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Abstract The forces and stresses along a casing string are modelled using a stiff string torque and drag model. A post analysis of casing loads and stresses, considering wellbore tortuosity and centralisation is performed in addition to the effect of 3D orientated casing wear. A post analysis case study is presented to show the resulting effect on axial, burst, collapse and VME safety factor as well as VME body and connection design envelopes. While running in hole (RIH) a tubular, the industry standard is to assume a smooth wellbore when performing a torque and drag calculation. The drilling process can cause significant local doglegs and ultimately increase the tortuosity of the wellbore. When applying a soft-string torque and drag model, it is possible that the stiffness, radial clearance, and high frequency surveys are not directly considered. The stiff string torque and drag and buckling model can model these effects, as well as the addition of rigid and flexible centralisers. This study involves the comparison of different casing design load cases, using the actual tortuosity of a drilled wellbore considering a 3D orientated casing wear. The results show that there can be noticeable differences in overall axial stress with the addition of tortuosity. The stiff string model can directly calculate the additional bending stresses experienced by the tubular and this additional stress can be particularly prevalent while RIH casing with centralisers and high tortuosity. The reduction in API and VME stress envelope is also quantified using a 3D orientated casing wear model. A better understanding of axial stress state reduces risk of well integrity issues and can pinpoint areas along the casing in which special care must be taken during well intervention. This paper will show the benefits of using a stiff string torque and drag model during casing design. Highly tortuous wellbores, especially ERD and HPHT wells, may exhibit stresses that are vastly different than assumed during preplanning phase. The design API/VME envelope may also be reduced due to casing wear.
- Well Drilling > Drillstring Design > Torque and drag analysis (1.00)
- Well Drilling > Casing and Cementing > Casing design (1.00)
Abstract Casing integrity is extremely important to downhole zonal isolation and preventing well instability. The reduction of casing strength not only occurs in directional drilling, but is also observed in vertical drilling with a slight deviation angle. Deteriorated casing in most hydrocarbon wells is reported from the onset of casing wear by the presence of friction force during the rotation of drillpipe. The friction on the casing wall causes the reduction of casing strength. Furthermore, the combination of corrosive drilling fluids with the rotation of drillpipe could dramatically degrade the casing strength. Although casing burst and collapse strength have been emphasized by many researchers, little research has presented the mechanical response of the worn casing. The studies that do exist on casing wear are not relevant for field applications because they do not consider the effects of high temperature and the surrounding formation. Therefore, it is urgent to obtain a proper stress profile of worn casing in order to reveal the true downhole information. Based on the boundary superposition principle, we propose an analytical solution for the worn casing model that accounts for the contribution of thermal stress. We focus on the stress evolution in worn casing from the effects of high temperature and the confining formation. The predicted results show that the higher thermal loads largely increase the stress concentration of the worn casing, subsequently weakening the casing strength. The finite element solutions indicate that the radial stress in worn casing is not impacted as much as the hoop stress. The remaining part of the worn casing is subject to compression failure, along with an increase of the burst pressure or the elevated temperature.
1. Abstract Extended Reach Drilling (ERD) is increasingly becoming the means of expanding production of aging oil fields. With ERD also come problems associated with high drilling torque and excessive casing wear. This paper addresses the issues of casing wear protection and drill string torque reduction with the use of Non-rotating Drill Pipe Protectors (NRDPP). The design principle of operation, and operational limitations of NRDPP are discussed. Analysis methods for placement and typical applications are discussed. Analysis results typically include the determination of contact loads of the drill string to the casing and application of loading criterion based on design performance. Placement recommendations limit the side wall contact loads to an experimentally determined criterion for safe NRDPP operation. Four operational experiences are discussed to allow comparison of various types of applications and field problems. Operational experiences include cases in Alaska, Gulf of Mexico, North Sea and New Zealand. Other related considerations associated with the use of NRDPP include drill string vibration and hot hole environments. This report concludes that properly placed NRDPP can substantially reduce drill string torque by 10-30% and that casing wear is prevented where the protectors are applied. 2. Introduction ERD is critical for optimizing development of many fields in the North Sea. the Gulf of Mexico, Alaska, and other locations throughout the world. ERD is increasingly important because it offers the potential of reduction of location footprint or platform size, access to restricted areas, and greater utilization of existing facilities. These benefits result in lower cost. However, ERD also imposes additional technical problems. Teel discusses technologies for successful ERD wells. These problems include drill string capacity and BHA design, bore hole stability, hole cleaning, solids control, casing placement as well as high drill string torque and increased casing wear. High drill string torque and excessive casing wear are frequently serious problems in ERD wells. High drill string torque can threaten well completion by exceeding the capacity of Top Drive systems or drill string. Casing wear can necessitate the use of casing patches, liners, and entire casing string replacements. These procedures increase well completion times and costs. One approach to reducing drill string torque and preventing excessive casing wear is the use of Non-Rotating Drill Pipe Protectors (NRDPP). For example in the Bass Strait, NRDPPs were used successfully as part of the changes implemented to reduce torque and prevent casing wear. Over the last six years NRDPPs have been used successfully in hundreds of ERD wells world wide for torque reduction and casing wear prevention. 3. Purpose This effort examines the use of Non-Rotating Drill Pipe Protectors in Extended Reach Drilling specifically with respect to torque reduction and casing wear prevention and related considerations. P. 161
- North America > United States > Alaska (0.56)
- Europe > United Kingdom > North Sea (0.46)
- Europe > Norway > North Sea (0.46)
- (3 more...)
- Well Drilling > Drillstring Design > Drill pipe selection (1.00)
- Well Drilling > Casing and Cementing > Casing design (1.00)
Abstract Casing wear by drillstring results in a thinner portion of casing wall and a reduction on casing burst strength (the ability to hold internal pressure). How to estimate the reduced casing burst strength on such a "crescent-worn" casing has been an important issue in oil and gas industry, as it is directly related to how to safely design casing strings. A common approach is to estimate the reduction of casing burst strength of such worn casing from API burst strength equation with a linear reduction by the remaining wall thickness or the wear percentage, equivalent to a "uniform-worn" casing model, despite a question on whether such a linear reduction of casing burst strength is over-conservative and may result in a higher casing cost. This paper presents a further study on hoop stress and deformation of such a "crescent-worn" casing and discusses the reduction of casing burst strength. The hoop stress in the thinner portion of such a "crescent-worn" casing is found close to that from a "uniform-worn" casing, when local bending in the thinner portion of "crescent-worn" casing is ignored. The reduction of burst strength of casing worn by drillstring may still be estimated from casing yield or rupture burst strength with a linear reduction by wear percentage for sweet service well conditions, while more and non-linear reduction of burst strength of casing worn by drillstring may be needed for sour service well conditions, to prevent an "earlier" casing burst on sulfide stress cracking. Introduction Casing wear by drillstring is an increasing problem for drilling deep wells and/or extended-reach wells. Such casing wear develops from a long time exposure of the casing to a rotating drillstring in the drilling process, with large contact forces between drillstring and casing when casing is bent (Fig. 1), which results from setting casing in a dogleg well section or due to casing buckling under large axial compressive load. The casing burst strength (the ability to hold internal pressure) will be reduced due to the wear of casing. The more wear on casing the more reduction on casing burst strength. A hole could even be worn out on a casing string resulting in a total casing failure. Figure 2 shows the measured and predicted casing wear on the top 2500 m of 13 3/8" casing installed at 2508 meters MD at an inclination of 68 degrees in Gullfaks Well A-42 at North Sea.2 Casing wear was measured by an ultrasonic imager log and the maximum wear was indicated about 35% of the casing nominal wall thickness at 480 meters MD. The casing wear was due to drilling and back-reaming the next open hole to 5334 MD, with high drillstring tension load and casing dogleg severity of 2.9 degree per 30 m. The reduction of casing burst strength on such worn casing needs to be correctly estimated in order to do a safe casing design, as well as to decide whether an additional casing needs to be set to cover a worn casing before further drilling operations. Although there have been some studies on modeling worn casing burst strength,3, 4 a common approach is still to use API burst strength with a linear reduction by the remaining wall thickness or the wear percentage, despite a question on whether the linear reduction on worn casing burst strength is over-conservative and may result in a higher casing cost. This paper is to present a further study on this issue and discuss the reduced casing burst strength on such worn casing.
- North America > United States (1.00)
- Europe > United Kingdom > North Sea (0.24)
- Europe > Norway > North Sea (0.24)
- (2 more...)
Abstract This case study presents the challenges faced and learning curve built while achieving longer departures with light / slim casing design instead of conventional / heavier design in shallow coastal water field in UAE. This paper intends to explain the challenges that were encountered and the process of mapping the lessons learnt to ensure improvements along the process. The process involved the casing points analysis evaluating the competent formations options, continues optimization of well trajectory by increasing the inclination across problematic formations while drilling the intermediate section (limited in previous drilling campaign in the area), the evaluation of the impact caused in the consecutive 8 ½" phase (longer section), implementation of best practices to mitigate stability issues and Invisible Lost Time (ILT) methodology application to minimize hole exposure duration. The challenging campaign had the objective of saving cost by reducing one [FQ1] construction [FQ2] phase and continues achieving longer departures successfully which was a milestone during the well construction, thus a learning curve was built focused on continuous improvement of key operations. After completing more than 100 wells, the most beneficial point this change has offered is drilling long departure wells saving one phase in comparison with the conventional design in the area, which is the key element for cost reduction and also allowed to reduce crew exposure to heavier casing handling improving HSE risks. Currently, a maximum departure/vertical section of 10,700 feet has been achieved with light/slim casing design. Overall duration saving is 16 days compared with the best heavy casing design duration and 20 days with average heavy casing design duration with 35% saving duration. Drilling light casing design instead of conventional heavy casing design enable average of USD 2 million saving per well. The consolidated experience built throughout planning and execution since the first well, enabled an important performance improvement based on the learning curve built along the years. Nowadays, many fields require drilling wells with long vertical section / departures to reach further targets, away from the feasible surface locations. Additionally, cost reduction is another concern due to Oil Market fluctuation by applying new strategies and optimizing the performance without jeopardizing but improving the HSE at the same time. This paper presents a novel approach to well construction by showing the lesson learn that allowed well duration reduction, drilling more wells per year and consequently bringing early production, increasing efficiency and significantly reducing cost, therefore increasing productivity and profitability, at the time of contributing to HSE improvement.
- Asia > Middle East > Saudi Arabia > Thamama Group > Kharaib Formation (0.99)
- Asia > Middle East > Qatar > Arabian Gulf > Arabian Basin > Arabian Gulf Basin > Block 6 > Al Khalij Field > Laffan Formation (0.98)