Lost circulation mitigation in low permeability formations using fluid additives that encourage fracture termination against pre-existing fractures
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Lost circulation is a long-standing challenge in the petroleum industry and a major contributor to non-productive rig time during drilling. Over the years, the industry has developed various lost circulation mitigation (LCM) techniques, several of which have yielded positive results. Lost circulation remains a particular problem in formations that have very low permeability but which do not have high clay content. Low permeability formations, especially shales, often contain natural fractures. When a hydraulic fracture is induced during drilling, it may interact with these pre-existing fractures and other planes of weakness by either terminating or crossing. We investigated whether these interactions could be exploited to mitigate lost circulation. A novel hypothesis for how low matrix permeability could encourage termination through a time-dependent poroelastic effect was developed and tested using a hydraulic fracturing simulator (CFRAC). Previous studies have shown that crossing occurs when hydraulic fractures are able to reinitiate on the other side of the plane of weakness. A sensitivity study was performed to investigate the effect of permeability, tensile yield strength, and the rate of hydraulic fracture propagation on the ability for incipient fractures to initiate on the opposite side of the preexisting fracture. Results showed that in low permeability formations, a high rate of hydraulic fracture propagation may cause termination. Based on the hypothesis and the results of the sensitivity study, a semi-analytical time-dependent model to predict crossing was developed and implemented into CFRAC. CFRAC’s ability to simulate the injection of fluids with different injection rates and fluid viscosities was used to design a two-step LCM pumping sequence of high injection rate and low fluid viscosity, followed by lower injection rate and high fluid viscosity.