Use of Concrete Technology for High-Density Cement Systems in South Texas

摘要

Historically cementing the deep high-pressure, hightemperature (HPHT) gas wells in South Texas has oftenexceeded the capabilities of existing technology. The highdensitymud systems and narrow margin between pore andfracture gradients require efficient mud removal and stableslurries with low equivalent circulating densities, and effectivegas migration control, especially when cementing 'slim hole'completions. The high bottom hole temperatures along withthe use of long liners where the static temperature at the top ofliner (TOL) is often less than the bottom hole circulatingtemperature (BHCT) place additional requirements on theslurry designs to ensure early compressive strength at the TOL.A liquid concrete slurry system based on optimizingthe packing volume fraction (PVF) of the dry blend usingsized inert particles provides a cost-effective solution tocementing these HPHT wells. Using the concept of liquidconcrete technology, slurry properties are a function of the dryblend rather than additives. Adjusting the particle sizedistribution enables the density, compressive strength andrheological properties of the slurry to be tailored for specificwell conditions. While the use of inert particles reduces theconcentration of cement additives by 50% making it possibleto have extended pump times while ensuring rapidcompressive strength development at the TOL when using aninorganic 'set control' additive.By optimizing the PVF of the dry blend thepermeability and porosity of the set cement are reduced due toimproved particle packing. This makes it possible to provide acost-effective solution to annular gas migration control.High-density concrete slurries from 17 PPG to 23PPG have been utilized to successfully cement HPHT gaswells with bottom hole circulating temperatures in excess of400 0F. These slurries exhibit low rheologies, fast earlycompressive strength development and effective gas migrationcontrol.This paper outlines the development and applicationof high-density liquid concrete slurries and their application incementing HPHT gas wells.