Unconventional Bradenhead Cementing in the Delaware Basin – Case History

Abstract

This Delaware Basin case history describes a bradenhead cementing method that improves zonal isolation and top of cement (TOC). Common solutions for cementing depleted formations include stage tools, low-density slurries and reverse circulation. For this bradenhead method, cement is pumped through the wellhead valves and down the annulus to a target loss zone. Field data, lab data and the engineering model support the improvement bradenhead cementing provides across depleted formations. The depleted Brushy Canyon formation serves as an injection interval for a two-stage bradenhead cement job. This approach isolates formations below the Brushy Canyon with a conventional first stage, while achieving TOC with the second stage pumped down the annulus. Fracture gradients of the injection interval and casing shoe constrain the cement design. To achieve adequate cement placement, the design phase includes the pressure calculations required to initiate flow and injection for the bradenhead stage. Reactive spacers are utilized to prevent annulus fluid level drop in extreme cases. A benchmarked cement bond log (CBL) quantifies the results and validates this unconventional cementing method. More than 50 two-stage bradenhead cement jobs were executed with a TOC success rate of 100% in intermediate and production hole applications. CBL data obtained after cementing the intermediate casing confirms the two-stage bradenhead as a placement method. In areas constrained by casing shoe pressures, CBL data identified potential areas of shallow injection. These data resulted in a modification of the fluids pumped. Use of these re-engineered fluids reduced injection initiation pressures and improved cement bonding across salt and anhydrite formations. Cementing costs were reduced by eliminating stage tools, annular casing packers, and low-density cement slurries. Pumping the bradenhead job offline (off the rig's critical path) reduces cost further. These features support bradenhead cementing as an effective solution for wellbore sections with a potential injection zone. The regulatory requirement to place cement above depleted formations resulted in many innovative cementing methods. Stage tools, low-density slurries, and reverse circulation are attempts to avoid formation breakdown, but these methods increase cost and have limited reliability and integrity. Bradenhead cementing takes advantage of the depleted interval to aid in cement placement. Although counterintuitive, bradenhead cementing has proved to be a cost-effective solution that improves zonal isolation and eliminates integrity risks associated with stage tool failures.