Axial Resistance of Drill & Grouted Well Conductors in Deepwater Clays Based on Operational Experience

Abstract

Abstract Typical deepwater wells in soft clay sites employ jet pipes as the well foundations, i.e., the jetted conductors. The jetting process during the installation of the conductors causes disturbance to the surrounding soil rendering the low axial capacity of the jetted conductors. An alternative well foundation to the jetted conductors is the drill & grouted (D&G) well conductors, in which case an enlarged hole will be drilled first and then the steel pipe is installed with cement pumped to the annulus to grout the soil and the steel. D&G well conductors have been successfully deployed in the deepwater Brazil Basins. The excellent field performance leads to the further refinement of the axial capacity model for D&G conductors. The objectives of this paper are (i) to calibrate the axial resistance model of D&G well conductors in deepwater soft clays based on field operations mainly in Brazilian pre-salt area, and (ii) to propose a new axial resistance model for D&G well conductors in deepwater clays for industry use. In this paper, information on 10 deepwater subsea wells was collected including the site-specific soil data, well schematics, and loading estimation on wells. Each of the 10 wells was analyzed and the maximum loading on the wellhead was compared to the theoretically predicted conductor axial resistance. Then a Monte Carlo simulation based on Bayesian updating technique was developed to calibrate the axial capacity model for D&G well conductors based on the field performance. This finding, supported by operational experience, can not only lead to cost-effective D&G conductors design, but also contribute to international industry guideline developments for D&G conductors design.