Workover

The industry is increasingly acknowledging the value of oontractors and service companies in improving their individual core capabilities through alliances, i.e. a joint venture for a particular project or a number of projects. A lead contractor e.g. a drilling company may form alliances with a number of sub contractors to be able to cover a wider spectrum of activities e.g. completions, workovers and well interventions. 

To reduce this tendency the well should be produced at low rate, and the perforations should be as far away from the OWC as possible. Once the unwanted fluid breaks through to a well, the well may be recompleted by changing the position of the perforations during a workover, or the production rate may be reduced. 

Operations Maintenance Engineering Operating costs - maintenance - workover - manpower requirements... 

The capital cost estimates are generated by the Engineering function, often based on 50/50 estimates (equal probability of cost overrun and underrun). It is recommended that the operating expenditure is estimated based on the specific activities estimated during the field lifetime (e.g. number of workovers, number of replacement items, cost of forecast manpower requirements). In the absence of this detail it is common, though often inaccurate, to assume that the opex will be composed of two elements fixed opex and variable opex. 

Tubing corrosion due to FIgS (sour corrosion) or COg (sweet corrosion) may become so severe that the tubing leaks. This would certainly require a workover. Monitoring of the... 

Wells are worked over to increase production, reduce operating cost or reinstate their technical integrity. In terms of economics alone (neglecting safety aspects) a workover can be justified if the net present value of the workover activity is positive (and assuming no other constraints exist). The appropriate discount rate is the company s cost of capital. 

Cross flow inside the casing can also be prevented by isolating one zone. However, this may still result in reduced production. Installing a selective completion can solve the problem but is an expensive option. To repair cross flow behind casing normally requires a full workover with a rig. Cement has to be either squeezed or circulated behind the production casing and allowed to set, after which cement inside the casing is drilled out, and the producing zones perforated and recompleted. 

Siace 1980 over 1000 patents have been issued for drilling fluid systems and materials ia the United States alone. A 1994 listing of products from 117 supphers offers ca 3000 trade names (6). This array of trade name products actually represents less than 100 separate chemical types that may be purchased iadividuaHy or as a blend. Moreover, some of these materials are for completion and workover fluids. These differ from drilling fluids ia that completion fluids are used after the well has been drilled and prior to the initia tion of production whereas workover fluids are used duting remedial work on older wells. 

Calcite and siderite (27) are used occasionally because of their solubiUty in hydrochloric acid which offers a method of removing mud filter cake deposited on productive formations. Calcite and siderite are used most frequently in workover or completion fluids when a nondamaging fluid is required, ie, one that can be removed by acidising at a later time. 

Sohd salt, ground and packaged in several particle size grades, can be used in saturated salt brines to increase the fluid density (28). However, sized salt is most often used as a water-soluble material for bridging or sealing porous formations. At one time the sized salt systems were used primarily for completion or workover operations, but use has increased as ddU-in fluids for horizontal wells (29). 

Table 3. Soluble Salts that Increase the Density of Drilling Mud and Workover and Completion Fluids...

HEC hydroxyethyl cellulose nonionic 110 viscosity builder, acid degradable primarily for completion/workover fluids... 

A fourth alkalinity control additive is magnesium oxide [1309A8A], which is used in clay-free polymer-base fluids (47). Magnesium oxide provides an alkaline environment and, as it is only slightly soluble, also has a buffering effect. It enhances the thermal stabHity of polymer solutions by preventing a pH decrease to neutral or slightly acidic conditions at elevated temperatures. It is mainly appHed in completion or workover operations where clay-free acid-soluble fluids are desired. 

The use of certain non-armored cables is acceptable to API RP 14F in Division 1 areas on drilling and workover rigs where ignitible concentrations t)f gases and vapors do not occur for appreciable lengths of time. 

Secondary recovery, infill drilling, various pumping techniques, and workover actions may still leave oil, sometimes the majority of the oil, in the reservoir. There are further applications of technology to extract the oil that can be utilized if the economics justifies them. These more elaborate procedures are called enhanced oil recovery. They fall into three general categories thermal recoveiy, chemical processes, and miscible methods. All involve injections of some substance into the reservoir. Thermal recovery methods inject steam or hot water m order to improve the mobility of the oil. They work best for heavy nils. In one version the production crew maintains steam or hot water injection continuously in order to displace the oil toward the production wells. In another version, called steam soak or huff and puff, the crew injects steam for a time into a production well and then lets it soak while the heat from the steam transfers to the resei voir. After a period of a week or more, the crew reopens the well and produces the heated oil. This sequence can be repeated as long as it is effective. 

Testing of Drilling Fluids 652. Composition and Applications 664. Oil-Based Mud Systems 675. Environmental Aspects 682. Typical Calculations in Mud Engineering 687. Solids Control 691. Mud-Related Hole Problems 695. Completion and Workover Fluids 701. 

Figures 4-16, 4-17, 4-18, and Table 4-5 show recommended radii of hoisting tool contact surfaces. These recommendations cover hoisting tools used in drilling, and tubing hooks, but all other workover tools. Contact radii are intended to cover only points of contact between two elements and are not intended to define other physical dimensions of the connecting parts.

Frequency of Inspection. Field inspection of drilling, production, and workover hoisting equipment in an operating condition should be made on a regular basis. A thorough on-the-job shutdown inspection should be made on a periodic basis, typically at 90 to 120-day intervals, or as special circumstances may require. 

The liquid phase of saturated saltwater muds is saturated with sodium chloride. Saturated saltwater muds are most frequently used as workover fluids or for drilling salt formations. These muds prevent solution cavities in the salt formations, making it unnecessary to set casing above the salt beds. If the salt formation is too close to the surface, a saturated saltwater mud may be mixed in the surface system as the spud mud. If the salt bed is deep, freshwater mud is converted to a saturated salt water mud. 

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