Fracture Characterization Through Rate Correlation Analysis

Abstract

Abstract Statistical correlations in flowrate fluctuations between wells from many fields appear to bear out the expectation that the hydraulic conductivities of faults and fractures in reservoirs can be influenced by geomechanical perturbations due to production operations: the fluctuations are characterised by high correlations over very large separation distances between wells; and those correlations appear to be stress-related and fault-related. An entirely separate relationship derived from observations in multiple fields is a strong bias of directionalities shown by injected fluids towards the local orientation of modern-day major principal horizontal principal stress axis (SHmax). These two sets of independent field observations provide mutually supporting observational evidences for the general geomechanical sensitivity of faults and fractures. However, whilst peaks in flowrate correlations are observed at about 30° to SHmax, the preferred flooding directionalities are at smaller angles to SHmax. A recently proposed machanism is able to explain the orientational relationships in both sets of data. It involves interacting, stress-aligned, compliant micro-cracks near a critical density; there is a large background of observations of shear-wave splitting in many types of formations that supports the prevalence of such micro-cracks. As a practical low-cost tool, analysis of flowrate correlations can provide valuable information about the major reservoir pathways as an adjunct to reservoir characterisation studies. This information can aid history-matching of reservoir models, particularly those involving fractures. The technique is also well-suited to monitoring reservoir behaviour in time-lapse fashion.