Additional Boreholes Research Articles

In-Situ Stress Measurement - Results of Experiments Performed at the Asse Salt Mine - Federal Republic of Germany

ABSTRACTHigh-level nuclear wastes are heat generating wastes. Heat will be transferred to the surrounding salt formation. This heating of the host rock will result in an increased temperature and in stress changes.From 1983 through 1985 two underground tests were conducted in the Asse Salt Mine (Federal Republic of Germany) in which among others thermally induced stress changes were investigated.In the Temperature Test 6 which was conducted at the 750 m-level only electrical heaters were used to simulate the heat generating high-level waste. Three hydraulic stress monitoring stations were arranged in the un-heated area at a distance of about 40 meters to the central heater. Measurements using AWIO flat jacks were also carried out in the heated region of the Temperature Test Field 6 (TVF 6).The joint US/FRG Brine Migration Test (BMT) - a nuclear waste repository simulation experiment - was performed at the 800 m-level and used radioactive sources and electrical heaters to impose the heat load on the host rock. Stress change measurements during this experiment were performed using hydraulic pressure cells and straingaged stressmeters.During 1985 an experimental area for the first in-situ test disposal of high-level radioactive sources was created at the 800 m-level within the Asse anticline structure. Thirty high-level radioactive canisters will be emplaced in six down-boreholes located in two test galleries in the experimental area. There is one additional borehole in each gallery equipped only with electrical heaters. Hydraulic pressure cells, AWID flat jacks, and straingaged stressmeters were installed in the HAW-test field for stress change measurements.

HDR Experiments at Falkenberg/Bavaria

A test site for HDR experiments has been set up in granite in the Bohemian massif in east Bavaria. A large fracture was stimulated by hydraulic fracturing in a depth of 250 m. The orientation of the fracture was investigated by seismo-acoustic recording during the frac-experiments and by examining the fracture pattern initiated in the injection interval of the borehole by an impression packer and by acoustic televiewer measurements. Geoelectric measurements for fracture location at the surface were also tested before attempting to drill through the fracture. The fracture has now been intersected by 6 additional boreholes at distances between 2 m and 70 m from the initiation interval. According to the results of seismo-acoustic recording, temperature logging and acoustic televiewer measurements in the intersection boreholes, a single plane artificial fracture has been produced, striking E-W and dipping 50°S. The orientation of the fracture, which should be normal to the least compressive principal stress, and the value of the normal stress on the fracture are not consistent with the direction and the values of the principal stresses determined by wire line hydraulic fracturing stress measurements. Various hydraulic experiments were performed in the different boreholes to investigate the mechanical reaction of the fracture due to varying fluid pressure, the hydraulic properties of the fracture, the fluid losses and the heat exchange within the fracture. The models developed to interpret the results make it possible to translate the results to greater depth and higher flow rates.

Probabilistic Analysis Of Offshore Site Exploration

The uncertainties associated with the predicted bearing capacity of an offshore gravity platform arise from incomplete knowledge about the type of material that is encountered at different points along the slip surface and the strengths of these materials. Uncertainty about material strength is caused by scatter in test data and differences between measured strength and in-situ strength. The probability of finding indifferent materials, given the materials as identified at the location of boreholes, is evaluated from the proximity rule. This is combined with the uncertainty due to data scatter and inaccuracy of the test methods to estimate the variance of the foundation resistance. The procedure makes is possible to evaluate the uncertainty about foundation resistance at various stages of a site exploration program. The effects of additional boreholes and improved testing methods can be evaluated separately and used to help decision making in site exploration. The site exploration data from the Brent B-G site are analyzed as an example.

Three-Dimensional Seismic Lithologic Modeling to Delineate Abruptly Changing Reservoir Facies: Case History from Alberta, Canada: ABSTRACT

Although river-channel reservoirs are attractive because of their potential high porosity and permeability, they are difficult to develop because of abrupt variations in sand and shale distribution. The Taber-Turin area of Alberta Canada, is a known oil province characterized by such reservoirs. To delineate potential reservoirs in detail, a 4-km/sup 2/ three-dimensional seismic survey was carried out, resulting in a uniform grid with traces 20 m apart. Data were wavelet processed, corrected for near-surface time anomalies, and migrated three-dimensionally. The seismic lithologic modeling (SLIM) process was then applied to provide a thin-layer interpretation of the processed data. Although the initial model for the SLIM process was based on information from only one borehole (primarily for calibration purposes), the derived velocity model showed detailed evidence of the thin glauconitic reservoirs (0-30 m thick) that are the targets of the delineation effort. All six boreholes drilled in the area (four producers and two dry) are consistent with the SLIM interpretation. Using the SLIM results, three additional boreholes have been proposed, and drilling results will be available by spring 1986.

Heat flux measurements in southwestern British Columbia: the thermal consequences of plate tectonics

Measured heat fluxes from previously published data and 34 additional boreholes outline the terrestrial heat flow field in southern British Columbia. Combined with heat generation representative of the crust at 10 sites in the Intermontane and Omineca belts, the data define a heat flow province with a reduced heat flow of 63 mW m−2 and a depth scale of 10 km. Such a linear relationship is not found or expected in the Insular Belt and the western half of the Coast Plutonic Complex where low heat fluxes are interpreted to be the result of recent subduction. The apparent boundary between low and high heat flux is a transition over a distance of 20 km, located in Jervis Inlet 20–40 km seaward of the Pleistocene Garibaldi Volcanic Belt.The warm, thin crust of the Intermontane and Omenica Crystalline belts is similar to that of areas of the Basin and Range Province where the youngest volcanics are more than 17 Ma in age. Processes 50 Ma ago that completely heated the crust and upper mantle could theoretically produce such high heat fluxes by conductive cooling of the lithosphere. But it is more likely that the asthenosphere flows towards the subduction zone, bringing heat to the base of the lithosphere. Since the reduced heat flow is high but constant, large differences in upper crustal temperatures within this heat flow province at present are caused by large variations in both crustal heat generation and near-surface thermal conductivity. The sharp transition in heat flux near the coast is the result of the combined effects of convective heating of the eastern Coast Plutonic Complex, pronounced differential uplift and erosion across a boundary within the Coast Plutonic Complex, and the subducting oceanic plate.

The state of stress in the upper part of the earth's crust

The object of the present article is to present new results of absolute rock-stress measurements performed in the upper part of the earth's crust as a contribution to the discussions of the problem of 1. (1) whether the earth is expanding or contracting and 2. (2) whether continental drift and convection currents exist. A description of the prevalent uniform stress patterns found by extensive absolute rock-stress measurements in the Fennoscandian bedrock area is presented. Further measurements have been performed outside Fennoscandia, from Spitzbergen in the north to Zambia in the south. These measurements indicate that the horizontal stress field found in Fennoscandia may belong to a general stress system according to which large parts of the earth's crust are stressed. Measurements performed in the Atlantic area in coastal zones, on Iceland and other islands seem to show that the Atlantic ocean floor behaves as a rigid plate stressed by horizontal compressive and shear forces, in all probability, emanating from the zone of contact between ocean floor and continental crust. The Mid-Atlantic Ridge and the numerous east—west fracture zones in the ocean floor seem to represent an orthogonal fracture system probably deriving from horizontal shear stresses in the floor. The method of measurement used enables a complete and highly accurate determination of the three-dimensional state of stress in the earth's crust, thus including the magnitude and direction of the shear stresses. The magnitude and orientation of the stress ellipsoids at depths of 160 and 400 m in a granite massif in Zambia are shown in tables and in ellipsoid models. The horizontal stress field in the earth's crust probably has changed its direction and magnitude in geologic times as may be inferred from the present measurements. A study of the directions of shear-fracture lines occurring in old and resistent granite bedrock will tell about these changes. At many places there would seem to exist a close relationship between the state of stress in the upper part of the earth's crust (today as well as in past geologic times) and the direction of the fracture systems in the bedrock as manifested, for instance, by the river courses. An example is provided by the reported measurements in Zambia. If this were a general situation throughout the world it would show that the shear stress in the crust constitutes an important factor for the formation of the landscape. Horizontal compressive stresses in the bedrock were found at all points of measurement on Iceland, in specific areas of the same order of magnitude as in Fennoscandia. Where the Mid-Atlantic Ridge is assumed to encounter Iceland, the orientation of the maximum horizontal shear in the Icelandic bedrock agrees with the orientation of the ridge; this suggests that the ridge may have its origin in shear stresses in the crust. The maximum horizontal pressure acts in a direction at 45° to the ridge instead of the 90° direction to be expected, where new material extruded to form the Atlantic Ocean floor. In the southwestern corner of Iceland stress measurements were made in a large bedrock area of granophyre. Age determinations of the rocks were made in additional bore-holes drilled down to 130 and 115 m below sea level. Disturbances of dynamic stress equilibrium now acting in the earth's crust seem to be due to changes in the horizontal stress field. Since earthquakes are most probably due to sudden changes in the stress field of the earth's crust, a continuous recording of the absolute values of such changes seems to provide a possibility to predict earthquakes. In the last part of the article comments are presented on some objections raised to the interpretation of certain observations regarding the earth's crust adduced as evidence for theories of expansion and continental drift.

Additional borehole measurements in the Athabasca glacier

Savage and Paterson [1963] have discussed measurements of inclination made in boreholes in the Athabasca glacier during the years 1960 to 1962. A further set of measurements has been made in one borehole. The results, which are consistent with the earlier ones, are given in this letter. We also take this opportunity of listing corrections to this paper and an associated paper [Paterson and Savage, 1963].