EXPERIMENTAL STUDY ON OIL WELL CEMENT RESISTANCE TOWARDS HYDROCHCLORIC ACID ATTACK

Hydrochloric acid (HCI) and Hydrofluoric acid (HF) are used in acidizing
treatment to stimulate oil and gas production. It is proven that these acids had
successfully increased the oil well production worldwide. However, on the other hand,
it has been observed that several oil wells, after submitted to acidizing operations,
exhibited zonal intercommunication problems. This is attributed to the occurrence of
reactions between the hardened cement slurry in the annulus and the acid. The indication
of cement deterioration is the motivation of an extensive experimental program to study
the involved mechanisms.
The objectives of this study are to investigate the effect of curing temperature
and pressure towards the compressive strength and acid resistance towards Class G
oilwell cement. Various concentration of HCI solution is exposed to cement cube
samples under different curing condition for the analysis of samples of hardened cement
slurries (2-inch cement cube), aiming the verification of changes in chemical
compositions due to acid attack. Also, the tests are conducted on the analysis of the acid
solutions, aiming the identification and quantification of the elements liberated from the
cement into the acid solutions. The techniques of X-ray fluorescence (XRF) , Scanning
Electron Microscopy (SEM) and equipment compressive strength tester are to be used
for this purpose.
Based on the results, the depth of the acid attack and the influence of the acid
solution composition and of the cement chemical composition on the degree of acid
attack are to be evaluated. In previous study, it is observed that HCI will react with
calcium oxide forming calcium chloride and water. The higher the curing temperature
and pressure, the stronger the compressive strength of the sample of cement slurries,
leading to the stronger acid attack resistance.
This study will enable a better comprehension of the process of acid attack on
cement, and consequently a reduction of this problem in the field will be obtained.