Experimental investigation of propped fracture conductivity in tight gas reservoirs using factorial design
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In this study we have undertaken a systematic investigation of the interactive effects of the key parameters that affect the final conductivity of a propped fracture, including flow back rate, proppant loading, polymer loading in the fracture fluid, the presence or absence of breaker, closure stress, and reservoir temperature. Fracture conductivity for conditions representative of field conditions was measured using a dynamic fracture conductivity testing procedure in which a fracture fluid/proppant slurry was pumped through a fracture conductivity cell, and then shut in and closure stress applied. Water-saturated gas was flowed through the fracture for a period of time at each closure stress to mimic gas flow back during the early stages of production. In all experiments, the proppant used was 30/50 mesh ceramic proppant. We used a fractional factorial design, methodology to determine the relative importance of the fracturing parameters varied. The fractional factorial design method examines the combined effects on conductivity of potentially interacting parameters, while minimizing the number of experimental runs required. The effects of the investigated factors arranged in order of decreasing impact on conductivity are closure stress, temperature, flow back rate, polymer loading, proppant concentration and presence of breaker. Increases in closure stress, flow back rate, temperature and polymer loading were observed to have deleterious effects on fracture conductivity. In particular, at high closure stresses and high temperatures, fracture conductivity was severely reduced due to the formation of a dense proppant-polymer cake. Dehydration of the residual gel in the fracture appears to cause severe damage to the proppant conductivity at higher temperatures. Also, at low proppant concentrations, there is the increased likelihood of the formation of channels resulting in high fracture conductivities. Copyright 2012, Society of Petroleum Engineers.
