Production Case Studies

Fractures and Fraccing

Rock mechanics is divisible into two disciplines, rock properties and the stresses acting upon the rocks. Both have been traditionally engineering pursuits based on post-drill well logs and laboratory derived data such as rock strength.


Since PSI has demonstrated that earth stresses can be determined pre-drill from seismic, geologists and geophysicists can usurp the second discipline. Further, there is an intermediate area of natural fractures which result from prior stresses acting on the rocks and therefore complicating the rock physical properties in situ.

Natural fracture evolution and description can be readily determined from PSI’s 4DGeoStress. PSI is therefore ideally placed to make the links between present and past stresses and resulting natural fractures. This increases the variables but tends to constrain models for assessing hydraulic fraccing projects.


This case study will show how combining knowledge of stress history and rock deformation can determine the best drilling and fraccing approach in tight and unconventional reservoirs.



Frac Planning

PSI was requested to review the impact of stress, pore pressure, faults, fractures and bedding on a planned frac of a tight, interbedded Early Cretaceous arkosic sand play. A comprehensive data set was examined. (the area has not been identified in this case study).


In March 2010, PSI used a 27km2 3D seismic survey to determine SHD & SHM from its patented 4DGeoStress software. At the Top Eocene at Well-A, SHD = 120° (blue bars, right) and SHM = Extensional Strike Slip Stress State, mid green (SH/SV>1 & Sh/SV≤1).


At the Early Eocene, SHD = 003° and SHM = almost Compressional Strike Slip Stress State (right). Note, PSI’s SHD & SHM are determined from seismic alone, therefore is generally used pre-drill.


Although reverse faults were apparent, PSI could not accurately map the Top Early Cretaceous. The Early Cretaceous fault (dashed, opposite) would cause SHD to rotate to approximately azimuth 160° and SHM to increase to almost Reverse Fault Stress State (pink) at the 2440m TD of Well-A.