The Zhahaquan tight oil field is located in the late tertiary siltstone of the Qaidam Basin, Gansu Province, P.R. China. The field's conventional and tight reservoirs are currently being appraised with an aggressive drilling campaign. Despite an average plug permeability of about 0.3 mD and a modestly overpressured reservoir (12–16 kPa/m), hydraulic fracturing (HF) stimulations are deemed necessary to produce the light oil (31° API) at commercial rates. Stress modelling and fracture diagnostics confirm a predominately normal faulting stress regime throughout the basin, but vertical stress contrasts between formation layers highlight no potential frac barriers.

Initial hydraulic fracturing stimulations in 8 vertical wells resulted in 6 out of 11 stages screening out prematurely, while the remaining 5 could only be completed with light proppant concentrations below 10% of fluid volume, resulting in only modest production rates. Subsequent well stimulations were designed based on refined modelling results, with which screen- outs could be avoided and initial production rates tripled.

This study puts forward the modelling and execution of one horizontal well with 27 perforation clusters divided into 10 stages, in which the effects of fluid rheology, proppant concentration and injection rate on the resulting fracture geometry are highlighted. The study further shows that unlike in preceding simulations, the cluster- and stage spacing were optimised with respect to the stress interference between parallel fractures.

You can access this article if you purchase or spend a download.