Successfully Replacing Oil-Based Drilling Fluids With Water-Based Drilling Fluids: Case Study Demonstrates Value of Extensive Planning and Execution in an Extended-Reach Well
- R. Stawaisz (Britannia Operating Ltd.) | S. Taylor (Britannia Operating Ltd.) | T. Hemphill (Shell Intl. E&P Inc.) | U. Tare (Shell Intl. E&P Inc.) | K. Morton (Chevron Petroleum Technology Co.) | T. Valentine (Flowco Integrated Drilling & Environmental Services Co. Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2003
- Document Type
- Journal Paper
- 332 - 338
- 2003. Society of Petroleum Engineers
- 1.1.3 Trajectory design, 4.3.4 Scale, 2.1.7 Deepwater Completions Design, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.6.1 Drilling Operation Management, 1.1 Well Planning, 1.11.4 Solids Control, 1.10 Drilling Equipment, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 5.1.8 Seismic Modelling, 1.2.3 Rock properties, 4.1.9 Tanks and storage systems, 4.1.2 Separation and Treating, 4.3.1 Hydrates, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc)
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An extended-reach well was planned and successfully drilled with a water-based drilling fluid in an area where wells historically have been drilled with mineral oil- and ester-based drilling fluids - the North Sea central Graben. The high cost of cuttings drilled with inverts that must be shipped to shore for processing and disposal coupled with the potential shutdown of drilling operations in times of bad weather (when cuttings could not be transferred from the rig to supply vessels) led the operator to revisit the use of water-based drilling fluids, especially in the large-diameter hole section in which large amounts of cuttings are generated. However, many water-based systems have been used in the central Graben with little success. The need to develop a stable, shale-inhibiting, waterbased mud (WBM) system capable of performing well in extended- reach drilling (ERD) applications was identified. Extensive prewell modeling of wellbore stability in problematic shale zones and of hole cleaning in the large-diameter interval contributed to the success of this challenging project. This article discusses the planning, preparation, and successful drilling of the intermediate interval with a water-based drilling fluid
The drilling program for this development well called for the intermediate hole interval to be drilled from the 20-in. casing shoe at ±3,500 ft measured depth (MD) [±3,400 ft true vertical depth (TVD)] to a total depth (TD) of ±8,900 ft MD (±7,600 ft TVD) with a final hole angle of 63°. A schematic of the planned well path is found in Fig. 1.
This paper discusses the planning, preparation, and drilling of the intermediate hole interval for Well B-17 with a water-based drilling fluid. Several types of water-based systems have been used previously with little success. Developing a stable, shale-inhibiting WBM system was necessary because there would be a significant quantity of cuttings generated in the large-diameter interval. Because of the specific well plan, the success of achieving the objective would be dependent upon setting the 13three eighth piece fraction-in. casing at the end of the build section. This would allow the target productive zone to be drilled at the optimum angle of attack, as predicted by wellbore-stability modeling.
Well Design and Planning
The well discussed in this paper was drilled as an extended-reach, platform, development well. Wellbore-stability issues were raised in both the interval containing the kickoff point and in the following one containing the tangent section. Information pertinent to both intervals is presented in this paper. Only in the large-diameter interval immediately under the 20-in. casing were hole-cleaning and hydraulics issues considered particularly demanding. Hence, the hydraulic issues raised in this paper are pertinent only to the large-diameter interval. After kicking off in this interval, the angle was planned to build quickly to 40° and was held there until near the end of the interval, when hole deviation was planned to increase to 65° from vertical.
The choice of a suitable water-based drilling-fluid system for this ERD application was based on:
Shale inhibition and formation analysis.
Hole-cleaning efficiency (HCE).
Shale Inhibition and Analysis.
Mineral oil-based drilling fluids traditionally have provided the most inhibition in this area. The challenge was to design a water-based drilling-fluid system with performance near that of the mineral oil-based drilling fluids. The shales encountered in the central Graben area of the North Sea are some of the most chemically reactive found in any drilling area; they contain high percentages of mixed-layer illite/smectite clays, which are prone to swelling and dispersion and can lead to diminished control of mud rheological properties. Laboratory work on shale samples from a nearby well included X-ray analysis, cation exchange capacity (CEC), and exchangeable cations characterization; testing verified their high chemical reactivity.
The dielectric constant measurement (DCM) technique1 was also used to identify and quantify the risk associated with hydratable and reactive formations as encountered in the Hordaland group. A DCM analysis was performed on (unwashed) cuttings from the 17.5-in. hole interval of Well B-15, previously drilled with mineral oil-based drilling fluid. The DCM provides a quantitative determination of rock properties by measuring the specific surface area per unit weight (m2/g), thus representing the total hydratable surface area of a cuttings sample. The DCM is dominated by the presence of smectite and also is strongly influenced by other hydratable clays, the presence of which can be correlated with specific surface areas, as shown in Table 1. The measured results in Fig. 2 clearly show that the DCM increases from a base of 250 m2/g at the 20-in. casing shoe to a maximum of 580 m2/g at 7,500 ft TVD in the Alba and Lothian formations. For drillingfluid- optimization purposes, the DCM results showed where the most reactive shales would be encountered and at what point increased fluid-inhibition properties would be required.
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