Interwell Communication By Concurrent Fracturing - A New Stimulation Technique
Authors: Moschovidis Z.A. 
Published: March 2010

A new fracturing technique is proposed, referred to as "concurrent fracturing", to effect communication between two (or more) adjacent wellbores. As the name implies, two (or more) wells can be fractured concurrently to enhance the chances that the created fractures interconnect. The technique can be applied primarily for horizontal fractures. It can also be applied for vertical fractures provided that the wells are spotted roughly in the direction of fracture zimuth. The rationale for the potential success of such a fracturing technique is based on the following argument: when two fractures are in relatively close proximity and propagate toward each other, the induced tensile stress fields ahead of the tips reduce the effect of the closure stress and cause the fractures to interconnect. The treating pressure of each well is expected to drop concurrently when the fractures interconnect, and to stabilize afterward to a lower level. This simultaneous pressure drop depends on the sizes of the fractures when they interconnect and can be used to detect fracture communication.

In the following, some motivation jar concurrent fracturing is given as well as the theoretical basis for its potential effectiveness. Two examples of well treating pressure monitoring scenarios are also presented.

Introduction

There is both theoretical and experimental evidence that two hydraulic fractures in relatively close proximity interact with each other and mutually- affect their path of propagation. This is due to the tensile stresses which reduce the effect of the in situ closure stress in a fonnation region joining the fracture tips. There, the fractures propagate more easily than if they were isolated from each other, and tend to interconnect. By fracturing concurrently two (or more) adjacent wells, there is a better chance of fracture communication.

Interwell communication is desirable for some steamflood and waterflood operations to achieve optimal productivity. For shallow tar sand formations, hydraulic fractures tend to propagate primarily in the horizontal direction and tend to migrate upward. A useful completion strategy is to communicate two adjacent wells by inducing hydraulic fractures so that steam can be circulated to heat-treat the formation and product the heavy oil. This type of strategy was applied at the Gregoire Lake In Situ Steam Pilot (GLISP); however, only one wellbore was fractured with the intent of intersecting the second wellbore. The created fracture did not communicate the wells effectively and may have intersected the second wellbore high in the pay section. If concurrent fracturing were applied, theory suggests that both fractures would propagate lower in the pay section, provided that they were initiatedt the bottom of the pay. Consequently, concurrent fracturing may have the additional benefit of reducing the upward propagation tendency of horizontal fractures in tar sands for effective steamflooding.

For deeper formations where the fractures are vertical, two adjacent wells spotted approximately in the direction of fracture azimuth can be made to communicate by concurrent fracturing. Well communication may be effected both between injection wells and/or between production wells, so that the resulting fracture network may be favourable for a line drive waterflooding strategy which has optimal sweeping efficiency.