Fluid-Induced Seismicity: Theory, Modeling, and Applications

Operations including borehole fluid injections are typical for exploration and development of hydrocarbon or geothermic reservoirs. Microseismicity occurring during such operations has a large potential for understanding physics of the seismogenic process as well as in obtaining detailed information about reservoirs at locations as far as several kilometers from boreholes. We propose that the phenomenon of microseismicity triggering by borehole fluid injections is related to the process of the Frenkel–Biot slow wave propagation. In the low-frequency range (hours or days of fluid injection durations) this process reduces to the pore-pressure diffusion. We search for diffusion-related features of induced microseismicity. Two types of such signatures are considered. The first one is related to the geometry of microseismic clouds. Another type of signature is related to the probability of microearthquakes. On this basis we introduce a concept for interpretation of microseismic data which provides a possibility to infer information about hydraulic properties of rocks. Such information can be of significant importance for industrial applications and for understanding physical properties of geological structures.     

Estimating the Hydraulic Conductivity of Landfilled Municipal Solid Waste Using the Borehole Permeameter Test

This paper reports the in situ field saturated hydraulic conductivity of municipal solid waste at a landfill in Florida. The saturated hydraulic conductivity (Ks) was estimated at 23 locations using the borehole permeameter test, a method commonly used for determination of the Ks of unsaturated soil. The Ks of the landfilled waste was found to range from 5.4×10?6 to 6.1×10?5?cm/s. The Ks was found to be on the lower end of the range of Ks reported by previous studies. The hydraulic conductivity of the waste decreased with depth, the likely result of greater overburden pressures associated with deep locations of the landfill. Permeability values (kw) of the landfilled waste calculated based on Ks were compared with permeability values estimated using air as the fluid (air permeability, ka). Values of ka were found to be approximately three orders of magnitude greater than those of kw. The lower permeability of the waste to water was primarily attributed to entrapped gas. Other factors such as potential clogging of media and short-circuiting of air along the well may also have contributed to the differences in ka and kw.     

Forms of Hydraulic Fractures in Shallow Fine-Grained Formations

Hydraulic fractures have been created in fine-grained formations at depths of 2–10 m to improve the performance of environmental remediation projects at dozens of locations and in a wide range of geologic conditions. The effectiveness of a hydraulic fracture during remediation will depend primarily on its form; that is, its shape, thickness, orientation, length, width, and location with respect to the borehole. The forms of many hydraulic fractures have been determined by mapping exposures in excavations and by compiling split-spoon sampling data. These observations indicate that a typical hydraulic fracture at shallow depths is gently dipping, slightly elongate in plan, and slightly asymmetric with respect to the parent borehole. Shallow hydraulic fractures lift the ground surface to produce gentle domes, and the pattern of uplift reflects the location and thickness of the fracture at depth. The forms of hydraulic fractures created over a narrow range of depths at the same site are similar, but the forms can vary markedly between sites and at different depths at the same site. This indicates that the forms of hydraulic fractures will be relatively consistent when they are created under similar conditions, but changes in geologic conditions can markedly affect fracture form.     

Development of a New Water Supply for Fort William

The development of a new water supply source for the Fort William/Corpach and Caol area in the West Highlands of Scotland is described with particular reference to the hydrological and groundwater investigations. Attention is given to a study to reduce the level of leakage and to the analysis of improvements in water quality between well and direct river abstraction. The effect on fisheries in the River Lochy is described, and a preliminary design identified for the recommended scheme.     

Instrumented Borehole Drilling for Subsurface Investigation

The successful application of instrumented borehole drilling techniques in offshore exploration has encouraged its further use on-shore as a ground investigation tool. The drilling of holes for grouting tubes creates the potential for obtaining supplementary ground information, which may be valuable to the succeeding tunnel construction. The instrumented drilling system was therefore investigated to determine its power to discriminate between ground strata. The configuration of the drilling system in terms of plant, equipment, and testing procedures was standardized and applied at a site in Kennington Park in London. The general characteristics of the measured drilling parameters are given and qualitative and quantitative methods of interpreting the drilling parameters are demonstrated. The possible soil–machine interactions that are responsible for the measured drilling characteristics are examined. A new method of data interpretation is proposed for identifying soil formation changes. Previously published correlations and analyses of drilling were examined and tested by comparing the trend-lines of drilling data in London clay against known undrained strength data. The degree of correlation was found to be limited.     

The Reliability of Groundwater Sources to Meet Increasing Demands

The groundwater resources of the Lee Valley Water Company have been examined in a joint study with the University of Birmingham. The Company is modifying its operating policy to make maximum use of the groundwater resources, which has involved the development of new methods of estimating the reliable output of the groundwater sources under differing conditions. The technology transfer involved in the project has enabled the Company to gain a greater understanding of the operation of its sources, and the University has modified existing techniques so that they are of greater practical use.     

The Effect of Borehole Sealing on the Southern Lincolnshire Limestone Catchment

The Southern Lincolnshire Limestone is an important groundwater resource; however, for many years water has been lost from the aquifer system through uncontrolled artesian flow from wild-bores in the Fenland area. During 1991–92, there was an extensive programme of sealing or controlling the wild-bores, and compensation flows for ecological and farming purposes were provided at some sites.
This paper describes a field study which was designed to identify the important features of part of the catchment; this was followed by the development of an existing groundwater model to provide an improved representation of the uncontrolled and controlled wild-bores. The model is used to assess the consequences of controlling or sealing the wild-bores.     

Three-Dimensional Finite Element Analysis of Underground Caverns

Detailed performance monitoring studies have been carried out for determining the deformations and stress distribution around underground powerhouse caverns in nonhomogeneous rock mass, using three-dimensional finite element method. The behavior of rock mass has been analyzed by elasto-plastic model. The effect of weak zones and creation of multiple caverns in the rock mass has been investigated. The deformations predicted in the surrounding area of the caverns are compared with those obtained by multi-point borehole extensometers (MPBX) measurements. It is observed that the computed deformations compare reasonably well with the MPBX measurements.     

Drilling Fluid Considerations in Design of Engineered Horizontal Directional Drilling Installations

A literature review is presented that identifies a number of areas where procedures for the engineering design of bored installations in soil using horizontal directional drilling (HDD) can be improved through a more realistic consideration of drilling fluid drag effects and skin friction coefficients. The current HDD practice of calculating annular frictional pressure loss caused by drilling fluid drag based on the assumption of concentric annular flow of a Bingham plastic fluid is demonstrated to be overly conservative. Consequently, critical design parameters, such as depth of cover, which affects crossing length, and drilling equipment size, which is selected based on anticipated pulling load, cannot be optimized. This can result in overly conservative design and unnecessary construction costs. Parameter values currently employed in HDD pulling load prediction are challenged suggesting that the viscous shear of drilling fluid is significantly less than typically quoted and that the friction coefficients often employed are not representative of all skin friction effects in HDD. A new real-time monitoring cell for large-scale HDD is described that can be used to optimize installations and to assess and update current prediction models.     

Porochemothermoelastic Solution for an Inclined Borehole in a Transversely Isotropic Formation

A generalized anisotropic poromechanics formulation for chemically active poroelastic media under nonisothermal conditions, termed as porochemothermoelastic, is presented. The pore fluid is modeled as a two-species constituent comprised of the solute and the solvent. Governing equations are developed and applied to obtain the analytical solution for an inclined borehole in chemically active transversely isotropic formation subjected to a three-dimensional state of stress and nonisothermal conditions. Numerical examples are presented to demonstrate the thermochemical effects on stress and pore pressure distributions in the vicinity of the borehole and their potential impacts on borehole stability.