In Alberta there are over 50,000 horizontal wells. Some 5,500 of these wells are suspended and some offer opportunities for refracturing. There ae companes in Alberta today looking at these wells and trying to high grade candidates for recompletion. A large majority of these were most likely fracked using the geometric technique of evenly spaced fractures with little regard to rock or reservoir quality – more fracs – more sand – more water – no science. The geometric method of fracturing unconventional wells is based on the assumption that these reservoirs are homogeneous. One would be hard pressed to find a homogeneous reservoir anywhere in the world. Even the great Canadian oil sands have a great deal of heterogeneity, to the point that in mining operations the area to be mined is cored every 100 m to determine oil sand quality which is then used to set the plant intake and treatment parameters to match each different cell (area to be mined).
Because unconventional wells have such low permeability and porosity, rock mechanical properties play a big role in how a fracture will perform. Rock properties such as confined/unconfined compressive strength (C/UCS), Young’s Modulus (YM) and Poisson’s Ratio (PR) can be very important in deciding where to place a fracture. As a result, the current practice of equally spaced lateral clusters and stages can lead to uneven hydraulic fracture growth and non-productive clusters. There is an opportunity to engineer the placement of perforation clusters along the lateral by using YM trends to understand the relative brittleness of the rock. Shell Global has done a great deal of work in this area and even have a set minimum values for YM in different unconventional formations. They use YM and UCS signatures in correlation with fracture gradient to engineer placement of perforation clusters. Shell realize that lateral heterogeneity exists in unconventional reservoirs. An example for the Haynesville is shown below.