The operation of oil and gas fields is associated with maintenance costs. If the fields are operated according to their technical condition and are classified as hazardous industrial, the industrial safety examination (ISE) extending the service terms will be costly. In this case, two time parameters are of special importance: the intended lifetime and residual life of objects, the values of which affect ISE amount performed during operation period. In the absence of relevant tests results or statistics on actual reliability, the life of the objects is usually assigned (for example, for economic reasons or similar to objects of the same type). As practice shows, the designated service life is much less than the actual reliability of objects - a gamma-percentage resource. Therefore, the assigned life time should be adjusted taking into account the actual reliability of objects.
Residual resource is determined according to the technical state of the structural support of objects.
For wells - this is a support consisting of casing and cement cases. If the support is considered as a multicomponent construction its resource is determined by the minimum of the values calculated for each element. Remaining life calculation of casing is correct, the actual strength parameters of string pipes are determined, the presence of strength reserve to operational loads is determined and the dominant damage mechanism is taken into account for the projected period of operation. When calculating the residual life of cement cases, such certainty is absent. The calculation is performed using indirect data and quality metering methods. The result does not reflect either the technical state of the cement case or its residual resource. And yet, this result can determine the residual well resource.
Statistical data on the technical condition for UGS wells testify to the absence of destruction of cement cases as a structural element.
The article examines the role of cement cases for operating life of wells taking into account such statistics. The author substantiates the proposition that operating life of wells should be associated with flow string period of service.
References
1. Bolotin V.V., Prognozirovanie resursa mashin i konstruktsiy (Forecasting the resource of machines and structures), Moscow: Mashinostroenie Publ., 1984, 321 p.
2. Bulatov A.I., Formirovanie i rabota tsementnogo kamnya v skvazhine (Formation and work of cement stone in the well), Moscow: Nedra Publ., 1990, 409 p.
3. Bulatov A.I., Novokhatskiy A.F., Rakhimov A.K., Korroziya tamponazhnykh shlakovykh tsementov (Corrosion of oil well slag cement), Tashkent: FAN Publ., 1986, 75 p.
4. Shamshin V.I., N.G. Fedorova, Dubenko V.E., Safe lifetime estimation of oil and gas wells operation (In Russ.), Stroitel'stvo neftyanykh i gazovykh skvazhin na sushe i na more, 2014, no. 3, pp. 30–32.
