comparison of the Measured Properties of Annular Cement With Ultrasonic Cement-Evaluation Logs,” by Dave Gardner, SPE, Hans Joakim Skadsem, and Katherine Beltrán-Jiménez, SPE, Norwegian Research Centre, et al. The paper has not been peer reviewed. In this work, different measurement methods have been used to investigate the quality of the cement sheath inside two cemented “sandwich” sections, including high-resolution ultrasonic cement-evaluation logs, sample analysis, mechanical loading, and fluid-seepage measurements. The examined sections were recovered from a North Sea well during a permanent plug-and-abandonment operation. The measurements have been analyzed with an aim of describing in detail the spatial variations in the cement properties and relating them to the logs. The data analysis has improved the understanding of the cement-sheath mechanical properties, seal quality, and response of the ultrasonic cement-evaluation logs. Introduction A well drilled at the Valhall Field was permanently abandoned in 2018 after being in production since 1985. To install the surface plug, the 9⅝-in. and 13⅜-in. casings were both cut and retrieved to surface in sections simultaneously. After the well abandonment, two of the cemented casing-in-casing sandwich sections were sent to shore for further analysis, including relogging. The deepest section, recovered from the interval between 251 and 263 m, was named Fish 11. A visual inspection of the section showed complete annular cement coverage at both ends but with signs of mud contamination, especially at the casing/cement interface and primarily on the narrow side of the annulus. The 9⅝-in. casing had an eccentricity of 70% compared with the outer casing and equivalent to the standoff created by the 9⅝-in. casing-collar thickness. The uppermost sandwich section covering the top of the cement was retrieved from 119 to 131 m and was named the transition joint. The eccentricity of the inner casing compared with the outer casing was 60% for this section. The bottom of the section had complete cement coverage; however, some mud intrusions were apparent in the bulk cement as well as mud contamination between the casing/cement interface. The 9⅝-in. casing was originally cemented in two stages because of the presence of a weak formation. Both the transition joint and Fish 11 were retrieved from the upper part of the section, which was cemented in a second stage by bullheading slurry from the surface and down the annulus. In this operation, the denser slurry was displaced from above the spacer fluid and the oil-based mud was used to drill the 12¼-in. section into the formation. The authors speculate that the mud displacement during the bullheading operation was instantaneous, with no backflow. The fact that the sections were cemented by bullheading may have influenced the properties of the cement, particularly close to the top of the cement.

Comparative analysis of the geopolymer and Portland cement application as plugging material under conditions of incomplete displacement of drilling mud from the annulus

Portland cement is traditionally used in cementing of oil and gas wells. However, Portland cement has a number of shortcomings. The most important of these are the formation of microannuli between the cement plug and the rock or casing, as well as the formation of cracks and permeable channels in the cement matrix. Recent research shows that geopolymer can be a perspective alternate to portlandcement by overcoming beforementioned issues. The article comparatively analyzes the changes in the parameters of plugging materials containing geopolymer and Portland cement while contamination with water-based drilling mud. The results show that geopolymerbased solutions are more resistant to contamination with water-based drilling mud than Portland cement-based solutions. Thus, mixing Portland cement slurry with water-based drilling mud increases its viscosity and fluid loss, and sharply reduces its compressive strength. However, when a geopolymer solution is mixed with a water-based drilling fluid, its viscosity is almost unchanged, its fluid loss is reduced, and reduction in its compressive strength is less than in Portlandcement based material. Keywords: portland cement; geopolymer; fly ash; cementing; water based mud; mud contamination.

Characterization of the mud displacement in an enlarged wellbore: An integrated rock-fluid model

Cement-mud displacement plays a crucial role in the sealability of cement sheaths. Irregular geometric features of a wellbore due to washout can have a negative impact on mud and cement mobilization. An unstable interface between two fluids always leads to mud channeling, interfluid mixing, and cement contamination, degrading the cement quality. Many factors, such as mechanical and rheological properties of fluids, annulus geometry, flow pattern, and flow rate, significantly influence the displacement efficiency. This study investigates the characterization of the mud displacement in an irregular horizontal well using a 3D computational fluid dynamics (CFD) model. Mud is displaced in an enlarged wellbore by geopolymer and neat class G cement. The wellbore geometry is developed based on the caliper log data from an unconventional shale well in the Tuscaloosa Marine Shale (TMS) lithology. The effects of pump rate, density difference, and mud contamination are evaluated by numerical simulations. The results present those residual muds mainly exist in the upper annulus of the enlarged section. Geopolymer has a better sealing performance and can resist more water-based mud (WBM) contaminations than neat class G cement. The scenario with a low mud-cement density difference and high cement injection rate results in a high cement volume fraction, mitigating the gas migration.

Cement properties characterization from a section retrieved from an oil production well after 33 years of downhole exposure

A unique data set has been constructed based on the study of class G cement recovered from an oil well on the Norwegian continental shelf. The cement was placed between two casing sections and submitted to downhole conditions for 33 years. The aim of this research is to analyze the aging of the cement and its consequences for the well integrity. Additionally, the findings represent a baseline for future assessments of old age cement from oil and gas wells. The characterization includes: petrophysical properties (porosity and permeability); mechanical properties (uniaxial compressive strength (UCS) and Young’s Modulus); and compositional analysis using Computed Tomography (CT), Scanning Electron Microscopy (SEM), X-ray Fluorescence (XRF) and Quantitative X-ray Diffraction (XRD). Findings suggest that the overall decrease of cement integrity appears to be low, since the magnitudes of permeability and porosity fall within the ranges of early age cement. However, the chemical characterization shows that mud contamination may have an effect on the cement performance and is found to be relevant for a reduction in compressive strength. • In-depth characterization of class G cement exposed to downhole conditions for 33 years. • The results presented provide a baseline to assess the effect of aging on cement. • Findings suggest that the decrease in cement integrity appears to be low.

AN EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF CUTTINGS SIZE ON MUD RHEOLOGY

Effective hole-cleaning is vital for a successful drilling operation and has significant effect on optimizing factors such as penetration rate, bit optimization and well stability. Efficient transportation of drilling cuttings are dependent on factors such as fluid properties and rheology, cuttings size and shape, fluid velocity, cuttings concentration, cuttings transport velocity and rate of penetration. This experimental work examined the effects of cutting sizes on drilling fluid rheology. To achieve this, two fresh samples of mud were prepared and the rheological properties were analyzed at different temperature ranges representing the operating conditions of most Niger Delta wells. A mesh analysis was carried on dried fresh drill cuttings from the Anieze North Field and dried cuttings taken from the laboratory and two samples were selected at ASTM#40 and #18. 10 % of these cuttings samples were added to each mud sample and the rheological properties were measured at similar temperature ranges as the original mud samples. The results gotten shows that at the various temperature ranges, mud contamination with smaller drill cuttings size (ASTM #40=400um) showed a better performance than the larger particles. The mud rheological properties (viscosity, yield point, YP, plastic viscosity, PV and density) measured at different temperatures showed a remarkable non-linear behavior as shown in the results. KEY WORDS: Cuttings Size, Drill Cuttings, Mud Contamination, Mud Rheology, Temperature

Can cuttings replace cores for porosity and pore size distribution analyses of coal?

Core data play a significant role in analyses of fundamental petrophysical properties, such as porosity and pore size distribution (PSD), which can be used to estimate the storage capacity and recovery rate of hydrocarbons. However, coring is time-consuming, and it is sometimes difficult to retrieve an intact core, particularly from coal reservoirs that are characterized by low mechanical strength and development of fractures. In most cases, only drill cuttings are available for analysis. Therefore, it is important to determine whether drill cuttings can adequately represent formation properties such as porosity and PSD. In this study, coal samples were prepared for analysis, including three groups of artificial drill cuttings—group-A (particle size of 1.00–1.70 mm), group-B (2.36–3.35 mm), and group-C (4.75–6.70 mm)—as well as one core plug. Nuclear magnetic resonance (NMR) measurements and mercury intrusion porosimetry (MIP) were performed to determine the porosity and PSD. The results for the porosity and PSD from the three groups of cuttings agree well with those from the core plug, which suggests that the effects of mechanical-pulverization and size fractionation during the sample preparation can be neglected for cuttings with particle sizes of ≥1 mm in most cases. The exception is one sample that having high mineral contents, because many mineral blocked pores in the sample can be released during mechanical-pulverization. The recommended particle size of drill cuttings for determining the porosity and PSD is 1–1.7 mm, which can provide accurate analytical results and avoid interference from other factors such as wellbore collapse, particle gravity dispersion, and drilling mud contamination.

Core versus cuttings samples for geochemical and petrophysical analysis of unconventional reservoir rocks

Core samples from petroleum wells are costly to obtain, hence drill cuttings are commonly used as an alternative source of rock measurements for reservoir, basin modelling, and sedimentology studies. However, serious issues such as contamination from drilling mud, geological representativeness, and physical alteration can cast uncertainty on the results of studies based on cuttings samples. This paper provides a unique comparative study of core and cuttings samples obtained from both vertical and horizontal sections of a petroleum well drilled in the Canadian Montney tight gas siltstone reservoir to investigate the suitability of cuttings for a wide range of geochemical and petrophysical analyses. The results show that, on average, the bulk quantity of kerogen or solid bitumen measured in cuttings is comparable to that of the core samples. However, total organic carbon (TOC) measurements are influenced by oil-based drilling mud (OBM) contamination. Solvent-cleaning of cuttings has been shown to effectively remove OBM contamination in light, medium, and heavy range hydrocarbons and to produce similar kerogen/solid bitumen measurements to that of core samples. Similarly, pyrolysis methods provide an alternative to the solvent-cleaning procedure for analysis of kerogen/solid bitumen in as-received cuttings. Microscopic study substantiates the presence of significant contamination by OBM and caved organic and inorganic matter in the cuttings, which potentially influence the bulk geochemistry of the samples. Furthermore, minerals in the cuttings display induced micro-fractures due to physical impacts of the drilling process. These drilling-induced micro-fractures affect petrophysical properties by artificially enhancing the measured porosity and permeability.

Revised biostratigraphic and thermal alteration interpretations for the Paleozoic of the Hopedale Basin, offshore Labrador, Canada

Abstract Paleozoic rocks occur in seven wells in the Hopedale Basin, offshore Labrador (Hopedale E-33, South Hopedale L-39, Tyrk P-100, Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87), where they represent erosional remnants primarily associated with Cretaceous syn-rift half grabens. Previous palynological studies have reported a range of ages for the Paleozoic in these wells, including Ordovician, Devonian, Carboniferous, and undifferentiated Paleozoic. Palynological analyses in the present study confirm that recovery is limited, primarily due to the predominance of lithologies that hinder palynomorph preservation, specifically dolostones. Palynomorphs (predominantly acritarchs and chitinozoans) have been analyzed from new and archived samples from the seven wells and have, for the first time, produced consistent age determinations for the Paleozoic strata in all wells: palynomorph assemblages considered in place indicate a Middle to Late Ordovician age. Thermal maturity was determined from Ordovician acritarchs and leiospheres observed in the Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87 wells, with thermal alteration indices (TAI) ranging from approximately 5+ to 6+ (dry gas). Carboniferous miospores are present from Paleozoic strata in the southern Hopedale Basin wells, where their TAI values range from 3+ to 4. These miospores are interpreted as contaminants introduced into the samples via cavings or as drilling mud contamination. The data presented here provides new biostratigraphic constraints for the Paleozoic of the Hopedale Basin (Middle to Late Ordovician), facilitates the correlation of the Paleozoic intervals in these wells, and enables the consideration of Labrador margin Lower Paleozoic strata in regional studies as well as in paleogeographic and paleoenvironmental reconstructions.

Experimental study on the effects of cement contamination in a water based mud

Drilling mud is used to ensure save and cost-effective drilling operations. In every phase of the drilling operation, contaminants are encountered which directly affect the properties of the drilling mud. The severity of drilling mud contamination depends on the type of drilling mud used, the type of contaminant and the degree of contamination. In most drilling operations, cement contamination occurs one or more times when casing strings are cemented and the plugs are drilled out. Drilling mud is discarded when cement contamination is too high such that it is practically unreasonable to treat it. It is therefore important to monitor the mud's properties against contamination to ensure the basic functions of the mud. To perform effective monitoring of a drilling mud requires proper knowledge of the drilling mud chemistry, properties, and contaminants. This will help oil operators to apply the right control measures and treatment methods during drilling operations. This paper presents an experimental study on the effect of various concentrations of cement contamination on some physical properties of water based mud (WBM). Four mud samples were prepared of which three of them were contaminated with 10 g, 20 g and 30 g of class G cement. Rheological properties at temperatures of 25 °C, 40 °C and 60 °C as well as the pH, fluid loss and density of the mud were determined. The findings showed that the yield point and gel strength at all test temperatures increased as the concentration level of cement increased. However, the plastic viscosity decreased slightly with cement concentration of 10 g and 20 g and further increased with 30 g of cement contamination at 40 °C and 60 °C. The fluid loss, density as well as the pH of the WBM increased gradually as the concentration of cement increased. It is recommended that the effect of cement contamination in WBM at temperatures higher than 60 °C should be investigated. Cited as : Broni-Bediako, E., Amorin, R. Experimental study on the effects of cement contamination in a water based mud. Advances in Geo-Energy Research, 2019, 3(3): 314-319, doi: 10.26804/ager.2019.03.09

Assessing the legacy of red mud pollution in a shallow freshwater lake: long-term chemical recovery in the water column

ABSTRACTLittle is known about chemical and ecological recovery following red mud leachate pollution in fresh waters. This deficiency is confounded by a lack of knowledge on the chemical composition of red mud leachate and the changes in composition that occur as a result of interactions with sediments and freshwater organisms during transport through aquatic ecosystems. We used over 30 years of data from a shallow lake (Kinghorn Loch, Fife, Scotland) with a well-documented history of several decades of red mud leachate pollution to characterise the chemical loads (during a pollution period from 1981 to 1983), resultant impacts on surface water chemistry (comparison between 1983 and 2009), and recovery trajectories following leachate diversion (1983–2010) of constituents that pose a risk to the environment. Between 1981 and 1983, the input of leachate resulted in loads of total aluminium (Al), total arsenic (As), total vanadium (V), and phosphate (PO4-P) to the lake of 107, 2.3, 3.3, and 2.3 g m−2 (lake surface area) yr−1, respectively. During the same period, the lake acted as a sink of Al, As, V, and PO4-P, retaining 63.6, 0.6, 0.8, and 1.6 g m−2 yr−1, respectively. We used generalised additive modelling to assess the response trajectories and recovery end points of these constituents. Our results demonstrate the complexity of sediment–pollutant interactions during pollutant transport through the aquatic environment and provide insight into likely recovery trajectories in other aquatic ecosystems following red mud contamination. The PO4-P, total As, and total V surface water concentration recovery times, defined statistically as the point on the time series beyond which no further significant decrease in concentrations was observed, ranged from 18 to 26 years. Total Al concentrations continued to decrease significantly following the end of the monitoring period in 2010. In Kinghorn Loch, the legacy of red mud pollution continues to represent an environmental risk, demonstrating the importance of long-term monitoring and management strategies following similar pollution events.

An Adaptable Water-Based Mud System for Multiple Applications While Drilling

Due to significant variations of the subsurface geology from the surface to the top of reservoir and requirement of different fluid characteristics for drilling various hole there is a need to use various mud systems. These may include a simple spud mud for surface hole section, an inhibitive drilling fluid for reactive shale section, a salt water-based mud for salt diapirs and salt formations, and a highly lubricating mud for deviated hole sections with high dogleg severity.To optimize each of these separate and distinct scenarios, there is a need to change the mud system while drilling to overcome the technical challenges associated with these formations and wellbore profiles. The change over from one mud system to another is typically done between casing points while constructing the well to overcome specific drilling challenges associated with next whole section.There is significant time and effort required to clean the mud circulation system adequately before a mud change over in order to avoid any contamination of the new mud system.This is especially true when displacing a waterbased mud by an oil-based mud or an oil-based mud by a water-based mud.If this is not done properly, contamination of the new mud by the old mud could be a source of major problems due to partial or complete loss of functional ability of the new mud system. An adaptable drilling mud system that can easily be transformed from a spud mud system to an inhibitive, or a high lubricating or a salt water mud can provide the industry a versatile fluid system with multiple hole section applications.This removes much of the NPT associated with mud changeover, reduces the mud cost as compared to mixing a totally new mud system and eliminates concerns regarding mud contamination as well as any disposal or recycling cost for the replaced system. This paper describes a volcanic ash-based drilling mud that can be used as a spud mud to drill the surface hole, can easily be converted to an inhibitive mud system to drill reactive shale sections of a borehole, a salt water-based mud to drill the salt sections and also a high lubricating water-based drilling mud to reduce torque and drag problems in deviated and horizontal boreholes. The flexible and easily convertible nature of the base volcanic ash-based drilling mud has potential to reduce total drilling cost significantly as it eliminates a significant portion of non-productive drilling time associated with mud changeover, cleaning of mud circulation system, new mud preparation, incorporation of new mud in the circulation system and displacement of the old mud from the borehole by the new mud, etc.