Fiber Optics Improve Cement Performance and Drilling Cost in the Bakken

Abstract

Abstract The cement barrier represents the first line of defense to maintain well integrity on a multimillion-dollar asset, and an integral barrier for stage isolation for completion expenditures. The actual cement slurry design parameters are often based on historical precedent, trial and error, and simulation modeling but frequently have limited direct measured validation. What measurements have been completed, including wellbore static temperature measurements, are often known to be tens of degrees off from actual conditions. Cement placement effectiveness can be qualitatively evaluated via logging tools but is based on assumptions associated with the design and can be subjective based upon interpretation. This paper will present a monitored cement slurry as, it cures in real-time, on two wells in the Williston Basin, H4 and H5. The slurry designs were monitored via a fiber optic cable, pressure, and temperature gauges installed on the outside of casing. The pressure and temperature gauges were run concurrently with the fiber optic allowing further evaluation along the lateral during prejob circulation and the cementing operation. The fiber optic cable and gauges were primarily deployed for completion evaluation and drainage mapping. Taking advantage of this equipment enabled monitoring of the heat of hydration of the cement slurry, and the annular pathways via gauges, from pump down through final curing along the entire lateral length. The distributed temperature data provided visibility into the top of cement, curing temperatures, quality of circulation and curing behavior of the slurries. The observed Geothermal temperatures prior to cement placement were not consistent with previously reported temperatures via wireline or drill bit. The slurry design based on these temperatures responded to its actual downhole condition in a variety of surprising ways: (1) Slurry curing time was delayed beyond the heat of hydration predicted start time (2) heat of hydration of the slurry occurred at different depths along the lateral, possibly relieving hydrostatic pressure on the slurry column. The wellbore itself, in one case, was observed to still contain obstructions in the annulus preventing a consistent slurry placement in both wells. Adjustments to the design were necessary based on the data and implemented once observed. The implemented changes were cost neutral and significantly better results were observed in the fit for purpose, engineered cement slurry design. The specific observations from this case study are not unique. In the last three years several cement monitoring programs have been conducted with similar results indicating a systemic issue in the industry regarding cement design.