Abstract

The current practice of pumping large volumes of low salinity slick water in hydraulic fracture stimulation treatments in Canadian oil and gas shales and ultra-tight formations has proven extremely beneficial. These zones, however, are typically considered to have sub-irreducible water saturations. Nevertheless, water treatment volumes of 10,000 – 20,000 m3 per well are routinely performed. Conventional thinking would expect reduced hydrocarbon production due to formation damage or water block. Cleanup efficiencies of these massive water volumes during flowback is driven by the desire to minimize fluid invasion into the matrix. Water (load fluid) cleanup is essentially driven by viscous forces to counteract the capillary forces in the mix-wettability pore network. Operational and seasonal restrictions at times prevent wells being tied into pipelines immediately to continue the load fluid clean-up process. Once wells are placed back on production however, positive and dynamic fluid changes are observed. Conventional thinking suggests that once the invaded water zone saturation reduces to irreducible levels during flowback (cleanup operations), hydrocarbon can then freely flow into the wellbore. However, the flowback behavior in unconventional reservoirs is quite different than conventional reservoirs where soakback and slowback techniques are implemented. These wells can undergo weeks or even months of shut-in following the hydraulic fracturing treatment. It is believed that extended shut-in periods promote the counter-current imbibition phenomena, where the residual hydraulic fracturing fluid can imbibe deeper in the formation matrix driven by osmotic and capillary forces.

This paper demonstrates the true benefit of multi-functionalized surfactant (MFS) with formations of mixed-wettability characteristics using both lab and field tests. Amott Cell results, a test for spontaneous imbibition using various stimulation fluid types, demonstrated MFS significantly outperformed common surfactant chemistry when tested on mixed wettability core samples.

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