Improved Prediction of Shallow Sediment Fracturing for Offshore Applications
- Eirik Kaarstad (U. of Stavanger) | Bernt Sigve Aadnoy (U. of Stavanger)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2008
- Document Type
- Journal Paper
- 88 - 92
- 2008. Society of Petroleum Engineers
- 1.2.2 Geomechanics, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.1 Well Planning, 2.1.7 Deepwater Completions Design, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6.6 Directional Drilling, 3.3.2 Borehole Imaging and Wellbore Seismic, 1.7 Pressure Management, 1.6.3 Drilling Optimisation, 1.14 Casing and Cementing, 4.2.4 Risers
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- 535 since 2007
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The complexity of oil and gas wells has increased significantly during the past decades. In addition to improved equipment, a better understanding of the subsurface environment is required to efficiently drill these wells.
Fracturing, as related to circulation losses, is a continuous challenge when drilling these wells. For that reason two modeling activities have been pursued in Norway during the past decades: 1) establishing a fracturing model for shallow sediments offshore, and 2) developing a fracture model for deepwater drilling.
Data from seabed investigations as well as from conductor and surface casings were collected and normalized for varying water depths. This model works well and has been used for many years. When deepwater drilling started in 1997, the same concept was applied, and the results show that the same type of model also applies for deepwater drilling. Wells from Norway, UK, the Gulf of Mexico, Angola, and Brazil have been analyzed and show remarkably similar behavior when the water depth is considered.
This paper brings this work further by presenting a generalized fracture model for shallow sediments in relaxed depositional environments. Data normalization is a key method for making the fracture model applicable for all water depths. Normalization methods are presented so fracture data can be converted to other water depths and serve as a prognosis for new wells (based on rig floor elevation, water depth, differences in overburden stresses, and on mud properties).
Several field cases are presented with water depths ranging from 380 m to 1350 m, demonstrating the wide applicability of the new model.
It is shown that the generalized fracture model for shallow sediments provides a good correlation with an error within a few percent.
The shallow formations have not received much attention as compared to deeper formations. However, experience shows that both shallow gas and circulation losses are often challenges. In Norway, there has been an increased focus on both the design of the upper-casing strings and rock mechanics behavior of the less-consolidated sediments. Shallow sediments may exhibit properties similar to surface soils, resulting in (with deepwater wells in particular) an increased number of drilling problems. Some of these are weak top holes with low-fracture strength, borehole collapse, water flow into the borehole, cementing problems, riser problems, and shallow gas to mention a few. This paper addresses issues related to circulation losses and fracturing.
|File Size||464 KB||Number of Pages||5|
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