Water-Gas Migration Control and Mechanical Properties Comparison With a Quick-Setting Slurry Design (QSSD) to Be Applied in a Production Cementing Job for Ecuador

摘要

A slurry design based on Sorel cement technology with a median particle size of 5 to 10 microns has been optimized without using Portland cement. This mechanically modified slurry with quick-setting technology is designed to withstand the operational changes that may play a crucial role in the performance of the cement sheath once the well is drilled, completed, and in production. Two additional mechanically modified slurries were designed using local Class "G" cement for comparison. The control of gas migration can be enhanced by obtaining a transition time value of less than 30 minutes. Transition time is defined as the length of time it takes for the static gel strength (SGS) to change from 100 lb/100 ft2 to 500 lb/100 ft2. The SGS tests were performed under simulated downhole pressure and temperature conditions. A value of 10 minutes for transition time was obtained. SGS tests were carried out with a static gel strength measuring device (SGSMD). It is important to mention that the zero gel time (ZGT), is defined as the amount of time the slurry can remain static after placement time and still transfer almost full hydrostatic-pressure from fluids before reaching an SGS of 100 lb/100 ft2; it can also be adjusted in regards to the cementing job. The mechanical properties of this quick-setting slurry design (QSSD) were comparable and in some aspects were improved. The results included a Young's modulus around 5E+05-psi, Poisson ratio of 0.23, and a tensile strength of 250-psi. The bottomhole circulating temperature (BHCT) was 172°F and bottomhole static temperature (BHST) at MD was 208°F. Cylindrical samples were cured at 208°F and 2,000-psi for seven days and were used for measurement of mechanical properties. This slurry design was developed for Ecuador to solve three major problems on production liners: 1. Water-gas migration throughout the annulus 2. Long waiting-on-cement time (WOC) to develop compressive strength 3. Improvement of the mechanical properties to minimize the effect of failure mechanisms on the cement (cracking, debonding, shear failure) that can result in poor cement bond logs and remedial cementing jobs