NANO CEMENT SLURRIES WITH ENHANCED STREGNTH FOR OILWELL CEMENTING

Cementing is among the important steps in the drilling and completion of an oilwell as it has the function of holding the steel casing in place by acting as the bonding agent between casing and the formation body. But upon certain types of reservoir, the formation fluid is under very high pressure, causing the fluid to flow at very high flow rate towards the well and promotes channeling of the fluid into the cementing job. This can cause the cement to crack and allowing uncontrolled flow of hydrocarbon liquid and gas into the wellbore. Besides that, the increase in downhole pressure and temperature causes stress on the cement sheath which later causes cement shrinkage and degrading. Therefore, nanosilica is introduced in cement slurries formulation to enhance the strength of the cement in order to withstand these abnormal conditions.
This paper focuses on investigating the effect of nanosilica on strength of cement cured under High Pressure and High Temperature (HPHT). An experiment was conducted to prove the effectiveness of nanosilica in increasing the compressive strength of cement. Four cement formulations with addition of different percentage of nanosilica were prepared before the start of the experiment. The percentages of nanosilica used were 0%, 0.5%, 1.0% and 2.0% by weight of cement used. No other additives were used in the cement. The materials were then mixed using a constant speed mixer and poured into the metal moulds. Two curing conditions were used for this experiment: 3000 psi with 120°C and 3000 psi with 60°C. Four cement slurries were prepared to be cured at respective conditions (total of 8 cement slurries). The prepared metal moulds were put into the curing chamber and were left to be cured for a total of 24 hours. The finished cement cubes were brought out of the chamber and left to dry at room condition for less than 1 hour. After that, the compressive strength of the cubes were tested using a manual compression tester. Each of the cubes was put into the tester, positioned at the centre of the compressor. The test was run and the compressive strength readings were recorded by computer. From the test, it was found that the cement cubes with higher nanosilica concentration gave higher compressive strength. This is due to the nanosilica particles filling up the space between cement particles thus, provide stability to the cement structure. Since 60°C is the lower temperature for cement curing, the compressive strength of the cubes cured at this temperature are much higher, showing the shrinkage effect experienced at 120°C.