Revisiting Microfrac In-situ Stress Measurement via Flow Back - A New Protocol

Abstract

Abstract The minimum in-situ stress is an important parameter for many applications including cap rock integrity, hydraulic fracturing design and well bore stability. Microfrac testing is the most reliable and direct technique for measuring it and involves creating a hydraulic fracture. The pressure at which the created fracture closes is commonly associated with the minimum in-situ stress. The pump-in/flow back test is one of several procedures that can be done during microfrac testing, and it produces a very characteristic pressure signature at closure. In this paper we demonstrate the pitfalls of the traditional interpretation of the flow back data based on data acquired during shallow microfrac tests in a shale formation. The importance of identifying the transient flow regime and the significance of the pressure rebound are discussed. To circumvent the drawbacks of the conventional flow back test a new protocol using an incremental flow back/shut-in procedure is proposed. The excellent results demonstrate the merits of the new procedure.