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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling in the Qiongdongnan Basin, offshore China's Hainan Island Province, has often resulted in failure to reach desired objectives.Bottomhole temperatures up to 475°F, and pressures requiring mud weights up to 19.5 lbm/gal equivalent, place severe limitations on the performance of drilling fluids and often contribute in failure to reach the desired drilling objectives.Well Yacheng 21-1-4 was drilled in this basin with the COSDC semi-submersible rig Nanhai V and was spudded on 27 th November 1998. TD of 5,250 meters was attained on 20 th May 1999 where the bottomhole static temperature was 414°F and the pore pressure was 18.5 lbm/gal equivalent. Logs were run to bottom without incident with no significant drilling fluid related problems and the primary drilling objectives achieved. The success is attributed to innovative, fit-for-purpose drilling fluids and rigorous pre-well planning over a 2-year period prior to the well commencing.The paper describes the holistic approach to drilling fluid engineering for extreme well conditions. The development of innovative drilling fluids specific to these well conditions, and the rigorous laboratory testing necessary to generate detailed engineering guidelines, are described. Large-scale abrasion and pressure tests were also conducted. Modifications made to the rig design facilitated the management of drilling fluid properties at high density with high flow line temperatures. A portable drilling fluids laboratory, staffed with trained technicians, was installed on the rig to continually pilot test drilling fluid samples and treatments under simulated downhole conditions. The importance of good communications and global technical support networks proved invaluable during the pre-well planning and for the execution phase of extreme high temperature and high pressure wells drilling.

This paper presents the results and implications of a research project* to study, under controlled laboratory conditions, the influence of oil based mud physical properties and chemical composition on the quantity of oil retained on cuttings. Substrates, representing common rock types drilled, were exposed to different oil mud formulations in which one variable was altered as far as possible independently of other properties. The most influential parameters were found to include the use of strong oil wetting agents such as amidoamines and imidazolines (which promote oil imbibition), the percent oil in the formulation and the water activity imbalance between formation and oil mud. Less influential, but nevertheless an important consideration for oil mud formulation, is the effect of plastic viscosity and intermediate oil wetting surfactants.Mud weight and HTHP fluid loss have a minor effect.

Increasing environmental constraints on the use of oil-based drilling fluids have prompted close cooperation between operators and service companies to maintain the technical performance of drilling fluids while reducing oil discharge. This paper describes how Amerada Hess Ltd. (AHL) and IntI. Drilling Fluids Ltd. (IDF) cooperated by extending laboratory developments into controlled field trials and how feedback from the field has allowed rapid progress toward performance and ecological goals. We achieved success through two developments. First, as a result of a jointly funded research project, we developed a novel, oil-free, highly inhibitive water-based drilling fluid. The inhibition offered by this fluid approaches that offered by oil-based fluids. Second, we developed invert-emulsion and direct-emulsion fluids with low oil/water ratios for low oil-on-cuttings applications. The cooperative process improved the technical performance of these fluids demonstrably and reduced the oil on cuttings.

Heat-transfer rates are reported for turbulent free convection in a finite-length horizontal pipe containing sodium. Heat is added at one end and removed at the other. A generalized equation which correlates the data is proposed giving the ratio of heat transfer with turbulent convection to that on pure conduction in terms of the L/D ratio, Prandtl number, Grashof number, and Reynolds number. The solution is extended to inclined pipe with one or both ends open to plenums.