XS gas reservoir in Western Sichuan Basin is a typical tight sands hotspot in China, of which the target stratum, namely the 3nd Member of Penglaizhen Formation is braided channel deposition. The sand body with good communication along the river channel is opposite perpendicular to the channel. Moreover, the reservoir with horizontal drilling shows diverse type of sand bodies and strong heterogeneity in vertical and lateral directions. Multi-stage hydraulic fractured horizontal wells have been proven to be effective to enhance gas recovery in tight sandstone gas reservoir. However, one major obstacle has been the previous inability to place the hydraulic-fracture in the complex fluvial tight reservoir to maximize gas production.
This paper provides a 3D fracturing design method (3D FDM) considering the influence of various sand-body and flow units on the hydraulic fracture propagation in fluvial tight reservoirs. Firstly, the reservoir was classified into three grades based on its porosity and permeability. A 3D geostatistical reservoir model which was divided into three types, was developed with the sandstone body distributions in vertical and lateral directions. Subsequently, the flow unit boundary was determined by the sand-body permeability and thickness. Then the detailed fracture parameters were implemented in the 3D models and reservoir simulation was used to select the fracture number, space, length and conductivity to achieve economical flow rates. At last, the fracturing simulator was utilized to confirm whether the treatment parameters were appropriate.
Results show that the flow unit boundary is a log function of sand-body permeability and thickness. The influence of reservoir grades on fracture space is obvious, which indicates that the fracture space is large in high-grade reservoirs. Comparing various qualities of reservoirs, the fracture length and conductivity in poor-quality reservoirs is considered to be the most significant.
Comparison with the fracturing wells with conventional fracturing design method in Xinma gas reservoir, the post-production of the well with 3D FDM increases by 41%, and it shows that 3D FDM is appropriate for the gas development in Penglaizhen Formation.