Summary. Several special stimulation techniques have been proposed for soft, unstable formations. One example is a combination of acid and proppant, which leaves the acid channels full of sand. This paper proppant, which leaves the acid channels full of sand. This paper discusses an alternative completion technique that involves only normal sand fracture procedures and is effective where acid is ineffectual or undesirable. Because the procedure is aimed primarily at creating short, high- conductivity fractures in soft formations, its use can be extended to any formation where such a treatment is practical and economically feasible. The fracture design is based on intentionally screening out the tip of the fracture with sand and then continuing to pump slurry to increase the fracture width and to pack the fracture with proppant to obtain high conductivity. Because this involves severe risk of a premature screenout, and because failure to achieve the tip screenout will not yield the desired stimulation, special prefracture tests are required to determine fracture design variables. The implementation and analysis of these tests are discussed, along with the theory behind the fracture design schedule. This theory is then compared with fracture pressure data and production performance from two wells completed in an Upper Cretaceous production performance from two wells completed in an Upper Cretaceous chalk formation in the Norwegian Sector of the North Sea. Introduction From time to time, the oil industry is faced with completing wells in very soft, unstable formations, such as chalk. Such rocks create unusual situations regarding drilling, completion, and production practices. Many normal stimulation techniques are rendered ineffective by the mechanical properties of the formation. For example, acid-etched channels quickly collapse and close as the pore pressure is reduced, or the proppant from a normal sand pressure is reduced, or the proppant from a normal sand fracture quickly embeds in the formation, leaving little or no fracture conductivity. In some formations, perforating the pay section may even be undesirable because of perforating the pay section may even be undesirable because of solids production and possible casing collapse. In this situation, fracturing is required to create a highly conductive flow path from the pay zone to perforations in a more stable formation. A unique well completion and stimulation program has been applied to a chalk reservoir located in the Norwegian Sector of the North Sea-unique in the sense that the hydraulic fracturing stimulations attempt to achieve on purpose what often occurs accidentally. That is, the purpose what often occurs accidentally. That is, the success of the stimulation depends on the creation of a controlled screenout to achieve enough propped fracture width to ensure lasting fracture conductivity. Problems associated with well completions and stimulations in soft chalk formations have recently been covered thoroughly and will not be discussed here, except to note that both studies concurred that very wide propped fractures with in-situ proppant concentrations on the order of 2 lbm/ft3 (32 kg/m3) are necessary to achieve adequate fracture conductivity. Other investigators have arrived at similar conclusions for another soft formation, diatomaceous earth. For soft chalks, Ref. 2 noted that propped hydraulic fractures are probably the best propped hydraulic fractures are probably the best stimulation technique, but if job size is limited for any reason, normal fracturing stimulation procedures may not achieve an adequate in-situ proppant concentration. For such cases, a procedure was proposed involving a combination of acid fracturing and proppant fracturing where the proppant would leave the wide acid-etched channels proppant would leave the wide acid-etched channels propped open. For diatomaceous earth, Ref. 4 propped open. For diatomaceous earth, Ref. 4 recommended use of very-high-viscosity crosslinked gels to achieve sufficient width for fracture conductivity. For reasons discussed in this paper, these procedures were not applicable to this particular field. Fig. 1 shows a type log of the two main producing zones of the reservoir in question. Early in the exploration program, we determined that stimulation was required in both program, we determined that stimulation was required in both zones to achieve desired producing rates. For the lower zone, the relatively low permeability (1 to 2 md) common to many chalks required stimulation to develop the reserves adequately, while stimulation was required in the higher-capacity upper zone because of wellbore skin problems and possible stress-sensitive permeability. Besides problems and possible stress-sensitive permeability. Besides the need for stimulation, the properties of the upper zone dictated that only oil-based completion fluids be considered. The strength of this zone was found to be very low because of its high porosity (often greater than 45 %); as a result of in-situ oil saturations greater than 90%, any contact with water further degraded this strength. SPEPE p. 95

Talisman operates several fields on the Norwegian Continental Shelf (NCS), many of these mature fields are taken over at the end of their design life. These old fields represent challenges with respect to well integrity and overall profitability.Talisman is a member of the Well Integrity Forum (WIF), a co-operative effort between the operating companies on the NCS to define a unified approach for handling well integrity. Using WIMS and the WIF recommendations together with internal guidelines improves Talismans ability to handle well integrity issues throughout the production phase of a well and in compliance with regulatory requirements. This paper describes how Talisman Energy Norway (Talisman) manages well integrity for their assets, and discusses the benefits, challenges and lessons learned from implementing a well integrity management system, focusing on technical and organizational aspects.

Well 2/4-14 in the Norwegian Sector encountered well control problems in January 19S9 at a depth of 4734 m. After some days effort to reestablish normal pressure control the well blew out on surface of the floater and had to be closed in using the shear ram. This left the subsea BOP closed and with a shut in wellhead pressure of 10000 psi. In addition a full string of drillpipe with approximately 4500 m of coiled tubing was left in the well. After an attempt to regain control by bullheading heavy mud, in which a flexible kill line bursted, the well was left for a periode. Preparations were made to reenter the well with high pressure snubbing equipment to fish out the drillpipe and coiled tubing, so that the well could be circulated dead. In parallel to this effort a relief well was started immediately. After the well was reopened it was discovered that the casing had bursted and that the well was blowing out underpound. On December 12, 1989, 295 days after the shear ram was closed, the well was killed. Another four months were required to finish cleanup and final abandonment of the blowout well. The paper presents the case history and indicates some of the tools and technology that was developed to regain control of this well.

Inadequate hole cleaning during a drilling operation may result in immediate problems such as excessive torque or pack-off situations, or it can lead to delayed problems such as while running in hole with a casing/liner or a completion string in a leftover cuttings bed. It is therefore desirable to provide quantitative information about hole cleaning conditions: at the planning stage, while drilling or when investigating incidents. Because the ability to transport cuttings particles varies with their position in the borehole and the current drilling parameters, hole cleaning modelling is a history-dependent problem. The precise modelling of the movement of solid particles during a drilling operation gives the possibility to estimate whether they are in suspension in the drilling fluid, settling on the low side or being eroded from a cuttings bed. These estimations may be confirmed through the change of the active volume or by the increase of downhole pressure, when PWD (Pressure While Drilling) measurements are available. A transient cuttings transport model has been used for planning and monitoring an ERD (Extended Reach Drilling) well drilled in the North Sea. The model has been used to compare the expected performance of different mud systems on both hydraulic and mechanical limits that could be expected prior to drilling. For another challenging drilling operation, the model has been used to post analyze the sequence of actions that led to problems while running in hole with a liner. Here also, the observations tended to confirm the predictions made by the hole cleaning model. Furthermore, an active use of such an advanced hole cleaning model may help determine the time required for circulation procedures prior to pull out of hole. This can help reduce the flat time associated with circulation procedures and at the same time decrease the duration by which the hole stays open thus reducing the risk of hole instability.

Coiled Tubing (CT) equipment in the Norwegian sector of the North Sea has traditionally been heavy, due to CT reels using larger sizes of CT - a trend also observed in other areas. Due to the requirement of performing well interventions in longer wells and larger completion sizes, CT drums weighing 40–60 t have been utilised. Not many platform cranes are capable of lifting such heavy CT drums and during bad weather periods operations are often delayed, even when using significantly lighter CT drums. Using spoolable CT connectors allow for a long and heavy CT string to be lifted on board of a platform on two or more separate drums and joining them together again once onboard. More than 50% weight reduction has been achieved making operational schedules more predictable. In the geographical areas considered, spoolable CT connectors have outperformed traditional methods like boat spooling and butt-welding from a safety, operational and economical point of view. Due to the reduction in weight, larger CT sizes have become available on older platforms as well. New CT applications that were previously considered unfeasible, like selective, high-rate acid fracing through CT, have been performed, extending the capabilities of CT interventions beyond previous logistical and technical limits. Being able to select the correct size of CT, with less dependency on offshore crane limits and weather has a fundamental impact on the usage of CT in the offshore industry. Rather than discussing the spoolable CT connector itself, the primary intention of the paper is to re-view case histories that were performed during the last 5 years. Operational challenges that have been mastered, successes, failures and further developments are presented. A new CT reel configuration to simplify spoolable CT connector installation will be presented. The new applications made possible by this technology and their economic impact on the Norwegian CT market since year 2003 will be reviewed. Introduction Reducing the weight of CT reels has been an ongoing objective, especially in the offshore CT industry. Several methods have been established, ranging mainly from reducing the CT size itself, butt-welding, spooling the CT from a boat to the offshore installation or using split-reel systems (drop in drums). The trend to larger CT sizes observed in many markets during the recent years clearly demonstrates the desire not to compromise on the CT size itself. Especially in markets using larger sizes of CT, split-reel systems have become the standard during day to day operations. Butt-welding and spooling of CT from a boat to the offshore installation has a substantial track record for CT sizes of usually up to 2". All of these methods have their advantages and disadvantages mainly circling around issues like economic feasibility, required special resources for implementation, offshore logistics, operational flexibility and reliability. The development of the spoolable CT connector has been described in previous publications [H.B.Luft et al, 2004]. Field implementation has been successfully performed [L.Link et al, 2005] in the Norwegian and Danish sectors of the North Sea as well as adding new types of CT applications to the conventional CT offshore market [K.Ormak et al, 2003]. The track record established for the spoolable CT connector during the last 5 years in the Norwegian sector of the North Sea clearly indicates acceptance from the operators. It has been recognised as a method of further reducing the lifting weight of CT reels and reliably performing CT operations using larger sizes of CT. Using this method CT strings have been lifted onboard the offshore installations in two or more sections (2 or more CT drums) and joined together using the spoolable CT connector.