An innovative approach for long term zonal isolation in HT/HP gas wells

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. In addition, stage tools are considered weak point and not good for long term seal. 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 (dolomite) formation in a single stage using a lower density cement based on hollow microspheres at 9.35 lb/gal. The objective of this work was to compare hollow microspheres cements to bentonite cement which are used in multistage cementing. The tests included shrinkage, compressive strength, porosity, gas and brine permeability. There are potential hole problems that are faced while drilling for the casing point in BJD. These problems such as water flow which might have H₂S require good cement durability to provide zonal isolation. The total vertical depth (TVD) of the casing point in BJD is ± 10,000 ft and the mud density is ±9.09 lb/gal. Testing conditions were temperature of 260 °F, crushing pressure of 5,000 psi, and confining pressure of 3000 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 1400 psi; neither shrinkage nor liquid permeability was observed during the three months of testing. The use of the hollow microspheres cement will help to bring cement to surface in one stage which will save time and cost to current drilling operations in Saudi Arabia.