AI For Sheep Using Frozen-thawed Semen.

End of Project ReportInternational experience has been that cervical insemination of sheep with frozen-thawed semen usually yields unacceptably low pregnancy rates (10 to 30%). An exceptional case has been Norway where non-return rates in on-farm usage are around 60%. The objective of the work described in this report was to develop an AI procedure for Irish conditions, based initially on Norwegian protocols, using semen from individual rams. Such a procedure would greatly facilitate and enhance genetic improvement programmes for sheep. The work undertaken had two separate aspects:- (i) studies on semen, including processing and freezing methods, laboratory evaluation of semen quality post thawing and the relationship of in vitro evaluation to fertilisation rate in vivo (ii) studies on pregnancy rate following AI in relation to issues such as ram breed effects, effects of synchronisation, operator differences and the role of ewe breed inducing the timing of ovulation and various physical and physiological assessments of the cervix at AI. The main results in relation to semen studies were that, while a range of differential staining procedures could be used to objectively evaluate semen with respect to proportion of live speramatozoa and the integrity of sperm cells after thawing, these results were not useful as indicators of fertilisation capacity in vivo. The in vitro fertilisation (IVF) of sheep oocytes recovered from abattoir material gave promising results as a method for evaluating the fertilisation capacity of frozen-thawed semen. The technique requires further validation.Department of Agriculture, Food and the Marin

Estimating flow heterogeneity in natural fracture systems

Examples of small to medium scale fault systems have been mapped in Jurassic sedimentary rocks in north Somerset, England. These examples include contractional and dilational strike-slip oversteps as well as normal faults. These maps form the basis of calculations performed to investigate heterogeneity in natural fracture systems with the aim of predicting fluid flow localisation in different fault styles. As there is no way to measure fracture aperture directly, we use vein thickness to represent an integrated flow path or ‘palaeo-aperture’ from which we derive a representation of the flow distribution. Three different methods are used to estimate flow heterogeneity based on: (1) fracture density (the ratio of fracture length to area), (2) fracture aperture (fracture porosity) and (3) hydraulic conductance (fracture permeability normalised to the pressure gradient and fluid properties).Our results show that fracture density and hydraulic conductance are poorly correlated and that fracture density does not fully represent the natural heterogeneity of fracture systems. Fracture aperture and hydraulic conductance indicate stronger degrees of flow localisation. Different types of structures also seem to display characteristic and predictable patterns of heterogeneity. Normal fault systems show the highest magnitude of localisation along the faults rather than in the relay ramps, while contractional and dilational strike-slip systems show very strong localisation in the faults and oversteps, respectively. In all cases the amount of damage in the oversteps can modify such patterns of heterogeneity. <br/

Study of fracture-induced anisotropy from discrete fracture network simulation of well test responses

Different conceptualizations of fracture networks have been generated in order to simulate well tests in fractured reservoirs. These models have two purposes: firstly to investigate whether the behaviour of realistic fracture networks can be emulated with more simple models; and secondly to assess whether different sources of anisotropy have characteristic and recognizable influences on the pressure derivative. The anisotropy of the fracture networks was increased by decreasing the angle between two originally orthogonal fracture sets, and by increasing the permeability contrast between two orthogonal fracture sets. Results indicate that simple models can capture the first-order behaviour of more realistic examples. However because early time data are strongly influenced by the connectivity of the fracture network, the degree of anisotropy can only be assessed at later times in a test. Increasing anisotropy results in increasing heterogeneity and compartmentalization, and permeability anisotropy in an orthogonal system can only partially replicate the behaviour of a geometrically anisotropic syste