Efficient Large Volume Acid Fracturing in Openhole Horizontal Well with Pre-Created Circular Notches

Abstract

Tight carbonate reservoirs often require acid fracturing stimulation treatments to exploit them economically. In a horizontal well with a long openhole interval across a tight carbonate reservoir, multiple acid fracturing stages might be desirable, however this typically requires permanent completion devices to isolate discrete target intervals into specific stages. Multistage completions face many complications, such as hole-shape dependence, risk of communication between stages, completion deployment risks, and cost. A simplified completion technique was proposed to enable placement of multiple fractures along the openhole reservoir section without a complex completion. The main challenge in fracturing long openhole horizontal wellbores is limited or lack of control in positioning and orienting initiated fractures. One way to lower the fracturing pressure and force the hydraulic fracture to initiate at one or more desired target depths is to mechanically weaken the formation at specific points along the wellbore. An example of such a weak point is a cavity in the shape of a circular notch cut into the openhole wall. This technique was implemented in a multilateral horizontal water injector well drilled in a tight carbonate reservoir. Four circular notches were cut at predefined depths before stimulation with a goal of creating four separate fractures during one pumping operation. The volume of treating fluids required for the operation was significantly larger compared to a conventional acid fracturing job with only a single fracture propagating. To increase the effectiveness of stimulating all four intervals, degradable particulate diversion material was used during the treatment to temporarily isolate already stimulated fractures and divert treating fluids into less stimulated intervals. The stimulation treatment was successfully placed after the circular notches were created by coiled tubing using a rotational jetting tool with hydrochloric acid. As the primary result of the circular notching and acid fracturing stimulation, the injectivity index of this well increased almost four times. Temperature, caliper, production, and saturation logs were taken before and after fracturing to evaluate the applied completion approach. These measurements confirmed improved overall injectivity and highlighted areas for further improvements to the new technique, mainly related to preventing overstimulation of untargeted laterals in a multilateral well.