Improved Bond Logs on Intermediate Casing in North Dakota
Intermediate casings in the Williston Basin pose unique challenges to providing a quality cement bond log. Top of cement across the Dakota (a permeable, gas producing formation) is required. There are multiple salts, sands and shales, including the depleted Mission Canyon and over pressured Bakken and Three Forks formations. The drilling fluid is typically oil based to prevent washout of the salts. The casing is landed at 90 degrees, in either the Bakken or one of the Three Forks benches. These formations are high pressured, and produce gas and oil, which can lead to higher potential post placement annular fluid influx risk.
In order to combat the challenges, ALTCem designed a fluids system package specific to the basin. The first key to the fluid package was ALTCem’s CD Spacer – OBM, a spacer system rheologically optimized to the drilling fluid properties. Utilizing ALTCem’s patent-pending liquid additive system, the spacer was pumped with surfactants and solvents designed and tested to provide maximum water wetting capabilities. By utilizing the liquid additive system, foaming and pump cavitation are avoided, as well as the need for a batch mixer on location, reducing cost and rig-up time.
The lead cement plays a critical role in the cement column. It must be lightweight to prevent fracturing of lower zones, while still having a quick transition time with good fluid loss to prevent gas migration. ALTCem designed a 12 ppg system with pre and post set expansion characteristics, along with low fluid loss, and modified gel strength. The lead cement was also designed to fit the rheological hierarchy between the spacer and the tail cement.
The tail cement was designed to have high compressive strengths, low fluid loss, and low dynamic settling to protect the casing from mobile salts along with ensuring an excellent bond in the deviated portion of the well and across the Mission Canyon. A blend of loss circulation materials (varying in particle size) were employed to prevent whole fluid leak-off. ABX-30, an aggressive pre-set expansion agent, was utilized to combat any potential post placement annular fluid influx, and improve bond.
Utilizing CEMRPO+ cement modeling software, the ALTCem team was able to optimize job pump rates, to ensure optimal hole cleaning while minimizing ECD’s across zones with low fracture gradients, ultimately providing an excellent bond and top of cement as desired.
When the operator switched from their traditional cement company to ALTCem, they experienced substantially better bonds logs, and tops of cement above design, allowing for reduced excess and cost. Bond logs from the same pad indicated the ALTCem design provided superior bonding and enhanced zonal isolation drastically reducing the possibility of an expensive remedial job.
Bond Logs on Intermediate Casing Across the Mission Canyon
Competitor Bond Log
ALTCem Bond Log on Offset Well