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Collaborating Authors
Jimenez Chavez, Maria
Abstract The subject field (Field NG) is one of the largest matured oil accumulations located in the South of Oman Salt Basin. Production and integrity issues have been the main challenge in recent years, manifesting in abnormal behavior of water-cut with time. Hence, detailed technical multidisciplinary studies were conducted in order to identify causes and propose mitigations. The base historical performance of the field showed water cut progression behaving as a matrix block, however, in recent years new wells started showing unexpectedly higher initial water production (fracture like behavior). A thorough investigation was carried out utilizing numerical simulation models calibrated to Field NG production history in order to characterize the type of rock behavior (matrix behavior, conductive streaks, fractures, faults, etc). The study concluded that the water cut behavior was due to naturally-occurring fractures which are limited in length and not vertically extensive. During the early stages of production, when the initial water-cut shows matrix like behavior, the bottom water is not in contact with the fracture network. However, after years of production and rise of the water table, the fracture behavior became dominant as the water gets in contact with the small vertical fractures. The presence of these fractures were confirmed by a total of 11 FMI data taken since 2015. The proposed solutions included detecting fractures early on using bore-hole imaging techniques and utilizing EZIPS in sealing as many fractures as possible. This completion method resulted in delayed water production and increased NPV by 2-3 $MM per well. Moreover, new and efficient WRFM technologies such as Autonomous Inflow Control Devices (AICDs) have been deployed in horizontal wells which selectively limit water flow. Initial results from the early implementations of AICDs are very encouraging.
- Asia > Middle East > Oman (0.72)
- North America > United States > Texas (0.54)
- Research Report > New Finding (0.66)
- Overview > Innovation (0.40)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.47)
- Geology > Sedimentary Geology (0.46)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (0.49)
- North America > Trinidad and Tobago > Trinidad > Southern Basin (0.99)
- Asia > Middle East > Oman > South Oman > South Oman Salt Basin > Al Khlata Formation (0.99)
- Asia > Middle East > Oman > Central Oman > South Oman Salt Basin > Nahr Umr Formation (0.94)
Abstract Water Shut-Off (WSO) actions are remedial activities that are being implemented in the heavy oil N Field, with the objective of reducing the water inflow of the well by closing zones which are major contributor to the high water cut. WSO are commonly executed as a mitigation action in operating wells with previous economic value. The purpose of this study is to develop a thorough knowledge of the rate of success of WSO activities linked to the time of WSO implementation, type of well (either horizontal or vertical) and the presence or lack of PLT (Production Log Test). Success was evaluated by reviewing the net oil production rate before and after WSO activity with the gained net oil rate being converted to US Dollars. There is no significant difference found in the success ratios between horizontal wells and verticals. However, in the horizontal wells, 74% of the successful ones were the heel shut-offs. WSO activities are found to have a success rate of 100% if the activity is implemented within the first year of the start of high water cut. Moreover, wells with WSO implementation within the first three years of observing high water-cut have a success rate of 65%. Noticeably, the success rate decreased dramatically with time, with wells having high water-cut for seven years and up to eleven years to the time of WSO implementation. These wells show success rates of 50% and 33% for seven and eleven years respectively. A numerical sector model and well model were created to explain these findings. During oil production because of a localized decrease in pressure, the water-oil interface may rise up and deform into a conical shape near the well. This phenomenon is known as ‘water coning’. At the time of water breakthrough, the cone is observed to be narrower than more advanced stages when the water cut has risen to higher levels. At these times, the cone has broadened and, depending on spacing between adjacent wells, has lifted the overall level of the oil/water interface, decreasing the distance between the wellbore and the water. As a result, water shutoff becomes less effective with time. It is recommended to start WSO activities on wells within the first three years of high water-cut indications. In case there is no PLT or other data, heel shutoff for the horizontal wells have a better success rate.