The Niger delta sedimentary basin is a depositional complex of Cenozoic-aged sand and shales that extend from an approximate of longitude 3° to 9° east and latitude 4° 30' to 5° 20' north. This delta is characterized by progradation, rapid sedimentation, continual loading of sediments and gravity-driven syn-depositional deformations. Hydrocarbon exploration in the Niger delta started in 1937, mainly onshore. Exploration and production now extends offshore.
Given the enormous resources that go into drilling a well, the objective is to get it right the first time (especially when drilling high-angle and horizontal wells with their associated problems of true vertical depth uncertainty and resolution of surface seismic). In drainhole sections, geological uncertainty and production technology pushes geo-steering to the limits. Sometimes, these challenges put forward questions such as: is the reservoir faulted, compartmentalized, thin, undulating or show vertical lithological changes; how far from the roof must the trajectory be; what is the minimum required drain length; and how much dogleg is acceptable?
To achieve success in the reservoir navigation of any well, some success factors must be considered: the drilling strategy, available downhole tool (drilling system and formation evaluation), surface software, personnel and communication protocol. This paper examines these success factors using the example of Well-X. The goal is to bring more understanding to the procedures involved in reservoir navigation, the challenges posed by geology, the factors to consider when planning a modern geo-steering job, the importance of teamwork, the benefits of integrated interpretation and the value communication brings to the entire process.
Ndokwu, Chidi (Baker Hughes) | Okowi, Victor (Baker Hughes) | Foekema, Nico (Baker Hughes) | Caudroit, Jerome (Addax Petroleum Development) | Jefford, Leigh (Addax Petroleum Development) | Otevwe, Joseph (Addax Petroleum Development) | Fang, Xiaodong (Addax Petroleum Development) | Idris, Maaji (Addax Petroleum Development)
High-angle or horizontal wells pose many geological challenges that include maintaining well trajectory within a particular horizon in drain sections, detecting stratigraphic positions after passing a discontinuity, and subsurface feature identification. Geo-steering has shown increased value over the years because it uses data from different sources, including borehole imaging, to meet these challenges. Bulk density and gamma ray borehole images can be used to describe the near-wellbore environment, and that description can be analyzed further to explain the near-wellbore structural geology. In this study, structural analysis and zonation of bulk density and gamma ray images were used to detect the fault zone, while a geo-steering application was used to pick the true stratigraphic depth after crossing the fault. Provision of an alternative model to seismic-only interpretations and a better understanding of subsurface structures are the industrial benefits of this study. The Niger delta sedimentary basin of Southern Nigeria is a prograding depositional complex of Cenozoic-aged sand and shales that extends from about longitude 3 - 9 E and latitude 4 30' - 5 20' N. This paper demonstrates the importance of geo-steering, shows the application of geo-steering in a high-angle well drilled in the Niger delta sedimentary basin, and establishes the importance of structural analysis from borehole images in making final geo-steering interpretations. This paper also shows that borehole imaging is an additional and useful source of information in the planning stage of any drilling campaign.