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.
The Benchamas Development in the Gulf of Thailand is an oil play in a predominantly gas-condensate region. This development is unique in that the operator has significant oil reserves of high pour-point crude in several zones. Some zones have gas caps; others don't. Column heights are variable. The project is being developed as a waterflood with horizontal and monobore producers and injectors. The initial phase of horizontal producers were completed with sand exclusion capability, consisting of multilayerd sintered screens. This has so far proved to be effective. The Benchamas Waterflood project is comprised of eight stacked, compartmentalized, sandstone reservoirs. These sandstones are fluvial channels and are discontinuous. The waterflood is designed to maintain oil viscosity and gas cap location to maximize recovery. The economic impact of this waterflood is estimated to increase the recovery from an estimated 12–18% (primary) to 25–35% (secondary) of the OOIP. During the design stage of the waterflood project, simulation indicated that some horizontal injector wells would be required to enable the required injection rates. Three horizontal injectors were therefore planned. The drilling, completion, and clean up of these wells presented the Benchamas Asset Team with a series of unique challenges. Rock mechanics analysis was conducted in the decision process to address the need or lack of need for sand control. Results will be discussed. Drilling fluid and flow back aspects of the wells were carefully examined in order to avoid some of the problems of horizontal injectors drilled in other parts of the world by the company. An extensive literature search revealed that the laboratory work required to adequately address the issues comprehensively had not been done. The company and the fluids vendor collaborated to conduct the laboratory tests that were required to determine the correct combination of fluids and clean up procedures necessary to successfully install these wells. This paper will highlight the unique design challenges presented to the Asset Team, discuss the efforts that were undertaken to address these challenges and the results, and present the field results of the drilling, completion, clean up, and final injection results. Introduction The Benchamas Field is one of several fields located in the B8/32 Concession in the Gulf of Thailand. The concession is located some 180 kilometers to the South of Rayong and some 80 kilometers east of Koh Samui (figure 1). The Benchamas Field was discovered in 1995 by the concession partnership with the Benchamas 1 well. The Benchamas Production License Agreement was issued in June 1997. The Benchamas field covers 411 sq. km. and operates with 3 wellhead platforms, a processing platform, a quarters platform, and an FSO (figures 2&3). Production was initiated in June 1999. Production capacity was 25000 bbls per day oil and 180 MMSCF per day sales gas. Capacity has been increased to 40,000 bbls per day. Plans are underway to increase liquid production capacity to 75000 bbls per day. The field is uncharacteristic in the Gulf of Thailand in that it has several sizable oil zones in this predominately gas region. The Oil Reservoirs are in the BWA and BWB platform areas. The third and southernmost platfrom, BWC, is primarily gas and condensate. The field consists of multiple stacked zones of Miocene age sediments. The depositional environment is fluvial braided river channels. The depositional environment has resulted in a very heterogeneous set of reservoir packages.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn October 1999 Chevron assumed operatorship of Block B8/32 in the Gulf of Thailand. The continuing slimhole drilling program involves monobore production, horizontal production, horizontal injection and exploration wells, all of which typically have 2D or 3D well paths. Consequently, due to its inherent lubricity and hole stability, IEM (Invert Emulsion Mud) is used for drilling all 6 1 / 8 " reservoir hole intervals. Over the first several months of operatorship it became apparent that the UK DTI (United Kingdom Department of Trade and Industry) method used to measure the mass of cuttings and retained fluids discharged with the cuttings was inaccurate. Mass balances of fluid and materials consumed on various wells indicated the calculated IEM and base fluid discharge figures were notably less than that actually discharged.As part of the TFM (Total Fluids Management) process, an in-house program was initiated to accurately measure the mass of cuttings and retained fluids discharged with cuttings. The testing methodology, calculations and reporting format were developed over a period of 12 months during which time over 30 wells were drilled with a single rig. To date, results from slimhole drilling operations indicate that the method currently used by the industry throughout much of the world, generally in compliance with government regulations, significantly underestimates the mass of cuttings and commercial solids discharged to the environment.
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