New Aspects of Torque-and-Drag Modeling in Extended-Reach Wells
- Seyed Ahmad Ahmad Mirhajmohammadabadi (U. of Stavanger) | Mohammad Fazaelizadeh (U. of Calgary) | Eirik Kaarstad (U. of Stavanger) | Bernt Sigve Aadnoy (U. of Stavanger)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 19-22 September, Florence, Italy
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.14 Casing and Cementing, 1.1.3 Trajectory design, 1.6.1 Drilling Operation Management, 4.1.2 Separation and Treating, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.7.7 Cuttings Transport, 1.4 Drillstring Design, 1.10 Drilling Equipment, 1.4.3 Torque and drag analysis, 1.6 Drilling Operations, 4.1.5 Processing Equipment, 1.1 Well Planning
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The length and inclination of wells have increased significantly the past decades. The record horizontal departure today is about 11 km from the platform. Because of this evolution the number of offshore platforms to drain a field has been significantly reduced.
Excessive torque and drag can be critical limitations in extended-reach drilling (ERD). Torque and drag modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. It discusses how to use torque and drag calculations and measurements to plan long-reach well profiles, to execute drilling operations that minimize torque and drag effects, to monitor hole cleaning, and to plan jarring operations.
Torque and drag models have proven to be useful in all three stages of an extended reach well: planning, drilling and post-analysis. During planning phase the models are used to optimize the trajectory design to minimize the torque, drag and contact forces between drillstring and borehole wall. Used together with monitoring of hole conditions during drilling, T&D models are particularly useful in diagnosing hole cleaning problems, impending differential sticking, and severe doglegs as well as determining the possibility of reciprocating casing during cementing operations. In post-analysis the models help to determine true causes of hole problems that previously were unexplained or attributed to other factors such as mud weight, mud chemistry or problem shales.
In this study a general overview on most of the available literature on the subject is presented. Different models that have been developed for torque and drag predictions along with pros and cons of the models will be discussed and the validity will be checked by applying the model for one field case study from an ERD well in North Sea. The field case also demonstrates the challenges and importance of buoyancy effects and well path effects.
After producing more accessible oil reservoirs first, it becomes very important to drain these in an optimum way. The development of longer reach wells became very important not only to drain older fields more efficiently but also to reduce the number of offshore platforms on new development projects. [Aadnoy 1998]
There are number of causes for excessive torque and drag, including tight-hole conditions, sloughing shale, key seats, differential sticking, cuttings build-up caused by poor hole cleaning and sliding wellbore friction. Conversely, in wells with good hole conditions, the primary source of torque and drag is sliding friction [Johancsik 1984, Sheppard 1987, Lesage 1988].
Drag is defined as the incremental force required moving the pipe up or down in the hole; torque is the moment required to rotate the pipe. In wellbore applications because of drillstring contact with the wellbore wall the friction force is generated in opposite to movement of drillpipe. As a result it is a critical issue in long extended wells.
Torque and drag (T&D) modeling is required in well planning because it helps to predict and prevent drilling problems that might occur during the drilling process. Although T&D software has existed since the 1990s, some confusion still exists over the validity of the models that are used to characterize drilling operations, especially as we extend the length of modern horizontal wells.
The increased torque and drag could be due to ineffective hole cleaning, hole instability, differential sticking and solids in the mud system or the wellbore geometry. [Sheppard 1987, MacDonald 1987, Lesage 1988 and Brett 1989]
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