Cement bond logs were compared to downhole pressure and temperature gauges to understand the relationship between cement bond quality and communication between stages during horizontal fracture stimulation in a tight sand formation.
Fracturing was performed using a coiled-tubing-conveyed packer and sleeve system inside cemented casing. Pressure and temperature were recorded above and below the packer to measure communication between stages. In three wells, ultrasonic imaging tool (USIT) logs were run prior to stimulation to analyze cement bonding 360° along the lateral. USIT log evaluation, gamma ray logs and recorded pressure and temperature data were evaluated to determine the correlation between cement bond and stage isolation.
In one well, the bond log showed no cement bond in approximately half the lateral. With no other form of isolation behind pipe, communication between stages would be expected. There was virtually no communication, however, between stages according to the pressure and temperature gauge data. In the other two wells, the bond log showed excellent bond quality, but communication was seen on the bottom-hole pressure/temperature gauge during several fracturing stages. These counterintuitive results initiated further evaluation. Gamma ray logs were compared to the pressure and temperature data to determine if there was a stronger correlation between stage communication and rock quality. Other qualities of the frac design were also investigated. The results indicated that rock quality in combination with stage spacing have more of an impact on stage communication than cement bond quality. These findings have since been used to determine optimal stage spacing and to support a shift from cemented to open-hole completions.