There are various techniques available for forensic search teams to employ to successfully detect a buried object. Near-surface geophysical search methods have been dominated by ground penetrating radar but recently other techniques, such as electrical resistivity, have become more common. This paper discusses magnetic susceptibility as a simple surface search tool illustrated by various research studies. These suggest magnetic susceptibility to be a relatively low cost, quick and effective tool, compared to other geophysical methods, to determine disturbed ground above buried objects and burnt surface remains in a variety of soil types. Further research should collect datasets over objects of known burial ages for comparison purposes and used in forensic search cases to validate the technique. Suggested Reviewers:NOTICE: this is the author's version of a work that was accepted for publication in Forensic Science International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Forensic Science International, v. 246, January 2015, doi:10.1016/j.forsciint.2014 AcknowledgementsAn EU ERASMUS student training award part-funded the placement of Matteo Giubertoni.A 2011 and 2014 U.K. Nuffield Foundation summer placement award funded the coastal and test hole studies respectively. The authors wish to thank the numerous physical science under-and post-graduate students at Keele University for undertaking pilot investigative projects. The Keele University meteorological observation station provided weather data for the campus case studies. John Cassella and Staffordshire University are thanked for provided facilities and logistical support for the urban case study. AcknowledgmentsThe use of magnetic susceptibility as a forensic search tool
A gas kick in high-temperature well drilled with oil-based mud represents a significant challenge, as the understanding of physical and chemical interactions play a substantial role in the interpretation and decision-making processes. This work provides theoretical and physical explanations for the multiple phenomena observed during an actual well control event, and their impact on the interpretation of the well behavior. Moreover, this paper provides useful insights on the additional capabilities offered by the usage of the Managed Pressure Drilling (MPD) technology in managing a gas kick. A peculiar well control situation occurred in a MENA exploratory well while drilling the 12 1/4" x 13 1/2" section. The particular wellbore features such as high-temperature conditions, gas bearing reservoir layers and oil-based mud, all contributed to make the management of the dry gas influx more challenging and difficult to interpret. Several procedures were needed to regain the control of the well, that was complicated by the effects of oil-based mud thermal expansion, gas solubility and diffusivity principles. Managed Pressure Drilling System (MPD) was also deployed to manage the influx, with a non-conventional dynamic pore pressure evaluation performed during the well control situation. The uncommon conditions in which the kick occurred, made the interpretation of the well data particularly challenging. The paper will present a detailed engineering analysis and data interpretation required to manage in a safe and efficient manner a gas kick during well construction operation via the understanding of the interaction between multiple phenomena like gas migration, oil-based fluid thermal expansion and oil compressibility, gas diffusivity and solubility. In the presented application, MPD technique is displayed as an added value useful to better understand the well behavior and drive the decision of the required kill mud weight needed to regain control of the well. Since geological uncertainties are likely in an exploratory context, and high temperature conditions with oil-based mud may exacerbate the risk of a kick due to the Equivalent Static Density (ESD) reduction caused by thermal expansion, the paper will provide the tools and principles needed for a thorough understanding of the wellbore behavior in similar situations.
During drilling of three exploration wells challenging conditions encountered, such as temperatures up to 180°C, interbedded highly reactive shales/silts, formation pressures which required mud weights up to 2.35 sg and narrow margin between pore and fracture gradients, posed a host of technical, logistical and cost challenges to Eni activities. These conditions required an accurate drilling fluids design to maximize operational efficiency and to minimize the risks related to such an extreme environment. Technical demands were particularly critical since the reactive shale formations had historically proved to be difficult to inhibit when drilled with Water Based Mud and might have caused swelling, tight hole, sticky wireline runs, bit-balling and accretion that could have resulted, among other issues, in low penetration rates (ROP). The formation nature coupled with ECD (Equivalent Circulation Density) constraints due to the high mud weight required to cope with high pore pressure, which also caused high mud rheology readings, were therefore the main limits to be overcome to achieve the well objectives. A tailored drilling fluid program was thus proposed which consisted of an inhibitive HPWBM (High Performance Water Based Mud) that could be converted to an HT-HPWBM, (High Temperature-High Performances Water Based Mud) while drilling, to cross the deeper and hotter sections of the well. This fluid was specifically engineered and optimized after each well in order to contain high concentration of a combination of monovalent salts to guarantee inhibition and reduce solids loading, dedicated polyamine shale inhibitor and fluid loss additives to minimize API/HPHT filtrate and filter cake thickness with the aim to reduce shale water invasion throughout the drilling campaign, graphite to minimizes fluid invasion and fracture propagation and ROP (Rate Of Penetration) enhancer continuously injected using dedicated pump to act as anti-balling and anti-accretion additive. The achieved results were drilling targets delivered safely, on time and with good overall fluid performances which either reduced or eliminated many of the challenges seen in offset wells, including: no barite sag, rheology stability, and stable long-term mud properties and wellbore conditions even during extended formation logs acquisitions. This paper covers the design, execution and accomplishments of the water-based drilling fluids employed on three HP/HT wells drilled, together with all of the lessons learned captured, highlighting the evolution of these systems to reach a step-change in terms of performances in such a harsh environment.
Circular economy has become in the last decades one of the major subjects of debate for corporations around the globe. The ever-growing attention towards the environment and a more sustainable exploitation of the resources of the planet have led the major Oil Companies worldwide to reconsider their internal processes and approaches to business. In this context, the efforts aimed at identifying and implementing initiatives and operative processes pertinent to the concept of circular economy triggered to reconsider Synthetic (low-toxic) Oil-Based drilling fluids (muds) as one of the main actors in terms of successful operative circular initiatives in the oil business. Thanks to their inherent durability in time and scarce tendency to degrade, Synthetic Oil Based Muds unfold many opportunities of recycling and re-use which could not be possible with other drilling fluids systems. In this regard, a correct management of Oil Based drilling fluids which permits treatment, storage, and re-utilization in new wells of the same field or new projects, can significantly reduce the CO2 emissions related to drilling fluids life cycle. The aim of this paper is to quantitatively show the results that can be achieved in terms of reduction of emissions of greenhouse gases by the recycling of Synthetic Oil Based drilling fluids thanks to a considerable volume requirement decrease in relation to drilling operations, and the correlated utilization of resources.
This paper discusses how an organophilic clay-free invert emulsion fluid (OCF-IEF) was customized with a fast-acting hydrogen sulfide (H2S) scavenger to drill a high temperature (HT) exploration well offshore UAE with high H2S concentrations. This application was the first in country to drill through a high H2S formation using an invert emulsion fluid maintaining all parameters within required specifications setting new drilling performance limits. Exploratory HT wells are associated with notable challenges requiring extensive fluid design and qualification. The additional risk of mitigating high H2S was a key consideration in the fluid design phase. A specialized H2S scavenger was selected based on its fast reaction rates proven through testing. The drilling fluid rheology profile and hydraulics were optimized for HTHP drilling conditions, with the fragile gel structure providing adequate suspension while minimizing pressures running the liner. This paper discusses the design approach to fluid customization in the planning phase and procedures followed during execution ensuring trouble-free performance managing the high H2S risk while drilling an HT Exploration well. Proper planning and execution, using best-available drilling practices, enabled drilling of this record-breaking well without encountering significant issues that could impact rig time and increase costs. The fast-acting H2S scavenger ensured no acidic gas detection on surface throughout drilling the section, confirmed through continuous Garett Gas Train (GGT) testing on site proving no traces of the acidic gases were left untreated. This fact was confirmed through pressure, volume and temperature (PVT) sampling showing the formation drilled contained 33% H2S. The section was drilled with constant background H2S and CO2 as well as hydrocarbon gas presence and was left open for 82 days with high percentages of gas at every bottoms up. Despite this, no H2S was recorded at surface. The OCF-IEF was subjected to several static periods of up to 145 hours at temperatures between 337°F and 390°F with superior fluid stability which saved on tripping time to condition the fluid prior to logging. Proper planning and risk mitigation were key in the success of this application. The OCF-IEF system proved to be a key success factor in delivering this critical interval due to the narrow clearance while running casing, preventing any surge or swab effects. The specifically designed OCF-IEF including a fast-acting H2S scavenger displayed superior performance in treating out the acidic gases compared to other scavengers on the market and brought innovation to reality, treating H2S concentrations greater than 33% v/v with no gas released on surface. Successful deployment of this technology in such a challenging environment provides confidence in planning future exploration wells.
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