Summary In 2009, QGC (a BG Group company) began developing coal-seam-gas (CSG) feedstock for its new liquefied-natural-gas (LNG) plant and required a subsurface model and field-development plan to underpin the investment case for the project. Fundamental to the modeling process was acquiring appropriate data to calibrate subsurface models and enhance confidence in their predictive quality. As part of an integrated reservoir-surveillance strategy, specific pressure- and temperature-monitoring wells were required. This paper describes the successful laboratory and field implementation of an innovative completion technique that converts suspended coreholes into reservoir- and aquifer-monitoring wells. The coreholes are re-entered, and vibrating wire piezometers attached to capillary coiled tubing are positioned and cemented in place alongside selected reservoir intervals. The well is then “plugged and abandoned,” and the lease is remediated to leave only a small surface footprint for the data logger and telemetry. The cement is effectively impermeable to fluid movement, but possesses sufficient permeability to transmit reservoir pore pressure to an adjacent piezometer. Recompletion of coreholes provides a cost-effective means of acquiring valuable downhole data while eliminating the need to drill a well specifically for monitoring in the same vicinity. Data gathered over the reservoir interval (the Walloon Coal Measures) can inform and help resolve reservoir properties on a regional scale, enhance understanding of the contribution to flow, and provide data points to pressure match a reservoir model. Data gathered over the aquifers within Springbok sandstone and Gubbermunda sandstone enable estimates of any CSG-production effects on groundwater.

The deconvolution of well test pressure transient data provides a constant rate pressure response that applies for the duration of the test. By extrapolating this response in time, the future performance of a well can be predicted. The extrapolation can include constraints defined by estimates of the volume of reservoir connected to the well but otherwise, relies only on information that is normally available at the time of testing. Uncertainty in either the deconvolution or the connected volume will result in a variety of extrapolations that defines the range of expected well performance. The advantage of this procedure is that a well's future production profile can be estimated very quickly and easily. Such a scoping exercise helps to understand a well's potential and to define the expected range of outcomes from more detailed modelling. Furthermore, it can be an efficient method for screening prospects when time and resources are limited. By monitoring the actual well performance against its prediction, underperforming wells can be identified for work-over. If permanent downhole pressure gauge data are available, the deconvolution can be continuously updated thus improving the production forecast. Where a production well is planned that is of a different type to the tested well (e.g. a horizontal or hydraulically fractured well instead of a normal vertical well), a technique is described to modify the tested well's deconvolved response to account for the change in well type whilst preserving the pressure transient response due to the reservoir and its boundaries. Two field examples of gas well tests are presented which demonstrate the method and the predicted production profiles are compared with observed data. Introduction A well's production can be estimated by building flow models and simulating future production for a given set of well and facility constraints. Simulation relies on what can often be uncertain geophysical, geological and petrophysical information. Generally, it is more accurate if it has been calibrated (history matched) to existing production data. Alternatively, the previous production history can be examined directly, trends identified and extrapolated to forecast production assuming that the operating conditions remain unchanged. This type of decline curve analysis uses no model but does require significant flow history in order to establish the trends for extrapolation. Production data analysis using simple analytical models is also possible (e.g. Fetkovitch, Blasingame) but also requires significant production data. In the initial stages of reservoir development, there is no production and the reservoir simulation model may be quite uncertain or unavailable because of insufficient information. This paper presents a method to forecast well production based on information obtained almost entirely during well testing without the need to build a dynamic model. The method involves four steps:AcquisitionDeconvolutionExtrapolationPrediction Each step is described in the following sections and the underlying assumptions are highlighted. Two field examples are presented and conclusions drawn.

In 2009, QGC (a BG Group business), began developing coal seam gas (CSG) feedstock for its new Liquefied Natural Gas (LNG) plant and required a subsurface model and field development plan to underpin the project's investment case. Fundamental to the modeling process was acquiring appropriate data to calibrate subsurface models and enhance confidence in their predictive quality. As part of an integrated reservoir surveillance strategy, specific pressure and temperature monitoring wells were required. This paper describes the successful lab and field implementation of an innovative completion technique that converts suspended coreholes into reservoir and aquifer monitoring wells. The coreholes are re-entered and vibrating wire piezometers (VWP) attached to capillary coil tubing, are positioned and cemented in place alongside selected reservoir intervals. The well is then "plugged and abandoned" and the lease remediated to leave only a small surface footprint for the data logger and telemetry. The cement is effectively impermeable to fluid movement but possesses sufficient permeability to transmit reservoir pore pressure to an adjacent piezometer. Recompletion of coreholes provides a cost-effective means of acquiring valuable downhole data while eliminating the need to drill a bespoke monitoring well in the same vicinity. Data over the reservoir interval (the Walloon Coal Measures) can inform and help resolve reservoir properties on a regional scale, understand contribution to flow and provide data points to pressure-match a reservoir model. Data over the aquifers within Springbok Sandstone and Gubbermunda Sandstone enables estimates of any CSG production effects on groundwater.