Improving Performance in Elgin HPHT Infill Drilling Despite Increasing Challenges

M. Alahmad, Oliver Eatough
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引用次数: 5

Abstract

Following the significant reservoir depletion on Elgin / Franklin fields since 2007, drilling infill wells was considered to not only be high cost but also carry a high probability of failure to reach the well objective. The recent campaign on the Elgin field, one of the most heavily depleted reservoirs worldwide, demonstrated that infill drilling can be achieved safely while improving performance. Drilling of HPHT infill wells on the Elgin field faced increasing challenges arising from the reduction of reservoir pressure that changed the stresses in the formations above and influenced the overall pressure regime. This stress reorganization in the overburden has affected the fracture network in these formations resulting in reduction in Fracture Initiation Pressure (FIP) and increase of gas levels. Challenges were faced during the drilling of three wells in the 2015-2017 campaign. Loss events in Chalk formations in the intermediate sections significantly decreased the already Narrow Mud Weight Window (NMWW). A strategy to define and validate the minimum required MWW in 12-1/2" and 8-1/2" sections was developed following a complex subsurface well control event. Managed Pressure Drilling (MPD) technique was extensively used to safely manage gas levels and assess pore pressure. Reservoir entry with more than 850 bar of overbalance remains the main challenge in infill drilling. A total loss event during first reservoir entry in the latest campaign confirmed the limitations of wellbore strengthening mud and stress caging materials available today. Lessons learned from each well in this campaign were implemented to address these challenges and improve performance. This paper describes the Elgin HP/HT infill drilling experience and the specific techniques and practices that were developed to address these challenges and improve performance. The importance of Equivalent Circulating Density (ECD) management with very narrow MWW, successful high gas level management with MPD and depleted reservoir entry, shows that even in a highly complex environment, drilling performance can be improved allowing for further economical development drilling. The successful and safe delivery of the Elgin 2015-2017 infill drilling campaign demonstrates this at a time the industry moves toward unlocking the reserves of more challenging HPHT fields.
在挑战日益增加的情况下,提高Elgin高温高压钻井的性能
自2007年以来,Elgin / Franklin油田的油藏大量枯竭,钻井填充井不仅成本高,而且很有可能无法达到钻井目标。最近在Elgin油田(世界上最严重的枯竭油藏之一)的活动表明,在提高性能的同时,可以安全实现填充钻井。由于储层压力降低,改变了上述地层的应力,并影响了整体压力状态,因此在Elgin油田进行高温高压井的钻探面临越来越大的挑战。上覆岩的这种应力重组影响了这些地层的裂缝网络,导致裂缝起裂压力(FIP)降低,含气量增加。在2015-2017年的钻井过程中,三口井面临着挑战。白垩地层中间段的漏失事件显著降低了本已很窄的泥浆比重窗口(NMWW)。在一次复杂的地下井控事件之后,开发了一种策略来确定和验证12-1/2”和8-1/2”段所需的最小MWW。控压钻井(MPD)技术被广泛用于安全管理气体水平和评估孔隙压力。超过850巴过平衡的储层进入仍然是充填钻井的主要挑战。在最近的一次作业中,第一次进入储层时发生了全漏失事件,这证实了目前可用的井筒强化泥浆和应力保持材料的局限性。为了应对这些挑战,提高作业效率,作业人员从每口井中吸取了经验教训。本文介绍了Elgin的高温高压钻井经验,以及为解决这些挑战和提高性能而开发的具体技术和实践。等效循环密度(ECD)管理(MWW非常窄)、MPD成功的高含气量管理和耗尽储层入口的重要性表明,即使在高度复杂的环境中,钻井性能也可以得到改善,从而进一步实现经济开发钻井。Elgin 2015-2017年的成功和安全的钻井作业证明了这一点,同时该行业正朝着开发更具挑战性的高温高压油田的储量迈进。
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