Vertical Fracture Monitoring by Multi-Rate Through-Barrier Diagnostics

Abstract

Hydraulic fracturing has been demonstrated to be a cost-effective method of developing low-permeability heterogeneous clastic reservoirs with vertical wells. In the presence of a thin shale layer as a seal, monitoring effective fracture height becomes extremely important. The conventional approach of a single-regime production logging may be ineffective due to the complex geometry of fluid flow in the near-wellbore zone around the well. The paper describes the experience of the multi-rate through barrier diagnostics as a method of improving hydraulic fracturing evaluation. The standard way to diagnose the effectiveness of hydraulic fracturing is to log a survey under current operating conditions. In general, temperature and passive spectral acoustic measurements provide useful information on identifying the boundaries of fluid movement behind production casing; however, it is difficult to determine if flow occurs in the vertical hydraulic fracture or channeling through damaged cement in a single-regime survey. The multi-rate through-barrier diagnostics allow analyzing the flow dynamics of the wellbore-fracture-formation system under different flowing regimes, enabling a more accurate assessment of fluid movement in the near-wellbore environment within several meters. The paper includes the results of the multi-rate logging survey campaign in vertical water injection wells drilled in a low-permeability clastic reservoir. A proppant-based hydraulic fracturing of the target formation was carried out in the wells. The geological structure of the developed reservoir includes a thin shale layer (break) that separates the target oil-saturated interval from the overlying water bearing reservoir. In order for the operator to optimize future stimulation programs identification of effective hydraulic fracture height in reservoir regions with different shale thicknesses is crucial. The upper boundaries of the injected fluid movement behind the casing were determined based on the survey results. Analysis of the acoustic and temperature field dynamics helped more reliably evaluate the nature of the fluid movement behind the casing, whether flow happens in vertical fracture or cement channeling. This results in a more precise quantitative assessment of the injection profile in the targeted and untargeted reservoir units.