Borehole Closure Research Articles

Heat transfer modelling of thermal anti-freezing method for ice hot-point drilling

The melting water produced from ice during hot-point drilling can easily freeze and cause the hot-point drill to stick. Two different thermal anti-freezing methods exist to prevent water-filled boreholes from refreezing: the heating cable method and lateral heating method. However, the required power density and ice temperature distribution when using these two methods have not been fully discussed. In this study, heat transfer models of the two thermal anti-freezing methods were first developed based on a simplified heat conduction equation by considering the downward movement of the hot-point drill. Subsequently, case studies were conducted to determine the characteristics of the heat transfer during hot-point drilling. Finally, the variations in the power density, power consumption, borehole closure time, borehole closure length, and thermal layer thickness for both thermal anti-freezing methods were evaluated. We recommend that the heating cable method should be used to drill boreholes with shallow depths or small diameters in temperate ice, whereas the lateral heating method can be applied to a wide range of ice temperatures, borehole diameters, and borehole depths. Generally, the paper presents useful guidance for designing the heating cable and lateral heater and reducing the risk of borehole freezing.

An anisotropic viscoplasticity model for shale based on layered microstructure homogenization

AbstractViscoplastic deformation of shale is frequently observed in many subsurface applications. Many studies have suggested that this viscoplastic behavior is anisotropic—specifically, transversely isotropic—and closely linked to the layered composite structure at the microscale. In this work, we develop a two‐scale constitutive model for shale in which anisotropic viscoplastic behavior naturally emerges from semianalytical homogenization of a bilayer microstructure. The microstructure is modeled as a composite of soft layers, representing a ductile matrix formed by clay and organics, and hard layers, corresponding to a brittle matrix composed of stiff minerals. This layered microstructure renders the macroscopic behavior anisotropic, even when the individual layers are modeled with isotropic constitutive laws. Using a common correlation between clay and organic content and magnitude of creep, we apply a viscoplastic modified Cam‐Clay plasticity model to the soft layers, while treating the hard layers as a linear elastic material to minimize the number of calibration parameters. We then describe the implementation of the proposed model in a standard material update subroutine. The model is validated with laboratory creep data on samples from three gas shale formations. We also demonstrate the computational behavior of the proposed model through simulation of time‐dependent borehole closure in a shale formation with different bedding plane directions.

Can Heating Induce Borehole Closure?

The current study shows that heating a cased borehole in low-permeability shale rock can induce plastic deformation, leading to the closure of the casing annulus and decreasing annulus connectivity. The thermally induced borehole closure is interesting for the field operation of plug and abandonment (P&A), as it potentially saves operation cost and time by avoiding cutting casing and cementing. Lab experiments and numerical simulations are implemented to investigate the thermally induced borehole closure. Pierre shale and a field shale are tested. The lab experiments are performed by heating the borehole wall in a 10-cm-OD hollow cylinder specimen. Here, a novel experimental setup is applied, allowing for measuring temperature and pore pressure at different radii inside the specimen. Both the experimental data and the post-test CT images of the rock samples indicate the rock failure by borehole heating, and under certain conditions, heating results in an annulus closure. The decrease of hydraulic conductivity through the casing annulus is observed, but this decrease is not enough to form the hydraulic-sealed annulus barrier, based on the results obtained so far. Lab-scale finite-element simulations aim to match the lab results to obtain poro-elastoplastic parameters. Then the field-scale simulations assess the formation of shale barriers by heating in field scenarios. Overall, (i) the lab experiments show that heating a borehole can increase the pore pressure in shale and hence induce rock failure; (ii) the numerical simulations match the experimental results reasonably well and indicate that the heating-induced borehole closure can sufficiently seal the casing annulus in the field-scale simulation.

Experimental investigation of water freezing and estimating refreezing time in ice boreholes

Borehole closure owing to the refreezing of meltwater poses a serious limitation in ice thermal drilling, and estimates of the refreezing rate are essential for determining safe drilling rates. In this paper, we describe the results of water cooling and freezing experiments in cylindrical ice holes with a diameter of 200 mm at a setup temperature within the range of −20 to −50 °C. These experiments represent a new means of estimating cooling/refreezing rates using two mutually perpendicular diametric sets of thermoresistors installed inside the holed ice sample. In a colder environment, water cooled/froze faster than in the warmer setup: the cooling rates for a hole diameter of 200 mm were 33.3 to 38.5 °C h−1 at −50 °C and 8.5 to 9.5 °C h−1 at −20 °C, while the average freezing rates were 32.3 to 35.1 mm h−1 at −50 °C and 14.9 to 20.9 mm h−1 at −20 °C. Data from the refreezing rates are applied for practical ice drilling purposes, and a method for predicting safe hot-point drilling performance in cold ice is suggested.

Subsalt pressure prediction in the Miocene Mad Dog field, Gulf of Mexico

Sandstone pressures follow the hydrostatic gradient in Miocene strata of the Mad Dog field, deep-water Gulf of Mexico, whereas pore pressures in the adjacent mudstones track a trend from well to well that can be approximated by the total vertical stress gradient. The sandstone pressures within these strata are everywhere less than the bounding mudstone pore pressures, and the difference between them is proportional to the total vertical stress. The mudstone pressure is predicted from its porosity with an exponential porosity-versus-vertical effective stress relationship, where porosity is interpreted from wireline velocity. Sonic velocities in mudstones bounding the regional sandstones fall within a narrow range throughout the field from which we interpret their vertical effective stresses can be approximated as constant. We show how to predict sandstone and mudstone pore pressure in any offset well at Mad Dog given knowledge of the local total vertical stress. At Mad Dog, the approach is complicated by the extraordinary lateral changes in total vertical stress that are caused by changing bathymetry and the presence or absence of salt. A similar approach can be used in other subsalt fields. We suggest that pore pressures within mudstones can be systematically different from those of the nearby sandstones, and that this difference can be predicted. Well programs must ensure that the borehole pressure is not too low, which results in borehole closure in the mudstone intervals, and not too high, which can result in lost circulation to the reservoir intervals.

Environmental considerations of low-temperature drilling fluids

AbstractThe introduction of low-temperature fluid into boreholes drilled in ice sheets helps to remove drilling cuttings and to prevent borehole closure through visco-plastic deformation. Only special fluids, or mixtures of fluids, can satisfy the very strict criteria for deep drilling in cold ice. The effects of drilling fluid on the natural environment are analyzed from the following points of view: (1) occupational safety and health; (2) ozone depletion and global warming; (3) chemical pollution; and (4) biological pollution. Traditional low-temperature drilling fluids (kerosene-based fluids with density additives, ethanol and n-butyl acetate) cannot be qualified as intelligent choices from the safety, environmental and technological standpoints. This paper introduces a new type of low-temperature drilling fluid composed of synthetic ESTISOLTM esters, which are non-hazardous substances. ESTISOLTM 140 mixtures with ESTISOLTM 165 or ESTISOLTM F2887 have an acceptable density and viscosity at low temperature. To avoid the potential for biological contamination of the subglacial environment, the borehole drilling fluid should be treated carefully on the surface.

Drilling fluid technology in ice sheets: Hydrostatic pressure and borehole closure considerations

The drilling of deep boreholes in ice sheets requires that the hole is filled by a liquid to compensate the ice-overburden pressure. Density is the most important drilling fluid property, so the hydrostatic pressure of the fluid column should be sufficient to prevent closure of the borehole. However, it is impossible to prevent borehole closure at all, because the upper part of glaciers contains a lot of air inclusions and the density of snow–firn zone is much less than the rest stratum, and the expansion coefficient and the compressibility of fluids and ice are rather different. That is why at all accounts there are parts in the borehole, where the ice pressure is higher than the pressure of fluid. One of the main ideas of ice deep drilling technology is the limitation of the closure rate by controlling the density of the drilling fluid. First, it is proposed to choose the depth of the pressure equilibrium and the average fluid density at average temperature in the borehole. Then, the hydrostatic pressure and pressure difference at the borehole walls can be estimated. Finally, the diameter changes in the interval with negative pressure difference are predicted and compared with maximal safety values. This method allows to choose the correct fluid density and the fluid level below surface for the concrete drilling site and to ensure accident-free drilling in ice sheets.

A technique for continuous detection of drill liquid in ice cores

AbstractWhen drilling ice cores deeper than ∼100 m, drill liquid is required to maintain ice-core quality and to limit borehole closure. Due to high-pressure air bubbles in the ice, the ice core can crack during drilling and core retrieval, typically at 600–1200 m depth in Greenland. Ice from this ‘brittle zone’ can be contaminated by drill liquid as it seeps through cracks into the core. Continuous flow analysis (CFA) systems are routinely used to analyse ice for chemical impurities, so the detection of drill liquid is important for validating accurate measurements and avoiding potential instrument damage. An optical detector was constructed to identify drill liquid in CFA tubing by ultraviolet absorption spectroscopy at a wavelength of 290 nm. The set-up was successfully field-tested in the frame of the NEEM ice-core drilling project in Greenland. A total of 27 cases of drill liquid contamination were identified during the analysis of 175 m of brittle zone ice. The analyses most strongly affected by drill liquid contamination include insoluble dust particles, electrolytic conductivity, ammonium, hydrogen peroxide and sulphate. This method may also be applied to other types of drill liquid used at other drill sites.

Probabilistic analysis of borehole closure for through-salt well design

Probability levels, in the form of marginal cumulative distribution functions, are determined for the time it takes salt to contact a casing, which penetrates a salt canopy, and the time it takes the casing to yield once salt has contacted the casing, in support of through-salt well design activities required for deep-water, sub-salt environments. The finite-element method coupled with an advanced reliability method is used to perform the analyses. Randomness caused by uncertainties in salt properties, lithostatic stress, drilling-mud pressure, production temperature, and borehole ellipticity is handled by including statistics and probability distributions for each of these random variables. The advanced reliability method takes full account of the random variables and processes without Monte Carlo simulation, by using a method for assessing reliability statistics that computes response probabilities in a direct and efficient manner. This advanced reliability method falls under the general category of fast probability integration schemes.

Closure of deep boreholes in ice sheets: a discussion

AbstractThe most frequently used relation between ice deformation rate, έ, and stress, ፐ, is the power law, commonly called Glen’s flow law, έ = Aፐn, in which A is an ice stiffness parameter and n is an empirical constant. A can be estimated from the simple exponential relation where A0 is a constant independent of temperature; E, commonly called the enhancement factor, depends on ice crystal orientation, impurity content and other factors; Q is the activation energy for creep; R is the universal gas constant; and T is the absolute temperature. Laboratory experiments yield values of A0 = 9.514MPa–3a–1 for secondary creep. Typical borehole closure experiments then give E ≈ 0.16. This low value probably results from the fact that, when deforming into a borehole, ice is subject to stresses that are inconsistent with the preferred orientation of c axes that has developed over many years under a stress configuration with no borehole present. Closure data from Vostok hole 3G yield E ≈ 0.7. This higher value may reflect a unique stress environment yielding fabrics that are somewhat better oriented for borehole closure.

Borehole logging with an eight-arm caliper–inclinometer probe

AbstractA newly designed eight-arm caliper–inclinometer probe for borehole logging is presented. The caliper sounding gives eight points of cross-sections of the borehole at 1 cm intervals along its axis. Regression circles and ellipses are calculated and used as obvious hypotheses to be tested in order to obtain information on strain rates in the horizontal planes and isotropic or anisotropic borehole closure. The scratching of identifiable marks into the wall of the borehole enables material displacement to be tracked, in particular in the vertical direction, thus providing information for determining vertical strain rates along the borehole. Measurements in two boreholes drilled on high-altitude glaciers in the Swiss Alps are used to demonstrate both the potential and the limitations of the probe and of the mathematical methods presented.

Dating ice cores from a high Alpine glacier with a flow model for cold firn

AbstractA flow model for cold firn proves to be very successful in calculating the age-depth relation of several deep ice cores drilled on Colle Gnifetti, Monte Rosa, Swiss Alps. The compressibility of firn is taken into account by an appropriate constitutive equation, first employed in glaciology by Gagliardini and Meyssonnier (1997), which is implemented in a finite-element code. Flow models of the Colle Gnifetti saddle glaciation in two and three dimensions are based on digital elevation maps of the surface σnd the bedrock, based on radio-echo soundings of the ice thickness. Firn density and the englacial temperature fields are either prescribed or calculated in coupled models. Measured surface velocities, density profiles, the ages of chemically dated layers in ice cores and the closure of a 100 m deep borehole provide benchmarks for the models. The good agreement of modeled and measured quantities confirms that the model includes the relevant physical processes and particularly that the firn flow law is well suited for this type of glacier. The study provides new constraints on the age of the ice near the base as well as the source regions of the ice in the cores.An exceptional flow behavior of the basal ice layer was detected in measurements of borehole closure and inclination. Measurtxl6ed deformation rates exceed upper bounds derived from the flow models, and are thus attributed to altered rheological properties.

The BAS hot water drill: development and current design

Over the past decade the British Antarctic Survey has developed a hot water drilling system that uses components easily carried by Twin Otter aircraft. The system has recently been upgraded and was successfully used in the 1990/91 and 91/92 field seasons to penetrate ice up to 562 m thick on Ronne Ice Shelf, Antarctica. Holes of at least 0.13 m in diameter were created and maintained. The hot water drill incorporates 300 kW of heating power with a water re-circulation system, removing the need for continuous snow melting while drilling. The drill nozzles have been designed to combat the problems of the rapid re-freezing of the water-filled hole. In the event of borehole closure above the nozzle, a less powerful but still effective drilling action is available upwards. A compressible mechanical valve system is incorporated which increases the back pressure when the operator is drilling too fast. This system ensures the nozzle is always freely suspended, resulting in a vertical hole. The work has allowed oceanographic measurements to be made in the sea-water underlying George VI Ice Shelf and Ronne Ice Shelf, Antarctica. The access holes have also been used for the installation of sensors in the ice and the ocean for long term temperature monitoring.

Input uncertainties and calculated borehole closure : Fossum, A F; Senseny, P E; Thacker, B H Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10–12 July 1991P987–994. Publ Rotterdam: A A Balkema, 1991

Input uncertainties and calculated borehole closure : Fossum, A F; Senseny, P E; Thacker, B H Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10–12 July 1991P987–994. Publ Rotterdam: A A Balkema, 1991

Results from Simulated Remote-Handled Transuranic Waste Experiments at the Waste Isolation Pilot Plant (WIPP)

ABSTRACTMulti-year, simulated remote-handled transuranic waste (RH TRU, nonradioactive) experiments are being conducted underground in the Waste Isolation Pilot Plant (WIPP) facility. These experiments involve the near-reference (thermal and geometrical) testing of eight full-size RH TRU test containers emplaced into horizontal, unlined rock salt boreholes. Half of the test emplacements are partially filled with bentonite/silica-sand backfill material. All test containers were electrically heated at about 115 W/each for three years, then raised to about 300 W/each for the remaining time. Each test borehole was instrumented with a selection of remote-reading thermocouples, pressure gages, borehole vertical-closure gages, and vertical and horizontal borehole-diameter closure gages. Each test emplacements was also periodically opened for visual inspections of brine intrusions and any interactions with waste package materials, materials sampling, manual closure measurements, and observations of borehole changes. Effects of heat on borehole closure rates and near-field materials (metals, backfill, rock salt, and intruding brine) interactions were closely monitored as a function of time. This paper summarizes results for the first five years of in situ test operation with supporting instrumentation and laboratory data and interpretations. Some details of RH TRU waste package materials, designs, and assorted underground test observations are also discussed. Based on the results, the tested RH TRU waste packages, materials, and emplacement geometry in unlined salt boreholes appear to be quite adequate for initial WIPP repository-phase operations.

3D thermal stress analysis of WIPP room T RH TRU experiments : Arguello, J G; Molecke, M A; Beraun, R Rock Mechanics as a Guide for Efficient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19–22 June 1989P681–688. Publ Rotterdam: A A Balkema, 1989

A three-dimensional finite element thermal stress analysis of the RH TRU experiments in WIPP Room T has been performed. This analysis aids in the interpretation of the borehole closure results being obtained from the Room T experiments and helps in assessing potential performance impacts in a typical storage room, during the waste retrieval period. Computed results are presented and compared to available in situ data, and a qualitative agreement between measured and computed closures is seen. Results indicate that if the boreholes are drilled 3 years after excavation of a typical storage room, the closure should not impede retrieval of the canisters during the 5 year waste retrieval period. 11 refs., 10 figs.

Assessment of using borehole‐closure data to determine the constitutive behavior of salt

AbstractBorehole closure data have often been used to determine the constitutive behaviour of rock salt. This is an inverse problem and analysis of the data is confused by the fact that borehole closure is a structural response that does not uniquely determine constitutive behaviour since both the stress and deformation depend on the constitutive behaviour.This application brief assesses the conclusion of a recent study that the transient power law, ϵ = K τmtn, which includes no term to account for steady‐state deformation, is a better constitutive model for salt than are models that account for steady‐state straining, and that an empirical model developed from the borehole closure data could be extrapolated to give conservative predictions of long‐term closure of single or widely spaced openings.

Hot-water Drilling And Bore-hole Closure In Cold Ice

AbstractDrilling bore holes in deep, cold ice masses by hot-water methods and maintaining these holes with sufficient diameter to allow down-hole experimentation poses a major obstacle to the investigation of conditions beneath ice sheets and ice streams. Closure of the water-filled holes by refreezing is the dominant difficulty. In this paper, we describe calculations of heat transfer from the drilling system to the ice and the subsequent time-dependent motion of the phase boundary defining the bore-hole wall. Results are presented with the view of optimizing the bore-hole radius at depth for a fixed drill performance and a variable rate of drilling.Calculation of melting/refreezing rates at the bore-hole wall requires the use of a one-dimensional, time-dependent numerical heat-flow model with a distorting mesh which follows the changing hole size. The delay of hole closure is discussed with a view to keeping holes open long enough to allow instruments to be lowered to the glacier bed, while realizing that drilling-system performance may be marginal because of logisitical and/or expenditure constraints. The relative merits of drilling a large hole, which is very time consuming with a small drill, and the use of water-soluble antifreezes, which have a history of creating plugs of ice slush, are discussed. A method of creating a stable hole filled with antifreeze in which ice slush does not occur is described.The recent application of these theoretical ideas to the planning and implementation of successful hot-water drilling programs in Antarctica and Greenland is also presented.

Borehole closure in salt : Fuenkajorn, K; Daemen, JJK Key Questions in Rock Mechanics: Proc 29th US Symposium, Minneapolis, 13–15 June 1988P191–198. Publ Rotterdam: A A Balkema, 1988

Constitutive law parameters are determined from salt behavior characterization experiments. The results are applied to predict creep (time-dependent) closure of boreholes in salt specimens subjected to various loading configurations. Rheological models (linear and nonlinear viscoelastic and viscoplastic models), empirical models, and physical theory models have been formulated from the results of uniaxial creep tests, strain and stress rate controlled uniaxial tests, constant strain rate triaxial tests, cyclic loading tests, and seismic velocity measurements. Analytical solutions for a thick-walled cylinder subjected to internal and external pressures and for a circular hole in an infinite plate subjected to a biaxial or uniaxial stressfield have been derived from each of the linear viscoelastic models and from one of the empirical laws. The experimental results indicate that the salt samples behave as an elastic-viscoplastic material. The elastic behavior tends to be linear and time-independent. The plastic deformation is time-dependent. The stress increment to strain rate increment ratio gradually decreases as the stress level increases. The transient potential creep law seems to give the simplest satisfactory governing equation describing the viscoplastic behavior of salt during the transient phase. 204 refs., 27 figs., 29 tabs.

Closure Rate of a 700 m Deep Bore Hole at Mizuho Station, East Antarctica

Measurements of the bore-hole diameter were made with three-contact-point calipers from the shallow layer to a depth of 700 m at Mizuho Station, East Antarctica, in 1984–86. The minimum strain-rate (i.e. secondary creep rate) of the bore-hole closure was estimated from the observed creep curve at each depth. A relation between stress and strain-rate was deduced for a temperature of −35°C and a stress range from 0.8 to 1.65 MN m−2, as where is the effective strain-rate (s−1) and τ is the effective shear stress (MN m−2). This result shows that, for comparable overburden stresses and temperature, the bore-hole closure rates at Mizuho Station are higher than those measured in bore holes at Byrd Station and in the Northern Hemisphere ice caps (Paterson 1977).