The objective of this work is to show that the estimated stimulate reservoir volume (SRV) from micro seismic analysis under dynamic conditions not always represents the SRV acting as hydrocarbon collector and need to be calibrated with total organic content (TOC), vertical and areal distribution. Furthermore, unlike conventional reservoirs, the potential leakoff damage caused during the fracturing and the SRV generation process, are not detectable by pressure transient analysis (PTA), but us a change on SRV transmissibility.
Integrating PTA, net pressure behavior during fracture treatment and micro seismic analysis results, allow us to better understand the reason that seismic events from one or more monitoring wells, might conduct us to wrong interpretation of the active SRV. Field cases show how PTA conventional technique helps to identify the existence or absence of an effective SRV connected to each individual hydraulic fracture stage and its associated best quality TOC thickness.
Results confirm that active SRV, generated by hydraulic fracture treatment in lower Vaca Muerta, where the seismic events practically are no detected, PTA analysis has an excellent infinite conductivity fracture behavior on the best TOC thickness. Production potential depends on different factors, net pay with TOC percentage greater than 2.5 %, vertical and areal distribution associated to rock porosity, natural fissured and SRV are the most important parameters. It is critical to understand the system deliverability potential, it must be evaluated under production conditions and the active SRV adjusted with TOC percentage and distribution, taking into account the effects caused by SRV pore pressure drop. Network of natural fissures originally in place and changes generated around the main fracture, combine to enhance the quality system.
An improvement of active SRV transmissibility was detected after the buildup period, increasing from 20 to 80 % oil production and more than three times the initial production. As in conventional reservoirs, where pressure test results are related to formation transmissibility, in unconventional reservoir pressure test results are related to SRV transmissibility and TOC percentage.
It can be concluded that the best zones to be fractured are determined by PTA associating to logging and cutting geochemistry analysis. PTA evaluation will determine only chocked fracture damage and not surface fracture damage.
PTA allows us to improve well completions efficiency and amount of fractures. Vertical wells production performance and best zones knowledge, will allow a better choice of zones to be developed thru drilling horizontal wells. In spite of industry belief, PTA analysis can give us a better understanding of SRV behavior in contact with the generated primary fracture.