Drilling fluids, removal

Earlier on when we described the cutting action of the drill bit we learned about the drilling fluid or mud. The mud cools the bit and also removes the cuttings by carrying them up the hole outside the drill pipe. At the surface the mud runs over a number of moving screens, the shale shakers (Fig. 3.11) which remove the cutting for disposal. The fine particles which pass through the screens are then removed by desanders and desilters, usually hydrocyclones. 

Removal of Solids. Sohds incorporated in the mud during drilling generally are separated mechanically, reduced by dilution, or removed chemically by flocculation. It is desirable to maintain a low concentration of drill sohds (4—8 vol %) and in some cases total removal is required. In the latter case, the drilling fluid is clear, consisting of fresh water or brine, and high drilling rates can be achieved. Polymeric flocculants added in small (0.03—0.06 kg/m (0.01—0.02 Ib/bbl)) quantities maintain a clear hquid (139). 

The chemical treatment methods reduce dispersability property, of drilling fluids through the increase of size of cuttings which improves separation and prevents the buildup of colloidal solids in the mud. These methods include ionic inhibition, cuttings encapsulation, oil phase inhibition (with oil-base muds), and flocculation. The mechanical solids removal methods are based on the principles presented in Table 4-55. 

A degasser is installed on the mud line to remove gas from drilling fluid while penetrating gas bearing formations. Samples of gas are analyzed using the gas chromatograph. 

Other uses of thickening agents include pharmaceutical preparations, paper production, and oil well drilling fluids. This latter use is necessary because oil is obtained from rock that is porous. In order to remove the oil without altering the mechanical properties of the porous rock, viscous liquids ( drilling fluids ) are pumped into the rock to replace the oil. Among the substances that can be used for this purpose are thickened aqueous solutions of polymers such as poly(acrylic acid) or poly(acrylonitrile). 

Zinc compounds have a high reactivity with regard to H2S and therefore are suitable for the quantitative removal of even small amounts of hydrogen sulfide [1831]. However, at high temperatures they may negatively affect the rheology of drilling fluids. 

To remove filter-cake, a physical method can be applied wherein a fluid is oscillated in the annulus prior to cementing [948,949]. The direction of flow of the fluid in the annulus is changed at least twice. The oscillatory flow of the fluid removes the drilling mud and the filter-cake from the annulus. After this oscillatory flow treatment, the cement slurry is pumped into the annulus. 

J. Weaver, K. M. Ravi, L. S. Eoff, R. Gdanski, and J. M. Wilson. Drilling fluid and filter cake removal methods and compositions. Patent US 5501276, 1996. 

Well development refers to the process of removing drilling fluids and fine-grained materials from near the well screen. Their removal helps the subsequent collection of nonturbid samples and improves the hydraulic connection between the well and the aquifer. 

After completion of the drilling operation, steel casing is lowered down the well bore and into the drilling fluid. A spacer fluid is then pumped down the well bore to remove the drilling fluid and prevent contact of the drilling mud with the cement slurry. Efficient displacement of the drilling mud also promotes bonding of the cement slurry to rock surfaces. 

Apparent vis.=18.5 cp, Plastic vis.=13.0 cp, Yield point=ll lb/100 ft.2 These values are characteristic of a superior, low-solids, drilling fluid that promotes a high drilling rate and good solids removal. In addition, maximum inhibition of hydrating clays is provided. 

Air percussion U or C 2000+ M,R,I drilling fluids dangerous with flammable fluids Fast cuttings removal rapid good in consolidated formations... 

Potential treatment and disposal methods for drilling fluids include (1) fluid ejection, (2) pit and solids encapsulation, (3) injection into safe formations, (4) removal to disposal sites off location, (5) incineration, (6) microorganism processing, and (7) distillation, liquid extraction, and chemical fixation [13]. 

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