Design, Construction, and Optimisation of Big-Bore Gas Wells in a Giant Offshore Field

Abstract

An extensive big bore gas well drilling and completions program is in progress to develop the giant North Field, offshore Qatar. Benefits of the big-bore concept, compared to the prior 7-in. monobore design, include reduced development costs by requiring fewer wells, and deferred installation of compression by providing higher flowing wellhead pressures. This is the widest known application of a big bore design in one single field and involves a large number of wells. Many of these wells are drilled and completed to date and believed to be among the world's most prolific gas producers. These are also the first offshore wells to incorporate big bore well design for large-scale field development and feature industry advances in equipment design and manufacture. An extensive system of detailed design review, equipment performance testing, and quality programs has been implemented to meet challenging project requirements for well reliability. The wells feature a tapered tubing design known as the "Optimized Big Bore" (OBB). This paper discusses the challenges of planning and executing these OBB wells. It reviews the initial OBB well design, anticipated North Field drilling challenges, critical equipment specifications, and design revisions resulting from optimisation efforts over the past four years. Introduction Discovered in 1971, the North Field of Qatar is the world's largest non-associated gas field, extending over 6,000 km2, and contains approximately 900 TCF of abnormally pressured natural gas. Development has taken place in several stages, commencing with initial production by Qatar Petroleum in 1991 to supply the domestic gas market. This was followed in the mid-to-late 1990s by RasGas Company Limited (RasGas) and other projects to provide LNG to export markets. More recently, the growth in global LNG demand has sparked much more extensive development. RasGas is responsible for the development of a large area of the North Field, covering more than 500 Km2, to provide natural gas supply for both new LNG trains and the growing domestic gas market. The RasGas expansion plan requires a large number of wells to be drilled in the period 2002 to 2010 from several new wellhead platforms. Production is from the massive Khuff carbonate formation, which includes several productive intervals (K1, K2, K3, and K4), situated at approximately 10,000 ft TVD. This would differ from the earlier projects of the 1990's that developed only a part of the Khuff reservoir. In total, RasGas will operate more than 90 wells producing a total of 8 Bscfd. Well deliverability from the K1 to K4 reservoirs is very high due to both formation quality, near initial reservoir pressure, and high net pay thickness. Non-hydrocarbon gas composition varies between the four Khuff intervals within each well and also across the field. Well designs evolved from packer / tubing completions intended to produce at 60 MMscfd in the initial Qatar Petroleum project, to high-rate 7-in. monobore wells in the first LNG projects able to deliver in excess of 100 MMscfd.1 However, it was recognized by RasGas and its major shareholders Qatar Petroleum and the former Mobil Oil (now ExxonMobil) that higher capacity well designs, capable of producing in excess of 150 MMscfd, could be suitable for the planned RasGas expansion projects. Although individual wells would be more expensive to construct, there were two significant advantages that would result in a more cost effective project. These would be:

Design, Qualification, QAQC and Operational Performance of Completion Fluid, Reservoir Drill-in Fluid and Breaker - Tamar, Offshore Israel

“…The primary scope of the study was to review existing developments to understand field proven designs. The study focused on a global review 2,3,4,5,6,7,8,9,10,11,12,13,14,15,18 of ultra-high rate gas wells which included nine (9) areas and over 130 wells. 16 This study, combined with the experiential knowledge of the team, resulted in a design that integrated the field proven lower…”

Analysis of the shear failure of surface methane capture boreholes for improving the drainage period efficiency: A lithological perspective

“…To reduce the probability of borehole failure, previous studies on borehole failure mainly focused on the evaluation of drilling design, including borehole construction and trajectory, casing material and drilling fluid, generally assumed that rock materials are isotropic and linear elastic in deformability and strength (Bradely, 1979;Kiran et al, 2017), and extended the analysis of the homogeneous or anisotropic strength (Ajalloeian and Lashkaripour, 2000;Lee et al, 2012;Mohammed et al, 2019;Pe´rie´, 1990;Tien et al, 2006) and geostress of the lithology (Song, 1998;Yan et al, 2017). The chemical-mechanical or physical-mechanical interactions between drilling fluids and clay minerals as well as groundwater also affect drilling damage (Haimson and Song, 1993;Liang et al, 2015;Zeynali, 2012), but these effects may be applied to improve drilling methods and maximize the effectiveness of drilling (Bennion et al, 1996;Clancey et al, 2007).…”

Analysis of Shear Failure of Surface Methane Capture Boreholes for Improving Efficient Drainage Period–A Lithology Perspective

“…For example, 12 of 22 SBCMs in the Huainan coal field ceased to produce gas as a result of borehole failure, adversely affecting the extraction efficiency [6]. To reduce the probability of borehole failure, previous researches on borehole failure mainly focused on evaluating drilling design, including the well construction and trajectory, casing material, drilling fluid and typically assuming that the rock material is isotropic, linear elastic and homogeneous in deformability and strength [7][8][9], and extending analyses to anisotropic strength of lithology [10][11][12][13] and geostress [14][15][16].Borehole failure is also influenced by the chemical-mechanical or physical-mechanical interactions between clay minerals and drilling fluids as well as groundwater [17,18], but these effects may be applied to improve drilling methods and maximize the effectiveness of drilling [19][20][21].…”