Reservoir navigation is a common and integrated part of the drilling process to steer wells very precisely. It is a requirement for many of today's complex deviated and horizontal development wells steered through challenging and small geological targets that can be as small as two metres in size. The capability is a key enabler for the oil industry and has contributed significantly to the prolongation of the economic well being of most oil producing provinces around the world. In order to be successful, reservoir navigation must combine advanced downhole logging while drilling (LWD) tools, telemetry of LWD data to surface in real-time, the ability to steer while drilling, fit-for purpose software applications and perhaps most important of all, skilled personnel. That said, it is currently common practice for reservoir navigation to be performed with a dataset that is restricted to a vertical ‘curtain’ section derived from the development well. This is an unnecessary restriction that is often self imposed because of the limitations of the software applications being employed. With improving computer power, it can and should be superceded in favour of a more holistic approach. The new reservoir navigation analytical processes are all designed to be performed at speed and in real-time while drilling the reservoir, on demand, at any stage, within minutes. These enhancements quantitatively illuminate the critical financial consequences of a well's geological drilling results. These are usually greater than the economic benefits of more efficient well operations. It means well owners can now operate in an information rich environment leading to better multi-disciplined team work and improved operational decision making. The benefit is better wells that produce more hydrocarbons at lower cost. A real data set comparing a pre-well 3D model with realistic real-time geological updates and visualisations in three dimensions demonstrates the validity of the method. The pre-well and real-time 3D models can also be utilized to generate quantitative volumetrics calculations while drilling. The workflows provide an information rich environment for operational decision making leading to better wells.
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.
Oil and gas drilling has fully embraced the practice of drilling horizontal and extended-reach wells in place of deviated wells to avoid multi-platform drilling and increase hydrocarbon recovery. However, the producer is still faced with multiple challenges that include lateral facies change, lateral variation in reservoir properties and structural uncertainties. Consequently, it is paramount that continuous advancement is achieved in combining fit-for-purpose, real-time logging-while-drilling (LWD) solutions to assist further in the enhancement of hydrocarbon recovery. Reservoir navigation services (RNS) involve predicting the geology ahead of the bit to place the wellbore correctly in the zone of interest in a horizontal or near-horizontal path. LWD data, obtained from downhole drilling suites, transmitted in real time through mud pulses to a surface computer where the data are interpreted and used to steer the well in the desired direction. Formation pressure while drilling (FPWD) is a process of acquiring reservoir pressures downhole and this is done with a specialized downhole LWD pressure-testing tool. The use of RNS in Well-MX played a significant role in the drilling project – landing Well-MX in the targeted M reservoir bed and drilling the lateral section. The major geosteering technologies used are the at-bit resistivity and azimuthal propagation resistivity, which provides geostopping capability, reservoir bed boundary mapping and accurate distance to bed boundary calculation. These technologies helped in keeping the wellbore within the hydrocarborn unit of the M reservoir. Performing formation pressure testing in realtime, the team was able to carry out a reservoir gradient analysis which helped with reservoir fluid identification, fluid contact determination, and connectivity of hydrocarbon zones before drilling was concluded. Well-MX is a horizontal well located in the Mirum field of the Niger Delta Basin, offshore Nigeria. The well was drilled to target the deep multi-lobed M reservoir to a total hole depth of 11,307ft MD. By using Well-MX as a case study, this paper discusses how the combination of reservoir navigation service and real-time formation pressure sampling helped meet drilling objectives for this well. Some of the challenges encountered includes vertical seismic interpretation uncertainty, poor reservoir quality along the drain hole section, change in depth of oil to water contact and undulating bed boundaries. Other challenges and decisions taken to successfully geosteer the well will be reviewed in this paper.
Today's complex and challenging reservoirs are now accessible using state-of-the-art technology in drilling and logging-while-drilling (LWD). The drive for advanced, capable technologies to explore the full production potential of these reserves cannot be overemphasized. In addition to the drive for increased production from existing fields, there is an increased focus on precisely placed horizontal wells in the best part of the reservoirs. The drilling is carried out by using the existing well stock and employing re-entry techniques. The dramatic adjustment in the crude oil price has made cost-effective drilling and geosteering solutions increasingly critical for delivering efficient, economic wells. Reservoir navigation services involve predicting the geology ahead of the bit to optimize the placement and drilling of a horizontal wellbore in a complex reservoir. These predictions are based on formation evaluation data gathered while drilling using deep-reading azimuthal resistivity LWD tools and innovative interpretation techniques to update the geologic model in real time. Adjustments to the well trajectory based on the updated geologic model are enabled by downhole systems that have good directional control and use continuous proportional steering technology to steer the bit. Well QH is a 3D complex well located in the Adanga Field of the Niger Delta Basin, offshore Nigeria. The well is drilled to a total hole depth of 9,512 ft MD. The Q reservoir is shallow, at approximately 3,600 ft true vertical depth (TVD), and it required complex 3D well planning to precisely land and drill a horizontal well in the thin, intercalated sand and shale sequence. There are other directional challenges inherent in a brown field development when drilling from a complex multiple slot platforms with existing producing and suspended wells. This paper discusses the well QH as a case study, showcasing how reservoir navigation services with fit-for-purpose LWD data can result in increased net lateral production in a complex, thin multilayered reservoir. The case study highlights how the uncertainties encountered during planning stage and challenges in the execution stage were turned into a success story. This paper also discuss the application of well placement through advanced, user-friendly software, grounded on the state-of–the-art LWD and rotary steerable technology and their significant impact on the project, challenges and lessons learned.
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.
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