Abstract
Cementing a string in one stage is a challenging task, especially in the presence of weak formations. Cement slurry losses during placement is highly possible if the equivalent circulating density (ECD) exceeds 11 lb/gal during placement. A conventional method to overcome this challenge is to use multi-stage cementing by setting the stage tool above the loss circulation zone. However, field data indicate that the tool can fail, thus causing serious delay and economic loss. A second method for zonal isolation is to use low density cement.
In this study, we considered cementing the intermediate and production casings in HP/HT BJD formation (dolomite) in a single stage using low density cement that was based on hollow microspheres at 9.35 lb/gal. The objective of this work was to compare hollow microspheres cements to bentonite cements, which are used in multistage cementing. The tests included shrinkage, compressive strength, porosity, gas, and brine permeability. There are potential hole problems that were faced while drilling for the casing point in BJD. These problems included water flow, which might contain H2S. This problem will require good cement durability to provide zonal isolation.
The total vertical depth (TVD) of the casing point in BJD was ± 10,000 ft and the mud density was ± 9.09 lb/gal. Testing conditions were temperature of 260°F, crushing pressure of 5,000 psi, and a confining pressure of 3,000 psi. No work was done before to investigate hollow microspheres cements at these conditions. The testing was performed in Saudi Aramco facilities to improve current cementing practices in oil and gas fields.
Data generated during three months supported the use of the hollow microspheres to cement casings at the conditions tested. The compressive strength did not change significantly with an average of 1,400 psi; neither shrinkage nor liquid permeability did change during the testing period.
This paper will discuss case histories that include job design, execution, and evaluation of the low density cement system. Field treatments were conducted without encountering any operational problems. The treatments were successful, which confirmed lab data.
