Determination of casing string burst pressure when offshore well drilling

Abstract

The purpose of the article is to focus on the value of the casing string burst pressure under drilling for oil and gas on the shelf and offshore. When drilling offshore casing strings are subjected to additional stress in comparison with drilling on the land. The lack of allowance for the features of offshore drilling can lead to complications and even accidents. The repair of casing strings at underwater well mouth involving several auxiliary vessels and repair equipment is very complicated and costly. The complexity of repair works in the North and the Far East of the Russian Federation is aggravated by severe and ice conditions in the most part of the year. There is practically no information on this problem in the domestic literature. The author has performed a refined analytical calculation of the casing string burst pressure at the underwater position of the well mouth. For casing string burst pressure determination, it is proposed to make corrections for the depth of the shelf (sea) and the height of the rotor table above the average level of the shelf (sea) surface. This is especially important when drilling in deepwater where the pressure of sea water increases significantly. The article presents the derived empirical formula for determining the magnitude of the fall in the choke line when the choke is put into operation. Knowing the hydraulic losses in the choke line, it is possible to correct the annular pressure in the casing string by the value of pressure drop. The refined calculation of the casing string burst pressure under drilling on the shelf (offshore) by an analytical method is an important task, since it gives the real value of pressure, which will enable to prevent possible complications and accidents.