Unconventional reservoirs need to be fractured for them to produce economically. To evaluate the reservoir parameters such as permeability, time to reach the boundary, fracture permeability, etc. the well needs to be shut down for well testing purpose. The method outlined in this paper, eliminates the need of this shut down for well test, which forms the basis of calculating these parameters.
The limitations of such conventional method are overcome by a new approach that is based on using flow data and making use of dimensionless productivity index and its derivative. Essentially the variation of this index with dimensionless time gives us the idea of the area of propagation of dimensionless average reservoir pressure in the reservoir. As a result, a well flowing with constant pressure can be analyzed along the principles of pressure transient analysis. This approach overcomes the inability of rate transient analysis to decouple permeability with the flow area associated with in dual porosity reservoirs. The method is shown for linear flow regime and for constant volume fractures.
The results of this approach are shown for early time and late time to reach the boundary of the reservoir. This, in turn, determines the stimulated rock volume created by the pressure boundary in between two laterals, given their spacing. The early time and late time to reach boundary have an impact on the long-term performance of the hydraulic fractures as it determines whether they approach infinite fracture conductivity behavior. The method is outlined with the help of published well data and a synthetic field wide model.
The significance of this approach is demonstrated by the fact that it not only helps to evaluate reservoir permeability and effects of lateral spacing but also ascertaining theoretical fracture conductivity for block (2D) matrix configuration. With this fracture conductivity in mind and the fact that a constant volume fracture having a same area/volume ratio, but different 1D, 2D or 3D matrix configuration will exhibit the same transient response, we can determine long term deliverability of such wells.
