|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Abstract Drilling in the Azerbaijan sector of Caspian Sea is very challenging and numerous drilling hazards must be overcome to successfully evaluate all exploration objectives. These challenges include numerous shallow hazards, complex pressure regimes, low fracture gradient, highly charged shallow water sands, reservoir sands that exhibit a pressure regression and the need to drill very deep to evaluate the geologic objectives. A comprehensive well plan was developed to address these drilling challenges and hazards. The well plan had to address a rapidly increasing pore pressure relative to the fracture gradient and had to honor the resultant narrow drilling mud weight window. The plan called for setting 7 casing strings to allow drilling to the target depth. The plan also incorporated the first use of a "Big Bore" subsea wellhead system in the Caspian to accommodate these multiple casing strings. The Nakhchivan #1 well was safely drilled to an Azerbaijan offshore depth record of 6746 m in 185 days. All exploration objectives were extensively evaluated and the well abandoned. Non-productive time was minimized though flawless execution of the well plan. This paper will describe potential surface and subsurface hazards in the region, the well plan that was developed to mitigate these hazards and summarize the operations that led to the drilling successes. Introduction First, safety is always the most important objective. If we cannot do a job safely, we will not do it. Safety was the top priority on this project. Second, drilling in the deep water of the Caspian Sea is as challenging as anywhere ExxonMobil drills in the world. Challenges here include:numerous shallow hazards complex pressure regimes where the fracture gradient is relatively low as compared to the pore pressure of the formations different pore pressure profiles exist across a structure highly charged shallow water sands pressure regression in the reservoir sands the need to drill very deep to evaluate the well objectives Third, these challenges and drilling hazards can be mitigated through the development of a comprehensive well plan and the flawless execution of that plan at the well site. And fourth, the key to any successful operation is the multi-functional team that works the project. Safety and Environmental Performance In the area of safety and environmental performance, a job-site safety plan was used (which includes the rig and service contractors' safety systems and ExxonMobil's safety philosophy) to achieve excellent results. ExxonMobil's safety philosophy is that all work can be done with no one getting hurt and that no work will be done until a safe way can be found to accomplish it. The Nakhchivan team suffered no lost time incidents in the 185 operating days required to drill and evaluate the well. In fact, there were only two minor injuries while drilling. These results were the direct result of the outstanding participation of the workers involved. Everyone wanted to work safely. Each worker is responsible for his or her own safety as well as the safety of their coworkers. The crews quickly and easily integrated their existing safe working practices with ExxonMobil's safety beliefs and programs where each person has the responsibility to stop the job if he or she feels that it is not being done safely. There were also no spills, environmental incidents or regulatory incidents during the drilling operations.
Abstract Seafloor and sub-seafloor interpretive maps derived from broad-band 3D Short-Offset seismic augmented with 2D High-Resolution seismic and seabed piston core data were utilized to assess potential hazards and constraints to mobile drilling operations over the Nakhchivan block, offshore Azerbaijan. The Nakhchivan block is located along the shelf break and upper slope environment of the Azerbaijan sector of the South Caspian Sea. Water depth ranges from 70 to 788 meters across a northwest trending ridge that is the seafloor expression of a subsurface anticline. A flat-topped mud volcano complex and associated mudflow deposits occur along the anticlinal crest within a large depression bound on three sides by steep high-relief slump scarps and rotated blocks. The depression opens to the east into a large sea valley bound on both sides by slump scarps. Surface mudflows trend seaward through this valley on the eastern flank of the anticline. Gravity cores acquired within the mud volcano complex and surface mudflows recovered liquid to very soft black to grey muds. Geochemical analyses revealed anomalous concentrations of methane in all these cores. A linear compressional anticline, trending from northwest-southwest to north-south, dominates the shallow structure. The axis of the structure, a complex fault graben, is truncated by a mud volcano. Immediately north of the mud volcano, a northwest to northeast trending radial fault pattern, aligned with the anticlinal axis, forms numerous narrow horst and graben structures. Four mapped horizons illustrate the subsurface structure and morphology. The latest Pleistocene Lower Khvalynian horizon is an unconformity that separates muds and minor sands above from interbedded clays, silty-clays, sands, and mudflow breccia below. The late Pleistocene intra-Lower Khazarian horizon is a transgressive surface that overlies a sequence of clays, thin sands, and mudflow breccia. The middle Pleistocene Apsheron horizon is an unconformity that overlies a sequence of thick clays, shales, and thin interbedded and basal channel-fill sands. The Akchagyl horizon, at the Plio-Pleistocene boundary, overlies thick clays, shales, interbedded and channel-fill sands, evaporites, and bioclastic carbonates. Sediments within the underlying upper Surakhany Series consist of interbedded shales, thin sands, and evaporites. Rapid structural growth, associated seismicity and mud volcanism that was initiated at the onset of Apsheron time continues to the present. During early Apsheron time mud volcanism exploited the faulted axial crest of the anticline to form a mud lake and associated mud cones at the seafloor. Subsequent periods of mud volcano eruption, fault movement, and seismicity precipitated the formation of large slump blocks and surface slides. These processes formed the seafloor caldera observed today. Seafloor mudflows, active slumps and slides represent potential foundation hazards. Structural and stratigraphic gas traps occur along the updip flanks of the anticline throughout the latest Tertiary and Quaternary section. Overpressured aquifers associated with interbedded sands and evaporites occur within the Akchagyl and Surakhany Series. Shallow overpressured water and gas sands represent a potential well-control hazard. Introduction The interpretive results of a mobile drilling rig site investigation on the SOCAR and ExxonMobil Nakhchivan exploration block are presented.