Blog Series: Mini-Frac Treatment, The Key to Successful Hydraulic Fracturing
Mini-frac is the holy grail to a properly designed and successfully executed hydraulic frac treatment. Hydraulic fracturing is a complicated and costly job, months of planning and thousands of dollars are at stake, therefore reliable formation evaluation is key to make it an economic success. Minifrac job is carried out with the same intention, to get as much information practically possible before investing in the humongous cost of executing main frac job. The data obtained from this is used to revamp the frac design.
A small volume of frac fluid is injected in to the formation above breakdown pressure and then pressure fall-off trend is observed. During fall-off different events occur which are critical for frac design fine-tuning. First parameter is formation breakdown pressure, second & arguably the most important one is fracture closure pressure. Further parameters that may be estimated are fracture gradient, net fracture pressure, reservoir leak-off (& subsequently permeability) and fluid efficiency etc.
Breakdown Pressure (Psi): The fluid pressure required to break the intact rock.
Closure Pressure, Pc (Psi): Practically it is same as minimum in-situ stress; it determines the minimum pressure to keep the rock open.
Fracture Gradient (Psi/ft): This value defines the amount of pressure required per unit length to extend the fracture.
Net Fracture Pressure, Pnet (Psi): The energy needed to keep the fracture open and propagating.
Pnet = PF – Pc
Fluid Efficiency (%): It is the measure of the fluid performance, the total fluid pumped vs stored fluid volume in frac. High fluid efficiency refers low leak-off and low permeability.
Typical Mini-frac Treatment pressure curve. Annotations inidicate typical points to extract respective data from plot.
This blog serves as the basic introduction to mini-frac treatment during hydraulic fracturing. In further subsequent blogs in this series, we will talk about specific analysis techniques, concepts, equations, common problems & discuss case histories. So stay tuned!
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