This paper illustrates a simple methodology for combining information obtained from certain LWD measurements, and prior information about reservoir context, to estimate the productivity of the well during the drilling process. The concept of this methodology was the subject of a previous publication (Zhang and Jalali, 2010); here the emphasis is on the linkage to LWD measurements.
The LWD measurements used in this procedure are the bed boundary logs, which are continuous in measured depth and are obtained from deep azimuthal electromagnetic measurements, and mobility logs, which are station measurements and are obtained from the formation testing while drilling operation.
The current implementation of this methodology is applicable to simple environments --a well drilled in a closed drainage area with flow being single-phase. This allows the estimation to be done automatically, in real-time and with quantification of spread or uncertainty.
The method can be adapted to more complex environments-such as a well traversing the two-phase capillary transition zone, or multiple compartments with pressure contrast-however, tradeoffs will become inevitable in terms of the degree of automation, hence frequency of estimation, resulting time-lag, and assessment of uncertainty.
This procedure allows the operator to combine reservoir information known prior to drilling, such as reservoir fluid properties and position of neighboring wells and boundaries, with fresh information obtained during drilling, to estimate the inflow potential of the borehole. When combined with standard methods of estimating the lift or outflow potential, for the envisaged well completion and lift method, the production capacity of the well can be estimated.
This procedure, therefore, can provide the earliest estimate of well production capacity, based on real-time formation evaluation measurements and evaluation, making it potentially useful to the operator in deciding whether the drilling or the completion plan needs to be updated, before the operational crew is disengaged from the wellsite.