Selection of adequate thermal operating parameters to ensure fluid containment and cap rock integrity under high-temperature, high-pressure steam injection is vitally important. Cap rock integrity is controlled by the mechanical properties of the rocks and the in-situ and applied stresses resulting from field operations. This paper describes recent minifrac tests carried out in the Lower Fars formation in South Ratqa Field in northern Kuwait to determine the in-situ stresses.
The main objective of the field tests was to obtain the minimum horizontal stress using a variety of Before Closure Analysis (BCA) techniques. A secondary objective was to perform After Closure Analysis (ACA) to obtain reservoir parameters such as permeability and initial pressure. All of this data is used as input into subsequent geomechanical studies. For BCA, it is important to identify various fluid flow regimes in the fall-off portions of the tests. The end of particular flow regimes indicates fracture closure. Fracture closure and the resultant minimum horizontal stress are therefore based on sound engineering principles.
The cases presented in this paper provide further evidences that a combination of various techniques is the best approach to identify the minimum horizontal stress. No single methodology provides a reliable answer in all cases. Field examples are given to illustrate the practical application of these techniques.