The huge resources of unconventional gas worldwide along with the increasing oil demand make the contribution of unconventional gas to be critical to the world economy. However, one of the major challenges that operators face to produce from unconventional resources is commercial stimulation technique that creates sufficient stimulated reservoir volume. Unconventional reserves trapped within very low permeability formations, such as tight gas, or shale formations, exhibit little or no production, and are thus economically undesirable to develop with existing conventional recovery methods. Such reservoirs require a large fracture network with high fracture conductivity to maximize well performance.
One commonly employed technique for stimulating low productivity wells is multi-stage hydraulic fracturing, which is costly and typically involves the injection of high viscosity fluids into the well. Fracturing fluid by itself could form a damaging material for the fracture due to high capillary forces. Thus, additional needs exist for an economical method to enhance production within a tight gas formation.
This paper discusses a new stimulation method to increase stimulated reservoir volume (SRV) around wellbore and fracture area, and therefore, improve unconventional gas production. The method entails triggering an exothermic chemical reaction in-situ to generate heat, gas and localized pressure sufficient to create fractures around the wellbore. In controlled experiment, chemical reactants were separately injected into core samples with a minihole and upon mixing inside the core, an exothermic chemical reaction occurred and the resultant heat and gas pressure caused macro-fractures. NMR-porosity imaging showed significant increase in macro pores throughout the core. Additionally Large scale experiments using cement blocks with a simulated wellbore cavity were performed. Once the wellbore was filled with the chemicals and upon introducing a triggering catalyst an in-situ chemical reaction took place which generated heat and gas with sufficient pressure to cause shear fractures in the surrounding rock. These experiments showed extensive fractured and shattered pieces and also provided preliminary design requirements for a field test. The chemical reactants then incorporated into a fracturing gel to simulate creating additional fractured from the main induced hydraulic fracture. The results were very encouraging and the generated high temperature and pressure caused the gel to break thus it is concluded that this technique effectively contribute to fracture cleanup in addition to creating required SRV. The experiments were very successful in proving the new concept of generating SRV in tight gas well and the developed stimulation technique is fairly easy to implement in the field.