No abstract

Hydrocarbon production from low permeability heterogeneous clastic reservoirs consisting of a sequence of thin, interbedded sand and shale laminations is challenging. Hydraulic fracturing is essential to achieve good production rates. An understanding of fracture geometry is very important for optimal reservoir management and development. This paper describes the application of an advanced logging system to evaluate near-wellbore vertical fracture properties. Conventional production logging focusing primarily on wellbore flow geometry such as perforation and behind casing flow through poor cement may not adequately evaluate fracture properties due to a limited radius of investigation. To overcome this, a campaign using an advanced logging system containing spectral acoustic and high precision temperature measurements to evaluate near-wellbore fracture flow distribution was implemented. The main feature of this logging technique is the ability to scan the active flow behind the casing a few meters from the wellbore. The reservoir flow profile is assessed by temperature modelling enabling differentiation of the different flow regimes and inflow contributions. Two vertical water injection wells hydraulically fractured into the low permeability clastic reservoir were logged. Vertical fracture geometry was precisely determined for each case and reservoir injection profile determined based on temperature modelling. Detailed pre-job modelling was necessary to define the logging program including optimal flowing and shut-in regimes. This enabled improved efficiency and accuracy when interpreting the results. The results enabled the determination of any out of zone injected volumes. This study revealed new insights in evaluating fracture geometry that can then be applied to reconcile post-job fracture modelling and improve reservoir management and water flood optimization.

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.