A well failure model is constructed as a matrix that identifies the most common modes of well failure seen by the Well Operator. For specific well types, well anomalies are assessed before they happen, in a what-if risk assessment. A traditional well failure model (WFM) includes a subset of possible anomalies and is based on subjective judgement. Total E&P Denmark's (TEPDK) new WFM uses quantitative analysis with an objective approach to risk assessment. This gives detail and clarity of actual risk (as a product of probability and severity) from well integrity anomalies not previously available. This Analytical WFM assesses well integrity barrier compliance and risk. It uses individual component failure mode probabilities and severities and analyses thousands of potential leak paths throughout wells. It includes potential flow from multiple pressure sources and to multiple pressure sinks, providing a comprehensive understanding of all possible failure cases, and their associated impact on risk. Quantitative Risk Assessment (QRA) was used to calculate maximum Safe Service Life for wells following component failure. Outputs from the analysis were used to build a detailed WFM. Immediate and long-term actions were developed in workshops and suitable response times agreed based on the Safe Service Life calculation. Engineers now spend 85% less time in well integrity risk assessments and failure management when anomalies arise because this work has been done in advance. This means engineers' time is freed for other valuable tasks. The company also saves management time, onshore and offshore, cutting down the need for management challenge and action justification. All personnel involved have a more consistent understanding of well issues, with routine anomalies dealt with much more efficiently. This means decisions are made at a lower level, including whether to continue to operate a well or shut it in. TEPDK has reduced the probability of process safety incidents from wells. This is because it has a far more sophisticated, clearer understanding of well risks, and actions and timeframes for anomaly response. It has also improved production efficiency, safeguarding on average 2,700 boepd, through a reduction in well shut-in time. This has an equivalent value of approximately $50 million / year.

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Well failure modelling uses pre-emptive risk assessment to address well integrity issues more effectively than risk assessing well barrier leaks and other integrity anomalies as they happen. Users of Well Failure Models (WFMs) benefit by spending less time doing risk assessments and achieve more consistent results; better understanding of well issues; more efficient well intervention planning and reduced well services costs; improved well reliability and thus reduced production losses and safer wells. By adopting a well failure model Maersk Oil Qatar rasies the bar with respect to HSE and management of their well integrity.Development of a WFM utilises a what-if risk assessment for specific well types, characterised by service, flow capability, well pressure, architecture and various environmental considerations. Well component leaks, failure modes and other integrity anomalies are analysed. Corrective actions, severity codes and repair grace periods are established for each issue for all well types.The Maersk Oil Qatar (MOQ) WFM has been in use since 2012. It considers failures and failure modes for all well barrier elements as well as preventative maintenance anomalies for the various well types in the Al-Shaheen field, offshore Qatar.The 2012 WFM has grace periods based on the subjective judgement of experienced drilling and production staff, agreed in facilitated workshops. In 2014 work was initiated to upgrade the WFM using quantitative risk assessment (QRA) techniques to calculate grace periods. This paper describes development and structure of the 2012 WFM. It also explains the QRA techniques used in the 2014 WFM upgrade and outlines the initial results obtained with both models. Currently MOQ are running the 2012 model and will soon begin to populate the 2014 QRA model with actual failure data in order to calibrate the model.Reductions in risk exposure and improvements in risk management are the most important objectives MOQ expect to realise from this approach. Further to this there potentially are substantial financial benefits for Maersk through efficiency gains, cost saving and increased production volumes, this underpins the company goal of being a top quartile performing operator with high focus on safety.

Maersk Oil Qatar AS, under the Exploration and Production Sharing Agreement with Qatar Petroleum, operates the Al Shaheen field, Offshore Qatar. In order to maximise recovery from the shallow and thin reservoirs, long horizontal ERD wells have been drilled in both, radial and line drive patterns with alternating producers and injectors. Recently, long horizontal wells pushing the limits of surface-controlled multi-zone completions in the reservoir were planned, drilled and completed. To achieve maximum reservoir contact, pre-drilled liners with open hole isolation packers were installed from the production casing shoe to TD (~6,800 ft to ~29,300 ft MDRT, ~3,450 ft TVDRT at 90° inclination) in multiple runs. The completion was installed to facilitate selective control of each of the 3 zones using surface controlled valves. The inner completion string was run to 22,985 ft by segmenting the completion string into 2 runs. This was achieved by having the lower section run on a drill pipe running string with a swivel to facilitate rotation of the running string to get to depth. The upper completion with multiple control lines was installed using floatation technique (~8,000 ft tubing length floated). One of the wells was subsequently acid stimulated using the Maersk Oil Patented controlled acid jetting (CAJ) technique. The objective of this paper is to share the installation experiences, detailed analysis, procedures used and lessons learnt completing these multi-zone wells. The paper also outlines procedures to establish initial conditions (using calculation spreadsheets to verify WellCat simulations), and then calculate all possible load cases expected during life of the well by using tri-axial design approach. A detailed analysis has been compiled to evaluate tubing length change, tubing-to-packer forces and casing-to-packer forces. The selective zone stimulation load case is analysed in detail. A detailed analysis of forces v/s limiting force envelopes for the tubing, packers and accessories for multi-zone completion has also been demonstrated. Introduction The Al Shaheen field has been under development since 1992 when Qatar Petroleum entered into an Exploration and Production sharing agreement with Maersk Oil Qatar AS as the Operator of the field1 (Fig. 1). The Al Shaheen field is located on the central axis of the Qatar Arch, some 70 kilometers North-East of the Qatar peninsula. It comprises of thin, stacked reservoirs (Fig. 2) mainly carbonates with low permeability. The aerial extent of the Al Shaheen field accumulations is substantial which requires a large number of wellhead platforms to develop the field. Moreover, due to relatively high oil viscosity vertical wells were found to be unable to sustain natural flow and gave low productivity with artificial lift. Therefore, the field is being developed with long horizontal wells drilled and completed from nine platform locations. The length of these horizontal wells has pushed the limit of directional drilling technology (Fig. 3). EOR techniques such as gas injection have been implemented in an effort to evaluate the scope for incremental field oil recovery2. The next step in this effort is to implement water alternating gas injection (WAG). Zone isolation is of primary importance for such WAG wells, which was the driver for installation of multi-zone completions with open hole isolation. This paper describes the planning, design and execution of drilling and completion of two pilot WAG wells that entailed a three zone completion with open hole isolation packers and selective completion.