Casing Running Challenges for Extended-Reach Wells

Abstract

Running long production casing strings in extended-reach wells is usually recognised as one of the most critical of all well operations. Failure to reach target depth often has a profound consequence on well deliverability and overall cost. In this paper, an overview on the status of current casing running tools and techniques is given. This is complemented with an assessment of the impact of drilling technology on the ability to run casing. The systematic collection of quality data and application of consistent analysis techniques can help identify common factors associated with both casing running success and failure. Results are given, where this approach has been applied to two current extended-reach developments. Introduction During the planning phase for drilling and completing an extended-reach well, casing running is frequently identified as a challenging operation. This is not necessarily due to lack of available running weight, but often due to the consequences of setting casing high. The subsequent knock-on effect of a leaner casing design and often substantial additional capital cost, must to be factored into the overall risk assessment and cost estimate. The drilling team is usually faced with designing the casing running operation to ensure success. There are potentially a large number of design variables and each of these has their own associated degree of uncertainty. All too often the impact of each design parameter is not well understood and both under-design and over-design frequently occurs. Usually this has a low impact on success, however occasionally the outcome of a wrong decision can be disastrous. For example, a common issue is the use of centralisers: are they needed, if so, how many, what type, and what should the installation frequency be? During ERD (Extended-Reach Drilling) well planning, torque and drag analysis is recognised as an essential part of the risk management process. For modelling purposes, careful consideration has to be given to choice of friction factors. Ideally, casing running data from offset wells should be collected, analysed and friction factors calculated. All too often this is not done and a large degree of uncertainty exists as to what values should be used. Another misconception is that friction factors calculated for the drilling phase of the well, can be directly applied to the ensuing casing run. This is not usually the case. In this paper, findings from BP's friction factor database are summarised, where results from over fifty ERD casing runs have been analysed. In the absence of good offset data, the database provides a valuable reference point for drag analysis. The latest BP drilling envelope is illustrated in Figure 1 and reflects many of the challenging ERD casing runs included the database. Recent advances in technology have also blurred the casing running decision process. These include the impact of rotary steerable tools in ERD wells; the increasing use of underreaming while drilling practices; the emergence of ad-hoc casing sizes; the deployment of flush casing strings; the applicability of SET (solid expandable tubulars); the relevance of casing drilling technology; casing floatation techniques and drag efficient casing centralisers. The potential impact of each technology is discussed and where appropriate, examined further in the two field case studies. Data collection and analysis are fundamental to a better understanding of how wells are drilled and the impact this has on the subsequent casing running operation. This topic is a common theme of this paper and best practice based on recent experience given. Frequent data sampling also gives new insights into both casing sticking detection and how changes to running techniques can help mitigate against this. The two case studies from the BP operated Harding and Chirag fields are used to highlight the benefits of data collection, modelling and the application of technology.

The Perfect Wellbore!

“…It is important to be mindful of the fact that even though a high quality wellbore may have been drilled, it is perfectly possible for a casing running operation to fail [13]. Depending on the circumstances and application, it is entirely possible to unknowingly design a casing running operation that will fail to run to depth.…”

Supersize Hole Creates Drilling Opportunity

“…In the Harding field located in the UK sector of the North Sea, oversized 12¼"x13½" holes have been drilled on several ERD wells 4 . This was primarily carried out to successfully manage a section of the overburden where stringers presented both tripping-out and casing running challenges .…”

The Determination of Ultimate Releasable Hook Load in Casing Running Through an Air-filled Wellbore

“…Much researches have been carried out about the mechanics characteristic of casing string. Mason et al [9,10] presented a number of papers devoted to various issues related to operational difficulties and predictions of casing running loads. Maidla and Wojtanowicz [11] used the soft string model to predict casing running performances of four directional wells with the well path restricted to the vertical plane.…”