The ‘A’ formation in the Abu Gharadig basin, northern Western Desert of Egypt is a carbonate reservoir characterized as a low-permeability soft chalk with medium porosity and low-quality natural fractures. Owing to these characteristics, achieving economical gas production rates and efficiently developing the reservoir have become increasingly challenging. To increase production from the field, a full development plan was initiated employing drilling of horizontal wells with multistage fracturing stimulation. An integrated and detailed programme of laboratory core testing was conducted to gain an in-depth understanding of this reservoir's rock mechanics behaviour and to help optimize the hydraulic fracturing and completion designs. Particularly, elastic properties and principal in-situ stresses were acquired to provide the following:
Static and dynamic mechanical property information for correlating well log data
Calibration to the mechanical earth models constructed from sonic-derived mechanical properties to help provide realistic deformation parameters for hydraulic fracturing design purposes.
Strength information for developing a failure locus for the material.
Mechanical properties testing was conducted on selected core samples and integrated logs from two offset vertical wells. The laboratory testing programme consisted of the following:
Indirect tensile strength testing (Brazilian method) at room temperature.
Unconfined compression strength (UCS) testing
Single-stage triaxial compression testing with concurrent ultrasonic velocity measurements.
All laboratory data, including procedures, tabulated results, stress-strain plots, computerized tomography scan images, and post-test sample images are provided for analysis and visualization of the failure mode. Understanding the reservoir geomechanical behaviour and the mechanical parameters that have a critical impact on hydraulic fracturing propagation facilitated improved decision-making in terms of fracturing design and optimization. Hydraulic fracturing simulation software was used to model the propagation of hydraulic fractures based on the integrated reservoir mechanical properties. Different scenarios of perforation clusters were run to model propagation of multiple horizontal fractures and predict the changes in stress anisotropy in the neighbourhood of the fractures.
