Method for determining a time window in which a casing pressure test can be performed without damaging a cement sheath
The present invention relates to a method for determining a time window in which a casing pressure test can be performed without damaging a cement sheath. The time window is determined by: determining the hydration degree of the cement at a given time for a considered pressure and temperature values in the well; and then comparing the determined hydration degree to a predetermined value. If the determined hydration degree is below the predetermined value, then the casing pressure test can be done without damaging the cement.
1. A method for determining a time window in which a casing pressure test can be performed without damaging a cement sheath, the method comprises:
determining a hydration degree of the cement at a given time for a considered pressure and temperature values in a well;
comparing the determined hydration degree and a predetermined value in an interval of 12%-30%;
if the determined hydration degree is below the predetermined value, determining that the casing pressure test can be done without damaging the cement sheath.
2. The method according to claim 1 , wherein the determination of the hydration degree comprises a monitoring of a heat flow of a cement sample, said cement sample having a composition similar to a composition of the cement, the cement sample being placed during the monitoring at a temperature equal to the temperature value and a pressure equal to the pressure value.
3. The method according to claim 1 , wherein the determination of the hydration degree comprises a monitoring of ultrasonic waves of a cement sample, said cement sample having a composition similar to a composition of the cement, the cement sample being placed during the monitoring at a temperature equal to the temperature value and a pressure that could be equal to the pressure value.
4. The method according to claim 1 , wherein the determination of the hydration degree comprises a monitoring of a mechanical response of a cement sample during cycles of constraints, said cement sample having a composition similar to a composition of the cement, the cement sample being placed during the monitoring at a temperature equal to the temperature value and a pressure that could be equal to the pressure value.
5. The method according to claim 1 , wherein the predetermined value is in an interval of 18%-20%.
6. A method for determining a time window in which a casing pressure test can be performed without damaging a cement sheath, the method comprises:
emitting waves in a cement sample,
monitoring, during a period of time, an evolution of the velocity of the waves in the cement sample;
determining a first time after starting the hydration of a cement sample corresponding to:
a maximum in the time derivative of the evolution of velocity during said period;
or an inflexion point in the evolution of velocity during said period;
if a second time after starting the hydration of a cement in the well is below a third time below the determined first time, determining that the casing pressure test is acceptable without damaging the cement sheath in a well.
7. A non-transitory computer readable storage medium, having stored thereon a computer program comprising program instructions, the computer program being loadable into a data-processing unit and adapted to cause the data-processing unit to carry out the steps of claim 1 when the computer program is run by the data-processing device.