3.5 Well completion - Treccani

1 IntroductionThe term completion , when applied to oil wells, isused to define all post-drilling operations that arenecessary to hydrocarbon production. completion has,on the whole, a permanent nature, which means thatplanning parameters must be carefully evaluated, andpossible solutions must undergo technical andeconomical planning involves choosing andorganizing the equipment to be used, selectingmaterials, establishing production line tubingdimensions, stipulating production intervals, andfinally defining the mode of formation fluidproduction. This evaluation must take into account theevolution of the productive characteristics of the well ,according to the production fact, the production characteristics of each welldepend on the interaction between the reservoir, the completion , and the surface macro-elements, in their interaction, set theconditions for production in relation to the flowingpressure and the flowing rate at the very important element that influences thefluid mechanics during production is the type ofproduced fluid.

2 This fluid can be a liquid, a gas, or amixture of liquids and gases. Therefore, the chemicaland physical characteristics of the produced fluid andits evolution over time must be known when planningthe completion . An understanding of the producedfluid s characteristics is the basic element needed todefine the pressure at the first separator, which willform the closing point of the reservoir, well andsurface plant s fluid mechanic system, and which is thestarting point when planning a production production capacity of a well is determined onthe basis of reservoir data such as reservoir pressure,permeability and the thickness of the pay rock aroundthe well , and according to the results of previousproduction tests, which are used to determine theProductivity Index (PI). Using the productivecapacity, defined as a function that combines the flowrate and the acting pressure regime, which is known asthe Inflow Performance Relationship (IPR), theservice conditions of the well are determined.

3 On thebasis of these, the diameter and thickness of the tubingare chosen. It is also important to consider theefficiency of the completion in the light of thedecrease in reservoir pressure over time, and toevaluate a possible substitution of the originalcompletion with one of a bigger diameter, to reducepressure loss, and guarantee the produced flow. If thereservoir pressure is insufficient for natural flow, itmay be necessary to consider an artificial lift presence of non-hydrocarbon components inthe produced fluid conditions the choice of thematerials. In fact, the frequent presence of carbondioxide and/or hydrogen sulphide in the hydrocarbon-water mixtures leads to the formation of acid solutionsthat attack the materials the completions are made is why the materials generally used, such asspecial stainless steels, elastomers, and compositematerials, have a good resistance to corrosive agents,and good retention of mechanical fundamental element to be taken intoaccount when planning the choice of materials and thecompletion s structural design is the temperature.

4 Aswe know, the subsoil temperature increases by 3 C forevery 100 m of depth. The metallic structure istherefore subjected to mechanical stress due to thermaldilatation. The temperature also influences in differentways the acidic components effect on the materials,and the mechanical behaviour and stability of theplastic and elastomeric I / EXPLORATION, PRODUCTION AND well completionThe type of completion adopted will depend onthe structural/geological characteristics of thereservoir, and on the type of mineralization. Thereare two categories of completions: conventionalcompletions and so-called smart completions. Thelatter were introduced in the early 1990s with the aimof allowing production management to take placedirectly in the well , thus avoiding maintenance workleading to interrupted production and additionalworking the course of a well s producing life, whichlasts several decades, interventions may be necessaryto restore the optimal flow conditions.

5 Theseconditions may be reduced because of clogging,scale, hydrate or asphaltene deposits or otherproblems in the hole or the formation. The operationsto be undertaken to remove possible obstructions, orto restore the production capacities of the formationmust be planned when designing the completion , inorder to reduce the costs and simplify completion jobs aim to prevent problemsthat may arise during the productive phase. Forexample, the completion could get clogged up bysolids dragged up through the production plant,causing erosion to the plant in general, or to specificparts of it, such as valves or bends. It is thereforenecessary to separate the solid particles from thefluids, by installing filters and sand-catchingdevices. The solid particles must then be properlydisposed Types of completionOverviewOil and gas well completions can be divided intotwo main categories: open hole well completions, andthe case-hole open hole completions the pay rock is kept as itis, and no cemented casing columns are needed.

6 Thistype of completion is realized when the formation isself-supporting or when, on the contrary, it is tooseverely fractured to guarantee successfulcementation. It is the optimal solution since the entiredrainage surface is available for production, andpressure drops are limited. Moreover, the absence ofcasing columns makes it easier to proceed to wellstimulation. On the other hand, in open holecompletions it is impossible to control the entrance ofsand and water in the hole, and it is therefore verydifficult to isolate the levels and proceed to completions are more widely used due totechnical reasons relating to the stability of the hole. Inthis case the well to be completed is one that has beenlined and cemented throughout its entire order to make production possible, it is necessary tore-establish hydraulic communication between the payrock and the hole.

7 This operation involves drilling thelining, the cementation and the pay rock. There are four possible solutions to establishcommunication between the productive formation andthe surface: a) tubinglesscompletion; b) packerlesscompletion (with a tubing string and without isolationbetween casing and tubing);c) single string withhydraulic isolation completion ; d) multiple tubingless completion method is used inwells where the pay rock pressure is low and highflow rates are required. In this case production musttake place directly through the final lining of thewell, with no support from production strings orisolation OF HYDROCARBONSDRILLING AND completion OF WELLS tubing hangertubing jointseating nipplepup jointpup jointpackerwirelineentry guidetubingseating nippleseating nipplepup jointwirelineentry guideFig. ( 2004 Baker Hughes,Incorporated).

8 Fig. string packercompletion ( 2004 Baker Hughes,Incorporated).Packerless completion is a more financiallyadvantageous system. Here, only the production tubingis placed in the well , and it is possible to produce boththrough it and through the annulus (Fig. 1). Theproduction tubing can be used for injecting inhibitorsor killing fluid. This method is somewhat limited interms of flow conditions and the protection of thetubing materials. Moreover, it is difficult to detectleaks in the tubing or the casing, and to gatherbottomhole pressure single stringe completion using hydraulicisolation and just one string is convenient when theproduction layer appears to be homogeneous and aselective-zone production is not necessary. It consistsin the use of a single tubing string that is lowered intothe well together with an isolation device for theformation section to be produced, called the packer(Fig.)

9 2). Where there are several production layers for onefluid, a single selective completion is used. Thissystem has only one tubing string and severalpackers that isolate the various production using wire-line operations it is possible to openand close the valves so as to allow production onsingle layers (Fig. 3). The multiple tubing string completion uses, at themost, two or three tubings, isolated by packers andproducing on different levels at the same time (Fig. 4).This solution is useful when the reservoir presentsdifferent layers of mineralization, for example gas andoil, or different types of oil, because it allows us toproduce selectively according to necessity, whilekeeping production active on various levels at thesame time. For the single tubing strings, it is alwayspossible to adopt a solution similar to the singleselective completion , thus obtaining a multipleselective completion .

10 This system s drawback is thelimited diameter of the tubing which in turn reducesthe flow capacity of each tubing completionsThe introduction of deviated well drilling, and inparticular the adoption of multilateral schemes has ledto the necessity to develop devices for ad hoccompletions. In general, completion technology for387 VOLUME I / EXPLORATION, PRODUCTION AND TRANSPORTWELL completion locator seal assemblylocator seal assemblyproduction packerproduction packerproduction packersliding sleevesliding sleeveseal bore extensionseal bore extensionseal bore extensionseating nippleseating nipplewireline entry guideblast jointlocator seal assemblyblast jointsafety valvesafety valvescoopheadseating nippleseating nippleblast jointsliding sleevesingle string retrievablehydraulic set packerhydraulic set dual packerhydro-trip pressure subwireline entry guideFig.