Completion fluid

Wellbore stabilizers are frequently included in drilling fluid formulations. These are used to control (limit) fluid interactions with the wellbore rock. One way to do this is to add particles whose sizes are chosen such that they can enter the wellface and near-wellbore region and plug the pores in the rock. Nanoparticles are being used for this, and this is currently an area of active research and development. 

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Sodium amalgam. The amalgam which is generally employed for reductions contains from 1 to 3 per cent, of sodium. Amalgams with a greater sodium content than 1 2 per cent, are solid at the ordinary temperature and can be powdered in a mortar the 1 2 per cent, amalgam is semi-solid at room temperature but is completely fluid at 50°. Two methods of preparation are available. 

It is instructive for the student to construct a rough melting point diagram (compare Section 1,13 and Fig. 1,12, 1) for mixtures of cinnamic acid and urea. Weigh out 1 00 g. each of the two finely powdered components, and divide each into ten approximately equal portions on a sheet of clean, smooth paper. Mix 4 portions of cinnamic acid (A) with 1 portion of urea B) intimately with the aid of a spatula on a glass slide, and determine the melting point (the temperature at which the mixture just becomes completely fluid is noted). Repeat the procedure for 3 parts of A and 2 parts oiB 2 parts of A and 3 parts of B and 1 part of A and 4 parts of B. Tabulate your results as follows —... 

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. 

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

Hydroxyethyl cellulose (HEC), a nonionic thickening agent, is prepared from alkali cellulose and ethylene oxide in the presence of isopropyl alcohol (46). HEC is used in drilling muds, but more commonly in completion fluids where its acid-degradable nature is advantageous. Magnesium oxide stabilizes the viscosity-building action of HEC in salt brines up to 135°C (47). HEC concentrations are ca 0.6—6 kg/m (0.2—21b/bbl). 

Oilfield Uses. Calcium chloride has two uses in the oilfield as a primary ingredient in completion fluids and as the brine phase in an invert emulsion oil mud. An excellent review of oil well drilling fluids is available (36) (see also Petroleum, drilling fluids). 

Productivity damage attributable to drilling or completion fluids results from three mechanisms ... 

SANDS Low pressure. Water or mud blocking. Loss of crude or diesel oil used as completion fluid. Minimum filtration rate water-base muds. Minimum filtration rate water-base emulsions. Miminum filtration rate oU-base emulsions. Oil-base muds. Inhibited muds. Minimum weight muds. Crude oil or diesel oil. Add oil-soluble lost circulation material. 

The emulsion blocking mechanism involves formation of emulsion in the pores either by self-emulsification of water-based filtrate with the crude oil, or oil filtrate from an oil-based fluid emulsifying formation water. The emulsions are viscous and can block the pores. The remedial design is to prevent emulsification either by eliminating oil from completion fluid or by the use of demulsifiers. 

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