Abstract

It is well known that Vaca Muerta oil and gas production comes from horizontal wells with multiple hydraulic fracture stages. It is desirable from an economic standpoint to get more Stimulated Reservoir Volume (SRV) per well, thus increasing the length of horizontal well paths has been a common practice through the years. The SRV per stage is mostly related to the stress regimen (described by the Vertical Stress Sv, the Minimum Horizontal Stress Sh and the Maximum Horizontal Stress SH), mechanical properties around the well and the stimulation design.

According to the relative values of the Sh, Sv and SH, hydraulic fractures will tend to be vertical where normal to strike slip stress regimes are present. On the other hand, hydraulic fracture could propagate with preferred horizontal components when the state of stress is close to reverse stress regime, leading to a smaller SRV. Therefore, mapping the variation of stress state may be helpful to aware zones with low anisotropy, to take actions from the fracture design viewpoint, to optimize the full field development (pad locations) and to understand some issues during stimulation (screen out, high pressure/lower rates, casing deformation, etc.).

The objective of this work is to estimate the stress regime state across the field (and along the wells) using the relative magnitude between the overburden (Sv) and a proxy of the horizontal minimum stress (Sh). In this case, the pre-frac instantaneous shut-in pressure (Pre-frac ISIP) was used as an indicator of minimum stress for each fracture stage. Also considering the availability of closure pressure data from DFITs (Diagnostic Fracture Injection Test), a correlation has been established between ISIPs values and closure pressure (Pc), leading to a corrected ISIP value (ISIPc) for a rough estimation of Sh per stage. Density logs, topography and structural position involving each horizontal length were considered in the estimation for Sv.

Mapping the relationship (Sv-ISIP) and (Sv-ISIPc) along the block could show some useful variations (tendences) to be considered in the full field development.

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