Two New Methods for Defining Shut-In Pressure in Hydraulic Fracturing Tests

Hydraulic fracturing is one of the most common methods to determine in-situ rock stress. The interpretation of the shut-in pressure to determine the minor principal stress is an important element of this method, and many different methods to interpret shut-in pressure have been studied and developed throughout the years. Each method has its advantages and disadvantages. With more than 50 years of research and development within the rock stress measurement field, especially in HF, SINTEF has established two practical ways of defining shut-in pressure. These methods are independent and termed zero flow and water hammer. The zero flow method has been used by SINTEF in more than 130 projects over the last 30 years. The methods clearly differ from the other methods as they are based on singular events in the development of pressure/flow versus time which enables us to read the shut-in pressure directly during testing. In this paper a comparison is made between different methods for interpretation of shut-in pressure, including 12 existing methods and the two SINTEF methods. Comprehensive laboratory tests were performed, and a field test was selected from SINTEF's database for demonstration and comparison of the methods. The SINTEF methods have been developed mainly for use in hard rock environment where the rock is a jointed aquifer and with low permeability. The application of the two methods have traditionally been hydroelectric power development, different types of tunnel and cavern projects, and also in mineral mining. The methods have not been used in deep petroleum applications such as oil wells or offshore in porous rock types. Highlights of the article: • There are 12 established methods for shut-in pressure estimation in hydraulic fracturing. All methods have certain advantages and disadvantages. • SINTEF has developed two methods namely zero flow and water hammer. • The SINTEF methods are documented through laboratory and in-situ tests. • A comparison of the two SINTEF methods with the existing methods has been done.