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A new numerical method is described for modelling the thermal disturbance around a borehole and a comparison is made with the commonly used line source model. The numerical model generally gives an estimate of the equilibrium formation temperature which is up to about 20 per cent higher than the 'Horner plot' method.The relaxation of the borehole temperature is sensitive to the contrast between the thermal properties of the drilling fluid and of the surrounding rock as well as to the disturbance time. The importance of vertical temperature gradients and fluid motion (both free convection in the borehole and flow in the formation) is also examined. It is found that vertical temperature gradients are unlikely t o be important provided temperatures are measured more than 10 borehole radii above the bottom. Convective heat transfer can be important under some drilling conditions.

Summary A case study of a heat flow anomaly in the E Midlands of England is reported. The anomaly has been suggested to be an effect of water movement at depth within the E Midlands basin, with recharge to the Lower Carboniferous limestones in their outcrop, eastward movement and ascent of water up a steep faulted anticline at Eakring where the heat flow measurements were made. Numerical modelling of heat and fluid flow has been undertaken for a section running from the Peak District through Eakring to the coast. The results indicate that, although an anomaly is expected for reasonable values of hydrological parameters, its magnitude is less than that observed. The geological structure at Eakring is such that three-dimensional flow is likely to be important, and this could easily account for the discrepancy between the modelling results and the observations. The regional water flow regime has other effects on heat flow, notably the depression of heat flow above the Sherwood Sandstone aquifer.

In 1993, there was a well control incident while drilling a prospect offshore Vietnam. This incidentnecessitated the implementation of an extensive seismic monitoring programme. It became rapidly apparent that conventional high resolution seismic techniques for identifying and monitoring gas in the subsurface were inadequate due to loss of signal power through the system. This problem drove the need for an innovative approach to acquiring a 'Medium Resolution 3D Suwey'. This had two important characteristics, namely significantly higher bandwidth than conventional 3D data and also having the penetration necessary in order to image the target reservoir, through a disturbed overburden. This paper describes the technology used in acquiring and processing the data, as this has relevanceto use of this type of acquisition for conventional reservoir description purposes. It also describes the attribute analysis developed to compare multiple vintages of seismic in order to be able to track fluid movement in the subsurface. The enhanced resolution achieved has relevance to enabling better reservoir characterisation in general. The attribute analysis is an example of how these type of data can then be conditioned in order to allow tracking of fluid in the subsurface, in appropriate situations. Introduction/background Using seismic data to track fluid movement is a fairly well known technique, but one that still needs considerable development for routine use. In certain situations the rock properties of an interval change significantly enough to create a measurably different seismic response. [n order to apply this technology it is necessary to establish an understanding ofThe distribution of rock properties in the interval of interestThe scale of the change in seismic response caused by different fluid fills (water, oil, gas)Whether the quality of the available seismic data has the amplitude, time and depth resolutions required to detect these changesAnd, for monitoring cases, whether the quality of the seismic is controlled sufficiently to enable comparisons between successive surveys In the case presented here, the interest was in monitoring possible subsurface gas movements following a well control incident. The technical problems and the approach, however, are quite generic; in that the same principles apply for fluid monitoring experiments in conventional production situations. For the particular problem presented here, it was necessary to establish the history of gas movement in the subsurface using a series of seismic data sets which had different acquisition and processing histories. The need was to understand to what extent it was possible to measure the extent of gas charged sands using these seismic data sets.

The Nova Scotia Department of Energy and Canada-Nova Scotia Offshore Petroleum Board have carried out a sound technical work program over many years to present potential licensees with the information to encourage them to invest in Nova Scotia. However, following some success, the result in terms of licence bids in Nova Scotia's offshore, wells drilled and hydrocarbons won, has proved disappointing. The value of the hydrocarbon province has not been fully unlocked. Although production and proven discoveries demonstrate that there is a working hydrocarbon system oil companies are leaving Nova Scotia in favour of other opportunities prior to completion of their exploration program. There is a view that, in order to attract new investors, it will be necessary to lower the barriers to entry. One of these is undoubtedly the ability of new investors to easily and quickly develop a good geological understanding of the Nova Scotia offshore basins and thus investment decisions. The intent is to conduct an industry-standard sequence stratigraphic based Play Fairway Analysis to a level of detail that is sufficient to give credibility to the outcome. It is also intended to conduct special studies that can help address the key exploration risks. Furthermore, this paper elaborates on the importance of the Geoscience Data Package for this program, and its effectiveness in re-invigorating interest in the Scotian Margin. Data availability, to support the comprehensive geotechnical evaluation, is key to reducing the barriers to entry into the region, but unfortunately it is not easily accessible to investors. The lack of a publicly available and industry-credible, geological framework, in conjunction with the fact that most geoscience data, specifically seismic data, is not freely available in full digital format is a major hurdle. The Offshore Petroleum Play Fairway Analysis and Geoscience Data Package program, for which the business rational is discussed in this paper, are aimed at addressing this issue.