The Application Of Attributes Derived From High Resolution Seismic Data In Horizontal Drilling — A Case Study From Shuaiba Formation West Kuwai

摘要

In the Minagish field, the Shuaiba formation has very low porosity and permeability, However, the presence of shrinkage cracks, joints and fractures make it ideal disposal zones. Karsts feature south east of the Minagish structure, containing an abundance of fractures and dissolution channels, have been identified for disposal. Karsts are formed by the passage of meteoric water through the carbonate rock and dissolved the rock as it passed. In the areas with significant dissolution, the formation has collapsed due to weight of overburden, creating areas of massive fracture and faulting. The karsts area have been successfully targeted with 2 horizontal wells drilled within last three years, with disposal capacity of 30000 to 40000 bw/day per well. Seismic attributes are one of the most routine technologies applied in geosciences interpretation and analysis of 3D seismic data, contain incredibly rich information in terms of amplitudes, frequency, geometry and texture. Since seismic attributes are sensitive to spatial variations in subsurface, these can acts as guide for horizontal wells specially in complex and unpredictable area. The Coherency Cube quantifies the measurement of local waveform similarity. Since it provides spatial change in the seismic waveform hence it can be related to sub surface features like Geometry of the subsurface reflectors, Faults, Pinchouts , Unconformities, changes in lithology, Changes in pore fluid density, Changes in elastic properties as well as depositional environments. In present case study seismic attributes specially coherency along with other data was applied to identify the shale dominated area and limestone formation near collapsed feature. The horizontal well targeted fractured limestone near the edge of collapsed feature. The drilling data was correlated with seismic attributes to identify the shale dominated area and Shuiaba limestone near the collapsed feature. It was observed that Shuiaba limestone was severely eroded inside the collapsed feature and filled with overlying base Burgan shales and silts. With this information well was side tracked toward the limestone formation and completed with its objectives. By correlating the seismic attributes with real time drilling data, more accurate information about the spatial variation in the vicinity of well is available. In case of drilling complications these information are very useful to find out best possible trajectory for side track as done in this Shuaiba disposal well. Hence seismic attributes can be applied not only for identifying the location but also for providing support during horizontal drilling. Above technique can also be applied in planning the different legs of multilateral well.