An Expandable Slotted Tubing, Fibre-Cement Wellbore Lining System (1996)

R.B. Stewart, SPE, Shell International Exploration and Production, D.S. Gill,* Shell International Exploration and Production, W.C.M. Lohbeck, Shell International Exploration and Production and M.N. Baaijens, SPE, Shell UK Exploration and Production Ltd. Abstract An expandable slotted tubing (EST), fibre-cement wellbore lining system has been developed. Its purpose is to temporary secure the integrity of a wellbore section in order to allow drilling operations to continue through deeper over pressured or depleted zones. The lining is installed below the previous casing with no or minimal reduction in hole diameter. The technology makes it possible to realise major reductions in well costs by avoiding the use of certain intermediate and contingency casing strings. It also helps in HP/HT well designs where the requirement for additional casing strings may become excessive. The paper outlines the technologies involved and installation/evaluation procedures. Details are given of onshore and offshore field trials in Europe and USA. Introduction Existing technology requires that we drill and complete wells in a telescopic fashion with successively smaller casings/liners and completion components being set at successively greater depths. As a consequence, large diameter top and intermediate holes have to be drilled and cased to allow relatively small diameter production casings and tubings to be run and installed. This is a wasteful process and a number of developments are in progress throughout the oil industry to make well designs more diameter efficient. Ideally we would like to drill wells with one hole size from top to bottom and line them with one size of casing. Alternative Borehole Linings (ABLs) are one step towards helping us to achieve this goal. The ABL system reported in this paper was developed to replace selected intermediate casing strings and to do so without reducing the diameter of the wellbore. The section of the wellbore to be lined is underreamed and a steel reinforced, fibre-cement wellbore lining placed in the overgauge hole. The lining is designed to be able to withstand 1000 psi pressure differentials between the borehole and the formation, in either direction, and to be sufficiently robust to maintain this capability whilst drilling deeper formations. Reasons for development The business drive for this development was two fold - Reduction in well cost.–Removal of deep HP/HT well design limitations. The penalty for incorporating a contingency casing string in a well design is high and is not just the cost of the extra casing. All borehole sections and casings above the "contingency casing section" have to be one size larger just in case the contingency casing is required. Most of these cost penalties are incurred irrespective of whether the contingency casing is used or not. Larger holes may take longer to drill and may involve more drilling trouble time. In offshore locations, larger risers may be required for the larger casings and larger platforms for the larger risers. There is therefore a strong cost incentive to be able to design a wellbore in such a way that no provision need be made in the design for contingency casing installation. If the need arises, an ABL could be installed instead and no diameter reduction penalty paid. P. 133