DensCRETE

When working on high-pressure, high-temperature (HPHT) wells, the fewerunplanned events there are, the smootherthe operation runs. An ideal cement system offers simple, robust design, lower viscosity, and the ability to easilyincrease slurry density on location.

An ideal systemDensCRETE* cementing slurry system produces high-density cements—normallyup to 2,876 kg/m3 [24 lbm/galUS]—with low,constant viscosity. Because of higher com-pressive strength (CS) and lower permeability,DensCRETE slurries outperform conventional-density slurries to isolate high-pressurezones for the life of the well. The primaryapplications for DensCRETE technology

include high-pressure primary cementingoperations, well control plugs, and whipstockplugs. DensCRETE slurries have an opera-tional temperature range of 38 to 232 degC[100 to 450 degF].

High-performance solutionHigh-pressure drilling can require suddenadjustments in mud weight. With DensCRETEtechnology, increase the slurry density by120 kg/m3 [1 lbm/galUS] on location, just asquickly as at the blending plant. DensCRETEeliminates reblending and saves remote and offshore operations time and money.The DensCRETE system offers a high-densitycementing alternative with higher performancethan conventional heavyweight systems.

Applications

� HPHT primary cementing operations

� Well control and whipstock plugs� Heavyweight slurry applications

Benefits

� Easier slurry placement in narrow fracture-pressure and pore-pressure margins

� Reduced risks associated withlong waiting-on-cement times

� Faster, easier, and more robustHPHT cementing designs

Features

� Stable systems at high temperatures without special additives

� Lower additive concentrationrequirement

� Resistance to mud contamination� Continuous mixing of high-

density cements � Greater fluid density differentials

achievable with high-densitydrilling fluids

DensCRETE systems offer better security and flexibility in high-pressure cementing operations.With DensCRETE designs, the slurry density can be increased without reblending the bulk powder.

The answer to HPHT cementing challenges

Case study—TexasIn a well in northeastern Texas, the client was preparing to perform a primary cementing job at 2,347 m[7,700 ft]. The job challenge was thatthe well had an overpressured zoneand a low fracture gradient zone atthe same interval to be cemented.Additionally, the drilling mud used wasan oil-based fluid with density increasedto 2,181 kg/m3 [18.2 lbm/galUS] to maintain well control across theoverpressured zone.

The DensCRETE cement slurrysystem was selected to address thechallenges because it offered a highand stable density, mixed at 2,253 kg/m3

[18.8 lbm/galUS]. It was coupledwith CemNET* advanced cementfibers to mitigate the risk of lossesacross the low-pressure zone. Thedesign also used GASBLOK* gas con-trol additive to minimize gas migra-tion during the cement setting phase.

To avoid contamination betweenthe DensCRETE cement slurry andthe oil-based mud during the job place-ment, a spacer system was designedto act as a buffer. The designedspacer density was 2,205 kg/m3

[18.4 lbm/galUS]. WELLCLEAN II*software was used to optimize themud removal design.

The DensCRETE cement slurrywas placed with no losses occurringduring the operation. The cementevaluation logs indicated a goodcement bond across the entirecemented section, which provided therequired zonal isolation.

1917

Slurry density, lbm/galUS

GASBLOKconcentration,

galUS/bbl

12

10

8

6

4

2

0

DensCRETE slurries

Standard slurries

Adjustable density rangeDesign density

16 17 18

Slurry density, lbm/galUS

19 20

DensCRETE slurry density can be adjusted by 120 kg/m3 [1 lbm/galUS] on location, allowing flexibilityfor last-minute adjustments.

DensCRETE slurries require lower concentrations of additives, such as GASBLOK gas migration control, than standard cements at equal density, reducing their cost and making them more environmentally friendly.

www.slb.com/oilfield05-CE-015 December 2005*Mark of SchlumbergerCopyright © 2005 Schlumberger. All rights reserved.Produced by Schlumberger Marketing Communications