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HIGH TEMPERATURE TESTING PROCEDURE

STIM-LAB Inc. in Duncan, Oklahoma, has recently evaluated Liquid Casing® under simulated field conditions. The study used a kill-fluid formulation where Liquid Casing® was incorporated into a polymer based formulation.

 

The test was carried out with equipment designed to evaluate formation damage under dynamic flow conditions of the fluid. The test fluid was in contact with a sandstone core, with an effective permeability of about 250 md at 250 °F, with laboratory processed North Sea seawater. The core was mounted in a Hassler sleeve under a closing pressure of 1,500 psi. The test fluid flowed past the face of the core with a differential pressure of 1,100 psi across the length of the core. The filtrate was collected in a pressurized container with 100 psi back pressure so the actual pressure drop across the core was 1,000 psi. Both the fluid and the core is heated to the required temperature. The filtrate volume was also determined as a function of time in ml / min.

 

The polymer based kill-fluid was formulated with 15 ppb of Liquid Casing®, 3 ppb of Xanthan gum polymer, and 8 ppb of modified starch. The fluid and core were heated in a series of stages on temperatures ranging from 200 to 350 °F, during different time frames in order to determine the dynamic fluid loss.

 

The test results are summarized in the following table:

Conditions Stage 1 Stage 2 Stage 3 Stage 4
Temperature 200 °F 250 °F 300 °F 350 °F
Time at temperature 4 hrs 4 hrs 5 hrs 1 hr
Dynamic Fluid Loss ml/min 0.01 0.01 0.01 0.4

These results show that the fluid rapidly forms a seal at 1,000 psi and drastically lowers the fluid lost to the formation. It can be concluded that the fluid was effective at temperatures up to 300 °F and displayed no signs of degradation. As the temperature was increased to above 310 °F, there was some indication of deterioration in performance,.  However, a seal was maintained as material, which had been stored at the elevated temperature, moved onto the filter face, although the dynamic fluid loss had increased.

 

At the end of the analysis, the core was cooled to 250 °F and it was back flowed with seawater at a differential pressure of only 1.3 psi, resulting in 92% permeability regain.

 

These laboratory tests established that Liquid Casing® would be effective in a polymer based fluid at temperatures above 350 °F, and that the filter cake can be easily removed by back flowing the well at very low pressures and with minimum damage.

 

The test results confirm the field experience and observation established by a number of operators.

 

It is worth noting that the temperature parameters in this study were limited by the thermal stability of the biopolymers.  The NAPC in the Kavala offshore area in northern Greece has used Liquid Casing® to kill wells with high levels of hydrogen sulfide and bottom hole temperatures of 290 °F.

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