Historically cementing the deep high-pressure, high temperature (HPHT) gas wells in South Texas has often exceeded the capabilities of existing technology. The high-density mud systems and narrow margin between pore and fracture gradients require efficient mud removal and stable slurries with low equivalent circulating densities, and effective gas migration control, especially when cementing ‘slim hole’ completions. The high bottom hole temperatures along with the use of long liners where the static temperature at the top of liner (TOL) is often less than the bottom hole circulating temperature (BHCT) place additional requirements on the slurry designs to ensure early compressive strength development at the TOL.

A liquid concrete slurry system based on optimizing the packing volume fraction (PVF) of the dry blend using sized inert particles provides a cost-effective solution to cementing these HPHT wells. Using the concept of liquid concrete technology, slurry properties are a function of the dry blend rather than additives. Adjusting the particle size distribution enables the density, compressive strength and rheological properties of the slurry to be tailored for specific well conditions. The use of inert particles reduces the concentration of cement additives by approximately 50% making it possible to have extended pump times while ensuring rapid compressive strength development at the TOL when using an inorganic ‘set control’ additive.

By optimizing the PVF of the dry blend the permeability and porosity of the set cement are reduced due to improved particle packing. This makes it possible to provide a cost-effective solution to annular gas migration control.

High-density concrete slurries from 16.5 PPG to 23.0 PPG have been utilized to successfully cement HPHT gas wells with bottom hole circulating temperatures in excess of 400 °F. These slurries exhibit low rheologies, fast early compressive strength development and effective gas migration control.

This paper outlines the development and application of high-density liquid concrete slurries and their utilization in cementing HPHT gas wells in South Texas.

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