Interpretation of flow dimensions from constant pressure injection test

Auli Kuusela-Lahtinen, Antti Poteri

    Research output: Book/ReportReport

    Abstract

    This report deals with interpretation methods of single-hole hydraulic tests. A special emphasis is on new analysis methods of a single-hole hydraulic test, called a constant pressure injection test. This hydraulic test type is used in Posiva’s site investigation at Olkiluoto. Single-hole hydraulic tests are examined in order to find out methods to analyse channelling of the flow that is related to transport properties along the flow paths.

    The flow dimensions inferred from the constant pressure tests are considered to indicate the channelling of the flow in the scale of a single fracture or in the fracture network. One can use semi-log derivates of measurement data plotted in log-log diagrams for the interpretation of flow dimension. After that the appropriate flow solution can be chosen to infer the values of conductivity and specific storage.

    Channelling is studied from Posiva's data by analysing the transient injection period of a constant pressure injection test. Software called AQTESOLV is used in a new procedure, which is illustrated by studying two examples. Both examples are based on single hole hydraulic tests that are performed in the borehole OLKR10 using a 2 m test interval approximately at the depth of the planned repository of the nuclear waste (depth of about 400 - 450 m). One of the test intervals is intersected by a filled fracture and the analysed flow dimensions also indicates flow in a fractures, with inferred flow dimensions of n = 1.5 or n = 2. The flow dimension n = 1.5 represents a possibility of narrowing flowpaths. The other analysed test interval is intersected by three filled fractures. In this case, analysis of the flow dimension show behaviour that is related to a fracture network (homogeneous porous media), with interpreted flow dimensions of n = 2.5 - 3.

    This report also shows results for simulation of a constant pressure test in an artificial heterogeneous fracture. Flow dimension is analysed by performing simulated pumping tests for different borehole locations over the heterogeneous fracture. The channelling of flow is not clearly reflected in the analysed flow dimensions. Most of the analysed cases showed rather similar behaviour that is represented by a flow dimension of two.

    It could be that the single-hole testing is more sensitive to the connectivity of the fracture network and channelling of the flow to different flow routes of connected fractures than on the channelling of the flow in the individual fracture planes. Hydraulic single-hole testing activates a limited volume of rock around the packed off section of the borehole. If the tested volume of rock is mainly limited to the fracture that is intersecting the borehole, then in principle, the transient flow characteristics can be used to separate linear (channelled) flow from the radial two dimensional flow. If a larger network of fractures is activated during the hydraulic testing, then the transient hydraulic response can be used to identify possible channelling of the flow that should show up as a lower flow dimension (n = 1 - 2) of the flow field compared to the cylindrical or spherical pressure field of the experiment.
    Original languageEnglish
    PublisherPosiva
    Number of pages41
    Publication statusPublished - 2010
    MoE publication typeD4 Published development or research report or study

    Publication series

    SeriesPosiva Working Report
    Number2010-35

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  • Cite this

    Kuusela-Lahtinen, A., & Poteri, A. (2010). Interpretation of flow dimensions from constant pressure injection test. Posiva. Posiva Working Report, No. 2010-35 http://www.posiva.fi/files/1335/WR_2010-35web.pdf