Holistic Approach to Determine the Fracture Propagation Pressure (FPP): Consistent Interpretation of Step Rate Tests Using Multiple Analysis Methods

A Step Rate Test (SRT)‘s is frequently performed method used to accurately measure fracture propagation pressure (FPP) of a given geologic formation. The injection rates in the test are increased in steps from low rates below fracturing pressure to high rates above fracturing pressure, allowing each rate to stabilize, and noting the stabilized injection pressure for each rate. Then, as classic approach, pressure at the end of each injection step versus injection rate are plotted. The fracture propagation pressure occurs at the intersection of the two straight lines. Then main assumption of the classic approach is that there are "2 distinct different regions with constant properties (i.e. KH & skin)" during multi rate injection test and those regions are the one without "induced fracture" region and the one with "induced fracture" region (i.e. post frac region). However, post-frac region properties is not going be constant since fracture dimensions changes injection pressure. Therefore, the purpose of this paper is; To explore the pitfalls of the classic approach (pressure versus rate) by including derivation of the mathematic model for classic approach;To develop/provide other alternative SRT interpretation methods: "Pressure Transient Analysis (PTA) – detailed skin analysis" and "PTA– fall-off analysis"To define a holistic approach using Multiple SRT’s Interpretation methods in order to determine the FPPTo demonstrate the applicability of proposed approach for several SRT cases The proposed holistic approach was successfully applied to several SRT tests conducted in Brunei, commingled waterflood injector wells. Results showed that; Derived mathematical model demonstrated that "classic approach" is underestimating the FPP: Depending on the reservoir fracturing characteristics, expected 2 regions, which is the basis of classic approach, may not be fully developed. This was also demonstrated by actual SRT data.Classic approach might result in misleading FPP results: 2 out of 4 case has no definitive conclusive results up and there is up to 9 % error in FPP estimation (classic versus PTA approach)Classic approach even sometimes might not provide conclusive FPP results: 1 out of 4 case has no conclusive resultPTA approach (i.e. detailed skin analysis and/or prep & post-frac fall-off analysis) was successfully applied to estimate FPP pressure and it seems to be most reliable method since it has provided conclusive results for all cases.PTA analysis could be extended to determine the induced frac properties (fracture, the fracture length, width & frac properties) Recommendations on how to perform a holistic approach for SRT analysis & how to verify the results with standard PTA approach is provided. In addition, since there is no analytical model for induced fracture (i.e. pressure dependent frac), adopted PTA approach using hydraulic frac modelling to make an estimate for frac length size is also presented