Material balance P/Z method is widely applicable concept in reservoir engineering to estimate GIIP in volumetric dry gas reservoirs. The application of conventional P/Z method is based on constant pore volume assumption and reliable production of GIIP & PVT data. In newly drilled prospects there is always huge uncertainty in dynamic GIIP due to unavailability of significant production & pressure data [1] and uncertainty of drive mechanism. However, production tests (Reservoir Limit Test, Interference Test, etc.) for longer duration are usually designed to acquire reliable production and average reservoir pressure data to have indicative estimates of GIIP and drive mechanism in order to have development & appraisal program with more certainty.

Low BTU gas with more than 50% inert in the gas cannot be allowed to be injected in the buyer's network. Commercial development of such discoveries for power generation needs firm commitments of gas supply which is based on GIIP estimates which usually have uncertainty due to lack of production and pressure data at the time of discovery.

In this paper we will give a brief insight on the techniques to acquire reliable production data with longer production tests & their limitations, Pros & Cons of conventional P/Z approach for GIIP estimation in the newly drilled prospect. The case study will show how the limited pressure & production data may also be utilized with caution to have minimum GIIP estimates using P/Z method especially in case of overpressure reservoir where drive mechanism is most likely volumetric by designing simplified numerical modeling approach without conducting longer production tests. However, this technique has limitations in case of poroelastic nature of reservoir.

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