Westside: Challenges and Contradictions in Horizontal Well Fracturing
Trial-and-error is the most popular tool for the design of fracturing treatments in horizontal wells in unconventional reservoirs. The technique has resulted in substantially better production than one would expect based on the permeability of these reservoirs. What is interesting is that the direction of some of these changes appears to contradict our general beliefs about fracture growth patterns in these reservoirs, specifically:
The belief that the high productivity of these treatments is due to activation of an existing complex natural fracture network is inconsistent with the trend of reducing the spacing between perforation clusters;
Fluid consumed in the activation of natural fractures should make the length of a “complex fracture network” shorter than a single fracture, however, fractures in horizontal wells routinely intersect offset wells, sometimes more than ½ mile away;
Assumption of the equality of the two horizontal in-situ principal stresses is inconsistent with the observation of uniform fracture orientations in the same and neighboring wells;
Even after pumping millions of pounds of sand in a single well, we do not see a gradual increase in the fracturing pressure or ISIP, which contradicts the presence of “Stress Shadowing”;
Analysis of pressure changes caused by well-to-well communication between offset wells during fracturing treatments shows intermittent presence and loss of communication.
Does a step increase in well productivity require revisiting our “accepted” beliefs?
Norris Westchase Center
9990 Richmond Ave., Suite 102
Houston , TX 77042