Improved In-Situ Stress Characterization Through Analysis of DiagnosticFracture Injection Tests DFITs Using the Changing Compliance Method andits Impact on Caprock Integrity Analysis

摘要

Diagnostic Fracture Injection Tests(DFITs)provide a critical piece of information on the competency ofthe top seal for injection projects and are therefore essential for Subsurface Containment Assurance(SCA)and Maximum Operating Pressure(MOP)determination.Results of DFITs provide the best estimate for theminimum principal stress component,which is a major input for tensile and shear failure tolerance analysis.Therefore,best practices in execution and analysis of DFITs is extremely important for safe and successfuloperations.Numerous DFITs have been conducted over the past ten years in Surmont to assess the integrity of thecaprock and determine the maximum allowable steam injection pressure.A combination of surveillanceand coupled reservoir-geomechanics simulations have been utilized to maintain a minimum of 20% safetyfactor for caprock failure.The tangent analysis method for determining fracture closure pressure has been extensively used in thepast decade for DFIT analysis in the industry [1 and 2].The validity of this method has been challengedrecently through more rigorous modeling of the hydraulic fracturing process and field observations.Analternative analysis method referred to as the compliance method has been proposed and successfully usedin many cases [3].In the past few years,we have demonstrated the potential to safely increase the maximum operatingpressure and its impact on production,through extensive caprock integrity analysis in Steam AssistedGravity Drainage(SAGD)operations [4 and 5].In this study,the DFITs carried out in Surmont were revisited to assess the potential impact ofcharacterizing in-situ stresses with improved accuracy on maximum allowable injection pressure andultimately production uplift.The analysis shows higher minimum horizontal stresses in the caprock aresupported by field observations,which could potentially allow for higher injecting pressure and close tofive percent additional production in the two selected SAGD pads.