Chemical composition is a critical factor determining the performance of water-based drilling fluids. During drilling, the circulating fluid undergoes chemical changes due to additions of mud products at surface, interactions with drilled formations and losses of fluid in discharges and on drilled cuttings. Chemical changes due to interactions with drilled formations may degrade the performance of the drilling fluid. Rigsite tools to monitor chemical composition as well as functional properties are required for optimum maintenance of a fluid specification during drilling. A rigsite system to monitor and control the ionic composition of water-based drilling fluids is presented. The system consists of (i) a measurement component which provides frequent determinations of the ionic composition of the aqueous phase of the fluid during drilling and (ii) an interpretation component which includes software for calculation of filtrate density and water activity, an advisor tool for designing fluid treatments and a data storage and processing package for constructing chemical logs during drilling. The Measurement component has two units; a cross-flow filtration unit for rapid preparation of filtrate from representative samples of the fluid entering and exiting the wellbore during drilling and an ion chromatography unit for rapid and accurate analysis of filtrate composition. The ionic compositions of filtrates prepared using the cross-flow filtration unit and a standard API static filtration apparatus are compared. Further laboratory and pilot-scale tests involving controlled additions of inorganic salts to simple water-based drilling fluids simulate chemical changes in fluid composition and provide data with which to assess measurement accuracy and precision. The use of the Interpretation component for calculating water activity and as an advisor tool in designing treatments to control fluid composition is described. Results from field case studies emphasise the importance of chemical monitoring in an optimum drilling fluids engineering service. Correlations between the chemical composition and functional properties of water-based drilling fluids are discussed with particular reference to the effect of divalent cations on the efficiency of water-soluble polymers.

fax 01-972-952-9435. AbstractWater-based mud designs as alternatives to oil-based or synthetic-based muds are compared versus history of use. Water-soluble designs and water-insoluble designs are discussed as well as a combination approach used by Woodside Energy to drill on the Northwest Shelf, Offshore Australia. Perfornance of a water-based 2-phase polyglycol mud system containing a Drilling Enhancer with an appropriate bit design was technically and economically equivalent to that with a synthetic-based mud.

An increasing area of concern for offshore drilling practices is the environmental impact of discharged drilled cuttings contaminated with drilling fluids. The standard retort anal-ysis is of limited accuracy and chemical specificity. Anticipating future requirements for a more complete accounting of mud chemicals discharged to the environment, we present here results for chemical monitoring using a modern comprehensive chemical analysis technique, Fourier transform infrared (FT-IR) spectrometry. A description is given of sampling methods found to be practical and the main calibration requirements are discussed. The techniques developed in the course of this work give a good mineralogical breakdown of mud solids (commercial and drilled solids) in addition to the environmentally relevant measurements relating to mud on cuttings. The possibility of using the new technique for the rigsite monitoring of drilling cuttings is demonstrated. Cuttings samples simultaneously from the flow line, shaker screen, desilter and mud cleaner were analysed. It is found that mud polymers and other organic additives can be measured with sufficient accuracy to measure the removal of mud products by discharged cuttings. The technique is also applicable to quantify the losses of oil-based mud on cuttings. Field testing has shown that the instrumentation used is sufficiently robust and simple to use for rig-site application.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIt has been demonstrated that Expandable Sand Screen (ESS) technologies can be implemented rapidly and effectively without the requirement of a dedicated completion brine and well clean-up. This paper will discuss a case history of the Kikeh #4 deepwater well test, performed in Block K, offshore Sabah, Malaysia. The test was performed in 4500 WD, from Diamond Offshore's fifth generation semi-submersible rig, "Ocean Rover". Due to poor flow performance on the initial frac-packed completion, the decision was made to fast track this nonconventional approach to deepwater well test design. Key topics of discussion include: an integrated oil-based drill-in and completion fluid, expandable sand screen (ESS) selection, well test objectives, and well performance. Other points of discussion will include recommended practices and lessons learned using this completion technique. The completion and well test exceeded the objectives at a reduced cost and lower risk than conventional completion methods. As a result of the success of this methodology, it will be adopted for subsequent well tests in the area and is currently under consideration as the mainstay completion technique for the Kikeh development program.